Lighting Handbook

2023 

FHWA 
2023 FHWA LIGHTING HANDBOOK

ii

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation 

(USDOT) in the interest of information exchange. The U.S. Government assumes no liability for 

the use of the information contained in this document. This document does not constitute a 

standard, specification, or regulation. It is guidance only and does not create any requirements 

other than those stipulated in statute and regulation. The U.S. Government does not endorse 

products or manufacturers. Trademarks or manufacturers’ names appear in this report only 

because they are considered essential to the objective of the document. 

Non-Binding Contents

The contents of this document do not have the force and effect of law and are not meant to bind 

the public in any way. This document is intended only to provide clarity to the public regarding 

existing requirements under the law or agency policies. While this document contains 

nonbinding technical information, you must comply with the applicable statutes and regulations.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve 

Government, industry, and the public in a manner that promotes public understanding. Standards 

and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its 

information. FHWA periodically reviews quality issues and adjusts its programs and processes to 

ensure continuous quality improvement.

Cover Photo, Ronald Gibbons, VTTI
2023 FHWA LIGHTING HANDBOOK

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TECHNICAL REPORT DOCUMENTATION PAGE

1. Report No.

FHWA-SA-23-004

2. Government Accession No.

No.

3. Recipient’s Catalog No.

4. Title and Subtitle

2023 FHWA Lighting Handbook

5. Report Date

February 2023

6. Performing Organization Code:

HSA

7. Author(s)

Dr. Ronald Gibbons, VTTI

Don McLean DMD and Associates

Paul Lutkevich, WSP Inc.

Dr. Rajaram Bhagavathula, VTTI

David Keith, WSP Inc.

8. Performing Organization Report No.

9. Performing Organization Name and Address

Virginia Tech Transportation Institute

3500 Transportation Research Plaza

Blacksburg, VA 24060

10. Work Unit No.

11. Contract or Grant No.

DTFH6116D00004L

12. Sponsoring Agency Name and Address

Office of Safety

Federal Highway Administration

6300 Georgetown Pike

McLean, VA 22101-2296

13. Type of Report and Period Covered

Technical Report

9/19/2020 – 2/28/2023

14. Sponsoring Agency Code

15. Supplementary Notes

The Contracting Officer’s Representatives was Joseph Cheung, Office of Safety

16. Abstract

This handbook has been prepared to provide recommendations to lighting designers and State, city, and town 

officials concerning the design and application of roadway lighting. It is not intended to be a detailed design guide.

It is primarily a resource for policy makers and the design and construction community to evaluate potential needs, 

benefits, and applicable references when considering a roadway or street lighting system. This handbook is an 

update of the document published in 2012 by the Federal Highway Administration (FHWA). 

17. Key Words

Roadway lighting, safety, lighting 

recommendations, Pedestrians, Warrant

18. Distribution Statement

No restrictions. This document is available to the public 

through the National Technical Information Service, 

Springfield, VA 22161.

http://www.ntis.gov

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

236

22. Price

N/A

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized.
2023 FHWA LIGHTING HANDBOOK

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Acronyms 

Abbreviations Definition 

AADT Annual Average Daily Traffic

AASHTO American Association of State Highway and Transportation Officials

AASHTO American Association of State Highway and Transportation Officials

ADT Average Daily Traffic

AMA American Medical Association 

BIPOC Black, Indigenous, and People of Color

CCT Correlated Color Temperature

CFL Continuous Freeway Lighting

CIE Commission Internationale de l’Eclairage

CIL Complete Interchange Lighting

CMF Crash Modification Factor

CMS Central Management System

CPTED Crime Prevention Through Environmental Design

CSAPH Council on Science and Public Health

C-V2X Cellular Vehicle-To-Everything 

DGONE Discomfort Glare in Outdoor Environments

FARS Fatality Analysis Reporting System 

FCC Federal Communication Commission

FHWA Federal Highway Administration

GHSA Governors Highway Safety Association

HID High-Intensity Discharge

HPS High-Pressure Sodium

IES Illuminating Engineering Society

IESNA Illuminating Engineering Society of North America
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ipRGC intrinsically photosensitive Retinal Ganglion Cells

ITS Intelligent Transportation Systems

LCS Luminaire Classification System

LDD Luminaire Dirt Depreciation 

LED Light-Emitting Diode

LLD Lamp Lumen Depreciation 

LLFs Light Loss Factors

LOS Level Of Service

LZs Lighting Zones

MTBF Mean Time Between Failure 

NCHRP National Cooperative Highway Research Program

NEC National Electric Code

PIL Partial Interchange Lighting

PPFD Photosynthetic Photon Flux Density

SPD Spectral Power Distribution 

SR Surround Ratio

SRTS Safe Routes to School

SSSD Safe Stopping Sight Distance

STV Small Target Visibility 

TAC Transportation Association of Canada

U.S. United States

UPD Unit Power Density

USDOT U.S. Department of Transportation

VPH Vehicles Per Hour

VTTI Virginia Tech Transportation Institute
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2023 FHWA Lighting Handbook

Purpose of Handbook

This handbook has been prepared to provide 

recommendations to lighting designers and State, city, 

and town officials concerning the design and 

application of roadway lighting. It is not intended to be 

a detailed design guide. It is primarily a resource for 

policy makers and the design and construction 

community to evaluate potential needs, benefits, and 

applicable references when considering a roadway or 

street lighting system. This handbook is an update of 

the document published in 2012 by the Federal 

Highway Administration (FHWA). 

Documents available from organizations such as the American Association of State Highway and 

Transportation Officials (AASHTO), the Illuminating Engineering Society (IES), the Transportation 

Association of Canada (TAC), and the Commission Internationale de l’Eclairage (CIE) offer 

recommendations on lighting levels, lighting configurations, and other considerations. This handbook 

directs users to that information where applicable and provides supplemental information on topics not 

addressed in those documents.

The primary goal of this handbook is to improve safety for common roadway lighting applications. It 

focuses on how best to apply roadway lighting in various applications and is therefore educational in 

nature. The handbook is also intended to further clarify and enhance elements discussed in the abovementioned publications. However, this document does not provide the lighting level recommendations 

found in other publications. Any lighting level recommendation tables are cited but not included. 

This handbook uses metric units, such as lux, which are defined in IES RP-8-21, CIE publications, and 

much of the research cited herein. The metric unit lux can be converted into footcandles (imperial) as 

follows: 1 footcandle = 10.76 lux.

This document is divided into two parts: Part I provides technical discussion and recommendations, 

while Part II provides lighting design examples to help illustrate the lighting design process. 

Part I consists of six areas of discussion: 

• Vision Principles and Lighting Metrics, including significant terms and concepts used in roadway 

and street lighting projects

• Lighting Considerations

• Warranting, including various warranting methods available when considering lighting

• Lighting Planning and Design Process

• Environmental Impacts and Mitigation

• Lighting Controls

The primary goal of this 

handbook is improving safety 

for common roadway lighting 

applications with a focus on 

how best to apply roadway 

lighting in various applications. 
2023 FHWA LIGHTING HANDBOOK

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Part II includes a section on general topics such as light source color and light trespass as well as 

examples that cover roadway lighting, tunnel lighting, and other roadway facilities as follows:

• Roadway Lighting

o Urban Street Lighting

o Rural Road Lighting

o Expressway Lighting

o Urban Freeway Lighting

o Suburban Freeway Lighting

o Rural Freeway Lighting

• Other Facilities

o Roundabout Lighting

o Walkway & Bikeway Lighting

o At-grade Railway Crossing Lighting

• Tunnel and Underpasses

o Short Tunnel Lighting

o Long Tunnel Lighting

o Underpass Lighting

Key documents that provide recommendations for roadway lighting design and associated applications 

further referenced in this document are listed below. The latest versions of these documents should be 

used as references for design projects.

• AASHTO GL-7 Roadway Lighting Design Guide (www.transportation.org) 

• NCHRP Solid State Roadway Lighting Design Guide (www.trb.org)

• ANSI/IES RP-8-21-Standard Practice for Roadway Lighting (www.ies.org) 

• ANSI/IES LP-2-20 Lighting Practice: Designing Quality Lighting for People in Outdoor 

Environments

• ANSI/IES LP-12-21 Lighting Practice: IOT Connected Lighting

• ANSI/IES TM-37-21 Description, Measurement and Estimation of Skyglow

• ANSI/IES RP-45-21 Horticultural Lighting

• FHWA-SA-14-015 Handbook for Designing Roadways for the Aging Population

(www.fhwa.dot.gov) 

• FHWA-SA-18-040/FRA-RRS-18-001 Highway-Rail Crossing Handbook, 3rd Edition 

(www.fhwa.dot.gov) 

• FHWA-HRT-14-050 Guidelines for The Implementation of Reduced Lighting on Roadways 

(www.fhwa.dot.gov) Design Criteria for Adaptive Roadway Lighting

• FHWA-HRT-14-051 - Design Criteria for Adaptive Roadway Lighting (www.fhwa.dot.gov) 

• FHWA-SA-20-062- Research Report: Street Lighting for Pedestrian Safety (www.fhwa.dot.gov)
2023 FHWA LIGHTING HANDBOOK

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• NCHRP 672 Roundabouts: An Informational Guide, 2nd Edition– Second Edition (www.trb.org) 

• TAC Guide for the Design of Roadway Lighting (www.tac-atc.ca)

Additional useful non-lighting related documents include:

• AASHTO RSDG-4 Roadside Design Guide 4th Edition (www.transportation.org) 

• AASHTO Highway Safety Manual (www.highwaysafetymanual.org) 

• AASHTO – A Policy on Geometric Design of Highways and Streets 7th Edition

(www.transportation.org) 

Purpose and Benefits of Roadway and Street Lighting

In general, the purpose of roadway lighting is generally defined as follows: 

• Provide a visual environment for road users to safely use the road system during hours of 

darkness. 

• Reduce the impacts of disability glare from approaching headlights and off-roadway lighting, 

thereby improving visibility. 

• Reveal objects on the roadway beyond the range of vehicle headlamps. 

From a safety perspective, the main benefits of roadway lighting include:

• Increased visibility that could reduce fatal nighttime crashes up to 65% (Box, 1989). Roadway 

lighting allows for increased visibility of pedestrians in crosswalks, sidewalks, and pathways 

(FHWA, 2021) and increased visibility and detection distance of other potential road hazards, 

such as cyclists, wildlife, and other unexpected objects (Edwards & Gibbons, 2008; R. Gibbons, 

B. et al., 2015).

• Mitigation of headlamp glare. 

• Increased visibility both in the roadway and along the sides of the roadway and greater visibility 

for older drivers (Gibbons, Edwards, Williams, & Andersen, 2008). 

Other benefits of roadway lighting include: 

• Enhanced personnel security. Lighting can enhance personal security by improving visibility of 

objects and other individuals in the roadway environment, including being able to discern 

intent. 

• Enhanced wayfinding. Lighting provides wayfinding for road users and pedestrians on 

sidewalks.

• Enhanced pedestrian safety. Lighting improves the visibility of pedestrian trip hazards on 

sidewalks. An example is shown in Figure 1 where a well-lighted street highlights the sidewalk 

and any potential curbs or trip hazards. 
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Figure 1. Photo. Pedestrian-scale lighting of a sidewalk (Image Credit: WSP).

• Economic benefits. Lighting may draw people into commercial areas by providing well-designed 

lighting for walkways and appropriate lighting design for the commercial area, which may

increase business visibility and a sense of personal security, thereby increasing commerce. 

Decorative lighting can be used for economic revitalization by contributing to a “sense of place” 

or supporting a community architectural/urban design theme (Figure 1). 

• Improved aesthetics. Lighting may draw attention to architecture and other aesthetic features 

on structures such as bridges and monuments. Figure 2 shows an example of aesthetic lighting 

on a bridge tower and cables. Aesthetic lighting cases that involve changing colors and light 

shows are becoming more commonplace. Such lighting should be reviewed carefully, as light 

show effects such as light chasing, flashing, and flickering may be distracting to drivers and, in 

some cases (3 Hz to 20 Hz), induce epileptic seizure (Wilkins, Veitch, & Lehman, 2010). Notably, 

aesthetic lighting, particularly on bridges, can also impact wildlife and fisheries (these issues are 

discussed later in the document).
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Figure 2. Photo. Bridge structure lighting (Image Credit: WSP). 
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PART I – Technical Background

1 VISION AND PHYSIOLOGY PRINCIPALS & LIGHTING METRICS ........................................ 1 

1.1 Light and Vision............................................................................................................................. 1 

1.2 Fundamentals of Visibility and Physiology.................................................................................... 5 

1.3 Lighting Metrics........................................................................................................................... 14

2 LIGHTING CONSIDERATIONS ................................................................................................... 23

2.1 Safety............................................................................................................................................ 23

2.2 The Value of Lighting Design...................................................................................................... 30

2.3 Security and Livability ................................................................................................................. 33

2.4 Equity ........................................................................................................................................... 34

2.5 Complete Streets........................................................................................................................... 38

2.6 Aging Population.......................................................................................................................... 38

2.7 Cost............................................................................................................................................... 41

2.8 Alternatives to Lighting................................................................................................................ 43

3 WARRANTING............................................................................................................................... 46

3.1 Warrants ....................................................................................................................................... 46

3.2 AASHTO Warranting System...................................................................................................... 47

3.3 Warranting Method for Collector/Major/Local Streets................................................................ 47

3.4 Crash Modification Factors (CMFs) ............................................................................................ 51

3.5 Warranting Method for Intersections ........................................................................................... 51

3.6 Pedestrian/Bicycle Facilities ........................................................................................................ 54

4 LIGHTING PLANNING AND DESIGN PROCESS ...................................................................... 56

4.1 Lighting Master Plans................................................................................................................... 56

4.2 Design process.............................................................................................................................. 57

4.3 Design Applications..................................................................................................................... 62

5 LIGHTING SYSTEM SELECTION................................................................................................ 68

5.1 Lighting Selection ........................................................................................................................ 68

5.2 Other Design Considerations........................................................................................................ 72

5.3 Luminaire Classification .............................................................................................................. 73

6 ENVIROMENTAL IMPACTS AND MITIGATION...................................................................... 76

6.1 Wildlife Impacts........................................................................................................................... 76

6.2 Human Health Impacts................................................................................................................. 81

6.3 Light Pollution Impacts................................................................................................................ 82

6.4 Five Principals in Reducing Environmental Impacts................................................................... 86

7 ADAPTIVE LIGHTING.................................................................................................................. 88
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7.1 Luminance Selection .................................................................................................................... 88

7.2 Adaptive Lighting Application................................................................................................... 100

7.3 Lighting Controls ....................................................................................................................... 101

7.4 Smart City Applications............................................................................................................. 105

7.5 Vehicle-to-Infrastructure/Infrastructure-to-Vehicle Communication ........................................107

7.6 Cybersecurity.............................................................................................................................. 107

8 SUMMARY ................................................................................................................................... 108

9 REFERENCES............................................................................................................................... 110

2023 FHWA LIGHTING HANDBOOK

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1 VISION AND PHYSIOLOGY PRINCIPALS & LIGHTING METRICS

1.1 Light and Vision

Many factors influence a road user’s ability to see an object, including both the luminance and color

contrast of the object (i.e., the difference between the object and its background); the person’s 

adaptation level (which is affected by the brightness of the road and its surroundings, how much glare is 

present from approaching vehicles’ headlamps and luminaires, etc.); and how long the person has to 

view other road users or a hazard. Understanding these factors is vitally important to developing an 

effective design for roadway and street lighting.

The eye adapts to different luminance levels, providing the capability to see under very low light levels. 

In practical terms, however, the nighttime driving scene does not consist solely of the road surface and 

potential hazards to be detected; it also includes extraneous light from bright sources such as opposing 

vehicle headlights, off-roadway light sources, and street lighting luminaires. 

To understand the basic principles of vision, it is important to understand how the eye works. The basic 

components of the eye are shown in Figure 3. The human eye is complex; a more complete description 

can be found in Wyszecki and Stiles (1982). 

Figure 3. Diagram. Fundamental structure of the human eye (Transportation Association of Canada, 2006). 

While the retina contains several photoreceptors, the only image-forming receptors are rods and cones.

Rods, which are most numerous in the retina, are more sensitive, function at lower light levels, and are 

not color sensitive. Cones are sensitive to color and are divided into red (64%), green (32%), and blue 

(2%) cones (Williamson & Cummins, 1983). The cones are concentrated in the center of the retina with 

the most being in the fovea, which contains only cones. Cones provide the sensitivity and high-acuity 

vision needed for daytime tasks.
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In the 1990s, a type of photoreceptor was discovered and named “intrinsically photosensitive Retinal 

Ganglion Cells” (ipRGCs). These ipRGCs are linked in the pineal gland in the brain, which is responsible 

for the production of melatonin, a hormone that drives the human sleep cycle and circadian rhythms. 

Ongoing research is exploring the links of these photoreceptors to human health and well-being. 

The range of luminance (physical brightness) to which the retina can satisfactorily respond is much 

smaller than the range of luminance that occurs in nature and that the eye must view. The eye is 

equipped with two control mechanisms to overcome this problem: 

• Alteration of pupil diameter. Pupil size is governed by the iris of the eye. Closing the iris reduces 

the pupil diameter, which decreases the amount of light entering the eye and falling on the 

retina. The iris is modified by a feedback system from the brain. If a bright object is viewed, the 

retina gives a signal to the brain, which then signals the iris to close. Thus, an unconscious 

control is continually exercised as the luminance of the field of view changes.

• Adaptation. The adaptation of the eye occurs in the retina as the eye adjusts to the varying 

brightness of a scene resulting from such things as the overhead lighting system, approaching 

vehicle headlights, and ambient lighting conditions. States of adaptation include:

• Scotopic vision – vision by the normal human eye when only the rods of the retina are 

being used and the adaptation luminance at the eye is 0.034 cd/m2 or lower. At this 

state of adaptation, there is no sensation of color.

• Mesopic vision – when both the rods and cones are active at varying percentages based 

on the conditions and the adaptation luminance at the eye is between 0.034 and 3.4 

cd/m2

. At this state of adaptation, the eye is sensitive to color (“bluer” at the lower end 

of the adaptation range and “redder” at the higher end).

• Photopic vision – when predominantly cones are active and normal color vision is 

possible. The adaptation luminance at the eye is 3.4 cd/m2 or greater. 

The various states of eye adaption as they relate to roadway lighting levels are defined in Figure 

4. The eye does not shift suddenly from photopic to scotopic vision; rather, it undergoes a 

gradual change as light levels are reduced through the mesopic “twilight” range. The eye's 

mesopic response is a combination of the photopic and scotopic responses.

For the purpose of roadway lighting, photopic adaption is used for lighting photometry. Mesopic 

factors (as discussed in the 2012 Lighting Handbook) have minimal impact on the lighting levels

and are typically not applied (refer to Section 1.2.4, Spectral Effects). 
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Figure 4. Diagram. States of eye adaptation as related to roadway lighting levels (Transportation Association of Canada, 

2006). 

1.1.1 Spectral Properties

Visible light represents a limited wavelength range of all electromagnetic radiation. Within this range, 

different wavelengths are seen as different colors. As Figure 5 demonstrates, radiation with a shorter 

wavelength on the visible spectrum is perceived as bluer in color, while radiation with a longer 

wavelength is perceived as redder in color. 

Figure 5. Diagram. Electromagnetic spectrum and visible spectrum (Transportation Association of Canada, 2006). 

The eye has varying sensitivity to different wavelengths within the visible spectrum depending on the 

state of adaptation. Figure 6 shows the curves of relative spectral luminous efficiency at different 
2023 FHWA LIGHTING HANDBOOK

4

wavelengths for day (photopic) vision (blue line with squares, known as the V Lambda [V(l)] curve) and

night (scotopic) vision (orange line with dots). For photopic vision, light sources with wavelengths in the 

more “yellow” range, such as amber high-pressure sodium (HPS) sources, are rated at a higher power 

value (lumen), than sources with the same amount of “bluer” content, such as correlated color

temperature (CCT) light-emitting diode (LED) sources. The scotopic curve, V’(λ), (orange line with dots)

represents the eye response when using scotopic vision and shows that at low light levels, sources with 

more blue content are perceived to be brighter for the same lumen value, as a result of higher visual 

sensitivity. 

Figure 6. Line graph. Eye sensitivity curves. (Image Credit: VTTI)

CCT is defined as the absolute temperature of a blackbody 

whose chromaticity most nearly resembles that of the light 

source (Illuminating Engineering Society, 2010). More simply 

put, CCT is a measure of the color appearance of a light 

source in degrees Kelvin. CCT is often used as a proxy for the 

color quality of a light source due to its ease of use. Two 

light sources with identical CCTs can be perceived

differently, however; these differences are not reflected by 

CCT due to the loss of information caused by reducing the

spectral power distribution of a light source into a onedimensional metric (Durmus, 2021). Therefore, while 

commonly used, CCT is not a good measure of the spectral 

properties of a light source. The spectral power distribution (wavelength in nm) should be used when 

assessing lighting sources for environmental impacts (see Section 1.2.4, Spectral Effects).

While commonly used, CCT is 

not a good measure of the 

spectral properties of a light 

source. The spectral power 

distribution (wavelength in nm) 

should be used when assessing 

lighting sources for 

environmental impacts. 
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1.2 Fundamentals of Visibility and Physiology

1.2.1 Contrast

Objects are seen by “contrast,” which is essentially the visible difference between an object and its 

background. There are two forms of contrast: the first is luminance contrast and the second is color 

contrast. Each contributes to visibility in a different way.

1.2.1.1 Luminance Contrast

For luminance contrast, an object that is darker than its background will be seen by “negative” contrast, 

while an object that is sufficiently brighter than its background will be seen by “positive” contrast. In 

Figure 7, the upright object shown in the upper frames is in negative contrast (a darker object 

silhouetted against a brighter background), and in the lower frames it is in positive contrast (brighter 

object against darker background). It is also worth noting that contrast may vary within the object itself.

The upper right frame shows the bottom portion of the object in negative contrast, and the upper 

portion in positive contrast. The value of contrast can also change along an object’s length. 

Figure 7. Luminance images and photos. Positive (lower) and negative (upper) contrast levels in pseudo-color (left) and 

visible (right) models (Image Credit: WSP). 

The formula for calculating luminance contrast (Weber contrast) is shown in Equation 1.
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Equation 1: Weber Contrast

To assess contrast, a pseudo-color luminance calculation model can be undertaken (example shown in 

the left side of Figure 7). This modelling would not typically be undertaken as part of a usual lighting 

design and would be undertaken to prove concepts and methods.

As an example of a negative contrast calculation, the luminance values shown in the upper left panel of 

Figure 7 have been calculated as follows:

• Background luminance (blue area 1 cd/m2

),

• Lower portion of the cylinder, where the roadway is the background (green area = 22 cd/m2

)

Negative Contrast Equation: (1 cd/m2 − 22 cd/m2

) / 22 cd/m2 = −0.95 cd/m2, with the negative value 

denoting negative contrast.

Similarly, for the object with positive contrast (lower left panel in Figure 7) the calculation is as follows: 

• Luminance of the cylinder is 10.5 cd/m2

,

• Background is a dark sky with a luminance of 0.5 cd/m2

Positive Calculation Equation: (10.5 cd/m2

 − 0.5 cd/m2) / 0.5 cd/m2 = 20 cd/m2, where the positive value 

indicates positive contrast. 

These two calculations are included only as examples and highlight an issue with the contrast metric: 

negative contrast is bound within the range of 0 to −1, 

whereas positive contrast is unbounded. 

How much contrast a person needs to see an object (i.e., 

the threshold contrast) depends on several factors, 

including the size of the object, how long a person looks 

at it, their age, and their adaptation luminance 

(determined by the luminance of the road, glare from 

lights, approaching headlights, and ambient lighting 

levels). Threshold contrast is defined as the probability of 

detecting an object 99.9% of the time (Adrian, 1989). The 

purpose of a roadway lighting system is to ensure that the 

actual contrast of an object on the road exceeds the 

threshold contrast required by the driver to detect the 

object. Blackwell and Blackwell (1971) suggested that good object visibility can be achieved if the actual 

contrast is three to four times the threshold contrast. Obtaining this level of contrast is primarily a 

function of the lighting placement and optical characteristics.

A roadway lighting system 

ensures that the actual contrast 

of an object on the road exceeds 

the threshold contrast required 

by the driver to detect the 

object. Obtaining this level of 

contrast is primarily a function 

of the lighting placement and 

optical characteristics. 

LObject = Luminance of the object 

LBackground = Luminance of the background 
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7 

Small target visibility (STV) is a contrast-based metric for roadway lighting that can be used to design 

roadway lighting installations based on object visibility in the roadway. While no longer used as the 

primary metric for roadway lighting, STV provided insights for the placement of luminaires along the 

roadway with respect to crosswalks and intersections as well as the effect of uniformity in the roadway 

installation. Ultimately, the variability of the roadway scene and the nature of the potential objects that 

appear in the roadway limited the applicability of STV. However, STV can be used in roadway lighting 

design to compare various lighting layouts that all meet luminance and other design requirements. 

Thus, while there is no design metric for contrast, there are 

specific applications for which contrast can be used to 

determine design layout. Luminance contrast for an object in 

the roadway is typically a result of luminance driven by the 

vertical illuminance on the object, with horizontal illuminance 

providing the background luminance. This means that

luminaires can be placed in a way that provides vertical 

illuminance on an object of concern. As an example, vertical illuminance on a crosswalk can increase the 

visibility of pedestrians within the crosswalk. In this case, contrast drives the visibility and is controlled 

by luminaire position (Gibbons et al., 2008). 

1.2.1.2 Color Contrast

Color also provides additive contrast benefits. As shown in Figure 8, color contrast can improve the 

visibility of objects and pedestrians. This effect depends upon the color of the object or clothing and the 

color rendering ability of the source used for roadway lighting. For example, in the left frame of Figure 8,

the pedestrian’s red shirt and the red color of the approaching vehicle provide additional visibility via 

color contrast. However, this effect varies based on the environment. Both the light source spectrum 

and the spectral reflectivity affect the detection of objects in the roadway, which makes color contrast 

quite situational and variable. As such, the impact is not easily quantified and is generally not currently 

built into lighting design standards.

Figure 8. Photos. Effect of color contrast. (Image Credit: WSP)

As mentioned, the color of the light source affects the ability to generate color contrast. Light sources 

such as HPS do not provide a complete spectrum, meaning certain colors are not fully visible. However, 

Color contrast is important in 

the detection of objects in the 

roadway and can add as much 

as 20% to detection distance. 
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8

LED sources allow for a more complete spectral output, and color becomes more significant. Research 

has shown that the selection of a 4000K light source provides an additional benefit over traditional ones 

through contrast and the balance of the spectrum in terms of red and blue content in the spectral power 

distribution (SPD). 

The impact of contrast design to roadway lighting can be considered first as the position and layout of 

the luminaires, to provide luminance contrast, and the light source selection, to provide color contrast.

1.2.2 Glare 

Non-uniformities in the visual field, particularly those caused by bright sources, affect the adaptation 

level of the eye. Because these sources tend to fluctuate as the road user proceeds, the adaptation level 

is constantly changing (“transient adaptation”). By stabilizing the lighting level on the roadway, roadway 

lighting thus aids the eye in adapting to an increased level of luminance compared to that provided by 

headlights alone. Bright sources create other effects, collectively termed “glare,” which should be 

avoided as much as is practical. 

Glare can be a significant problem that seriously impairs both safety and quality of life. Glare can be a 

serious safety hazard for both drivers and pedestrians because it demands attention (since one’s eyes 

are naturally attracted to bright light) and causes an issue called transient adaptation when the eye’s 

dark adaptation is destroyed and there is a loss of sensitivity to lower light levels while the eye 

adaptation recovers.

When cast into surrounding residential neighborhoods, glare not only detracts from quality of life, but it 

can also make it difficult for pedestrians and homeowners to see their surroundings. Glare is 

experienced when the light-producing source (such as a bulb or lamp) is directly visible, although it also 

depends on the luminance (brightness) of the light source and the contrast between the source and the 

surrounding background. For example, a very bright light source viewed against a daytime sky does not 

seem particularly glaring or objectionable; however, the same source viewed against a fully dark night 

sky would seem so bright as to be almost painful. 

Glare or excessive brightness is a complex and difficult-to-measure phenomenon. Often the impact of 

glare is confounded with several other issues, including mood, predisposition to brightness, and past 

experiences. This makes the assessment of glare in the roadway difficult and often requires 

consideration of several competing issues.

1.2.2.1 Disability Glare

Light rays passing through the eye are slightly scattered, 

primarily due to diffusion in the lens and the vitreous humor 

that fills the anterior chamber of the eye. When a highintensity light source is present in the field of view, this 

scattering tends to superimpose a luminous haze over the 

retina. The effect is similar to looking at the scene through a 

luminous veil. The luminance of this veil is added to both the 

luminance of the objects in the roadway and background 

luminance, thereby reducing contrast (Equation 1). This effect is termed “disability glare” or “veiling 

Disability glare is one of the most 

important elements to control in 

a lighting system. It affects the 

ability to adequately see, 

particularly for older drivers. 
2023 FHWA LIGHTING HANDBOOK

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luminance,” and it can be numerically evaluated by expressing the luminance of the equivalent luminous 

veil. Consider the example of trying to see beyond oncoming headlights at night. In this case, contrast is 

reduced by disability glare, leading to decreased visibility. Increasing luminance can counteract this 

effect by reducing the eye’s contrast sensitivity. A well-designed roadway lighting system will minimize 

glare by employing luminaires with proper optical design. Disability glare on the roadway should be 

limited to veiling luminance ratios recommended by AASHTO and IES.

1.2.2.2 Discomfort Glare

Discomfort glare results from overly bright light sources in the field of view and causes a sense of pain or 

annoyance. While its exact cause is not known, discomfort glare may result from pain in the muscles 

that close the pupil. Disability glare and discomfort glare normally accompany one another, and 

beneficial luminaire light control that reduces one form of glare is likely to reduce the other. While 

discomfort glare can cause effects ranging from increased blink rate to tears and pain, it does not 

automatically reduce visibility, and roadway lighting standards do not specify numerical limits for 

discomfort glare. 

LED and HPS light sources are not a significant source of discomfort glare for drivers on the roadway. 

The severity of discomfort glare is mainly affected by the light level, and even the highest roadway 

lighting level was not found to produce “noticeable” discomfort glare (Engineering & Medicine, 2020). 

Therefore, the sources of discomfort glare are typically off the roadway and do not include street and 

roadway lights (especially high-mast lighting) and illuminated signs. 

CIE 243:2021, Discomfort Glare in Road Lighting & Vehicle Lighting (Commission Internationale de 

l'Eclairage, 2021) discusses discomfort glare in the context of road and vehicle lighting. This report 

provides an overview of the research methods, mathematical models, and variables considered to 

influence discomfort glare. CIE 243:2021 also describes the difficulties associated with evaluating and 

measuring discomfort glare and the variance in the models. The goal of the IES committee, Discomfort 

Glare in Outdoor Environments (DGONE), is to define a metric to measure and calculate discomfort 

glare. 

Discomfort glare can be a source of complaint from residents 

located off the roadway. CIE 150, Guide on the Limitation of 

the Effects of Obtrusive Light from Outdoor Lighting 

Installations provides information for assessing the source 

intensity of light sources set against a dark background. This 

document defines the maximum allowable intensity in 

candela from a light source based on physical and design 

criteria such as the size of the light source, the environmental zone, whether pre- or post-curfew, and 

the distance from the lighting source. Some lighting software can calculate the intensity at given 

locations.

Several strategies can be applied to reduce or eliminate discomfort glare. For example, adding a

diffusing lens over the optical system of pedestrian-scale luminaries can minimize discomfort glare 

caused by those mounted at 10 to 15 feet above the walkway. Eliminating the direct view of the optical 

system, which can appear very bright in the case of LED lighting, can also mitigate discomfort glare off 

Discomfort glare can be greatly 

reduced by adjusting the 

mounting height and shielding 

of the optical system. 
2023 FHWA LIGHTING HANDBOOK

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the roadway. Discomfort glare can be greatly reduced by adjusting the mounting height and shielding of 

the optical system. 

1.2.3 Perception-Reaction Time

Perception-reaction time, often referred to simply as reaction 

time, involves several components. To stop or avoid a hazard 

or person on a roadway, a motorist must first detect the 

object’s presence, recognize or otherwise assess the object, 

and then react to that assessment. The mechanical operation 

of the braking/steering mechanisms and the road/tire/vehicle 

performance conditions also factor into perception-reaction 

time. 

The key elements involved in reaction time include whether a 

situation is expected, cognitive load and distraction, personal physical response attributes, and age. In 

terms of whether a situation is expected, the AASHTO Green Book (American Association of State 

Highway and Transportation Officials, 2018a) classifies reaction times as follows: 

• Expected: The driver is alert and aware of the possibility that braking will be necessary, providing 

the best reaction time possible. The best estimate is 0.7 seconds, which includes 0.5 seconds for

perception and 0.2 seconds for movement (the time required to release the accelerator and depress 

the brake pedal). 

• Unexpected: The driver detects a common road signal (e.g., braking by the car ahead or a traffic 

signal). The reaction time in this case is approximately 1.25 seconds (the AASHTO Green Book states 

that the reaction time is approximately 35% longer than in the expected condition) due to the 

increased perception time (> 1 second). The movement time remains around 0.2 seconds. 

• Surprise: The driver encounters an unusual circumstance such as a pedestrian or another car 

crossing the road in the near distance. In this case, extra time is needed to interpret the event and 

decide on a response. The reaction time depends to some extent on the distance to the obstacle 

and whether it is approaching from the side and first viewed in the driver’s peripheral vision. The 

best estimate for reaction time in this case is 1.5 seconds for side incursions and a few tenths of a 

second faster for straight-ahead obstacles. In surprise scenarios, the perception time is around 1.2 

seconds, and the movement time lengthens to approximately 0.3 seconds. 

The perception-reaction time affects the distance required for a driver to stop when encountering an 

object in the roadway. For example, a person traveling at 55 mph is moving at approximately 80 ft/sec.

The distance traveled during the reaction time alone can be anywhere from 40 to 120 ft. When this is 

added to the distance covered during actual stopping, the total distance traveled can be significant. The 

AASHTO Policy on Geometric Design of Streets and Highways ((American Association of State Highway 

and Transportation Officials, 2018a) includes a method for determining stopping distance based on a 

number of factors, including reaction time. Table 1 and Table 2 show examples of estimated safe 

stopping sight distance (SSSD) based on the AASHTO method with modifiers showing the impact of 

roadway grades. Note that the SSSD calculations are typically for wet pavement.

In many cases, a roadway 

lighting system is required to 

provide the visibility needed for 

a driver to detect a pedestrian 

or road hazard in time to stop 

at high speed. 
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Table 1. Metric AASHTO safe stopping sight distances on wet surfaces with variation due to grade (from American 

Association of State Highway and Transportation Officials (2018a)). 

Metric 

Design 

Speed 

(km/h)

Stopping Sight Distance (m)

Downgrades Upgrades

3% 6% 9% 3% 6% 9%

20 20 20 20 19 18 18

30 32 35 35 31 30 29

40 50 50 53 45 44 43

50 66 70 74 61 59 58

60 87 92 97 80 77 75

70 110 116 124 100 97 93

80 136 144 154 123 118 114

90 164 174 187 148 141 136

100 194 207 223 174 167 160

110 227 243 262 203 194 186

120 263 281 304 234 223 214

130 302 323 350 267 254 243

Table 2. U.S Customary AASHTO safe stopping sight distances on wet surfaces with variation due to grade (from American 

Association of State Highway and Transportation Officials (2018a)). 

U.S. Customary

Design 

Speed 

(mph)

Stopping Sight Distance (ft)

Downgrades Upgrades

3% 6% 9% 3% 6% 9%

15 80 82 85 75 74 73

20 116 120 126 109 107 104

25 158 165 173 147 143 140

30 205 215 227 200 184 179

35 257 271 287 237 229 222

40 315 333 354 289 278 269

45 378 400 427 344 331 320

50 446 474 507 405 338 375

55 520 553 593 469 450 433

60 598 638 686 538 515 495

65 682 728 785 612 584 561

70 771 825 891 690 658 631

75 866 927 1003 772 736 704

80 965 1035 1121 859 817 782

Although stopping distances are not generally applied to roadway lighting, with the exception of tunnel 

lighting systems, the distances shown in Table 1 and Table 2 demonstrate one benefit of roadway 

lighting. Assuming that most low-beam vehicle headlights are effective approximately 300 ft in front of 

the vehicle (American Association of State Highway and Transportation Officials, 2018a), the stopping 
2023 FHWA LIGHTING HANDBOOK

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distance exceeds 300 ft when the vehicle speed is 40 mph or greater. For a driver to detect a pedestrian 

or road hazard in time to stop at high speed, the roadway lighting system therefore needs to provide the 

necessary visibility.

1.2.4 Spectral Effects 

The color of light (wavelength) affects the response in the eye, which also depends on the eye’s state of 

adaptation. While response curves for adaptation have been established for the photopic and scotopic 

states (as discussed above, the increase in blue sensitivity in the scotopic rod-driven vision), none have 

been established for the mesopic state, where the eye spectral sensitivity changes depending on the 

adaptation luminance based on the balance of rod and cone usage. Scotopic levels are too low to be 

applied to roadway lighting. IES TM-12-12 and The Lighting Handbook, 10th Edition (Illuminating 

Engineering Society, 2010) suggested that mesopic adjustment factors may be relevant to street and 

highway lighting calculations. However, an FHWA project demonstrated that these factors had no 

significant impact in a live roadway application (Gibbons et al., 2015). Since the driver is primarily 

photopically adapted, mesopic adjustment factors are not appropriate for street and highway lighting 

calculations at posted speeds of 25 mph and higher. Therefore, calculations for street and highway 

luminance and illuminance should be based on the photopic luminous efficiency function without 

mesopic adjustment factors. 

The spectral contents of street and highway lighting products vary and are controllable to a limited 

extent. Luminaires are available with many different spectral contents from nearly monochromatic 

yellows and reds to combinations of red, blue, and green that appear as white light to many observers. 

Designers may select the spectral content of luminaires to achieve the effects of color in the 

environment of their projects (Illuminating Engineering Society, 2018). The color spectra of various light 

sources are shown in Figure 9. The spike around 450 nm in the spectra of the LED sources in Figure 9 is 

referred to as the “blue pump.” The LED sources also have a much broader range of color compared to

the HPS source.

Figure 9. Line graph. Color spectra for various light sources. (Image Credit: VTTI)
2023 FHWA LIGHTING HANDBOOK

13

Under some conditions, the color temperature of an LED or HPS light source does not affect the visual 

performance of drivers. However, as mentioned above, color contrast can be improved by the selection 

of the light source. National Cooperative Highway Research Program (NCHRP) research evaluated driver 

visual performance by measuring the detection distance of pedestrians at two different offset distances 

(2 and 10 ft on the right shoulder) and under two speeds (35 and 55 mi/h), three light sources (3000K, 

4000K, and 5000K LEDs), and two surround ratios (high and low). Visual performance was maximized 

under the 4000K LED at both offset distances (Figure 10) and speeds (Figure 11), especially at the higher 

surround ratio. This result indicates that at higher speeds, 4000K LED lighting might be beneficial for 

increasing driver visibility (Engineering & Medicine, 2020). Similarly, other research has shown that the 

use of 4000K light sources generally improves object detection distance (Clanton & Associates & Virginia 

Tech Transportation Institute, 2014; Mutmansky et al., 2010) 

Figure 10. Line graphs. Effect of light source, surround ratio, and offset on the detection distance of pedestrians (Engineering 

& Medicine, 2020). 

Figure 11. Line graphs. Effect of light source type, surround ratio, and speed on the detection distance of pedestrians 

(Engineering & Medicine, 2020). 

The CIE S 026/E:2018 international standard (Commission Internationale de l'Eclairage, 2018) defines 

spectral sensitivity functions, quantities, and metrics to describe the ability of optical radiation to 

stimulate each of the five photoreceptor types that can contribute to retina-mediated non-visual effects 

of light in humans via the melanopsin-containing ipRGCs. CIE S 026/E:2018 is applicable to visible optical 

radiation in the wavelength range of 380 to 780 nm. It also includes information on the effects of age 

and field of view when quantifying retinal photoreceptor stimulation for ipRGC-influenced responses to 

light. An α-optic calculation toolbox and user guide were developed and are available through CIE. 
2023 FHWA LIGHTING HANDBOOK

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Spectral effects as they relate to health and environment are discussed further in Section 6,

ENVIROMENTAL IMPACTS AND MITIGATION. 

1.3 Lighting Metrics

This section provides a brief overview of key lighting metrics used in lighting design. For a more 

complete explanation and definitions, refer to IES RP-8-21(Illuminating Engineering Society, 2021e). 

1.3.1 Illuminance

Illuminance is a measure of the lumens incident on the 

pavement divided by the area. Illuminance follows the 

inverse square law; that is, the illuminance on a surface 

varies by the square of the distance from the light source. 

Illuminance is not impacted by the pavement’s surface type 

or the angle of observation. Illuminance is measured as the 

number of lumens per unit area, either in footcandles (fc)

(lumens/ft2

) or in lux (lumens/m2). The conversion from fc 

to lux is 10.76, therefore 1 fc = 10.76 lux. 

As a lighting metric, illuminance is simple to calculate and measure. The determination of illuminance 

does not require consideration of the reflective properties of the roadway surface, and only an 

inexpensive illuminance meter is needed for field verification. The drawback to this metric is that the 

amount of luminous flux reaching a surface is often not indicative of how bright a surface is or how well 

a person can see.

Illuminance has two components (horizontal and vertical) and a third metric, semi-cylindrical 

illuminance, by which the light striking a semi-cylinder is measured (Figure 12). 

Figure 12. Diagram. Schematic showing the three aspects of illuminance.( Image Credit: VTTI)

The drawback to illuminance 

as a metric is that the amount 

of luminous flux reaching a 

surface is often not indicative 

of how bright a surface is or 

how well a person can see. 
2023 FHWA LIGHTING HANDBOOK

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1.3.1.1 Horizontal Illuminance

Horizontal illuminance (E) is the illuminance component falling on a horizontal surface, defined using the

cosine of the angle of incidence. Figure 13 highlights the calculation method and the impact of the 

inverse square law. Here, the illuminance (E) is equal to the intensity from the luminaire (I) divided by 

the distance from the luminaire (D) multiplied by the cosine of the angle between the light ray from the 

luminaire and the normal to the surface being measured (β). 

Figure 13. Diagram. Inverse square law calculation of illuminance at a point (Image Credit: IES).

Typically, illuminance is a poor measure of visibility. As an example, imagine a half-white/half-black 

surface. Due to the better reflectance of light on a white surface than on a black surface, the appearance 

of the white surface would be totally different from that of the black surface, even though each may be 

receiving identical illuminance. Our eyes do not see illuminance or the light incident on a surface; they 

only perceive the proportion of light reflected toward them. 

Illuminance is the primary metric calculated for intersections and roundabouts, curved roadways (curve 

radius < 2000’), sidewalks, and railway crossings. Rather than using luminance as is used in tangent 

roadway sections, illuminance is used due to the geometry of the view of the roadway. As discussed 

later in this document (Section 1.3.2), pavement surfaces are evaluated at a 1-degree down angle 

assuming a person is looking 83 m in front of them. This is not the case for intersections and curves, as 

the driver’s glance point is different (Gibbons, Edwards, Bhagavathula, Carlson, & Owens, 2012), nor for 

pedestrians on sidewalks. As such, illuminance is used because the required geometry for the luminance 

calculation does not apply.
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1.3.1.2 Vertical Illuminance

Vertical illuminance is the amount of illuminance that lands on a vertical surface. The units and 

properties are the same as horizontal illuminance. In roadway lighting, vertical illuminance is generally a 

reasonable criterion for determining the amount of light landing on pedestrians. It is also used as a 

criterion for determining adequate illumination for facial recognition from a security perspective. For 

roadway applications, vertical illuminance is most often used at a height of 5 ft above the roadway or 

sidewalk (the approximate height of a pedestrian’s face). Figure 14 highlights the calculation method for 

vertical illuminance (note the position of the angle β is normal to a vertical surface rather than a 

horizontal surface as in Figure 13). 

Figure 14. Diagram. Calculation of vertical illuminance.( Image Credit: IES) 

Because vertical illuminance can represent the amount of light falling on pedestrians, vertical 

illuminance is important in terms of the visibility and detection of pedestrians from a safety perspective, 

especially those in or approaching crosswalks. This is discussed further in the examples in Part II. 

1.3.1.3 Semi-cylindrical Illuminance

Semi-cylindrical illuminance is similar in principle and application 

to vertical illumination but is calculated differently. Semicylindrical illuminance is the average vertical illuminance on the 

curved surface of an upright semi-cylinder. It is calculated at 4.75

ft (1.5 m) above the road surface on a half-cylinder whose front is 

parallel to the main direction of pedestrian movement (for a road, 

the main direction of pedestrian movement is usually 

Semi-cylindrical illuminance 

is similar to vertical 

illuminance but shows all of 

the pedestrian profile. 
2023 FHWA LIGHTING HANDBOOK

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longitudinal). The calculation grid points are the same points as the roadway grid. Specific lighting 

calculation software is required to calculate semi-cylindrical illuminance. According to research (van 

Bommel, 2014), semi-cylindrical illuminance at face height is a better metric than vertical illuminance for 

recognition because the human face is three-dimensional and not flat. Therefore, semi-cylindrical 

illuminance is a better parameter to estimate visibility than a measure of illuminance incident on a flat 

surface (vertical/horizontal illuminance). It is important to note that semi-cylindrical illuminance has 

almost always been studied from the point of view of one pedestrian identifying another pedestrian on 

the street (Rombauts, Vandewyngaerde, & Maggetto, 1989). The effect of semi-cylindrical illuminance 

on the detection of a pedestrian by an approaching driver was investigated as part of a research effort 

for FHWA; the results suggest that semi-cylindrical illuminance is a similar metric to vertical illuminance 

but is more forgiving as it shows all of the pedestrian profile (Terry et al., 2020). As part of a cross-walk 

study, Gibbons et al. (2008) used a semi-cylinder as a surrogate for a pedestrian in human factors testing 

and found it to most closely models the detection of an actual pedestrian in the roadway.

1.3.2 Luminance 

Luminance is the amount of light that reflects from a surface 

in the direction of the observer. Luminance is often referred 

to as the “brightness” of the surface, although apparent 

brightness takes a number of other factors into consideration.

Luminance is a much better visibility metric than illuminance 

because it considers not only the amount of light that reaches 

a surface, but also how much of that light is reflected toward 

the driver. Luminance is calculated using a fixed group of 

conditions. The observer is 83 meters back from the 

calculation point, the eye height of the observer is 1.45 

meters, and the assumed viewing angle is down 1 degree (Figure 15). These conditions are fixed because 

of the limits of the R-tables (reflection tables) used to calculate luminance. Because of these fixed 

conditions, designers sometimes use illuminance-based calculations for areas like intersections and 

curved roadways where the assumptions of 83 meters back from the calculation point and a 1-degree

downward viewing angle are not applicable. 

Luminance is a much better 

visibility metric than 

illuminance because it 

considers not only the amount 

of light that reaches a surface, 

but also how much of that light 

is reflected toward the driver.
2023 FHWA LIGHTING HANDBOOK

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Figure 15. Diagram. Calculation of luminance. (Image Credit: IES) 

Luminance on the pavement is based on the quantity and direction of light, observer location, and the 

pavement reflectance characteristics. The overall average luminance of the road surface as observed 

from a specific point in cd/m2

 is used for roadway lighting calculations. Metric units for luminance are 

used regardless of the units used in the calculation specification. To calculate luminance, the observer 

position is 4.5 ft (1.45 m) above the pavement surface and 272.5 ft (83.0 m) back from the computation 

point along a longitudinal line parallel to the direction of travel. The observer line of sight is 1 degree 

below horizontal. Observer position changes relative to the curb line to align with each row of 

calculation points. A roadway luminance grid represents the calculation points for a single directional 

flow of traffic. To consider the entire roadway, a calculation grid should be created for each direction of 

traffic flow (Illuminating Engineering Society, 2018). 

IES RP-8-21 defines luminance as the primary metric to be calculated for lighting on roadways, whereas

AASHTO G-7 indicates that luminance or illuminance calculations can be used. Where possible, 

luminance is recommended to be used as it is a better measure of visibility. It is also important to note

that defining the veiling luminance ratio (see Section 1.3.3) requires a luminance calculation.
2023 FHWA LIGHTING HANDBOOK

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1.3.3 Veiling Luminance (Lv)

Veiling luminance (also referred to as disability glare) can be numerically evaluated for street and 

roadways. Because veiling luminance reduces contrast, it also decreases visibility. Increasing the 

luminance level can counteract this effect by reducing the eye’s contrast sensitivity. As glare limits 

visibility, veiling luminance is an important consideration. 

Both IES RP-8-21 and AASHTO G-7 define Lv as a lighting 

requirement; however, it is sometimes omitted in 

calculations of illuminance. Given the significant impact 

of glare on visibility, Lv should not be omitted from the 

calculation. 

As glare is a function of adaptation luminance, the road 

is used as the assumed scene from which the luminance 

reaches the eye. From this, the design metric (the veiling 

luminance ratio) is used as the metric of disability glare. 

Here, the ratio is calculated as the maximum value of 

calculated veiling luminance (Lv,max) divided by the 

average pavement luminance (Lavg). 

Equation 2: Veiling Luminance

For this calculation, the Lv from every luminaire is calculated at the same calculation points as pavement 

luminance with the observer 272.5 ft (83.0 m) back from each point under consideration. The observer 

height is 4.5 ft (1.45 m) above the road surface, and the line of sight is 1 degree below horizontal. 

The calculation of veiling luminance includes the contribution from poles before and after the 

calculation grid. For a proper calculation, the observer needs to be within the calculated array of 

luminaires. For further information refer to IES-RP-8-21, Chapter 3. 

1.3.4 Weighted-average Visibility Level or Small-target Visibility (STV)

STV is a measure of the visibility level of small targets as seen against the pavement background. The 

following factors are considered in STV: target 

luminance, background luminance, adaptation level, 

and disability glare. When considering the visibility 

level and STV, designs are created that produce 

negative and positive contrast, all positive contrast, 

and all negative contrast. The weighted average of 

the calculated visibility levels is the STV. The 

visibility levels are computed at the same points as the pavement luminance. As with all luminance 

calculations, the observer position is 272.5 ft (83.0 m) back from each point. 

The reduction of glare is one of the 

most important design factors 

related to visibility on the 

roadway. The calculation of veiling 

luminance is critical to quantifying 

that glare. Defining the veiling 

luminance ratio also requires the 

calculation of luminance. 

Although STV is not used as the 

primary metric, it can be used to 

compare lighting designs. 
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Although STV is not used as the primary calculated metric, it can be used as a method to compare

lighting designs. If multiple designs meet the luminance or illuminance, uniformity, and Lv criteria, the

optimal design could be determined as the one with the higher STV value. STV may be considered by 

those with the experience and knowledge to understand the concept and theory.

1.3.5 Uniformity Ratio

Uniformity is the evenness of light over a given area. Uniform lighting throughout an area would have a 

uniformity ratio of 1:1. A high degree of uniformity of street lighting is generally accepted as desirable. 

As discussed, lighting calculations involve a series of grid points at which the luminance or illuminance 

levels are calculated. The uniformity is assessed based on two ratios: (1) the ratio of the average 

luminance or illuminance from all points to the minimum calculated level at all points (the average-tominimum ratio); and (2) the ratio of the maximum calculated value to the minimum calculated value

(the maximum-to-minimum ratio). Uniformity ratios should be used for all lighting scenarios.

Newer technologies such as LEDs offer improved 

uniformity through efficient optical systems, making 

even uniformity (1:1 ratio) possible. However, 

completely even uniformity can actually limit visibility. 

As shown in Figure 16, an object on a roadway with a 

completely uniform lighting level fades into the 

background. Thus, a level of non-uniformity is required 

to improve visibility and reduce crashes. The nonuniformity in the roadway increases the contrast and 

thus increases visibility. 

 

Figure 16. Photo. Completely uniform roadway lighting results in poor contrast (Image credit: Paul Lutkevich, WSP). 

Completely even uniformity can 

actually limit visibility. Some nonuniformity in the roadway 

increases the contrast and thus 

increases visibility. 
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1.3.6 Surround Ratio

Roads and streets typically have lighting requirements for 

travel lanes and sidewalk areas. Providing additional 

lighting outside of the limits of the travel lanes has been 

shown to have significant benefits in terms of object 

detection (Engineering & Medicine, 2020). Accordingly, a 

surround ratio should be defined. The surround ratio is 

calculated as the ratio of the average horizontal 

illuminance on the outermost lane to that on a similar area 

off the roadway adjacent to the outermost lane (the 

surround illuminance; see Figure 17). For example, if the average horizontal illuminance on the 

outermost lane is 10 lux, to obtain a surround ratio of 0.8:1, the area off the roadway would require a 

maintained average horizontal illuminance of at least 8 lux. Figure 18 compares a high surround ratio 

(left) and a low surround ratio (right). 

Figure 17. Diagram. Surround ratio calculation layout from NCHRP 940. 

Figure 18. Photos. Images showing high (left) and low (right) surround ratios (Image credit: VTTI). 

As a result of the desire to reduce light trespass out of the roadway, LED luminaire manufacturers have 

focused on tight optical controls to reduce light spill and maximize the light on the roadway. This creates 

a dark surround (low surround ratio) and a “light tunnel” effect. Previous high-intensity discharge

lighting technologies had far less optical control and therefore provided a reasonable amount of 

surround lighting. Figure 19 shows a comparison of an HPS lighting system, which creates significant 

lighting off the roadway, with an LED lighting system, which provides tight optical control.

Providing lighting outside the 

limits of the travel lanes has been 

shown to have significant benefits 

in terms of object detection. 

Accordingly, it is necessary to 

define the surround ratio. 
2023 FHWA LIGHTING HANDBOOK

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Figure 19. Photos. Images showing surround ratios from LED lighting (right) and traditional lighting sources (left) (Image 

Credit: DMD).
2023 FHWA LIGHTING HANDBOOK

23

2 LIGHTING CONSIDERATIONS 

This section defines key lighting considerations, with the most significant being safety. Other 

considerations include the value of lighting design, security and livability, equity, complete streets, aging 

population, cost, and alternatives to lighting. Many of these impacts can be enhanced (the positive 

impacts) or mitigated (the negative impacts) through good lighting design. 

2.1 Safety

Safety is the top priority of the U.S. DOT. For FHWA, this 

means that road systems should be designed to protect 

their users through life-saving programs and 

infrastructure safety solutions. FHWA’s goal is eliminate 

all transportation-related fatalities and serious injuries 

across the transportation system. 

In reaching the vision of zero deaths and serious injuries, 

there are several considerations, including the approach 

to safety, the type of roadway user, and the roadway 

environment.

2.1.1 Safe Systems Approach

Design should follow the FHWA Safe System approach, which aims to eliminate fatal and serious injuries 

for all road users. It does so through a holistic view of the road system that (1) anticipates human 

mistakes and (2) keeps impact energy on the human body at tolerable levels. In a safe system, neither a 

human mistake nor force on the human body should lead to death, which means that the infrastructure 

should be designed in such a way as to manage the potential risk to any driver. 

Figure 20 defines the safe systems through six principles that form the basis of a Safe System: deaths 

and serious injuries are unacceptable, humans make mistakes, humans are vulnerable, responsibility is 

shared, safety is proactive, and redundancy is crucial. These six principles define the approach used in 

each of the five Safe System Elements (Safe Roads, Safe Road Users, Safe Vehicles, Post-Crash Care, and 

Safe Speeds), which together create the required layers of protection for the driver. One of the keys to 

the Safe System approach is the safety culture that an agency has that places safety first and foremost in 

their decision making.

Lighting falls into the Safe Roads element in a Safe System approach. As part of the roadway 

infrastructure, a well-designed roadway lighting system will improve visibility and make for safer roads 

and safer road users. Investment in lighting for a roadway is a critical decision for an agency to consider. 

For more information on the FHWA’s Safe System Approach, refer to 

https://safety.fhwa.dot.gov/zerodeaths/zero_deaths_vision.cfm

FHWA's goal is to reduce 

transportation-related fatalities 

and serious injuries across the 

transportation system. Designs 

should follow the FHWA Safe 

System approach to eliminate fatal 

& serious injuries for all road users. 
2023 FHWA LIGHTING HANDBOOK

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Figure 20. Infographic. The FHWA Safe System. (Image Credit: (Image Credit: FHWA)

2.1.2 Road User Safety

Over the last 50 years and more, many studies have

indicated significant benefits of roadway lighting with 

respect to crash reduction.

One of the more recent studies (Gibbons et al., 2014) 

examined over 2,000 miles of roadway lighting and 83,000 

crashes to build a link between the lighting level and the 

night-to-day crash rate ratio. Figure 21 shows the 

developed relationship. The drop in the night-to-day crash 

rate ratio is evident with increasing illuminance level. It is noteworthy that the benefit of the lighting 

decreases with increasing lighting level. This research also showed the impact of lighting on safety in a 

variety of road classifications. Figure 22 shows the drop in the night-to-day crash rate ratio for a lighting 

level by roadway classification. The horizontal dashed lines in this figure show where additional lighting 

does not improve the roadway safety aspects.

Pedestrians are 3 to 6.8 times 

more vulnerable at night. Lighting 

can improve visibility where 

pedestrians and cyclists are 

present. Lighting of roads with 

these users should be a priority. 
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Figure 21. Line graph. Night-to-day crash rate ratio at different horizontal illuminance (Gibbons, Guo, Medina, Terry, Du, 

Lutkevich, & Li, 2014). 

Figure 22. Line graph. Night-to-day crash rate ratio at different horizontal illuminance (Gibbons, Guo, Medina, Terry, Du, 

Lutkevich, & Li, 2014). 

This study and others indicate that road users such as pedestrians and bicyclists are affected by darkness 

far more than motorists. According to a National Center for Statistics and Analysis (2020) fact sheet,

three fourths of all pedestrian-related fatalities occurred during periods of darkness (76%). These data 

show that not only pedestrian crossing areas but all areas of the roadway where pedestrians might 

interact with the roadway should be included in lighting decisions. One of the primary factors 

differentiating other road users and the motorist is the active lighting on the vehicle itself. Headlamps, 
2023 FHWA LIGHTING HANDBOOK

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side markers, and taillamps define the presence and motion of a vehicle at night. As there is no similar 

active lighting system consistently carried by pedestrians, roadway lighting roadway lighting becomes 

very important in providing visibility for these roadway users.

Based on crash analyses from 2009 to 2018, Benson, Tefft, Arnold, and Horrey (2021) showed that most 

pedestrian fatalities occurred in darkness, accounting for 87% of the overall increase in pedestrian 

fatalities during this period. A University of Michigan Transportation Research Institution study showed 

that pedestrians are 3 to 6.8 times more vulnerable at night, and that lighting can improve visibility 

where pedestrians are present (Sullivan & Flannagan, 2002). In 2017, the National Highway Traffic Safety 

Administration (NHTSA) reported that 74% of all pedestrian fatalities occurred at night, and pedestrian 

and cyclist nighttime fatalities increased substantially from 2017 to 2018, as shown in Figure 23)

(National Center for Statistics and Analysis, 2020). Thus, proper lighting is needed to enhance pedestrian 

visibility to drivers. This figure indicates a trend that seems to continue even throughout 2020, with 

pedestrian fatalities remaining consistent with time but cyclist fatalities increasing by 5% in 2020 over 

2019 levels (National Center for Statistics and Analysis, 2022). 

Figure 23. Bar graph. Change in nighttime fatalities from 2017–2018. (Image Credit: DMD) 

Given increases in fatalities among vulnerable road users such as pedestrians and bicyclists, the lighting 

of roads with these users in mind should be a priority. As shown in Figure 24, speed is a significant factor 

in determining survivability when a pedestrian is hit by a motor vehicle, with higher-speed crashes 

resulting in a lower chance of survival. Therefore, the greatest need for lighting is on higher-speed roads 

(30 mph and greater). The needs for lighting should be defined using the policies and practices of the 

jurisdiction that owns the roadway along with sound engineering judgment. 
2023 FHWA LIGHTING HANDBOOK

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Figure 24. Infographic. Relation between vehicle speed and chance of pedestrian survival (Fesler, 2014). 

2.1.3 Intersections and Roadside Areas 

While there is a need to consider safety on all areas of the roadway, particular consideration should be 

placed on intersections and roadside facilities. These are the primary areas of the roadway for potential 

interaction of vulnerable road users and vehicles. 

Intersections are challenging locations for all road users but can be especially dangerous for pedestrians 

and bicyclists. Based on Fatality Analysis Reporting System (FARS) data, approximately 27% of 

pedestrians and 38% of bicyclists killed from 2014 to 2016 were struck at intersections (National Center 

for Statistics and Analysis, 2020). In urban areas, these numbers were even higher: 32% of pedestrian 

fatalities and 44% of bicyclist fatalities occurred at intersections or were intersection related. Often, 

these fatalities occurred while crossing two-way, undivided streets with no traffic control. Other factors 

such as a lack of roadway lighting, large number of lanes, and high vehicle speeds compound safety 

problems for non-motorized road users at intersections (Medicine, 2020). 

Ensuring safety in roadside facilities such as sidewalks and bike lanes is equally critical. According to a 

National Center for Statistics and Analysis (2020) fact sheet, in 2018, 74% of all pedestrian fatalities 

occurred at non-intersections (opposite of the statistic listed above) and 10% occurred on roadsides, 

shoulders, parking lanes, bicycle lanes, sidewalks, and midblock crosswalks, among other sites. This 

suggests the need to provide careful consideration of lighting for pedestrian facilities not only at 

intersections but along the roadway in areas such as sidewalks and bikeways as well. 

An important design factor for street crossings is providing sufficient sight distance for pedestrians, 

bicyclists, other road users, and motorists to view each other clearly on the approaches to any conflict 

points. All parties should be able to perceive and react to a potential conflict, and motorists should be 

able to come to a full stop before conflicting with a pedestrian, bicyclist, or other road users. 

The final aspect of lighting for a roadway is that other road users not only need to be seen but also need 

to see, meaning that they should be able to see their surroundings, which provides them with the ability 

to detect trip-and-fall hazards and provides perceptions of safety and security. 
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2.1.4 Safe Routes to School

Of particular concern are school-age children traveling to school. 

These children may travel at twilight in both the morning when 

going to school and in the early evening when coming from 

school, creating unique issues. Children are especially vulnerable 

to traffic. In addition to being small and easily distracted, 

children have difficulty judging the direction of sounds, 

estimating the speed and distance of oncoming vehicles, and 

anticipating driver behaviors. In a recent virtual reality 

simulation performed at the University of Iowa, 6-year-old children were struck 8% of the time when 

crossing busy one-lane streets, while the crash rates for 8-, 10-, and 12-year-old children were 6%, 5%, 

and 2%, respectively. Children’s limited ability to judge the available gap in traffic at a young age 

primarily attributes to this difficulty in crossing streets. Younger children also take more time to take the 

first step in crossing the street, shortening the available gap. However, children’s crossing speeds do not 

differ from those of adults (O'Neal et al., 2018). 

Safe Routes to School (SRTS) is an international approach using engineering, enforcement, safety 

education, and incentives to encourage children to walk and bike to school

(https://www.fhwa.dot.gov/environment/safe_routes_to_school/). Engineering approaches broadly 

incorporate design, implementation, operation, and maintenance of infrastructure improvements like 

traffic control devices or physical devices such as barriers and roadway islands. Enforcement approaches 

encompass strategies to stop unsafe behaviors in drivers, pedestrians, and bicyclists. Enforcement 

strategies also encourage all road users to obey all traffic safety rules and share the road with other 

road users. Education approaches involve teaching road users the benefits of SRTS and creating 

awareness about them. Encouragement approaches closely follow education approaches and aim to 

promote walking and bicycling by getting road users interested in those means of transportation. The 

Federal-Aid SRTS Program provides funding to enable and encourage children to walk and bike to 

school; to make bicycling and walking to school a safer and more appealing transportation alternative; 

and to facilitate the planning, development, and implementation of projects and activities that will 

improve safety and reduce traffic, fuel consumption, and air pollution in the vicinity of schools (23 U.S.C. 

208(c)). Funds can be spent on the Federal-Aid SRTS Program under the Surface Transportation Block 

Grant program (23 U.S.C. 133(b)(7)), the Transportation Alternatives Set-Aside (23 U.S.C. 133(h)(3)(B)), 

and the Highway Safety Improvement Program as a specified safety project (23 U.S.C. 148(a)(11)(B)(v)). 

SRTS funds can be used by States to provide financial assistance to State, local, Tribal, and regional 

agencies (23 U.S.C. 208(f)). Other programs that promote safety for schoolchildren can be implemented 

by a state department of transportation, metropolitan planning organization, local government, school 

district, or even a school.

Roadway and pathway lighting focusing on the visibility of children at night can serve as an SRTS 

intervention as current lighting guidelines focus primarily on the visibility of adult pedestrians. Recent 

research on the needs for pedestrian lighting provides recommendations for lighting in areas common 

to children who walk to school, in both rural and urban areas (Terry et al., 2020). Careful consideration 

to the characteristics of urban and rural environments should be given as contrast, visual clutter, and 

multiple light sources impact a pedestrian’s visibility. The scope of this research not only includes the 

visibility of children as pedestrians from the point of view of the driver but also the ability of 

Photo. emin kuliyev, shutterstock
2023 FHWA LIGHTING HANDBOOK

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pedestrians, children, and adults to detect hazards in their walking path under the same lighting 

conditions. This method ensures that any recommendation for lighting that benefits the visual 

performance of a driver also considers the visual performance of pedestrians of all ages.

2.1.5 Warrants for Pedestrian Lighting

Despite the high-risk pedestrians and bicyclists face, no 

lighting warranting system has been developed that gives 

suitable weight to pedestrian crossings and bike lanes. 

These areas should be highly prioritized, especially where 

motor vehicles and vulnerable road users conflict. More 

light is not always the best solution; the appropriate 

amount of light is critical to increasing contrast and 

making vulnerable road users more visible, especially at 

nighttime. Warrants are considered in much more detail 

in Chapter 4 of this document.

2.1.6 Roadway Environmental Factors

Weather can dramatically change the way light behaves and affects the human perception of brightness, 

glare, and depth. Weather conditions significantly impact the reflection properties of the pavement 

surface and can make the road surface reflect light specularly rather than diffusely, particularly in the 

rain. This leads to high contrast levels and poor visibility, as shown in Figure 25. 

Figure 25. Photo. Lighting performance in different weather conditions (Dry [Left], Rain [Center], Fog [Right]), (Image Credit: 

Paul Lutkevich, WSP). 

Gibbons and Williams (in review) studied the detection of pedestrians in clear, rainy, and foggy

conditions and found that the spectral impacts of the light source are diminished in rainy and foggy

conditions and that the effect of light source intensity is more important. The study also revealed 

significant impacts of weather conditions on vehicle speed and object contrast; thus, the results require 

careful interpretation. 

No lighting warranting system has 

been developed that gives suitable 

weight to pedestrian crossings and 

bike lanes, which should be highly 

prioritized, especially where motor 

vehicles and pedestrians/bicyclists 

conflict. 
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Wanvik (2009) performed a meta-analysis of crash data in three different countries and considered the 

impact of weather and road surface condition on crashes. Table 3 shows the effective reduction in 

collisions provided by street lighting under various conditions, demonstrating the significant impacts of 

weather and road surface conditions on the ability of street lighting to reduce collisions (Note that 

Wanvik also included crash type and road user type with similar results to those from U.S. data sources.) 

Table 3. Effects of lighting on collisions under various road and weather conditions on Dutch Roads (Wanvik, 2009).

Conditions Effect 95 % conf.

All -54% -56 %, -52 %

Weather 

conditions

Fine weather -54% -56 %, -52 %

Rainy weather -45% -53 %, -37 %

Foggy conditions 0% -15 %, +18 %

Snowy weather -26% -40 %, +8 %

Road 

surface 

conditions

Dry road surface -56% -59 %, -54 %

Wet road -46% -50 %, -43 %

Snow / ice covered -22% -31 %, -11 %

Road user

Pedestrian -70% -77 %, -61 %

Bicycle -60% -65 %, -54 %

Moped -61% -64 %, -56 %

Motorcycle -26% -42 %, -5 %

Automobile -50% -52 %, -47 %

Accident 

type

Hit fixed object -54% -58 %, -49 %

Frontal collisions -50% -55 %, -43 %

Flank collisions -46% -51 %, -41 %

Hit animal -57% -63 %, -50 %

Rear end collisions -51% -54 %, -46 %

2.2 The Value of Lighting Design

For a quality outcome for roadway users, a proper lighting design is an important aspect of the lighting 

development process. While the purpose of street and road lighting is to improve the driver’s visual 

performance, not all street lighting produces the same benefits. Some jurisdictions look at lighting in 

terms of standardized cookie-cutter layouts without requiring lighting calculations. This can significantly 

limit the value and benefits of lighting. Unlike HPS luminaires, which provided similar performance from 

product to product, allowing for one-to-one replacement regardless of the manufacturer, LED 

luminaires vary greatly in optical efficiency and light distribution from product to product. LEDs have 

opened the door to new manufacturers, optical systems, and light distributions; as such, many more 

specific optical systems are available. This means that simply defining a luminaire wattage, lumen 

output, and optical distribution (IES Type II, III, IV) and assuming all products meeting those 

specifications will produce equal results can reduce the overall effectiveness of the lighting system. The 

differences in current technologies and products are further discussed in Section 5.1.1.
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Given the vast differences in LED product performance, it is 

worth properly evaluating the performance of lighting 

designs. Lighting calculation software and the power of 

computing systems have evolved, resulting in quick and 

easy lighting calculations that provide methods to optimize 

a lighting design. 

One area IES RP-8-21 and AASHTO G-7 have not specified is 

the maximum average maintained illuminance or 

luminance level. This has led to an impression that

increasing the illuminance or luminance level will always 

improve visibility and safety. However, the benefits of increasing the lighting level reach a plateau 

beyond which there are diminishing returns. Figure 21 and Figure 26 demonstrate the diminishing 

returns observed in detection distance and night-to-day crash rate ratio when the lighting level exceeds

12 lux (Bhagavathula & Gibbons, 2019; Gibbons, Guo, Medina, Terry, Du, Lutkevich, & Li, 2014). This 

threshold level will vary with speed and road class; however, these figures show that over-lighting does 

not inevitably produce additional benefits, and lighting beyond the level defined in IES RP-8-21 and 

AASHTO G-7 may not have any real value. Therefore, it is recommended that lighting not exceed the 

maintained lighting level specified for the roadway by more than 50%. The 50% is a maximum target to 

allow for variability in the designs and is not absolute. Designers are encouraged to get as close as 

possible to the required maintained level while not going below that level. 

Figure 26. Line graph. Detection distances at various lighting levels (Bhagavathula & Gibbons, 2019). 

Typically, when lighting is mounted on utility poles, the necessary lighting levels are difficult to achieve 

since the pole spacing is defined by the power line design 

as opposed to the lighting design. In some cases, the 

poles are two to three times further apart than the 

distance required for achieving the minimum 

recommended uniformity ratios (this is often referred to 

as “half code” lighting). The rationale for half code is that 

some lighting is better than no lighting, even if well below 

the requirements (i.e., install half the lighting and get half 

the benefit). However, reductions in the required lighting 

The benefits of increasing the 

lighting level reach a plateau 

beyond which there are 

diminishing returns. It is therefore 

recommended that lighting not 

exceed the required maintained 

level by more than 50%. 

Selecting the most appropriate 

lighting system is best done 

through lighting design and 

calculation on a per-project 

basis as opposed to using a onesize-fits-all approach. 
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criteria and specifically uniformity may be more detrimental to visibility than the absence of lighting. 

Rather than providing lighting that does not meet the requirements, it may have a greater benefit to 

add lighting at critical conflict points such as intersections. 

From the perspective of under- versus over-lighting, there is clearly a sweet spot where the lighting 

system provides maximum benefits in terms of visibility, environmental impact, and energy efficiency. 

Selecting the most appropriate lighting system is best done through lighting design and calculation on a 

per-project basis as opposed to using a one-size-fits-all approach. 

When designing lighting for sidewalks, the lighting levels can be misleading as the reflective properties 

of sidewalks and buildings can affect the overall surround brightness and visibility. 

All designs should consider light blockage from landscaping and street trees as shown in Figure 27. 

Where trees are proposed, lights may have to be installed on arms that extend out over the roadway 

beyond the ultimate tree canopy. With the lighting extended over the roadway, additional pedestrianscale lighting will often be required to properly light the sidewalks. The proposed locations, spacing, pole 

height, arm length, and frequency of the trees may also need to be adjusted in conjunction with the 

lighting pole spacing. A pole spacing shorter than the calculated value may be required to compensate 

for anticipated light blockage, resulting in additional poles and luminaires. When a roadway or 

pedestrian lighting project includes new or existing trees near the lighting, an additional light loss factor 

should be included in the design for light loss due to shading. At this time, no research has quantified 

this factor; however, an additional 10% to 20% of light loss should be considered. In addition, it is 

recommended that the required pole spacing be adjusted so that luminaires are located outside of tree 

canopies.

Figure 27. Photo. Example of trees blocking lighting and creating shadows (Image Credit: DMD). 

In streetscape applications with trees and sidewalks separated from the roadway, it is recommended 

that the roadway lighting and sidewalk lighting be provided by separate luminaires, each of which is 
2023 FHWA LIGHTING HANDBOOK

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designed in consideration of the effects of the tree canopy. Refer to Figure 28 for an example of such 

lighting. 

Figure 28. Illustration. Examples of streetscape lighting (Image Credit: DMD). 

2.3 Security and Livability

A livable city promotes health and the happiness of its citizens. One primary concern is the security of 

the citizens as they use city facilities. Lighting is a key component in a livable city, as lighting has been 

shown to provide a sense of security to citizens (Painter, 1996). One of the considerations here is also 

uniformity of the lighting, as dark areas and lower lighting level can negatively affect the feeling of 

security for roadway users.

While street lighting and walkway (sidewalk) lighting have been shown to provide better visibility for 

pedestrians at night, the impact of lighting on crime is less clear. Research on the effects of street 

lighting on security and crime have been inconclusive. Some studies found that improved street lighting 

was effective in reducing crime (Atlanta Regional Commission, 1974; Lewis & Sullivan, 1979; Wright, 

Heilweil, Pelletier, & Dickinson, 1974), while other studies did not find any reductions in crime due to 

improvements in street lighting (Department, 1976; Inskeep & Goff, 1974; Quinet & Nunn, 1998; 

Sternhell, 1977). These differences may be a result of differing demographics and analysis approaches. 

In a more recent study, Chalfin, Hansen, Lerner, and Parker (2021) evaluated the effect of street lighting

on crime in New York City and found that street lighting was associated with an approximately 36% 

reduction in outdoor nighttime crimes and an approximately 4% reduction in overall crimes. 

Lighting can affect crime through two indirect mechanisms. The first is the obvious mechanism of 

facilitating surveillance by authorities and the community after dark. If law enforcement responds to a 
2023 FHWA LIGHTING HANDBOOK

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reported crime, improved lighting may enhance their ability to identify and apprehend a fleeing 

criminal. If criminals perceive the presence of surveillance as increasing effort and risk and this results in 

decreasing the risk/reward ratio for a criminal activity, the level of crime is likely to be reduced. The 

second mechanism by which lighting might affect the level of crime is by enhancing community 

confidence, leading to increased pedestrian activity and greater potential for crime detection. If 

community improvements (including lighting) give residents a sense of ownership and pride in an area, 

the probability of a detected crime being reported and/or impeded can also be increased. More 

significantly, the perceived likelihood of detection, reporting, and apprehension is likely to deter crime. 

Instead of providing lighting everywhere or 

indiscriminately, Crime Prevention Through 

Environmental Design (CPTED) is a common practice

for integrating security elements into lighting design 

by adopting certain strategies. CPTED is a proactive 

crime prevention strategy utilized by planners, 

engineers, police services, security professionals, and 

everyday users of space. Effective implementation of 

CPTED principles leads to environments that provide 

adequate visibility, encourage a sense of ownership, 

and facilitate desirable activities and traffic (e.g., an environmental design that gives pedestrians 

sufficient visibility to avoid hazards ahead). In CPTED terms, visibility allows the person to choose flight 

rather than fight. When a crime is in progress, those same visibility features along with the sense of 

ownership and pride among nearby motorists, business owners, residents, etc. improve the potential for 

intervention and reporting. 

From a livability and security standpoint, lighting sidewalks improves pedestrian visibility, provides 

guidance, and can create a feeling of comfort. Unlike motor vehicles, which have headlamps to improve 

visibility, pedestrians typically do not have their own lighting unless they carry flashlights. Outdoor 

lighting is the most practical aid to pedestrian visibility and guidance. Therefore, outdoor lighting is 

critical to prevent personal injuries due to tripping and falling, which in turn improves livability. 

Increasing light levels by 1 lux horizontally (between 0 and 18.6 lux) was found to promote pedestrian 

activity, as indicated by increased pedestrian and bicycle counts at night (Bhagavathula, Gibbons, & 

Hankey, 2018). Increasing light levels to 2 lux of average horizontal illuminance can also help pedestrians

detect tripping and falling hazards as well as enhance perceptions of safety, comfort, and visibility 

(Bhagavathula & Gibbons, 2020). No statistically significant improvements in visual performance or 

perceptions of safety, comfort, and visibility were observed by enhancing average horizontal illuminance

by more than 2 lux. 

2.4 Equity

Equity in the application of roadway lighting is an important consideration in the lighting planning 

process. The impact of the lighting system in terms of equity should include all aspects of race, gender, 

income, mobility, age, and living location. These considerations form the basis for the decision making 

on where, what level, and what type of lighting is implemented in an area. 

Research on the effects of street 

lighting on security and crime have 

produced mixed results. Crime 

Prevention Through Environmental 

Design (CPTED) is an industry accepted 

way to integrate security elements into 

lighting design. 
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This section has been written to create awareness of equity considerations. As the understanding of 

equity issues and lighting are an evolving body of knowledge, the latest information should be sought in 

the ideal application of the lighting. 

Black, Indigenous, and Hispanic people are disproportionately represented in nighttime traffic fatalities, 

according to a Governors Highway Safety Association (GHSA(Governors Highway Safety Association, 

2021) report that analyzed 2015–2019 FARS data. Figure 29 and Figure 30 show the comparison of 

daytime fatalities by ethnicity and nighttime fatalities by ethnicity, respectively. Of note is the change in 

rank order of the ethnicities between day and nighttime crashes. Even more demonstrative are the data 

indicating pedestrian deaths by race and ethnicity; here again, the rank order shows that the ethnicity of 

the pedestrian plays an important role in traffic deaths (Figure 31). 

Figure 29. Bar chart. Daytime fatalities per 100,000 population by race and ethnicity (GHRS, 2021). 

Figure 30. Bar chart. Nighttime fatalities per 100,000 population by race and ethnicity (GHRS, 2021). 
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Figure 31. Bar chart. Pedestrian deaths per 100,000 population by race and ethnicity (GHRS, 2021). 

Disparities between the amount of streetlight illumination provided in underserved communities may 

factor into the higher presence of Black, Indigenous, and People of Color (BIPOC) in fatal crashes. There 

are two primary issues: 

• Underserved communities may not have adequate roadway lighting infrastructure because of a 

history of disinvestment, complaints-based lighting repair processes, and underrepresentation 

in transportation decision making. 

• Underserved communities may have greater demand for well-lit pedestrian facilities as these 

areas also tend to have higher pedestrian volume.

These issues highlight the need for comprehensive efforts to address longstanding inequities that have 

led to the overrepresentation of BIPOC in crash statistics. 

As mentioned, lighting is an important treatment for roadways in terms of safety and interpersonal 

violence reduction, so design considerations with respect to lighting should be carefully made. The 

following are recommendations for dealing with lighting inequalities:

• The social equity of all roadway users and stakeholders should be considered in the design, and 

decisions should be based on data regarding the makeup of the people using the space and how 

they want to use it. This will require public involvement, particularly from the underserved 

communities, in the lighting design process.

• The area to be lit should be considered holistically, where the impact of the lighting 

encompasses not only safety and security but how the lighted space provides social meaning, 

aesthetics, and accessibility. 

• Lighting design that uses mockups and elicits stakeholder involvement is critical to maximizing 

the positive impact of the lighting implementation. This allows the designers and technical 

experts to understand and act on the decisions made by the public. 
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• The lighting system should be adaptable and user responsive to the changing nature of the 

lighted area to achieve the full potential of the lighting system (adaptive lighting is considered 

later in this document). 

• The value of the lighting system should be assessed both pre- and post-installation and be 

supported by the roadway authority and the local agency. These evaluations include both the 

lighting level assessment and the evaluation of the social impact of the lighting system after 

installation. 

• The agency should also prioritize post-installation maintenance of installed lighting systems. The 

impact of the installation of a lighting system to address inequities is lost if the system is not 

maintained properly. Lack of maintenance propagates the underservice of a community.

An approach to equity of lighting application has been undertaken by many cities. These efforts included 

the implementation of the Equity Impact Analysis into the decision-making process (Koonce, 2017). As 

an example of this, the City of Portland, Oregon, created a system of weights to consider a variety of 

analysis factors. These analysis factors include demographics, safety, and access. Each of these factors 

include subfactors and within each subfactor, like race, crashes and transit are considered when 

assessing lighting need. This evaluation was performed for a variety of communities to allow for 

prioritization of lighting need. Example tables from the Portland process are shown in Table 4 and Table 

5. 

Table 4. Example of City of Portland Equity Analysis (Illuminating Engineering Society, 2018). 

Criteria Category Measures Score Possible Score

Equity Race % people of color 3 3 

Equity Income % below poverty 3 3 

Safety Crime Annual crimes per sq mi. 2 2 

Safety Crashes Bike/Ped crashes 0 2 

Safety Sidewalks Lack of sidewalks 0 2 

Access Pedestrian Ped District or City Walkway 1 2 

Access Bicycle Bike Network 2 2 

Access Transit Transit Network 0 2 

Total 11 18

Table 5. Example of City of Portland Equity Analysis by Community (Illuminating Engineering Society, 2018). 

Location

# of 

LEDs

Equity 

Score

Safety 

Score

Access 

Score

Total 

Score

Lents 52 5 4 6 15

Cully 20 6 2 3 11

Powell Butte 68 3 1 2 6 

Eastridge 127 3 1 0 4 

Clatsop Butte 139 3 0 0 3 

Jenne Butte 53 0 1 0 1 
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For more information on this process, please refer to: https://nationalequityatlas.org/ and 

https://equityatlas.org/. 

2.5 Complete Streets

FHWA is working with State, Tribal and local transportation agencies across the United States to 

increase the proportion of transportation projects that Federal-aid highway funding recipients routinely 

plan, design, build, and operate that are safe and accessible for all users. Lighting is a critical element of 

this approach to safety. FHWA is encouraging the use of a Complete Streets design model

(https://www.transportation.gov/mission/health/complete-streets). A Complete Streets design model 

prioritizes safety, comfort, and connectivity for all users of the roadway, including but not limited to 

pedestrians, bicyclists, motorists, and transit riders across a broad spectrum of ages and abilities. In 

general, this design model includes careful consideration of measures to set and design for appropriate 

speeds; separation of various users in time and space; improvement of connectivity and access for 

pedestrians, bicyclists and transit riders; consideration of pedestrian access routes for people with 

disabilities; and addressing safety issues through implementation of safety countermeasures. 

One hallmark of a Complete Streets approach is the application of a variety of safety treatments, of 

which lighting can be an important treatment in the assessment. Typically, the lighting impact is 

assessed by the application of the crash modification factor (CMF) to the roadway to determine the 

safety impact. Other considerations such as those above can also be used to assess the whole roadway 

and the equity of the lighting application.

An important aspect of transitioning to a Complete Streets design model is to make it easier to routinely 

use these safety countermeasures. In the case of lighting, this may entail close coordination with the 

Public Works Department or another agency that has primarily responsibility for roadway lighting. 

Routine procedures, planning, and budgeting processes may need to be updated to ensure that lighting 

improvements for safety are given priority.

2.6 Aging Population

According to the IIHS, the number of drivers over seventy increased 75% from 1997 to 2020. As these 

older drivers have reduced visual capabilities, there is a potential for visibility issues at night (Insurance 

Institute of Highway Safety, 2022). A daytime vision of 20/20 can be reduced to 20/40 at night

regardless of age. Age has a significant impact on nighttime visibility due to the reduction in visual 

capability and the reduction in general physical ability that comes with aging. These factors combine to 

affect the safety of the older population. Such effects are particularly important as our population ages 

and life expectancy continues to increase.

As we age, visibility is reduced as the lens of our eye discolors, 

decreasing the amount of light that can penetrate the eye. This 

leads to a reduction in visual acuity and contrast sensitivity. The 

decline generally begins slowly after age 40 followed by an 

accelerated decline after age 60 (Richards, 1966)). Age also 

results in increased lens opacity and decreased pupil diameter

(Commission Internationale de l'Eclairage, 1987). The maximum 

area of the iris in eyes of people at age 60 is approximately half that of those at age 20 (Mortimer, 

Locations expecting 

increased roadway use by 

older drivers should 

consider reducing glare. 
2023 FHWA LIGHTING HANDBOOK

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1989). These changes result in less light reaching the retina. Weale (1961) reported a 50% reduction in 

retinal illumination at age 50 compared to at age 20, with this reduction increasing to 66% at age 60. 

Figure 32 demonstrates the significant reduction in visibility level for a small target on the roadway (STV) 

that occurs with age. Further information can be found in IES RP-8-21 and CIE 1995. 

Figure 32. Line graph. Decrease in visibility level with age (Illuminating Engineering Society, 2018). 

In addition to the reduction in light through the lens and the reduced visibility, the light is also scattered 

more significantly, which leads to additional veiling luminance in the eye and therefore additional 

impacts of glare (Adrian & Bhanji, 1991). 

For all road users, a vital factor is the ability to see the movement of potentially hazardous objects out of 

the corner of the eye. The ability to see movement 40 and 80 degrees away from the line of sight is 

reduced by as much as 60% for those over 60 years old. While a younger person can typically see in the 

presence of very little light, this ability is reduced by approximately one half at 80 or more years old. It 

can take up to 30 minutes for an 85-year-old person to adapt to low outdoor nighttime brightness after 

having been adapted to high interior brightness (Illuminating Engineering Society, 1999). This long eye 

adaptation time can be greatly reduced with roadway lighting.

Another aging-related issue is the limited agility and movement of older adults. Older drivers typically do 

not move their heads as much, resulting in a limited scan pattern (Antin, Wotring, & Foley, 2011). This 

reduced mobility further adds to the vision and visibility issues for older drivers by limiting their effective 

field of view. These limitations often cause older drivers to stop driving; thus, overcoming some of these 

limitations with roadway lighting may increase the mobility and level of comfort for aging drivers

(Bjørnskau & Fosser, 1996). 

The visibility factors noted above also apply to older pedestrians as reduced visibility reduces a 

pedestrian’s ability to see motor vehicles and avoid collisions. Reaction times for both the driver and 

pedestrian also decrease with age (Mortimer & Fell, 1989). As shown in Figure 33, while pedestrians 

ages 20 to 24 are at the highest risk of injury among all age groups, the proportion of fatalities also 

spikes for pedestrians over 70 years old. 
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Figure 33. Line graph. Pedestrian fatalities by age (City of Vancouver, 2012). 

Hills and Burg (1977) indicated no significant correlation between vision measures and crash data for 

participants under the age of 54. However, for drivers ages 54 and older, acuity showed significant

correlations with crash data. In an NCHRP study, increasing the lighting level improved detection 

distance for both the older and younger driver (Figure 34; (Engineering & Medicine, 2020). However, the 

detection distance for older drivers was significantly lower than that of younger drivers, even with the 

higher lighting level. These results highlight the effects of reduced driver visual capabilities and the need 

for adequate lighting.

Figure 34. Line graph. Detection distance by light level and age (Engineering & Medicine, 2020). 

In terms of lighting design, reducing the veiling luminance ratio is an effective way to improve visibility 

for older drivers. Simply increasing the luminance levels can also be considered; however, this should 

only be done to improve the veiling luminance ratio. The best way to reduce the veiling luminance ratio 

is by assessing various luminaire optical systems and photometric files using lighting design calculation 
2023 FHWA LIGHTING HANDBOOK

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software. The veiling luminance ratios defined in IES RP-8-21 are based on a 25-year-old driver. IES RP-8-

18 Table 3.6 (refer to Table 6) defines age factors by which the calculated veiling luminance can be 

multiplied to account for normal physiological changes in the eye with aging. Incorporating this age 

factor reduces the calculated veiling luminance ratio. 

Table 6. Veiling luminance age factors (Illuminating Engineering Society, 2018). 

Age Age Factor

25 1.0

35 1.1

45 1.2

55 1.4

65 1.7

75 2.3

85 3.2

The Handbook for Designing Roadways for the Aging Population (Brewer, Murillo, & Pate, 2014; Staplin, 

Lococo, Byington, & Harkey, 2001) provides information linking the declining functional capabilities of 

older road users to the need for design, operational, and traffic engineering enhancements keyed to 

specific roadway features. As noted in the handbook, although nighttime driving is associated with a 

higher crash risk for drivers of all ages, the effects of aging on the visual system are further compounded 

by the effects of darkness. Particularly difficult is the ability to notice and recognize objects at night and 

in low-light conditions such as dawn and dusk, rain, fog, haze, and snow. Between age 20 and age 70, 

aging directly reduces contrast sensitivity by a factor of about 3.0 (Blackwell & Blackwell, 1971); thus, 

aging drivers are at a greater relative disadvantage at low luminance levels than younger drivers. With a 

significant and increasing population over age 65, the quality of roadway lighting design is especially 

important. Today, the population of older individuals in the United States is increasing (the population 

of people ages 65 or older is up to 13.3% in 2011 from 12.4% in 2002 [Brewer, 2014]) and lighting design 

should be considered with them in mind. Roadway lighting has significant benefits for this population, 

and the value and benefits of roadway lighting will increase over time as the population both increases 

and ages. However, it is also important to consider that older drivers are far less likely to drive late at 

night compared to younger drivers. For those over 65 years old, it is important to maintain proper 

lighting levels, uniformity, and veiling luminance ratios on the roadways as well as proper sidewalk 

lighting levels. 

2.7 Cost

FHWA requires that federally funded lighting systems be 

adequately maintained. Under 23 U.S.C. 116(b), it is the duty of 

the State transportation department or other direct recipient to 

maintain, or cause to be maintained, any project constructed 

under the provisions of chapter 1 of title 23, U.S.C. The Federal 

Regulations (23 CFR 1.27) further state, “The responsibility 

imposed upon the State highway department, pursuant to 23 

U.S.C. 116, for the maintenance of projects shall be carried out in accordance with policies and 

procedures issued by the Administrator. The State highway department may provide for such 

maintenance by formal agreement with any adequately equipped county, municipality or other 

To define life cycle costs, 

both capital cost and 

maintenance and operating 

costs should be considered. 
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governmental instrumentality, but such an agreement shall not relieve the State highway department of 

its responsibility for such maintenance.”

As such, recipients of FHWA financial assistance should consider the cost of a system over its usable life, 

known as its life cycle cost. Life cycle cost analysis includes: 

• Capital cost (also known as construction cost). Capital cost varies widely by area and depends on the 

state of the economy and materials used. Because labor and material costs typically vary by 

location, it is difficult to establish standard costs for lighting installations. For budgeting purposes, 

however, it is appropriate to establish a per-mile cost or a unit pole cost, including wiring, boxes, 

and conduits between each set of typical poles.

• Maintenance and operating costs. These costs, which include power, corrective, and preventative 

maintenance costs, are typically calculated annually and are used by a jurisdiction to establish 

operating budgets. When calculating power cost, the method of payment used by the local electrical 

utility should be confirmed. Some utilities establish a monthly flat rate for various luminaire 

wattages. Others use a set kilowatt-hour rate for roadway lighting. Cleaning the luminaire optical 

system is a corrective maintenance cost that should be based on the luminaire dirt depreciation 

factor used in the design.

A lighting system is made of various components, some of which will last longer than others. The 

luminaire itself is a key component that may require repair or replacement during its life cycle. 

Manufacturer data often define an expected life of 100,000 hours (approximately 22 years), although 

this can be misleading as it does not define the product failure rate during that time. 

Luminaire products have different levels of reliability depending on their design and manufacturing. 

These differences can be considered in the prediction of luminaire failure rate. Generally, mean time 

between failure (MTBF) data from the luminaire supplier can be used to define the predicted failure rate

of the luminaire over a defined period, and the cost of replacement and repair can be considered when 

defining operating costs. MTBF can be calculated as follows (Transportation Association of Canada, 

2013): 

Equation 3. Reliability as a Function of Time and Mean Time Between Failures 

The recommended minimum MTBF should be as high as possible to minimize product failure; however, 

this should be determined by defining the number of product failures that can be tolerated. MTBF 

values provided by manufacturers typically range from 1,000,000 to over 2,000,000 hours. For example, 

a reliability prediction of failures for an MTBF of 2,000,000 hours for 10,000 luminaires operating for 20 

years (87,600 hours) would be:
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Equation 4. Example Reliability Calculations using MTBF

The failure rate typically varies by manufacturer. However, accurate MTBF data from the manufacturer 

can be hard to come by. 

Defining usable life involves the consideration of other factors such as corrosion resistance, damage via 

motor vehicle crashes, lightning strikes, power quality, and rodent damage. All these factors should be

discussed with maintenance personnel. 

2.8 Alternatives to Lighting

Although roadway lighting typically has high value for 

each dollar spent (Wald, 1998), it can be expensive to 

install and operate. Lighting generally has the highest 

value where pedestrians and cyclists are present.

However, vehicle headlamps may provide adequate 

vertical illumination on straight roads with speeds below

30 mph (IES RP-8-18 Section 3.1). The AASHTO Green 

Book suggests that for the assumed 24-inch height of 

headlamps, an object 16 inches above the roadway will 

be within the line of the headlamps at a distance equal 

to the stopping sight distance. Therefore, lighting is of 

less value on low-speed roads (< 30 mph). 

As noted by the FHWA Focus on Reducing Rural Roadway Departures (Federal Highway Administration, 

2020), roadway departures (i.e., lane departures) on the rural road network account for one third of all 

traffic fatalities. FHWA prescribes proven roadway departure countermeasures such as rumble strips, 

friction treatments, and clear zones to help keep vehicles in their travel lanes, reduce the potential for 

crashes, and reduce the severity of crashes that do occur. While lighting would provide benefits on rural 

roads, it may be impractical from a cost perspective, and lighting poles can themselves be a hazard 

when placed in the clear zone. 

Vehicle headlights are the primary system intended to assist drivers with detecting objects on and along 

the road. Traditionally, the contributions of vehicle headlamps are not considered in roadway lighting 

design. Figure 35 shows an example of vehicle headlights creating disability glare for the oncoming

driver. 

Vehicle headlights are the 

primary system intended to assist 

drivers with detecting objects on 

and along the road. The 

contributions of vehicle 

headlamps are not considered in 

roadway lighting design. 
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Figure 35. Photo. Example of glare from oncoming vehicle headlamps. (Image Credit: Ronald Gibbons, VTTI) 

A key benefit of lighting is mitigating glare from oncoming vehicle headlamps by improving the contrast 

ratio. An effective alternative to lighting is glare screens (Figure 36), which can effectively block car 

headlamps to mitigate the issue. 

Figure 36. Photo. Median-mounted glare screens (Traffic Safety Supply Company, 2022). 

In terms of driver guidance, retroreflective pavement markings and roadside delineators can be a costeffective option compared to roadway lighting. When roadway lighting is not present, nighttime 

navigation generally depends upon a road user’s visibility of the roadway and pavement markings via 

vehicle headlamps. Treatments such as retroreflective pavement markings and roadside delineators can 

be considered as alternatives to lighting in rural applications; however, (Carlson & Miles, 2011) reported 

that continuous roadway lighting provided better visibility of pavement markings at longer distances 

than unlit highways. Significantly, the use of retroreflective pavement markings and roadside delineators 

may aid in keeping a vehicle in their lane but does not address pedestrian/cyclist needs. 

Unlike motor vehicles (which have headlamps to make the retroreflective pavement markings visible), 

pedestrians do not typically supply their own lighting unless they opt to carry flashlights. Therefore, 

fixed outdoor lighting is the most practical aid to visibility and guidance for pedestrians. Sidewalks and 

marked bike lanes are a good indication that pedestrians are likely present. In these applications, 

retroreflective pavement markings would not be a good alternative to lighting because the markers do 

not help with visibility of the pedestrians as lighting would. 

Notably, no research has been reported on the trade-off between lighting and marking systems. 

However, delineators have been shown to reduce crashes (Crash Modification Factor Clearning House, 
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45

2022; Elvik, Vaa, Hoye, & Sorensen, 2009), and it has also been found that lighting systems improve the 

detection of markers and markings (Gibbons & Hankey, 2007). To assess the cost and benefits of 

retroreflective pavement markings and post-mounted delineators versus roadway lighting, a life cycle 

cost analysis that considers the capital and operational costs of both alternatives should be undertaken.
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3 WARRANTING 

This section discusses methods for determining lighting warrant for roadway lighting systems. AASHTO 

provides warranting methods for continuous freeway lighting, complete interchange lighting, and partial 

interchange lighting. Other methods for collector/arterial/local roads and intersections from the TAC are 

also included in this section.

It is important to note that warrants do not represent a requirement to provide lighting. Satisfaction of a 

lighting warrant does not in itself require the installation of a lighting system. Beyond the warrants, 

lighting is of a high value and should be considered where vulnerable road users such as pedestrians and 

cyclists are present. Given the distance limitations of car headlamps, lighting is also of higher value on 

higher-speed roadways, as defined in Section 1.2.3 Perception – Reaction Time of this document. 

Similarly, this treatment of the warranting process is only a summary, and the warranting method used 

should be followed in the source documents referenced below. 

FHWA administers funding for State roadway lighting projects under certain programs with specific 

requirements. These projects may qualify as highway safety improvement projects and may be eligible 

under Section 148 of Title 23, United States Code (Highway Safety Improvement Program) if the 

requirements of that program are met. In addition, these projects are eligible for the increased Federal 

share under 23 U.S.C. 120(c). When Federal aid is used for a lighting project, the applicant can support 

the need for a roadway lighting system by including the following items:

• A warrant analysis showing that lighting is a warranted safety feature.

• A project criteria document showing that the design criteria established by AASHTO or IES will be 

used and met as part of the design.

3.1 Warrants

Warranting is used by many State and local DOTs 

and safety practitioners to define the need for 

lighting. Currently, there are two main warranting 

systems for roadway lighting: one is found in the 

AASHTO Roadway Lighting Design Guide (American 

Association of State Highway and Transportation 

Officials, 2018b), which defines lighting warrants for 

freeways and highways; the second is found in the 

TAC Guide for the Design of Roadway Lighting (Transportation Association of Canada, 2006), which 

defines warranting for streets and intersections. Most warranting in the TAC guide is based on a 

weighted point score system developed in the 1970s and derived from an early 1970s NCHRP Report 

along with the 1978 FHWA Federal Highways Lighting Handbook. The AASHTO warranting system was 

developed in the early 1980s and has not changed significantly since then. 

Existing warrants for lighting were developed before active safety systems in vehicles, solid-state 

lighting, and the implementation of CMFs in roadway safety analysis. With the development of LED 

lighting systems, it is necessary to obtain new data to define modern lighting needs. In addition, 

warrants do not address safety-based alternatives to roadway lighting, which include retroreflective 

Warrants are not a requirement to light 

but an indication of situations where 

lighting should be investigated. Lighting 

should be considered where vulnerable 

road users such as pedestrians and 

cyclists are present. 
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pavement marking and roadside delineators. The FHWA safety initiative to enhance visibility for 

pedestrians includes various alternatives, with roadway lighting being one of the several solutions for 

consideration (https://highways.dot.gov/safety/pedestrian-bicyclist/step/). Recent research findings 

indicated there is a need to reduce the potential environmental impacts of roadway lighting, and 

jurisdictions often must balance the safety benefits of roadway lighting with the environmental impacts.

Roadway lighting can also be expensive to install and operate. Over-lighting and unwarranted lighting 

can result in excessive glare and lighting trespass in adjoining neighborhoods. Additionally, current 

warranting systems do not address the costs and benefits of roadway lighting as a safety 

countermeasure when compared to other safety alternatives. As a result, inconsistencies exist in terms 

of where and when roadway lighting is applied. 

Lighting warrants help evaluate locations where lighting will have the maximum benefit based on 

defined conditions or rating systems. Meeting these warrants does not obligate the State or any agency 

to provide lighting. In other words, warrants indicate where lighting may be beneficial but should not be 

interpreted as an absolute indication of whether lighting is required. The need for lighting should be 

determined by sound engineering judgment, and the decision should be made by the agency with 

jurisdiction over the roadway. From a consistency standpoint, a jurisdiction should develop a master 

plan (refer to Section 4.1 of this document) rather than allowing third parties to use warrants to decide 

whether to light or not. 

3.2 AASHTO Warranting System

Warrants for highways, freeways, interchanges, and bridges may be undertaken using the AASHTO 

Roadway Lighting Design Guide Warranting System. AASHTO defines warrants for continuous freeway 

lighting, complete interchange lighting, and partial interchange lighting based on warrant conditions 

including:

• Traffic volumes

• Spacing of freeway interchanges

• Lighting in adjacent areas

• Night-to-day crash ratio

AASHTO recommends providing lighting on long bridges in urban and suburban areas, even if the 

approaches are not lit. On bridges without full shoulders, lighting can enhance both bridge safety and 

utility and is therefore recommended by AASHTO. Where bridges are provided with sidewalks for 

pedestrian movements, lighting is recommended by AASHTO for pedestrian safety and guidance. 

3.3 Warranting Method for Collector/Major/Local Streets

The AASHTO warranting method does not cover collector, major, and local roads. For these types of 

roads, the TAC Guide for the Design of Roadway Lighting (Transportation Association of Canada, 2006), 

which was based on the 1974 National Cooperative Highway Research Program Report 152 (National 

Academies of Sciences Engineering and Medicine, 1974), Warrants for Highway Lighting, can be used. 

The warrant system is based on geometric, operational, environmental, and crash factors. For each 

factor, a numeric rating from 1 to 5 is defined, and each factor is assigned a weight to indicate its 

relative importance. The rating is then multiplied by the weight to obtain a point score for each factor 
2023 FHWA LIGHTING HANDBOOK

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that indicates the factor’s relative significance. The overall point score for all items indicates the need 

for lighting as well as the relative risk on that road compared with other roadways. Lighting under this 

method is warranted where a total point score of 60 or more is achieved. If the night-to-day crash ratio 

is 2:1 or greater, lighting is automatically warranted using this method regardless of the overall point 

score. Lighting may be prioritized solely based on the point scores, or in conjunction with a benefit/cost 

analysis. Benefits are typically based on the potential reduction in crash frequency and severity. 

Depending on road authority practice, costs typically include the initial cost of the lighting system, its 

ongoing (electricity) costs, and its maintenance costs. Initial costs may be substantial if a power source is 

not present.

When undertaking a warrant analysis, the length of the roadway segment being analyzed should be as 

long as possible where the variables remain constant (i.e., geometric, operational, environmental, and 

crash factors), and future development should be considered. When the roadway classification or 

roadway land use classification changes, a separate warrant analysis should be considered for each 

roadway section. Where classifications are relatively constant along the segment of roadway under 

consideration, a single warrant analysis may be undertaken.

The example warranting analysis sheet from the TAC Guide for the Design of Roadway Lighting

(Transportation Association of Canada, 2006) is shown in Figure 37. The classification factors listed on 

the warrant sheets are defined as follows. 

3.3.1 Geometric Factors

The warranting analysis considers the key geometric factors of the length of roadway to which the 

warrant is being applied. These factors include: 

• Number of lanes

• Lane width

• Number of median openings per kilometer

• Driveways and entrances per kilometer

• Horizontal curve radius (small curve radii have a much higher impact on the warrant than large 

curve radii) 

• Vertical grade

• Sight distance

• Parking

The applicable rating factors are used for the entire length of road being considered. If the rating 

changes over the length of the road being considered, then the worst-case rating value is used.

3.3.2 Operational Factors

The warranting analysis considers the operational factors for the entire length of roadway to which the 

warrant is being applied. These factors include: 

• Signalized intersections

• Left turn lanes 
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49

• Median width

• Operating or posted speed

• Pedestrian activity (conflict) levels (refer to IESNA RP-8-21 for the definition of high, medium, 

and low activity)

The applicable rating factors are applied for the entire length of road being considered. If the rating 

changes over the length of the road being considered, then the worst-case rating value is used.

3.3.3 Environmental Factors

The warranting analysis considers the environmental factors for the entire length of road to which the 

warrant is being applied. These factors include: 

• Percentage of development adjacent to the roadway. Adjacent development should be a reasonable 

distance from the roadway and should tie into the roadway for which the warrant is being 

undertaken via a driveway or intersection that generates a reasonable amount of traffic.

Determining the amount of ambient lighting present in an area depends on the judgment of the 

individual performing the warrant analysis. The following ambient lighting definitions may be helpful 

to consider: 

• Sparse: rural freeways and highways with little or no development outside of city 

boundaries.

• Moderate: rural or urban roads with some building lighting and development outside of 

commercial areas. Areas with residential and industrial development will typically have 

moderate ambient lighting.

• Distracting: downtown commercial areas with well-lighted building exteriors adjacent to the 

roadway. Distracting lighting can also include lighting from fuel stations, automotive sales 

lots, and other commercial development where lighting is used to attract attention to 

businesses.

• Intense: areas with large advertising signs, sports lighting, and other intense light sources 

adjacent to the roadway. Intense sources can be found in both rural and urban areas.

• Area classification

• Distance from development to roadway

• Presence of raised median curb

The applicable rating factors are used for the entire length of road being considered. If the rating 

changes over the length of the road being considered, then the worst-case rating value is used.
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Figure 37. Image. Example warranting analysis sheet for warrant for arterial, collector, and local roadways (TAC, 2006). 

3.3.4 Crash Factors (Night and Day)

Crash factors are included in the warranting forms based on the night-to-day crash rate ratio for the 

given length of road to which the warrant is being applied. As the warrant point score for this category is 

heavily based on the night-to-day crash ratio, it is important that detailed and well-defined crash data 

be applied. Where crash ratios are not known, engineering judgment should be applied using crash 

statistics from similar roads for which data are available. 
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Where a low number of crashes have been recorded, while lighting may meet the warrant crash ratio, it 

may be of less benefit than for other areas with similar ratios and higher numbers.

3.4 Crash Modification Factors (CMFs)

A safety analysis and study showing that a lighting system is a cost-effective safety alternative for the 

project may be considered. There are various ways of executing a study of this type. One is to use the 

AASHTO Highway Safety Manual (HSM; https://www.highwaysafetymanual.org/). The HSM assembles 

currently available information on crash frequency and severity so that various improvements to 

roadways can be quantified and evaluated in terms of their 

effectiveness. The effects of various treatments such as 

geometric improvements and operational changes on 

roadways are quantified as CMFs. CMFs represent the 

change expected in crash frequency due to a specific 

change in conditions.

For example, when looking at the impact of highway lighting on all roadway types that previously had no 

lighting, the HSM method indicates a CMF of 0.72 for nighttime injury crashes (indicating a 28% 

reduction in nighttime injury crash types). Thus, if the expected average crash frequency is 10 injury 

crashes/year for a no-lighting condition, after the implementation of a highway lighting system, one 

would expect 10 × 0.72 = 7.2 injury crashes/year resulting in a reduction of 2.8 crashes per year (1-.72 = 

2.8 crashes per year). 

3.4.1 CMF Clearinghouse

The amount of information for crash analysis and evaluation is actively growing and can be found in the 

CMF Clearinghouse at www.cmfclearinghouse.org. In this clearinghouse, the viewer can sort through 

data by type of countermeasure, crash type, crash severity, and roadway type. The viewer can also see a 

measure of accuracy and precision of the data as well as applicability, as judged by a panel of reviewers 

and rated on a 1- to 5-star scale. 

It is important to note that most CMFs provided in the clearinghouse for lighting use lighting as a binary 

“On/Off” metric only. There is very little information regarding the lighting level. Work in this area is still 

ongoing. 

3.5 Warranting Method for Intersections

The AASHTO Warranting method does not cover intersections. The TAC Guide for the Design of 

Roadway Lighting includes a warranting system for intersection lighting that can be used to define the 

need for intersection lighting. The warranting system is based on geometric, operational, 

environmental, and crash factors. The critical factors this warranting method uses to determine the 

need for illumination are traffic volumes and nighttime crashes. The warrant point score indicates 

whether full intersection lighting, partial lighting, or delineation lighting is needed. 

The critical factors used by this warranting method to determine the need for illumination are: 

• Traffic volumes (particularly on the cross street).

• The presence of crosswalks.

CMFs represent the change 

expected in crash frequency due 

to a specific change in conditions.
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• Nighttime crashes that may be attributed to the lack of illumination.

• The extent of raised medians.

Several secondary factors are also considered in the warrant but are given less weight in the overall 

point score. In the warrant, traffic volumes and nighttime crashes are given greater weight than raised 

medians, which can be designed, marked, or modified to reduce the risk associated with their presence 

in the roadway.

The following terminology is used with respect to the amount of lighting, as determined by the warrant 

system:

• Full Lighting – Denotes lighting covering an intersection in a uniform manner over the traveled 

portion of the roadway.

• Partial Lighting – Denotes lighting of key decision areas, potential conflict points, and/or hazards in 

and on the approach to an intersection. Partial lighting may also guide a driver from one key point to 

the next, and (if sufficient luminaires are used) place the road user on a safe heading after leaving 

the lighted area.

• Delineation Lighting – Denotes lighting that marks an intersection location for approaching traffic, 

lights vehicles on a cross street, or lights a median crossing.

An example analysis sheet for an intersection warranting analysis is shown in Figure 38.
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Figure 38. Image. Intersection warranting analysis sheet (Transportation Association of Canada, 2006). 

Based on the warrant analysis, the following conditions define the need for full, partial, or delineation 

lighting: 

• If the intersection is signalized, full lighting is warranted. 

• If the intersection is not signalized, the need for and the amount of lighting is determined by 

comparing the point score obtained from the warrant form categories to the following criteria:

1) Full lighting is warranted where the total point score is 240 points or greater. 

2) Partial lightning is warranted where the point score is between 151 and 239 points. 
2023 FHWA LIGHTING HANDBOOK

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3) Delineation lighting is warranted where the point score is between 120 and 150 points. 

Generally, a point score under 120 indicates that lighting is not warranted. This score suggests that 

neither the critical operational warranting factor (substantial traffic volumes) nor the critical crash

warranting factor (repeated nighttime crashes) is present.

Lighting may be prioritized solely based on the point score or in conjunction with a benefit/cost analysis. 

Benefits would typically be based on the potential reduction in crash frequency and severity at the 

intersection. Depending on the practice of the road authority, costs would typically include the initial 

cost of the lighting system, its ongoing (electricity) costs, and its maintenance costs. Initial costs may be 

substantial if a power source is not present at the intersection.

3.6 Pedestrian/Bicycle Facilities

There is no defined warranting system for pedestrians, but these road users are a critical aspect of the 

roadway environment. Typically, decisions about roadway lighting have considered crosswalks only as 

the location where there is an interaction between vehicles and people. 

In terms of warranting, a defined point score and weighting for pedestrians is included in the warranting 

point score system for roadways and intersections. Lighting of sidewalks and pathways provides the 

pedestrian both guidance and a feeling of security. Where the sidewalk is adjacent to roadway, the 

lighting can also make the pedestrian more visible to drivers. Bike lanes are not included in the current 

warrant point score system. Bike lanes come in a variety of configurations, but from a lighting 

perspective the main consideration is the bike lane defined via pavement markings or by a barrier, 

fence, or curb separation from roadway traffic. Lighting is of the greatest benefit where the bike lane is 

defined by pavement markings as there is no barrier to protect the cyclist from the motor vehicle. 

Further information on types of bike lanes can be found in the AASHTO Guide for the Development of 

Bicycle Facilities, 4th Edition, 2012 (American Association of State Highway and Transportation Officials, 

2012). The highest potential for conflict with a motor vehicle is at intersections and defined cross-over 

areas (e.g., dashed lines shown in Figure 39) where the motor vehicle and bicyclist are in potential 

conflict. 

Although not specifically defined in current warrants, 

bicycle lane lighting is of high value. NCHRP Report 926, 

Guidance to Improve Pedestrian and Bicyclist Safety at 

Intersections, noted: “Illumination at crosswalks and 

along the roadway can help increase visibility for 

pedestrians and bicyclists, particularly at approaches to 

crossings” (Medicine, 2020). (Harkey, 2008) reported that increasing or adding lighting to crosswalks, 

road segments, and intersections improves pedestrian and bicyclist safety by reducing crashes, 

increasing yielding and compliance with traffic control devices, and improving visibility, with a CMF of 

0.73 for injury crashes.

Although not specifically defined 

in current warrants, bicycle lane 

lighting is of high value. 
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Figure 39. Photo. Bike lane example (Warehouse, 2020). 

Figure 39 shows an example of a bike lane adjacent to a roadway. The example includes dashed 

pavement markings where vehicles and cyclists interact. It is the generally accepted practice that 

unprotected bicycle lanes adjacent to a roadway should be lighted. 
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4 LIGHTING PLANNING AND DESIGN PROCESS

4.1 Lighting Master Plans

Lighting master plans are formal documents created through a study and planning process. They can be

based on input from staff, public officials, lighting professionals, citizens, business owners, and others.

Lighting master plans define the purpose of lighting and contain area maps with road types, 

classifications, land use, pedestrian and cyclist routes, parks, and other infrastructure information. They 

can also contain information regarding luminaires and poles, light sources, lighting levels, design criteria, 

design and construction specifications, historical considerations, and recommendations. This 

information is combined in a single, organized package that becomes the basis for lighting projects. 

Lighting master plans consider anticipated economic and cultural changes, a community’s public image 

and economic development goals, and technological advancements. Public engagement is 

recommended, but jurisdictions can define how that takes place. The benefits of such plans include

coordination of various municipal lighting functions and the proactive planning of lighting for different 

areas of a community by recognizing their unique character and needs. The plans also allow for the 

scheduling of capital expenditures as well as implementation and maintenance strategies. Lighting 

master plans are based on the core concept that public facilities should enhance safety, encourage 

economic development, contribute to beautification, and provide a secure environment for people and 

property. Transportation-related lighting is generally a key component of community management.

Lighting master plans should include equity considerations. 

Lighting master plans are typically adopted by a jurisdiction through bylaw, resolution, or similar 

measure. As such, lighting master plans may dictate specific 

design requirements for roadway lighting. The purpose of a 

lighting master plan is to ensure adequate lighting is 

provided for future development and that public lighting 

will be installed in a consistent manner that considers the 

needs and desires of citizens. If an area is designated for historic preservation, the lighting master plan 

may define luminaires and light sources that are compatible with, preserve, and/or improve the area’s 

existing historical character.

Lighting master plans typically address the following major subject areas:

• Improved safety provided by lighting

• Improved sense of security provided by lighting

• Costs of lighting (capital and operating)

• Aesthetics of lighting (daytime and nighttime)

• Lighting design criteria

• Lighting-associated environmental issues and constraints, including the control of spill light, glare, 

and skyglow

• Energy used by lighting (through the definition of unit power density)

• Potential for economic development and the enhancement of nighttime activities through lighting

Lighting master plans should 

include considerations for equity. 
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• Considerations of equity and Complete Streets

• Preservation of areas of darkness (e.g., areas around observatories) 

• Maintenance requirements

A lighting master plan should define where to light from a corridor strategy, which will create 

consistency. Leaving decisions as to where to light to pure engineering judgment may lead to 

inconsistency. 

4.2 Design process

The lighting design process is highlighted in Figure 40.

4.2.1 Pre-Design 

Prior to starting any design, the roadway lighting designer should address the following typical predesign considerations:

• Identify applicable standards and requirements. 

• Review roadway geometrics and utilities. 

• Define the clear zone (refer to the AASHTO Roadside Design Guide). 

• Using warrants, determine the requirement for full or partial lighting for the type of installation 

under consideration. 

• Investigate site conditions for the following:

1) Availability of power (the lack of available power may affect the cost/benefit of a lighting 

installation). 

2) Proximity to aircraft landing facilities and railways, which may dictate specific lighting 

requirements. 

3) Presence of distribution and transmission power lines that require specific clearances, as 

defined by the local utility, Occupational Health and Safety Administration, and the National 

Electric Code (NEC). 

4) Environmental issues, including lighting impacts on humans, plants, and wildlife. 

5) Maintenance and operations considerations (e.g., access to light poles and luminaires for 

servicing). 

4.2.2 Lighting Design Criteria

Prior to undertaking lighting design, the designer should identify basic lighting criteria for the project. 

The criteria selected are generally based on the recommendations of the IES or the ASSHTO. A State may 

modify the recommended values based on their own experience and needs. The criteria include the 

following: 

• Pavement type (R1 to R4; refer to IES RP-8 -21 or the AASHTO Lighting Design Guide) 

• Roadway type and pedestrian activity level (refer to IES RP-8-21 or the AASHTO Lighting Design 

Guide) 
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• Recommended lighting level and uniformity (refer to IES RP-8-21 or the AASHTO Lighting Design 

Guide) 

• Roadway geometry, including the number and width of traffic lanes, median width, and sidewalks

• Light trespass (i.e., define lighting limitations outside of the right-of-way in reference to IES RP-8-21

and RP-33) 

Figure 40. Flow chart. Lighting project design process (Transportation Association of Canada, 2006). 
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4.2.3 Perform Lighting Design

Selecting a suitable luminaire, obtaining IES-formatted photometric files, and undertaking lighting design 

using computer lighting design software are typical steps in performing lighting design. A “trial and 

adjustment” process using computer design software to achieve the optimal design is generally 

performed based on the following variables: 

• Light source specification (type, wattage, CCT, CRI, fidelity, gamut) 

• Light loss factor (LLF; refer to IES RP-8-21 and TM-21) 

• Pole type, height, and luminaire arm length 

• Pole offset (the pole location relative to the edge of the edge of pavement or curb and gutter) 

• Luminaire type (e.g., cobra head, decorative, tunnel, wall pack) 

• Pole spacing (e.g., one sided, staggered, or opposite) 

Typically, the more experienced the designer, the shorter 

the trial and adjustment period. As photometrics of 

fixtures will vary from supplier to supplier for similar 

products, it may be appropriate to review photometrics 

from multiple suppliers. 

The design of intersections, crosswalks, roundabouts, 

parking lots, and interchanges will follow a similar process 

but without the benefit of optimization. The steps will be 

similar to those described above with the spacings pre-set and refined by trial and adjustment. The 

specific method of calculation to be undertaken will vary depending on the application.

Lighting design requires the use of computer lighting design software and the photometric files from 

lighting suppliers in IES format. For LED lighting, the photometric files should be “absolute,” meaning 

that the photometric file will be for the exact luminaire tested. The designer then selects photometric 

files for luminaires that light the roadway and sidewalks while minimizing light pollution. 

Light levels are based on the end-of-lamp life. However, in the past, a standard LLF was applied based on 

a given re-lamping cycle. Unlike other lighting technologies, LEDs typically do not fail catastrophically 

during use and will gradually depreciate over time, resulting in lower-than-required light levels over 

time. While LEDs can last beyond 100,000 hours, it is typically recommended that 88,000 (20 years) be 

applied as the useful life. 

For LEDs, the LLF is a combination of several factors representing the deterioration of the lamp and 

luminaire over their life span. Several individual factors combine to form the overall LLF, which is applied 

to a lighting design. The main factors in the LLF are lamp lumen depreciation (LLD) and luminaire dirt 

depreciation (LDD). LLF is calculated as LLF = LLD × LDD. Once defined, the LLF is incorporated into the 

design calculations. The calculation of LLF is discussed in detail in IES RP-8-21. 

The LLD is based on data measured by the manufacturer, as per IES LM80, and presented in the TM-21 

format, which defines LLD based on the end-of-lamp life. The LDD tables in RP-8-21 only define up to 8 

years and are dated. To better define LDD, the IES published IES RES-1-16, Measure and Report 

Luminaire Dirt Depreciation (LDD) in LED Luminaires for Street and Roadway Lighting Applications. This 

Lighting design is typically 

undertaken using a “trial and 

adjustment” process using 

computer design software to 

achieve the optimal design. 
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document is available from the IES at: http://media.ies.org/docs/research/IES-RES-1-16.pdf. This 

document defines LDD values based upon field examination and measurements of actual LED roadway 

luminaires. The report recommends different levels of LDD for different optical systems based on a fairly 

limited sampling of luminaires. As the actual factors are difficult to predict, good practice is to use a 

deprecation factor of 1% per year. The factor applied to the design depends on the cleaning cycle (i.e., 

0.9 for a 10-year cleaning cycle or 0.8 for a 20-year cycle). Lighting in tunnels is an exception because 

these lighting systems accumulate significantly more dirt than roadway lighting. 

To accommodate the LLF, a lighting system is overly bright when first installed and then depreciates 

over its life. LDD is recoverable with cleaning, whereas LLD deprecates over time. Adaptive lighting 

systems (see Section 7) can be of benefit as lighting can be dimmed and then ramped up over time to 

accommodate the LLF, which will save power and cost over the life cycle. This is sometimes referred to 

as “constant light output.” 

4.2.4 Other Considerations 

Other considerations involved in the lighting design process include:

• Electrical design considerations in accordance with NEC and any local requirements

• Structural and geotechnical considerations for poles and foundations in accordance with AASHTO 

Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals

• Plans specification and estimates in accordance with local jurisdiction documentation and 

requirements 

• Bid estimates in accordance with local jurisdiction documentation and requirements

• Construction (monitor and review construction) 

• Post construction (record drawings and operation & maintenance documentation along with field 

measurements of lighting) 

Examples of design elements typically considered when performing lighting design for freeway and 

urban roadways are shown in Figure 41 and Figure 42. Each of these elements in the roadway design

should be considered in the lighting analysis. These elements are further defined in NCHRP Report 940, 

Solid-State Roadway Lighting Design Volume 1: Guidance (National Academies of Sciences Engineering 

Medicine, 2020), and AASHTO GL-7, Roadway Lighting Design Guide (American Association of State 

Highway and Transportation Officials, 2018b). 

Part II of this Handbook includes examples for various roadway types and applications in addition to 

those described above.
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Figure 41. Photo. Freeway lighting design elements (National Academies of Sciences Engineering Medicine, 2020). 
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Figure 42. Photo. Urban roadway lighting design elements (National Academies of Sciences Engineering Medicine, 2020). 

4.3 Design Applications

4.3.1 Roadway

As previously stated, the lighting design criteria for roadways are typically drawn from the IES RP-8-21 or 

the AASHTO Roadway Lighting Design Guide and are not repeated in this document. Examples of the 

application of these criteria are highlighted for several common lighting applications in Part II of this 

document: 

• Urban Street Lighting

• Rural Road Lighting

• Expressway Lighting

• Urban Freeway Lighting

• Suburban Freeway Lighting

• Rural Freeway Lighting

• Roundabout Lighting

• Walkway & Bikeway Lighting
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4.3.2 Tunnels

Lighting tunnels is generally more complex than lighting a typical roadway. The lighting in a tunnel 

requires considering both daytime and nighttime conditions, the dark adaptation process of the eye, 

geographical orientation of the tunnel, and the portal design, to name just a few of the specific tunnel 

criteria. To add to the complexity of the tunnel lighting design, long tunnels are also divided into zones, 

each of which requires a different design and system specification. Considerations and design examples

for short, long, and underpass tunnel applications are defined in Part II, Design Examples. These are 

provided to aid in the design process and to clarify the requirements defined in IES RP-8-21. 

4.3.3 Pedestrian Facilities

Lighting for pedestrians is discussed in the IES- RP-8-21 guidelines that provide recommendations for the 

lighting of pedestrian facilities. Studies considering high pedestrian volumes and facilities for children 

such as school zones have been undertaken.

A recent research effort (Terry et al., 2020) primarily considered the visibility needs of children but 

included adults for comparison through a group of experiments that examined lighting needs from the 

perspectives of both the driver and pedestrian. The experiments included an effort in which drivers 

were asked to detect child-size mannequins at the side of a roadway, an effort in which both adult and 

child pedestrians detected trip-and-fall hazards, and a final effort in which pedestrians judged 

acceptable gaps to cross the roadway in front of a moving vehicle. The project allowed for the 

development of criteria for pedestrian lighting in areas where children are present such as school zones 

or event venues.

The research results show a correlation between the lighting level on the roadway and visibility of 

pedestrians. The research indicates that at a level of 9 lux semi-cylindrical or 3 lux vertical illuminance, 

additional light does not increase visibility. A higher lighting level is needed for high visual clutter on a 

roadway; however, this seems to indicate that a luminance level of 2 cd/m2 is required for visibility in 

urban settings. As there is a stronger link between the roadway luminance and the semi-cylindrical 

illuminance, it has been determined that the more stringent criteria for pedestrian lighting shall be used 

in areas with high pedestrian volumes and potential uncertainty in pedestrian behavior. These areas 

might include school zones or roadways with pedestrian levels of 100 pedestrians per hour, which is 

drawn from existing lighting design standards (Illuminating Engineering Society, 2021e). 

A grid of calculation and measurement points aligned along the side of the roadway for adjacent 

sidewalks or along the pedestrian walkway for separated pedestrian paths should be illuminated to a 

minimum level based on a line of calculation points along the path and spaced at no more than 2 m (6.6 

ft).

4.3.3.1 Crosswalk Lighting

Current research shows that crosswalk light levels should be at 10 lux vertical illuminance or higher

(Bhagavathula, Gibbons, & Kassing, 2021). Recognizing that this level is significantly higher than the 

levels recommended along the side of the roadway, these facilities are in the roadway and the path of 

the vehicle, and as such a higher lighting level is recommended. Further research is being developed for 

these criteria.
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In terms of lighting for pedestrians at crosswalks, results of this research indicated that neither light 

level nor light scale impacted the responses of children and adults in regard to the point at which they 

would no longer attempt to cross a roadway; however, it was determined that the presence of roadway 

lighting may inform an adult’s perception of depth more accurately. Most crosswalks are lit for the 

primary purpose of making pedestrians visible to drivers. The results of this study also indicate a benefit 

to the pedestrian in being able to make a more confident decision regarding the vehicle’s distance from 

the crosswalk. The decision-making abilities of children, however, are not improved with the addition of 

lighting, nor are they impacted by the lane positioning or speed of approaching vehicles (Terry et al., 

2020). 

4.3.3.2 Luminaire Height

On roadways, pedestrian lighting is typically provided by the roadway lighting system itself. However, 

pedestrian-scale lighting is used for some roadways and pathways. Typically, pedestrian scale lighting is 

mounted at a lower height and provides high levels of vertical illumination. Roadway lighting is mounted 

at a higher elevation and provides a higher level of horizontal illuminance. The issue with a lower 

mounting height is that luminaires that direct vertical illuminance towards the pedestrian also typically 

have higher glare rating for both the pedestrian and vehicle driver. As a result, the roadway luminance 

may need to increase to overcome the potential for disability glare. The glare should be confirmed via a 

veiling luminance calculation as per IES RP-8-21.

4.3.3.3 Recommendations

Based on the research results on pedestrian lighting performed for the FHWA and documented in report 

FHWA-SA-20-02 Research Report: Street Lighting for Pedestrian Safety (Terry et al., 2020), the criteria in 

Table 7 are extracted from the research report for pedestrian areas. Table 8 notes that while these 

recommendations can be applied to any light source, the color temperature recommendation typically 

applies to LED light sources only.

Table 7. Recommended criteria for pedestrian facilities including school areas. (Terry et al., 2020)

Pedestrian facility 

characteristics 

Pedestrian 

lighting 

minimum

Rural 

(Average 

Luminance) 

Urban 

(Average

Luminance)

Low/medium 

pedestrian volumes

2 lux 

vertical N/A 1 cd/m2

High pedestrian 

volume/ school zones 10 lux SC 1 cd/m2 2cd/m2

Light source spectral 

characteristics

3000 K to 

4000K N/A N/A

Pedestrian crosswalk 20 lux 

vertical N/A N/A
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Table 8. Pedestrian volume criteria (IESNA RP-8-21, 2018). 

Pedestrian volume levels Pedestrians per hour

Low 0–10

Medium 11—100

High >100

4.3.3.4 Design and Verification Approach

For the calculation and the verification of the lighting in the pedestrian sidewalks and areas, the 

calculation grid should be spaced between the luminaires and centered in the design area with a 

maximum spacing of 1.5 meters (5 ft) between grid points in each direction.

Verification of lighting levels should be made at the same location as in the calculation grid. Please refer 

to IES RP-8-21 for more information (Illuminating Engineering Society, 2021e). 

4.3.4 Railway Crossings

Unsignalized rail crossings pose high risk to both the train and road users in terms of collisions. The risk 

increases in hours of darkness when visibility is reduced. Road users at risk include motor vehicles, 

pedestrians, and cyclists. 

Lighting railway crossings (specifically those that are unsignalized) is very important given the increased 

risk to road users when trains are present. As trains do not have typical retroreflective markings and 

active lighting on the railcars, trains are essentially invisible at night at a rail crossing. Properly designed 

lighting will improve visibility of the train. Lighting for railway crossings was defined in the 2012 

Handbook but not included in this document, as it is well covered in IES RP-8-21. Consult the FHWA 

Highway Rail Crossing Handbook (safety.fhwa.dot.gov) for further information on rail crossings. An 

example design is provided in Part II of this handbook.

For more information on the FHWA Railway Crossing programs, refer to: 

https://safety.fhwa.dot.gov/hsip/xings/

4.3.5 Work Zones

Work zone safety is an important consideration for construction and maintenance activities on U.S.

roadways. In the last 10 years, the number of injuries and fatalities in work zones has risen considerably

(American Road & Transportation Builders Association, 2022), as shown in Figure 43. As traffic volumes 

increase and more construction activities occur at night, the safety issues grow more complex. Although 

traffic volumes are lower at night, travel speeds are generally higher and visibility is lower, leading to 

potentially higher risks for motorists and workers. 
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Figure 43. Graph. Fatalities and estimated injuries occurring in work zones from 2011 to 2020 (American Road & 

Transportation Builders Association, 2022). 

Work zone lighting increases the visibility for workers and their visibility to motorists entering the work 

zones, thus ensuring safety for workers as well as motorists. Work zone lighting typically involves the 

use of portable, high-intensity floodlights or balloon lights with portable generators to direct a high level 

of light onto the work area. These portable light towers can be a significant source of glare to motorists 

entering the work zone, if aimed incorrectly. Glare in the eyes of the drivers entering the work zone 

could reduce visibility and potentially increase the risk of a crash. Great care should be taken when 

prescribing lighting for work zones so that workers have adequate light levels to complete their tasks 

effectively and safely without introducing glare for drivers entering the work zone. Orientation of the 

portable light tower and their mounting height can significantly affect drivers’ perception of glare and 

visibility (Bhagavathula & Gibbons, 2017, 2018). For portable light towers that can be aimed, the angle 

between the light beam axis and the driver’s line of sight should always be greater than 90 degrees, and 

the angle between the light beam axis and vertical should be less than or equal to 30 degrees. For the 

portable light towers that can be aimed, a mounting height of at least 6 meters (~20 ft) is 

recommended. Light towers that cannot be aimed, like the balloon type portable light towers, should be 

located in the shoulder of the roadway and be mounted at a height of at least 8 meters (~25 ft). The 

features of different kinds of portable light towers commonly used in work zones is shown in Table 9 

and Figure 44. Lighting for work zones was defined in the 2012 Handbook but is not included in this 

document, as it is well covered in IES RP-8-21. Several common work zone lighting applications are 

defined in Part II, Design Examples. These are provided to aid in the design process. 
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Table 9. Pros and cons of different types of portable light towers used in work zones (Bhagavathula, Gibbons, Medina, & 

Terry, 2017). 

Type of Portable Light Tower Pros Cons 

Metal Halide Widely available 

Can be aimed

Offers excellent visibility

Could cause glare if aimed 

poorly

Light Emitting Diode Newer and energy efficient 

technology

Can be aimed

Can be dimmed

Could illuminate without light 

trespass

Visibility lower than metal 

halide and balloon portable 

light tower types

Balloon Newer technology and could be 

energy efficient

Aiming not required

Potential for lower glare

Offers excellent visibility

Susceptible to wind 

Figure 44. Image. Common portable light towers used in work zone lighting (a) Metal Halide, (b) LED, and (c) Balloon portable 

light towers. (Image Credit: Rajaram Bhagavathula, VTTI)
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5 LIGHTING SYSTEM SELECTION

5.1 Lighting Selection

A key task for the roadway lighting designer is the selection and specification of products and 

equipment. Many manufacturers produce outdoor lighting equipment that is marketed and available 

throughout North America. Variables that affect the pole layout and spacing include the pole style, pole 

height, arm length, luminaire wattage, optical distribution, and luminaire type (cobra head, decorative, 

etc.). 

5.1.1 Luminaires 

The use of high-quality products is critical to prolonging the 

overall operating life of roadway lighting systems. Quality 

relates to the features and characteristics of a product that 

impact its ability to satisfy stated or implied needs. While 

quality could be overlooked if low price is the primary 

criterion for product selection, it is an important consideration in product selection. There can be vast 

differences in product performance and quality of optical distribution and output that affect the light 

level and durability. In general, focusing on price alone will not deliver best-value installations. Simply 

put, you get what you pay for.

In addition to quality, other considerations when specifying a product include:

• Certification. Electrical products should bear an Underwriters’ Laboratories label. 

• Photometric performance (for luminaires). A photometric comparison of luminaires is critical to 

selecting the best product for a given application, as shown in Figure 45. Comparisons should be 

based on photometric data provided by the supplier from an independent testing laboratory. As 

mentioned earlier, LED luminaires are typically not swappable from one manufacturer to another. 

The optical design is particular to one product. Thus, an individual design is needed for each product 

used and maintenance and inventory levels may increase if multiple product types are used by one 

agency.

An important key task for the 

roadway lighting designer is the 

selection and specification of 

products and equipment. 
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Figure 45. Photo. Photo displaying luminaires of different correlated color temperatures (Image Credit: Rajaram, 

Bhagavathula, VTTI)

• Optical system and shielding. Luminaires have varying optical systems and shielding options that can 

produce differing effects such as disability glare (veiling luminance) impacts on drivers; therefore, it 

is critical to select luminaires that meet the veiling luminance requirements on the roadway. 

Luminaires can also produce varying light trespass impacts off the roadway. When using pedestrian 

scale luminaires (typically 20 ft or lower luminaire mounting height), consider a diffusing lens (also 

referred to by some manufactures as comfort optics) to reduce the direct brightness of the LEDs and 

reduce impacts. Shielding of optical systems, defined further in Section 6.3, will also help mitigate 

light trespass impacts off the roadway.

• Durability. Durability is the capability of a product to resist deterioration, damage, and corrosion 

over time. Designers should consider the potential for vandalism and the corrosive nature of the 

project’s environment when choosing specific products.
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• Aesthetics. The products selected should be aesthetically 

compatible with their surroundings. Manufacturers offer a 

wide range of equipment shapes, configurations, colors, and 

styles. Similar or identical-looking products should be used, if 

possible, when the new installation will be integrated with 

existing installations. The height of lighting structures should 

be visually compatible with the height of other structures in the area.

• Availability. Custom and/or decorative products or products manufactured in small quantities often 

have long lead times for replacement. Designers should verify that the products selected will be 

available to avoid construction schedule impacts. Designers should also confirm that parts or 

complete replacement units will be available following installation. If products or parts will not be 

readily available, the designer should advise the owner to consider purchasing replacement units or 

parts to stock for maintenance purposes.

• Maintenance requirements. Maintenance considerations include ease of access for servicing, 

maintenance frequency, and level of service required over the product’s anticipated useful life.

• Operations cost. Similar products can have different costs of operation. This is particularly true of 

products that consume energy. The designer should review operational costs when specifying 

products and choose those products that are both economical to operate and provide the required 

performance.

Based on the recommendations in NCHRP 940 and other state specifications, specific minimum

luminaire typical recommendations are as follows:

- Optical system ingress protection rating of IP66 or better 

- Min 3G vibration rating 

- Salt spray rating of 6 or better as per ASTM D1654

- Surge suppression rating of 20kV/10kA

- Ten-year warranty 

- Power factor of 0.9 or better

- Total harmonic distortion < 20%

- FCC 47 CFR Part 15 Inference Requirements for Class B (residential areas) 

- Glare shielding 

In addition, all luminaires should have a 7-pin photocell receptacle (as recommended per ANSI C136.41) 

and be enabled for adaptive controls via a 0-10 V dimming driver. A photocell would then operate each 

luminaire or a shorting cap would be provided if a single photocell would operate groups of luminaires.

It is important to note that, typically, the higher the drive current, the greater the light output, and with 

that comes a higher product failure rate. However, a lower drive current corresponds to a greater MTBF 

and thus a higher reliability (fewer failures over time). Obtaining accurate MTBF data from suppliers is 

challenging as the market is focused on maximum optical efficiency at the lowest cost; reliability and 

product failure rates are not typically considered. 

Another option offered by many suppliers is an adjustable driver current setting in the luminaire. In 

effect, this setting varies the luminaire wattage by providing 5 to 10 different wattages from the same 

Lighting systems should be 

selected to optimize the lifecycle cost of the system. 
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luminaire. The number of wattages depends on the product. Typically, the design is based on the middle 

setting so that the wattage can be increased or decreased if required. 

5.1.2 Energy Efficiency

To meet demand, energy-efficient roadway lighting 

technologies and adaptive controls have been developed 

and show significant potential for energy reduction, 

reduced maintenance, and cost savings. While LED 

lighting has scaled well into the market, adaptive lighting 

controls have lagged given the lower return on 

investment and longer payback based on power savings 

as compared to LED lighting (See Section 7 of this 

Handbook). The conversion to LEDs has resulted in good 

payback and return on investment, whereas lighting controls have not had the same levels of benefits.

Efficacy is a simple measure of the light output of the light source. It is measured in lumens per watt. 

Efficacy does not deal with how efficiently the light source delivers the light to the surface and is 

therefore limited as a measure of performance. In the past, all streetlights used high-intensity discharge 

lamps with similar inefficiencies with respect to how the light is distributed from the luminaire. Although 

LEDs have similar efficacies (lumens per watt) as some of the better high-intensity discharge sources, 

LEDs offer a far more effective optical distribution of light from the source, making them highly optically 

efficient. 

To ensure the selection of energy-efficient luminaires, a unit power density (UPD) analysis is a good 

method for defining optimal luminaire performance and energy efficiency. UPD is the ratio of the rated 

luminaire watts to the amount of lighting delivered for a given area; thus, a lower UPD indicates better 

lighting. It is an excellent way to assess the efficiency of luminaires for various roadway lighting 

applications. The determination of UPD does not mitigate the need to meet lighting criteria, however. 

UPD allows the consideration of multiple lighting criteria, road widths, and pole heights and spacings to

select the optimal product. The defined UPD value can be used as a benchmark to pre-approve products 

based on their performance. 

The UPD calculation is mathematically expressed in Equation 5 and shown schematically in Figure 46

(UPD is measured in Watts per meter squared [Watts/meters2

]). 

Equation 5. UPD Calculation (source TAC) 

To ensure the selection of energyefficient luminaires, a unit power 

density (UPD) analysis is a good 

method for defining optimal 

luminaire performance and 

energy efficiency. 
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Figure 46. Diagram. Geometry for the UPD calculation. (Image Credit: WSP) 

5.2 Other Design Considerations

In some cases, site conditions may dictate certain constraints on the design. Therefore, the following 

site conditions should be investigated:

• Availability of power. The availability of power is a major factor in determining if roadway lighting 

can be provided. If power is not available, the local utility should be consulted and cost estimates for 

power supply should be determined.

• Proximity to aircraft landing facilities. Prospective installations close to airports and helicopter 

landing pads may pose problems with defined glide paths and air traffic control operations.

Typically, an airport authority or their governing authority will have specific pole height limitations 

and/or optical requirements for the luminaires. Where a lighting installation is proposed close to an 

aircraft landing facility, the facility should be contacted so requirements specific to that facility can 

be met. 

• Proximity to railroads. Lighting systems near railroad tracks will have specific clearance 

requirements from the tracks. 

• Presence of overhead distribution and transmission lines. Distribution and transmission lines often 

conflict with lighting poles. Where transmission or distribution lines exist or are proposed and 

lighting is required, the designer should consult the local utility provider and investigate applicable 

codes and standards to determine clearance requirements. Typically, the higher the voltage of the 

overhead lines, the greater the clearance distance required. In the case of overhead transmission 

lines, the local electrical utility may define additional clearance requirements due to the potential 

sag of the transmission lines. Line sag will vary with the change in ambient temperature and power 

demand.

• Environmental issues. Local lighting ordinances may also dictate the type of lighting that may be 

installed along with light trespass and skyglow limits.

• Maintenance and operations considerations. Maintenance should be considered as part of the 

roadway lighting design. Where possible, maintenance personnel should be consulted by those 

undertaking the roadway lighting design. It is critical that the luminaires be safely accessible via 
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available service vehicles (used by those undertaking the maintenance) with minimal disruption to 

traffic. The height limits of maintenance equipment may impact pole height and location.

• Roadside safety considerations. Poles can be a potential hazard to errant motor vehicles. Clear 

zones and pole placement issues should be known and addressed. Additional information can be 

found in the AASHTO Roadside Design Guide (https://highways.dot.gov/safety/pedestrianbicyclist/safety-tools/51-52-roadside-design-guide-4th-edition. 

5.3 Luminaire Classification

A system exists to define optical distribution for roadway lighting (refer to IES RP-8-21). The system 

shows different light distribution patterns used to define the distribution (Figure 47). Prior to LEDs, this 

system worked fairly well to define the required luminaire wattage and optical system (e.g., 100-W HPS

with type II full cut-off distribution). 

Figure 47. Image. IES roadway luminaire classifications (Illuminating Engineering Society, 2018). 

The advent of LEDs with arrays of optical systems has rendered the existing classification system defined 

in IES RP-8-21 ineffective. Figure 48 compares four type II luminaires which produce quite different light 

distributions. Thus, this classification system should not be used generally to specify luminaires. 
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Figure 48. Image. Comparison of light distributions for four type II luminaires (Image Credit: DMD). 

Various luminaires of similar wattages in terms of their ability to meet various light levels based on IES 

RP-8-21 road classifications and pedestrian activity levels were compared. Luminaire photometric data 

were provided by eight different manufacturers based on common road geometrics. The photometric 

files were then applied in common lighting calculation models, and the spacing was optimized to meet 

the lighting criteria. The results showed vastly different pole spacings in each scenerio, indicating that 

performance varies greatly from supplier to supplier. Thus, standized pole spacings cannot be 

transferred from product to product. 

A luminaire classification system (LCS) was developed to define luminaire distribution and assess and 

mitigate light trespass, glare, and skyglow (see IES TM-15, Luminaire Classification System for Outdoor 

Luminaires (Illuminating Engineering Society, 2020b)). This LCS was intended to replace the luminaire 

cutoff classification system, which uses designations like 

cutoff, non-cutoff, semi-cutoff, and full cutoff. The LCS 

defines a method for evaluating and comparing outdoor 

luminaires. It provides a basic model that defines maximum 

lumens within defined angles of primary areas: back light,

up-light, and glare (BUG). The sum of percentages of lamp 

lumens within these three primary areas is equal to the photometric luminaire efficiency. The BUG 

ratings are further defined in IES TM-15 (Illuminating Engineering Society, 2020a). 

The intent of the BUG metric is to allow a designer to select the optimal optics for a given application 

while also reducing light trespass and skyglow. For a luminaire selection, the optimal up-light rating 

would be U0, which indicates reduced potential skyglow. The glare rating should not be used, as it can 

Standardized pole spacings 

cannot be transferred from 

product to product. 
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conflict with the veiling luminance ratio, which is a better measure of glare. Using the lowest back light

rating possible will achieve sidewalk lighting levels and surround levels, which should take priority in the 

design. 
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6 ENVIROMENTAL IMPACTS AND MITIGATION

This section discusses the impacts of lighting beyond its effects on safety. These impacts can be both 

positive and negative. Though safety should generally be the priority, these other impacts may warrant 

consideration during lighting design. 

6.1 Wildlife Impacts

Light is a major factor in controlling physiological and behavioral processes in organisms and thus plays a 

central role in the lives of many plants and animals. Over the past century, artificial lighting has 

transformed the nighttime environment for wildlife over large areas, influencing the movement, 

reproduction, and migration of various species. The large-scale conversion of traditional streetlighting to 

LED roadway lighting is beginning to occur in cities around the world. As such, scientific studies 

investigating how urban and suburban wildlife are affected by this 

conversion are lacking. 

According to World Atlas, there are approximately 8.7 million 

species on Earth, with studies suggesting that 86% of all land 

species and 91% of all sea species are yet to be discovered or 

noted (Mora, Tittensor, Adl, Simpson, & Worm, 2011). The 

animal kingdom comprises only approximately 0.4% of the total 

living organisms on Earth; plants comprise the most at 82%, and 

microscopic bacteria comes next at 13%. Existing literature

(discussed below) highlights the variability in wildlife responses 

to different lighting levels and spectral distributions. These variations stem from the large range of 

activity patterns (e.g., diurnal vs. nocturnal) and spectral perception and sensitives found among wildlife 

species. The wide variety of species and varying sensitivity to light make defining impacts difficult.

6.1.1 Lighting Impacts on Animals

Much animal activity takes place at night; almost all small rodents and carnivores, 80% of marsupials, 

and 20% of primates are nocturnal. Lighting in environmentally sensitive areas with animal activity 

should minimize the duration of lighting, direct the light only where needed, and reduce intensity as 

much as possible. As an example of the impact of lighting on wildlife, (Witherington & Martin, 1996)

found that lighting caused significant issues for turtle hatching and shore bird nesting on the coast of 

Florida. 

Roadway lighting can negatively affect animals by disrupting their habitats, disorientating them, or 

disturbing their circadian rhythms (van Bommel, 2014). An estimated 40% of the world has not 

experienced darkness at levels below moonlight (Swaddle et al., 2015). All animals with visual systems, 

including mammals, fish, and insects, are impacted by artificial light at night (Brüning, FranzHölker, 

Franke, Kleine, & Kloas 2016). Extensive literature is available on this topic: refer to (Rich & Longcore, 

2006). Typically, the issues associated with lighting are related to attraction and disorientation (Allen, 

1880), although lighting may also impact breeding, feeding, and behavior. For example, the timing of 

morning song in robins is significantly affected by the robin’s proximity to roadway lighting installations; 

however, lighting also increased the probability of siring offspring. 

Lighting in environmentally 

sensitive areas with animal 

activity should minimize the 

duration of lighting, direct 

the light only where needed, 

and reduce intensity as 

much as possible. 
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One of the early examples of the impact of light at night was on sea turtles. Sea turtle hatchlings are 

genetically programmed to use starlight and moonlight reflections off the water to guide them from 

their nest to the water. However, man-made light sources can confuse the hatchlings and lead them 

inland, away from the ocean and onto lighted roadways. Beach areas where both street lighting and 

turtle populations are present can discourage females from nesting. If a female fails to nest after 

multiple false crawls, she will resort to less-than-optimal nesting spots or deposit her eggs in the ocean. 

In either case, the survival outlook for hatchlings is slim (Silva et al., 2017). Lighting near the shore also 

can cause hatchlings to become disoriented and wander inland, where they often die of dehydration or 

predation. Scientists believe that hatchlings have an innate instinct that leads them in the brightest 

direction, which is normally moonlight reflecting off the ocean. Excess lighting from the nearshore 

buildings and streets draws hatchlings toward land, where they may be eaten or run over. Although 

further investigation is required to fully understand the safety impacts, custom “sea turtle-friendly” 

lighting appears warranted. Luminaires with amber or red LEDs with a spectral power distribution range 

of 580 to 640 nm are defined as turtle friendly and approved by sea turtle conservation groups 

(Witherington & Bjorndal, 1991),(Figure 49). 

Figure 49. Red LED (610 nm) green turtle-friendly lighting (Image Credit: DMD). 

Insects such as rain flies can be attracted to light sources. In this case, the flies are attracted to the light 

source, causing them to mate and die on the luminaire (Figure 50). 
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Figure 50. Photo. Rain flies on a luminaire (Image Credit: DMD). 

A method to assess the impact of lighting, particularly the lighting spectrum, on wildlife is provided in 

the research paper “Rapid Assessment of Lamp Spectrum to Quantify Ecological Effects of Light at Night” 

(Longcore et al., 2018a). This method considers the actinic (activating) spectrum for a variety of animals 

and effects (Figure 51). Notably, the example actinic curves represent only a small number of species 

and their relative sensitivities. Ongoing work is cataloging the spectral sensitivities of animals based on 

their biological taxonomy. To calculate the impact on the species, the curves shown in Figure 51 are 

convolved with the spectrum of the light source to estimate the effect of lighting. 

In the work by Longcore et al. (2018b), sample calculations with example spectrum were made to 

consider the light source color in CCT versus the impact on the species. In most but not all cases, lower 

CCT values corresponded to a lower impact on the metric of interest (Longcore et al., 2018b). The 

information in Figure 51 shows that, in the case of green turtles, the adults have different sensitivity to 

light than the hatchlings, which makes the selection of the light sources even more challenging. 
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Figure 51. Line graphs. Actinic curves for a variety of lighting effects (Longcore et al., 2018a). 

6.1.2 Lighting Impacts on Plants

Similar to the effects on wildlife, roadway lighting tends to affect plants that require a dark cycle to 

reach maturity (e.g., soybeans). Roadway lighting has been shown to affect the growth and maturity of

soybeans (Briggs, 2006; Palmer, Gibbons, Bhagavathula, Holshouser, & Davidson, 2017; Zong-Ming, 

2007) and maize (Sinnadurai, 1981). The effects of LED roadway lighting on plant growth and maturity 

have not yet been reported; however, laboratory studies have shown that LEDs with high blue contents 

make soybean plants more compact (Cope & Bugbee, 2013). Limiting the light that is emitted outside of 

the right-of-way can mitigate the impact of the lighting. The recommended limits for vertical and 

horizontal illuminance at the property line to reduce lighting impacts on soybean are shown in Table 10. 

Table 10. Lighting limits at the property line to reduce impacts on soybeans (Palmer, Gibbons, Bhagavathula, & Holshouser, 

2018). 

Illuminance Maximum value, lux

Horizontal 2.2

Vertical 1.8
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The method for evaluating the impact of lighting on plants is like evaluating lighting impacts on animals.

In the case of plants, the actinic curve for photosynthesis (see Figure 51) is used to characterize the light 

source. The result is a factor known as the photosynthetic photon flux density (PPFD), which represents 

the effective photon strength required for photosynthesis. A conversion factor for lighting for humans 

versus lighting for plants can be applied for a given light source. Given a similar lighting level, lower CCT

values correspond to higher PPFD conversion factors and thus stronger impacts on the plant being 

considered. Refer to IES RP-45 Horticultural Lighting (Illuminating Engineering Society, 2021b) for further 

information. 

6.1.3 Mitigating the Impacts of Lighting on Plants and Animals

While the impacts of lighting on wildlife have been studied, these assessments are much more difficult 

than studies on humans due to the sheer number of species to consider and the difficulty in monitoring 

animal behaviors. As a result, the effects on most species are not well understood in terms of the 

specific effects along with the associated lighting dosage and duration. Ecological Consequences of 

Artificial Nighttime Lighting (Rich & Longcore, 2013) provides a comprehensive assessment of the 

wildlife effects of lighting; however, little information is provided about mitigation, and no 

recommendations are provided on lighting dosage and duration, which are key factors when designing a 

roadway lighting system. 

The two primary concerns in terms of wildlife effects are the 

lighting spectrum and dosage. The selection of the 

spectrum can be made considering the animal sensitivity 

and the spectral output of the luminaires. However, the 

selection of dosage is more complicated. Identifying the 

lighting threshold that will not impact animals is difficult 

because nocturnal wildlife species are sensitive to levels of 

light ranging from the full moon (~0.1 lux) to a clear starry 

sky (~0.001 lux). Figure 52 graphically depicts these levels in 

comparison to moonlight and starlight. The lighting 

threshold for impact on melatonin in the species is listed in 

the figure and compared to the lighting levels in civil, nautical, and astronomical twilight as well as full 

darkness. Since the levels of natural light shown in Figure 52 indicate that all the magnitude of light 

levels are lower than that for roadway lighting, it is unlikely that any roadway lighting will fall below a 

threshold value for impacts at the roadway. Even melatonin suppression, which generally has a higher 

threshold value than behavioral responses, occurs in non-human vertebrates at full moon and lower 

levels (Grubisic et al., 2019). Thus, unlike for plant species, a minimum lighting level that would be below 

the threshold of impact on the species is likely not easily determined. 

Managing animal exposure to 

light relies on the selection of 

luminaire optics to reduce light 

trespass and skyglow along with 

dimming or even turning off the 

lighting system in times of critical 

animal behavior such as mating, 

migration, and birth. 
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ALAN – Artificial Light at Night / CT – Civil Twilight / NT – Nautical Twilight / AT – Astronomical Twilight 

Figure 52. Illustration. Melatonin suppression for vertebrates relative to moonlight and starlight (reprinted from Grubisic et 

al., 2019). 

Managing animal exposure to light relies on the selection of luminaire optics to reduce light trespass and 

skyglow as much as possible along with the application of dimming and even turning off the lighting 

system in times of critical animal behavior such as mating, migration, and birth.

6.2 Human Health Impacts

On June 14, 2016, the American Medical Association (AMA) announced its adoption of 

recommendations contained in CSAPH Report 2-A-16, Human and Environmental Effects of Light 

Emitting Diode (LED) Community Lighting. One of the key recommendations was, “That our AMA 

encourage the use of 3000K or lower lighting for outdoor installations such as roadways. All LED lighting 

should be properly shielded to minimize glare and detrimental human and environmental effects, and 

consideration should be given to utilize the ability of LED lighting to be dimmed for off-peak time 

periods.” While shielding the luminaire light sources from view off the roadway and dimming in offperiods are well-supported benefits, the recommendation that CCT not exceed 3000K has caused 

concern with the IES. The IES believes that CCT is inadequate for evaluating potential health outcomes

and that the AMA recommendations target only one component of light exposure (spectral 

composition) out of multiple established inputs that affect sleep disruption, including the quantity of 

light at the retina of the eye and the duration of exposure to that light (IES, 2017). 

NCHRP Research Report 968 (Bhagavathula, Gibbons, 

Hanifin, & Brainard, 2021) evaluated the impact of LED 

roadway lighting on driver sleep health and alertness in 

naturalistic conditions. LED lighting has a higher blue 

spectral content than traditional high-intensity discharge 

(HID) light sources. Exposure to light with higher blue 

spectral content such as those in LEDs in the evening has 

been shown to disturb circadian rhythms, resulting in sleep 

loss (Cajochen et al., 2011; Chang, Aeschbach, Duffy, & Czeisler, 2015). In contrast, there is evidence 

There are no differences between 

4000K LED roadway lighting, 

2100K HPS roadway lighting, and 

no roadway lighting in terms of 

salivary melatonin suppression. 
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that light with a high blue content can increase alertness and enhance cognitive performance in humans 

(Chellappa et al., 2011; Lehrl et al., 2007). LED roadway lighting with higher blue content could 

potentially make road users more alert and enhance nighttime traffic safety. To design effective 

roadway lighting, there is a growing need to understand the relationships between roadway light level, 

melatonin suppression, and driver alertness and health. This was one of the first empirical studies to 

quantify melatonin and alertness responses to the intensity and spectrum of roadway lighting in healthy 

drivers. The results indicated that there were no differences between 4000K LED roadway lighting, 

2100K HPS roadway lighting, and no roadway lighting in terms of salivary melatonin suppression as well 

as subjective and objective measures of alertness. There were also no differences in salivary melatonin 

suppression between LED and HPS roadway lighting when measured at the same light level (roadway 

luminance of 1.5 cd/m2 or a corneal illuminance of 1.9 lux). These results suggest that the SPD (or CCT)

of roadway lighting at the light level recommended by IES RP-8-21 is not a major factor affecting human 

salivary melatonin or alertness. The results from this research also indicated that the potential for 

melatonin suppression from exposure to consumer electronic devices such as televisions, monitors, 

smartphones, and tablets is considerably higher than from 4000 K LED roadway lighting. 

6.3 Light Pollution Impacts

The main elements of lighting pollution are (Figure 53) (Illuminating Engineering Society, 2021d): 

• Light trespass: The encroachment of light, typically across property boundaries, causing annoyance, 

loss of privacy, or nuisance. 

• Spill light: The light emitted by a floodlight that is outside the floodlight distribution as defined by 

the field angle classification. Although the definitions vary in practice, the terms spill light and light 

trespass are used interchangeably.

• Glare: The sensation produced by luminance within the 

visual field that is sufficiently greater than the 

luminance to which the eyes are adapted, resulting in

annoyance, discomfort, or loss in visual performance or 

visibility. Note that the magnitude of the sensation of 

glare depends on factors such as the size, position, and 

luminance of a source, the number of sources, and the 

luminance to which the eyes are adapted.

• Skyglow: The brightening of the night sky that results from the scattering and reflection of light from 

the constituents of the atmosphere (gaseous molecules and aerosols) in the direction of the 

observer. Skyglow has two separate components: natural skyglow and artificial skyglow.

It is important to note that the reduction or elimination of light trespass should never take precedence 

over the provision of adequate roadway lighting. Lighting the area adjacent to roadway travel lanes 

(surround) can benefit a driver’s peripheral vision as well as improve the visibility of crossroads, 

driveways, and sidewalks. Lighting the area adjacent to the road can also help in the detection of large 

animals that pose a safety hazard. While balancing the needs of the road user with any potential 

impacts of the lighting system can be difficult for many roadway types, this issue should be approached 

holistically. 

As a rule of thumb, if the view of 

the light source is blocked, the 

glare impact off the roadway 

will be eliminated. 
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Figure 53. Illustration. Spill lighting, glare, and skyglow (Image Credit: DMD). 

As a general rule, if the view of the light source is blocked, the glare impacts off the roadway will be 

eliminated. Luminaire shielding can be effective at reducing light trespass impacts such as spill light and 

glare. Examples of shielding are shown in Figure 54 and Figure 55. While shielding can effectively reduce

the brightness of LEDs behind the pole, most shields are not effective when viewing from across the 

road, with the exception of the custom shield in the image on the lower right side of Figure 55. These 

shields can also significantly reduce the lighting on the roadway; therefore, lighting calculation using 

photometric data provided by the manufacturer with the shielding installed should be undertaken to 

confirm the provision of the necessary light levels on the roadway and sidewalks. It is important to note 

that these shields can reduce light level and uniformity on the roadway (especially the eyelid shields). 

Photometric files with shields should be obtained from the manufacturers, and photometrics with the 

shield should be included in the light calculations. As there is no industry standard for shielding, what is

offered by each supplier should be considered when selecting a product. 

Figure 54. Photos. Eyelid shielding (Image Credit: DMD). 
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Figure 55. Photos. External back lighting and forward light shields (Image Credit: DMD). 

Typically, following an LED installation, the most common residential complaint is glare from the direct 

view of the light source. This glare is magnified when residents are looking up slope in the bright part of 

the optical system. Here, a back shield could be utilized given the steep angle between the resident’s 

view of the light source versus the flatter angle across the road. The key is to shield the view of the light 

source. 

Some manufacturers also offer optical systems with diffusing lenses that effectively diffuse the 

brightness of the LED over a larger area. In effect, the lens acts as a diffuser as shown in Figure 56. These 

optical systems are typically less optically efficient from a UPD standpoint; however, they can be 

effective in reducing the overall glare and pixelization of the luminaire. Some supplies refer to this as 

“comfort optics.” 

Figure 56. Photo. Luminaire optics with a diffusing lens (Image Credit: DMD). 
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Spill light levels are defined in IES RP-8-21 to assess and 

mitigate light trespass off the roadway. Maximum allowed 

vertical illuminance levels are based on the level of 

ambient lighting in the area defined as the lighting zone. 

The lighting zones vary from LZ0 to LZ4. The maximum

vertical illuminance levels are typically calculated and 

measured at the residence or property line. Reducing spill 

light can be effective for reducing light trespass. 

Glare from luminaires very distant from the roadway can

be a source of complaint from residents, particularly for

high-wattage luminaires at mounting heights of 50 ft or 

greater. Even when the light source is located well away from the residence and the spill light level is 

well below the defined limit, glare complaints can result where there are bright light sources set against 

a dark background such as the night sky. Blocking the light source from view via shielding or optical 

systems is an effective solution. Refer to Table 3 in CIE 150, Guide on the Limitation of the Effects of 

Obtrusive Light from Outdoor Lighting Installations (Commission Internationale de l'Eclairage, 2017), for 

assistance for assessing the intensity of light sources set against a dark sky. Based on the size of the light 

source, environmental zone, time of night, and distance from the lighting source, the maximum 

allowable intensity (brightness) can be defined in candela. Some lighting software can be used to 

calculate the candela values when viewed from given locations.

With respect to skyglow, increasing the short-wavelength content of the exterior lighting source 

increases the potential for skyglow. These effects can be reduced or completely offset by other features 

of LED street lighting luminaires. The three main characteristics of luminaires that influence skyglow are 

SPD, total lumen output, and luminaire light distribution (most importantly, the amount of that 

distribution emitted as up-light). Each of these characteristics can be specified through the selection of 

luminaires and should therefore be carefully evaluated as part of the system design. 

Except for installations made in the early years of LED street lighting, most conversions utilized 4000K 

CCT products up to 2016. Following the shift to 3000K LEDs in 2016 based on the AMA report (CSAPH 

Report 2-A-16), the majority of LED conversions involved 3000K LEDs. Although this cannot be confirmed 

without analyzing the specific SPDs for the new LED systems, a study suggests that for residents near the 

city, the visible contribution to skyglow from a typical LED street light conversion (i.e., half the output, 

0% up-light) should be no worse than before conversion and may be reduced. (Kinzey et al., 2017). Thus, 

when the conditions in the model calculations are achieved, skyglow from the streetlights should be 

considerably reduced (by roughly one third to one half) for any observatories near the city (Kinzey et al., 

2017). 

As skyglow increases, it obscures fainter stars until only a handful of the brightest stars are visible at 

night from urban areas. This is disastrous for both professional and amateur astronomers as well as an 

aesthetic and cultural concern for the public. The problem becomes much worse under cloudy skies; 

clouds are effective at backscattering upward light, making the nocturnal environment considerably 

brighter in overcast weather conditions. The key points with respect to skyglow include the following:

• Skyglow is a complex phenomenon that is difficult to control in urban areas, where roadway lighting 

is a relatively minor contributor; satellite-based measurements of emission (Kyba et al., 2021) and 

Because of its shorter 

wavelength, LED light tends to 

scatter more than HPS light, 

which increases the potential for 

skyglow. This effect may be offset 

by the improved optics of LED 

luminaires, which reduce up-light. 

 
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ground-based measurements of broadband night sky radiance (Barentine et al., 2020) indicated that 

roadway lighting contributed only 18% of total irradiance and 14% of light emittance, respectively. 

• The atmosphere and viewing point have a huge impact on skyglow.

• Because of its shorter wavelength, LED light tends to scatter more than HPS light, which increases

the potential for skyglow. However, this effect may be offset by the improved optics of LED

luminaires, which reduce up-light.

• To reduce skyglow, lighting designers should use luminaires with cutoff optical systems and avoid

over-lighting.

Luminaires with a low rating in each of the BUG rating categories will minimize skyglow, light trespass, 

and veiling luminance (glare) from the luminaire on and off the roadway, thereby improving overall 

visibility. BUG is a luminaire rating system developed by the IES to categorize a luminaire in terms of 

back light, up-light, and glare. BUG is typically not used in roadway lighting (See IES TM-15-15). 

Refer to IES TM-37 Technical Memorandum: Description, Measurement, and Estimation of Sky Glow

(Illuminating Engineering Society, 2021a) for further information.

6.4 Five Principals in Reducing Environmental Impacts

The International Dark-Sky Association and IES have jointly published Five Principles for Responsible 

Outdoor Lighting (Figure 57), (Liebel & Hartley, 2020). These organizations have the shared goal of 

reducing light pollution via the proper application of quality outdoor electric lighting. By applying these 

principles, properly designed lighting at night can be functional and enhance the nighttime environment. 

Projects that incorporate these principles will save energy and money, reduce light pollution, and 

minimize wildlife disruption. Thus, designers and jurisdictions are encouraged to follow these five 

principals when designing roadway lighting. It should be made clear that these factors potentially 

influence safety and roadway usability. A balance between safety and the potential impact on the 

surrounding area should be considered.
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LIGHT TO PROTECT THE NIGHT

Five Principles for Responsible Outdoor Lighting

USEFUL

ALL LIGHT SHOULD HAVE A CLEAR PURPOSE

Before installing or replacing a light, determine if light is needed. Consider 

how the use of light will impact the area, including wildlife and the 

environment. Consider using reflective paints or self-luminous markers for 

signs, curbs, and steps to reduce the need for permanently installed outdoor 

lighting.

TARGETED

LIGHT SHOULD BE DIRECTED ONLY TO WHERE NEEDED.

Use shielding and careful aiming to target the direction of the light beam so 

that it points downward and does not spill beyond where it is needed.

LOW LIGHT 

LEVELS

LIGHT SHOULD BE NO BRIGHTER THAN NECESSARY.

Use the lowest light level required. Be mindful of surface conditions as some 

surfaces may reflect more light into the night sky than intended.

CONTROLLED

LIGHT SHOULD BE USED ONLY WHEN IT IS USEFUL.

Use controls such as timers or motion detectors to ensure that light is 

available when it is needed, dimmed when possible, and turned off when not 

needed.

COLOR

USE WARMER COLOR LIGHTS WHERE POSSIBLE.

Limit the amount of shorter wavelength (blue-violet) light to the least 

amount needed. Light where you need it, when you need it, in the amount 

needed, and no more.

Figure 57. Infographic. Five principals in reducing environmental impacts (Liebel & Hartley, 2020). 
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7 ADAPTIVE LIGHTING 

Adaptive lighting refers to the dimming of roadway lighting during periods of low vehicular and 

pedestrian activity. The concept of dimming streetlights was developed and evaluated via pilot 

installations in Canada and Europe in the early 2000s. The technology for dimming street lighting gained 

popularity around 2010 with the use of LEDs, which allow for more effective dimming and control 

compared to previous high-intensity discharge sources. Other than energy efficiency, the ability to easily 

control and dim LED luminaires is one of their biggest 

advantages over other roadway lighting sources. 

Adaptive lighting is the most effective way to minimize the 

potential negative aspects of roadway lighting as it can be 

applied to reduce the impacts of exterior lighting systems 

on skyglow, glare, and light trespass while also saving 

energy and reducing maintenance costs. Although it is 

considered an emerging technology, adaptive lighting has 

already been effectively applied. The benefits of adaptive control can be quite different when used for 

highway lighting compared to street lighting; thus, the benefits are quantified based on roadway type.

The application of adaptive lighting is discussed in the Urban Street Lighting Example in Part II of this 

handbook. In this example the method considered for the adaptation of lighting levels is based on the 

existing IES RP-8-21 lighting recommendations. In this method, the pedestrian volume is used to discern 

the lighting level within a road category. As the pedestrian volume changes, the lighting level can 

change. 

A new method has been developed through research for the FHWA and is currently in the IES RP-8-21 as 

an alternative method for lighting selection. This method is defined below.

While the application of adaptive lighting practices have many benefits, the use of adaptive lighting is 

not required under Federal law or regulations

7.1 Luminance Selection

Selecting the appropriate lighting level for the given roadway is the key component to implementing the 

adaptive lighting. The approach specified here has been developed from the results of an analysis of 

crashes and lighting levels on the roadway (Gibbons, Guo, Medina, Terry, Du, Lutkevich, & Li, 2014; 

Gibbons, Guo, Medina, Terry, Du, Lutkevich, Corkum, et al., 2014). The lighting data were measured in 

situ on a variety of roadways in seven different states, and crash data were then used to determine the 

relationship of the lighting data to the crash rate. A variety of criteria were determined to be significant 

to the lighting-safety relationship, including traffic volume and roadway type. Other criteria were added 

to the selection process based on the design approaches and relevant literature. An accompanying 

document, Design Criteria for Adaptive Roadway Lighting, provides more detail on the criteria listed 

here. 

For the proposed methodology, three different selection criteria based on the IESNA approach are used 

to determine the lighting level. IESNA separates design criteria by the following facilities: roadways, 

streets, and residential/pedestrian:

Adaptive lighting refers to the 

dimming of roadway lighting 

during periods of low vehicular 

and pedestrian activity. 
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• Roadway lighting is provided for freeways; expressways; limited-accessroadways; and roads on

which pedestrians, cyclists, and parked vehicles are generally not present. The primary purpose of 

roadway lighting is to help the motorist remain on the roadway and aid in the detection of obstacles 

within and beyond the range of the vehicle headlamps (Figure 58). 

Figure 58. Photo. Roadway lighting. (Image Credit: WSP)

• Street lighting is provided for major, collector, and local roads on which pedestrians and cyclists are 

generally present. The primary purpose of street lighting is to help motorists identify obstacles, provide 

adequate visibility of pedestrians and cyclists, and assist road users in visual search tasks both on and 

adjacent to the roadway (Figure 59). 
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Figure 59. Photo. Street lighting (Image Credit: WSP). 

• Residential/pedestrian area lighting is provided primarily for the safety and security of pedestrians

(not specifically for drivers). These facilities typically have driving speeds slower than 25 mi/hr (40 

km/hr), where vehicle headlights provide adequate lighting for drivers (Figure 60). 

Figure 60. Photo. Residential/pedestrian area lighting (Image Credit: WSP). 

These three facility types that form the basis for lighting requirement selection are characterized as H 

(Roadway), S (Street), or P (Residential/Pedestrian) class. Each of these classes has a specific set of 

criteria for the selection of lighting requirements.
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Once the facility type has been selected and the class identified, the characteristics of the facility are 

used as weighting factors to determine the requirements of the lighting system. The Equation 6 for the 

lighting design class is shown below:

Equation 6. Lighting Class Calculation

The base value changes depending on the facility type as it is based on the number of lighting classes for 

each road class. For highways there are four classes, five classes for roadways, and five for pedestrian 

areas. Hence the base value for these facilities types Roadway, Street and Residential/Pedestrian are 5, 

6, and 6, respectively. 

To determine the lighting level, the sum of the weighting values is then subtracted from this base value, 

which then determines the lighting class. If the result is not a whole number, the next lowest positive 

whole number should be used (e.g., an H3.5 would use the H3 value). Negative numbers call for the 

highest lighting level class (i.e., H1, S1, and P1 are the highest classes and have the highest lighting 

requirements). Similarly, numbers resulting in a class lower than the lowest class would default to the 

lowest class (e.g., a lighting class of H6 would use the H4 value).

For an adaptive lighting system, the lighting level requirements change based on the roadway

conditions. In response, the current approach calls for changes in the corresponding weighting factors as 

the roadway conditions change, resulting in a different lighting class and, therefore, a different required 

design level.

7.1.1 Parameters

The parameters for each of the weighting factors are defined below. Each of these parameters has been 

determined to be an important aspect of the driving environment based on its relationship to vehicular 

crashes.

7.1.1.1 Speed 

The speed parameter is the posted speed of the roadway (as opposed to the design speed of the 

roadway). For an active adaptive system, the 85th percentile speed or other measured vehicle speed can 

be used instead.

7.1.1.2 Traffic Volume 

The traffic volume parameter typically used in the selection of a roadway lighting level is average daily 

traffic (ADT). While ADT is an effective parameter for the selection of a basic lighting level, it is not 

practical for the application of adaptive lighting. Actual traffic volumes vary by day of the week and hour 

of the day, limiting the applicability of ADT to driver needs at any particular time. 

The hourly traffic volume of a roadway is a recommended parameter for the application of adaptive 

lighting because it is indicative of current roadway conditions. For hourly traffic volume parameters, the 

level of service (LOS), as defined by the Highway Capacity Manual, can be used to determine the traffic 

flow level criteria for the adaptive lighting level. These levels are selected as they represent when the 
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road reaches maximum free flow (LOS B to C) and when crash rates begin to increase (LOS C to D). Note 

that the traffic volume values listed in Table 11, Table 12, and Table 13 are for single-direction travel. 

Thus, the values would have to be doubled when applied to undivided roads.

Table 11. Hourly traffic flow criteria for roadways. (FHWA)

Parameter Options Criteria Weighting 

Value 

Traffic Volume High > 2,000 Vehicles Hourly per lane 1 

Moderate 1,000 – 2,000 Vehicles Hourly per lane 0 

Low < 1,000 Vehicles Hourly per lane -1 

Table 12. Hourly traffic flow criteria for streets.

Parameter Options Criteria Weighting Value 

Traffic Volume High > 1,500 Vehicles Hourly per lane 1 

Moderate 750 – 1,500 Vehicles Hourly per lane 0 

Low < 750 Vehicles Hourly per lane -1 

Table 13. Hourly traffic flow criteria for residential/pedestrian roads.

Parameter Options Criteria Weighting Value 

Traffic Volume High > 750 Vehicles Hourly per lane 0.5 

Moderate 300 – 750 Vehicles Hourly per lane 0 

Low < 300 Vehicles Hourly per lane -0.5 

An agency may choose to recalculate these limits for their specific roadway conditions.

7.1.1.3 Median

The median parameter defines the presence of a median barrier. Typically, a median is present on large 

roadways to separate the two directions of travel. The median should have a barrier or be designed such 

that the light from opposing headlamps is limited and not visible by drivers approaching each other. The 

AASHTO Roadway Design Guide defines a median width of 15 meters where a barrier is not required in a 

roadway; this median width is suitable to limit glare between vehicles. Median widths between 10 and 

15 meters require a design review with engineering judgment.

7.1.1.4 Intersection/Interchange Density 

The intersection/interchange density parameter refers to the number of intersections and entrances 

into the roadway per mile or kilometer. This parameter represents the possibility of vehicles interacting 

in the roadway. In addition to other roadways, this parameter includes driveways and other entrance 

areas.
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7.1.1.5 Ambient Luminance 

The brightness and amount of light in the surrounding area impacts the lighting requirements for the 

roadway and is accounted for in the lighting level selection. To differentiate lighting and ambient zones, 

the IESNA has developed Lighting Zones (LZs) describing different ambient lighting conditions. 

7.1.1.6 LZ0: No Ambient Lighting

LZ0 represents areas where the natural environment will be seriously and adversely affected by lighting

(e.g., by disturbing the biological cycles of flora and fauna or detracting from human enjoyment and 

appreciation of the natural environment, although human activity is considered less important than 

nature in this zone). The vision of human residents and users is adapted to total darkness, and they 

expect to see little or no lighting. When not needed, lighting should be extinguished, although lighting is 

not typically applied in LZ0 conditions. 

7.1.1.7 LZ1: Low Ambient Lighting

LZ1 represents areas where lighting might adversely affect flora and fauna or disturb the character of 

the area. The vision of human residents and users is adapted to low light levels. Lighting may be used for 

safety and convenience, but it is not necessarily uniform or continuous. After curfew, lighting may be 

extinguished or reduced as activity levels decline.

7.1.1.8 LZ2: Moderate Ambient Lighting

LZ2 represents areas of human activity where the vision of human residents and users is adapted to 

moderate light levels. Lighting may typically be used for safety and convenience, but it is not necessarily 

uniform or continuous. After curfew, lighting may be reduced as activity levels decline.

7.1.1.9 LZ3: Moderately High Ambient Lighting

LZ3 represents areas of human activity where the vision of human residents and users is adapted to 

moderately high light levels. Lighting is generally desired for safety, security, or convenience, and it is 

often uniform and/or continuous. After curfew, lighting may be reduced as activity levels decline.

7.1.1.10 LZ4: High Ambient Lighting

LZ4 represents areas of human activity where the vision of human residents and users is adapted to high 

light levels. Lighting is generally considered necessary for safety, security, or convenience, and it is 

mostly uniform and/or continuous. After curfew, lighting may be reduced in some areas as activity levels 

decline. 

7.1.1.11 Pavement Marking Quality

The Pavement Marking Quality parameter refers to the presence and quality of the other non-lightingrelated visibility and guidance tools on the roadway. In particular, the quality of the pavement markings 

has been shown to interact with the lighting in terms of driver performance. The criterion presented 

here for guidance is the retroreflectivity of the pavement markings in mcd/m2

∙lx.
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7.1.1.12 Pedestrian/Bicycle Interaction 

The pedestrian/bicycle interaction parameter refers to the number of pedestrians and bicycles present 

in the roadway, either crossing or walking parallel to the roadway.

7.1.1.13 Parked Vehicles 

The parked vehicles parameter refers to the presence of parked vehicles along the side of the roadway.

7.1.1.14 Facial Recognition

The facial recognition parameter refers to the requirement of a driver or pedestrian to recognize the 

facial characteristics of a person walking in the roadway or on the sidewalk (Figure 61 and Figure 62). 

This parameter is related to the feeling of safety and security of the roadway users. Typically, facial 

recognition can be expected to be an important aspect of the roadway environment.

Figure 61. Photo. Facial recognition under low lighting. (Image Credit: Paul Lutkevich, WSP)
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Figure 62. Photo. Facial recognition under high lighting. (Image Credit: Paul Lutkevich, WSP)

7.1.1.15 Conflict Areas

Although not a specific criterion for the selection of the luminance level, conflict areas are a 

consideration in the design process and may be affected by the adaptive lighting design. Lighting in 

conflict areas, such as intersections and crosswalks, can also be adjusted in relation to the lighting levels 

of nearby roadways, streets, and residential/pedestrian areas. For example, the IESNA RP-8-21

recommended lighting level for intersections is the sum of the lighting levels of the intersecting roads. In 

an adaptive lighting design, if a change in use of the intersecting roads allows a reduction in lighting 

levels, the lighting level of the intersection will also be reduced.

7.1.2 Design Recommendation and luminance Selection

The parameters above are used to determine the lighting level. Table 14, Table 16, and Table 18 show 

the weighting parameters, while Table 15, Table 17, and Table 19 show the recommended lighting 

design levels (based on the lighting class) for roadway, street, and residential/pedestrian facilities, 

respectively. The base values for each facility type are also provided for each classification. It is 

important to note that the lighting design recommendations for the residential/pedestrian areas are 

horizontal and vertical illuminance, not luminance. Road luminance is the criterion for both roadway and 

street facilities.

It is also important to note that as the weighting values change, the lighting level can change. For 

example, the traffic volume or the number of pedestrians can change, which affects the weighting value 

of that parameter. This, in turn, may change the roadway lighting class; therefore, the lighting level 

requirements may change as well. This is particularly critical with respect to the traffic volume and 

pedestrian levels.
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7.1.2.1 Design Criteria for Roadways (H-Class) 

Base value for class: 5 (This value is used in the calculation of the road class)

Table 14. Roadway design level selection criteria (FHWA). 

Parameter Options Criteria Weighting Value 

Speed Very High > 60 mi/h (100 km/h) 1 

High 45–60 mi/h (75 –100 km/h) 0.5 

Moderate < 45 mi/h (75 km/h) 0 

Traffic Volume High > 30,000 ADT* 1 

Moderate 10,000 – 30,000 ADT 0 

Low < 10,000 ADT -1 

Median No 1 

Yes Should be glare blocking 0 

Intersection/ 

Interchange Density 

High < 1.5 miles between intersections (2.5 km) 1 

Moderate 1.5–4 miles (2.5 km – 6.5 km) between 

intersections 

0 

Low > 4 miles (6.5 km) between intersections -1 

Ambient Luminance High LZ3 and LZ4 1 

Moderate LZ2 0 

Low LZ1 -1 

Pavement Marking 

Quality

Good > 100 mcd/m2 lx** 0 

Poor < 100 mcd/m2 lx 0.5 

*ADT = Average Daily Traffic

**mcd/m2 lx = millicandela/meter squared lux

Table 15. H-Class lighting design levels (FHWA). 

Class Average 

Luminance 

(cd/m2)

Max 

Uniformity 

Ratio 

(avg/min) 

Max 

Uniformity 

Ratio 

(max/min) 

Veiling 

Luminance 

Ratio 

H1 1 3 5 0.3 

H2 0.8 3.5 6 0.3 

H3 0.6 3.5 6 0.3 

H4 0.4 3.5 6 0.3 
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7.1.2.2 Design Criteria for Streets (S-Class) 

Base value for class: 6 

Table 16. Street design level selection criteria (FHWA). 

Parameter Options Criteria Weighting Value 

Speed High > 45 mi/h (70 km/h) 1 

Moderate 35–45 mi/h (55–70 km/h) 0.5 

Low < 35 mi/h (55 km/h) 0 

Traffic Volume High > 15,000 ADT* 1 

Moderate 5,000–15,000 ADT* 0 

Low < 5,000 ADT* -1 

Median No 1 

Yes (or one-way) Should be glare blocking 0 

Intersection/ 

Interchange Density 

High > 5 per mile (1.6 km) 1 

Moderate 1–5 per mile (1.6 km) 0 

Low < 1 per mile (1.6 km) -1 

Ambient Luminance High LZ3 and LZ4 1 

Moderate LZ2 0 

Low LZ1 -1 

Guidance Good > 100 mcd/m2 lx 0 

Poor < 100 mcd/m2 lx 0.5 

Pedestrian/Bicycle 

Interaction 

High > 100 pedestrians per hour 2 

Moderate 10–100 pedestrians per hour 1 

Low < 10 pedestrians per hour 0 

Parked Vehicles Yes 1 

No 0 

*ADT = average daily traffic for a single direction on the roadway

Table 17. S-Class lighting design levels (FHWA). 

Class Average 

Luminance 

(cd/m2)

Max 

Uniformity 

Ratio 

(avg/min) 

Max 

Uniformity 

Ratio 

(max/min) 

Veiling 

Luminance 

Ratio 

S1 1.2 3 5 0.3 

S2 0.9 3.5 6 0.4 

S3 0.6 4 6 0.4 

S4 0.4 6 8 0.4 

S5 0.3 6 10 0.4 
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7.1.2.3 Design Criteria for Residential/Pedestrian Areas (P-Class) 

Base value for class: 6

Table 18. Residential/pedestrian design level selection criteria (FHWA). 

Parameter Options Criteria Weighting 

Value 

Speed High > 45 mi/h (70 km/h) 1 

Moderate 35–45 mi/h (55–70 km/h) 0.5 

Low < 35 mi/h (55 km/h) 0 

Traffic Volume High > 7,500 ADT* 0.5 

Moderate 3,000–7,500 ADT* 0 

Low < 3,000 ADT* -0.5 

Intersection/ 

Interchange Density 

High > 5 per mile (1.6 km) 1 

Moderate 1–5 per mile (1.6 km) 0 

Low < 1 per mile (1.6 km) -1 

Ambient Luminance High LZ3 and LZ4 1 

Moderate LZ2 0 

Low LZ1 -1 

Pedestrian/Bicycle 

Interaction

High > 100 pedestrians per hour 1 

Moderate 10-100 pedestrians per hour .5

Low < 10 pedestrians per hour 0 

Parked Vehicles Yes .5

No 0 

Facial Recognition Required 1 

Not Required 0 

*ADT = average daily traffic for a single direction on the roadway

Table 19. P-Class lighting design levels (E = Illuminance) (FHWA). 

Class E Average

Lux 

E Vertical 

(minimum 

point)

Ratio 

Eavg/Emin

P1 10 5 4 

P2 5 2 4 

P3 4 1 4 

P4 3 0.8 6 

P5 2 0.6 10 

7.1.3 Example of Lighting Design Criteria Selection

The following example illustrates how to select a roadway lighting class:
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• Speed limit of 70 mph.

• Equivalent of 35,000 ADT.

• 12 m median between opposing directions with no barrier.

• An average of 2 mi between interchanges.

• Zoned as an LZ3 lighting area.

• Has brand-new pavement markings measuring at 425 mcd/m2 lx.

The resulting weighting functions are shown in Table 20. 

Table 20. Example lighting level selection process for a roadway facility.

Parameter Options Criteria Weighting 

Value 

Speed Very High > 60 mph 1 

Traffic Volume High > 30,000 ADT 1 

Median No 1 

Intersection/Interchange Density Moderate 1.5–4 miles between 

intersections 0 

Ambient Luminance High LZ3 and LZ4 1 

Guidance Good > 100 mcd/m2 lx 0 

Sum of Weights 4 

The resulting road class is H1 (weighting value total of 4 subtracted from base value of 5), and the 

lighting design level has an average luminance of 1, maximum-to-average uniformity ratio of 3, a 

maximum-to-minimum uniformity ratio of 5, and a veiling luminance ratio of 0.3.

If this design was for an active adaptive system, the lighting design level would be changed based on the 

roadway conditions. For example, if the traffic volume of the roadway decreased from 35,000 ADT to 

15,000 ADT, the weighting value of traffic volume would decrease from 1 to 0, and the road class would 

change from H1 to H2, allowing for a decrease in the lighting level from 1.0 to 0.8 cd/m2 (shown in Table 

14 and Table 15).

An alternative method for defining the traffic volume is to use hourly traffic volume. For example, if the 

hourly traffic volume was 4,100 vehicles per hour (vph), the weighting value would be 1 (Table 11). This 

would still result in an H1 class, assuming the same variables listed in Table 20 are used. If the hourly 

traffic volume dropped to 1,000 vph, the weighting value would be −1, and the roadway classification 

would drop to H3.

A similar example is provided for a street facility. The design level criteria are shown in Table 21. Here, a 

change in the number of pedestrians per hour could result in a change in the recommended lighting 

level. 
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Table 21. Example lighting level selection process for a street facility. (FHWA) 

Parameter Options Criteria Weighting 

Value 

Speed Moderate > 35 mph (55 kph) 0.5 

Traffic Volume High > 15,000 ADT 1 

Median Yes Should be glare blocking 0 

Intersection/Interchange Density High > 5 per mile (1.6 km) 1 

Ambient Luminance Moderate LZ2 0 

Guidance Poor < 100 mcd/m2 lx 0.5 

Pedestrian/Bicycle Interaction High > 100 pedestrians per hour 2 

Parked Vehicles Yes 1 

Sum of Weights 6 

The sum of the weighting values is 6 in this example, which would be subtracted from the base value of 

6, resulting in a value of 0. This value would then imply the use of the lighting class S1 (Table 17). If the 

traffic volume changed to less than 5,000 vehicles per day, and the pedestrian volume changed from 

more than 100 pedestrians per hour to less than 10 per hour, the sum would change from 6 to 4, 

allowing for a reduction in light levels at the S2 class.

7.2 Adaptive Lighting Application

The approach taken for adaptive lighting affects where and when the lighting system should be 

controlled. This section applies specifically to active adaptive systems. 

7.2.1 Where to Adapt Lighting

Adaptive lighting can be used in most roadway scenarios. However, there are certain areas where it is 

not advisable to implement active adaptive lighting systems, such as in critical visibility areas where it is 

vital to see objects and vehicles in the roadway. Designers of adaptive lighting should evaluate areas of 

critical visibility such as roadways that have a significant number of curves with short visibility distances 

or locations where traffic and pedestrian volume are at consistent levels throughout the night (e.g., a 

hospital or other service facility). It is also important that adaptive policies not replace other responsible 

lighting activities such as luminaire maintenance and tree trimming (i.e., increasing light level to 

overcome regrowth). 

Another consideration when implementing adaptive lighting is the size of the area covered by the 

lighting system. Depending upon nighttime use and driver needs, dimming a roadway lighting system 

can occur broadly over all the roadways in the area or section by section on each of the roadways being 

dimmed. 

In general, dimming a large area will maintain a constant lighting level such that drivers do not 

experience a high lighting condition on one roadway and then turn onto a dark roadway, requiring 

significant adaptation between the lighting levels. Depending on the range of light level changes, the 

abruptness of the change, and the age of the driver, this transition can be uncomfortable and 

dangerous. However, dimming a large area without consideration of differences in road usage at night 

may cause some sections to be too dark.
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To control for varying lighting levels, the following recommendations are made for each of the road 

facility types:

For roadway facilities, each roadway should be assessed individually, but drivers should not experience 

greater than one lighting class change per mile (1.6 km) of travel.

For streets, each street should be evaluated in terms of the lighting needs. However, the difference in 

lighting classes for streets in a given vicinity should be no greater than two.

Residential/pedestrian areas should be adapted to a single lighting level. This means that a 

neighborhood would be considered as one lighting class and individual low volume residential streets 

would not be adapted to different lighting levels.

7.2.2 When to Adapt Lighting

The optimal approach to selecting the timing of adaptive lighting is to continually monitor the roadway 

and the environment. As an example, ITS systems can provide traffic and pedestrian counts as inputs to 

an algorithm that establishes the lighting level in real time. 

When ITS systems are not available (e.g., on smaller streets and residential/pedestrian areas), curfews 

are typically established to determine when the lighting system can be dimmed. The following criteria 

can be used to establish a curfew: 

• Changes in vehicular traffic level sampled over a period of time. 

• Typical closing hours of surrounding businesses.

• Changes in the transportation schedule.

• Changes in parking regulations.

• Sampled pedestrian activity level.

It is important that exceptions to the curfew (e.g., for sporting or entertainment events) be considered, 

and agencies should have the ability to override the adaptive lighting program on demand.

It is not advisable to adapt the lighting system during periods of adverse weather. The impact of 

dimming lighting during fog, snow, and rain is not clear. Some research has shown that visibility on a wet 

roadway is negatively impacted by dimming of luminaires. Further investigations are underway. 

7.3 Lighting Controls

Streetlights are generally controlled (turned off during the day) to reduce power consumption and cost. 

Photocontrols are typically used to control the lighting. A photocontrol is a solid-state or thermal device

that is connected to the luminaire(s) and includes an internal photo-sensor. This photo-sensor detects a 

defined level of ambient light and switches the connected load on and off using an internal relay. 

New technologies and wireless controls provide connectivity of street lighting and allow the data to be

transmitted and received via wireless nodes, either internal or connected to the luminaires. A typical 

adaptive control system is shown in Figure 63.
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Figure 63. Diagram. Major components of a wireless outdoor lighting control (Image Credit: California Lighting Technology 

Center, UC Davis). 

In today’s world of smart technology and smart cities, sensors can be included with lighting to provide 

important data to determine what type of lighting is needed to enhance visibility, improve safety, and 

maintain the lighting infrastructure over the long term. These data can be used to highlight what is 

happening at an intersection, fine-tune problems, and ensure that the investment in connected lighting 

pays off. Further, similar to traffic lights, the lighting can be controlled remotely. In addition to sensors, 

cameras can also be added to lighting controls to gather data. Combined with analytics, cameras can be 

used to evaluate pedestrians and their movement patterns over time. 

Developing streetlighting as digital infrastructure also has the unique value of future-proofing the built 

environment by providing a platform for the integration of new technologies as they come online. The 

data provided by connected lighting and smart infrastructure can support many services within a 

municipality, including law enforcement, environmental improvement, transportation, and natural 

disaster preparedness. The benefits of intelligent streetlights with sensors can be summarized in terms 

of the seven categories shown in Figure 64.
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Figure 64. Image. Benefits of street light sensors. (Image Credit: California Lighting Technology Center, UC Davis) 

Intelligent streetlighting applications provide opportunities for additional revenue generation for 

municipalities and/or their partners. Two currently available applications are Wi-Fi access points and 

electric vehicle charging stations. Wi-Fi hotspots 

installed on poles can generate revenue through data 

access leases, advertising, and usage fees. These 

hotspots can also improve internet availability in public 

spaces such as libraries and community centers and 

promote digital inclusion by providing free access in 

low-income areas. Demand for electric vehicles is 

growing faster than the availability of charging stations 

in many major municipalities.

The successful implementation of outdoor lighting 

networks with intelligent applications requires the 

engagement of key stakeholders to support the project 

champion, develop a robust business case, foster utility 

partnerships, advocate for good public procurement, and effectively monitor and report. Moreover, the 

setup, commissioning, testing, and operation of lighting controls system requires expertise and 

manpower. For more information on commissioning, refer to ANSI/IES LP-8-20, Lighting Practice: The 

Commissioning Process Applied to Lighting and Control Systems.

For adaptive roadway lighting, these control systems are information sharing systems that allow for 

both the production and consumption of data. Data can be used for energy analysis, maintenance 

planning, and the identification of environmental conditions and system status. Data consumption 

activities include dimming, time-of-day control, and remote control of the lighting system. These datarelated activities can then be divided into three functional categories: monitoring, control, and sensing.

7.3.1 Communication Protocols

Communication protocols are a set of rules governing how messages and data elements are encoded 

and transmitted between electronic devices. The equipment at each end of a data transmission must 

The successful implementation of 

intelligent outdoor lighting 

networks requires the engagement 

of key stakeholders to support the 

project champion, develop a 

robust business case, foster utility 

partnerships, advocate for good 

public procurement, and effectively 

monitor and report. 
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use the same protocol to successfully communicate. The protocol is very much like a human language

with an alphabet, vocabulary, and grammar rules used by everyone speaking that language. 

With a proprietary standard, the manufacturer owns the protocol, and the owner is committed to a 

single manufacturer. Another downside of a proprietary protocol is that operational issues may arise if 

the product is discontinued or updated and is not supported by the manufacturer. Questions as to how 

the product will be supported if it is discontinued should be addressed along with the longevity of the 

manufacturer because systems are not yet interoperable. 

Open standard protocols allow owner control and the potential for interoperability between systems.

Open protocols are updated and developed on an ongoing basis (National Transportation 

Communications for Intelligent Transportation Systems, 2011). 

7.3.2 Monitoring Center

For networked controls, data from the luminaires are collected and analyzed in a communications or 

monitoring center. Systems may be supplied where the data are stored and managed by the supplier via 

cloud networking and accessed via a web browser or perhaps stored and managed on the owner’s 

network system. The cloud is where all computing resources (hardware and software) are delivered as a 

service over a network (typically the internet). In this case, the owner should decide if it will manage the 

system or use a cloud system that, once installed, would require no further internal resources to 

manage.

Centrally hosted systems are typically web-based systems with a secure login (user ID and password). 

Data from the control network are processed by a service provider at a central location. The cost of 

hosting is often scaled to suit the overall size of the system. IT infrastructure, upgrades, and support 

resources are often provided as part of the service. Ongoing service fees (often charged) should be 

considered. 

Customer-hosted systems are typically located on the customer’s network. Servers, databases, and 

networks are usually owned and maintained by the customer’s IT resources. Upgrades and support are 

generally provided on a version-specific basis, thus minimizing security concerns and ongoing service 

fees. When considering a customer-hosted system, firewall requirements and system integration should 

be discussed early on with the customer’s IT group. 

7.3.3 Networks

Networked control systems conceptually consist of three interacting component sets: field devices, 

network infrastructure, and a central management system (CMS). Although the component sets contain 

different types of physical devices, information is shared across the entire system. Lighting control 

networks can be either wireless or hard wired.

Currently, field devices always include controllers, which necessarily consume data to implement some 

control function according to internal programming. Field devices may also include sensors that produce 

data. Multiple controllers are often used to route data through gateways that act as communication 

bridges to outside networks and may also communicate (via cellular) directly to the CMS. Field devices 

may be accessed and managed remotely by a CMS that consolidates and stores retrieved data, 

facilitates user interaction through graphical user interfaces, and consolidates and stores retrieved data. 

The CMS communicates to field devices through network infrastructure consisting of one or more 
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backhaul communication networks that may take various forms (e.g., wired, wireless, powerline 

communications).

7.3.4 Network Infrastructure

Wireless roadway lighting controls make use of three network topologies: mesh, star, and point to point. 

All topologies rely in some way on a point-to-point configuration as an example, creating a bridge 

between network gateways or routers. Limiting factors are distance, line of sight, and information 

density (capacity), which are resolved through frequency and network communication protocols. The 

frequencies used by wireless networks to communicate between the gateways and nodes are specific to 

the system. Communication between the gateways and a CMS are either hard-wired into the 

communications infrastructure or based on cellular communications. In all situations, the control system 

should maintain robust and redundant security along with continuity. 

7.3.5 Measuring Power Usage

The power savings provided by dimming lights using adaptive controls can help offset system costs.

Many roadway lighting systems in North America are supplied power on an unmetered (flat-rate) basis. 

For unmetered roadway lights, adaptive systems can provide accurate measurements of power 

consumption. Monitoring the power consumption of these adaptive systems should not, however, be 

confused with a “utility grade meter,” which may have specific regulatory requirements and 

recalibration requirements that go beyond the capability of an adaptive system.

If accepted by power utilities as an accurate means to measure power consumption, owners could be 

billed for power used, taking full advantage of energy savings. Including power consumption 

measurements as part of adaptive controls could resolve the shortcomings of the flat-rate system and 

make the full financial benefits of dimming available to owners. A typical power measurement system 

may require re-calibration and validation via utility grade check meters. Even if not acceptable to the 

local utility, power consumption monitoring can be used to track power costs for comparison to utility 

flat-rate billing. 

7.4 Smart City Applications

In recent years, the rapid rise of urbanization has coincided with a massive growth in connected devices 

(or things that talk to the internet). Cisco predicts that 50 billion connected devices will exist as of 2021. 

To be competitive in the emerging economy, there is significant benefit in employing connectivity to 

support smarter, healthier, and more sustainable communities. However, the increasing array of 

technology choices may be difficult for municipalities to navigate, preventing the full potential of 

connected devices from being realized. Digital master planning has recently emerged as a process for 

developing coherent strategies to develop intelligent communities. Digital master planning can be 

applied to produce roadmaps for the effective and beneficial integration of technologies.
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The term “intelligent community” is generally used to refer to applying digital information technology 

throughout the built environment to improve the overall quality of life for people at home, work, and 

play. The technology is used to provide opportunities for 

economic development and enhance urban services, 

resource conservation, and cost effectiveness. 

The Smart City “digital twin” approach is one strategy

(Petrova-Antonova & Ilieva, 2019) for adaptive lighting in 

which sensors and controls in the physical world are linked 

to data in a digital world (Figure 65). The result is that the 

status of the real world is reflected in the digital world, and decisions can be made based on these data 

to control applications in the real world. Traffic volume, pedestrian volume, or weather conditions, for 

example, can be used to control intersections or an adaptive lighting system.

Figure 65. Image. Smart City digital twin concept (Petrova-Antonova & Ilieva, 2019). 

Adaptive lighting is a critical application that can be enabled through a Smart City application allowing 

for high levels of control and an increased level of adaptability. Level 4 adaptability can be achieved 

through a Smart City application where lighting on demand is a possibility.

For network considerations, Smart City technologies should integrate into the Autonomous and 

Connected Vehicle framework that those systems use. Some authorities are considering 

communications/data backhaul networks to incorporate various systems into a single network. Others 

are looking for available bandwidth on adaptive control networks for connecting Internet of Things 

devices that do not have large bandwidth requirements. When implementing a Smart City network, all 

stakeholders should be engaged in a needs assessment. For further information on Smart Cities, please 

refer to ANSI/IES LP12-21 Lighting Practice: IOT Connected Lighting (Illuminating Engineering Society, 

2021c). 

When implementing a Smart City 

network, it is critical that all 

stakeholders be engaged in a 

needs assessment. 
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7.5 Vehicle-to-Infrastructure/Infrastructure-to-Vehicle Communication

Connected vehicle technology allows vehicles to communicate with each other and with infrastructure 

to transmit important safety information and other related information. Connected vehicle technology 

can also be used to communicate information from a vehicle to a lighting system to tell lighting when to 

dim or turn on and to detect pedestrians who are outside the line of sight of vehicle sensors. A pilot test 

of an on-demand and just-in-time lighting developed by the Virginia Tech Transportation Institute

(Gibbons, Palmer, and Jahangiri (2016)) demonstrated a connected vehicle/infrastructure system that 

detected a vehicle approaching a lighted roadway section and turned on the roadway lighting on 

demand. The system did not distract the driver and provided a safe driving environment. 

A recent decision by the Federal Communication Commission (FCC) repurposed the spectrum currently 

allocated for dedicated short-range communications (Stone, 2020). In its place, the FCC offers a smaller 

but exclusive spectrum for a newer technology called cellular vehicle-to-everything (C-V2X; (Federal 

Communications Commission, 2020). Given that C-V2X is still in its infancy, more research and 

development is required for the consideration for vehicle-to-infrastructure, infrastructure-to-vehicle, 

and vehicle-to-everything systems that include direct communication with roadway lighting systems. 

7.6 Cybersecurity

Cybersecurity is the practice of protecting systems, networks, and programs from digital attacks. 

Cyberattacks are usually aimed at accessing, changing, or destroying sensitive information; extorting 

money from users; and interrupting normal business processes. As new digital infrastructure and smart 

technologies are adopted, the benefits of increased infrastructure connectivity should be balanced 

against the new security, safety, and performance risks. A connected network can be vulnerable to 

cybersecurity attacks at varying threat levels. 

Governments across the globe have responded to the rising cyber threat with guidance to help 

organizations implement effective cybersecurity practices. For example, the National Institute of 

Standards and Technology has created a cybersecurity framework that recommends continuous, realtime monitoring of all electronic resources to combat the proliferation of malicious code and aid in early 

detection of cyber threats. 

Security programs continue to evolve new defenses as cybersecurity professionals identify new threats 

and new ways to combat them. To make the most of end-user security software, employees need to be 

educated on how to use it. Crucially, keeping such software running and frequently updating it helps 

ensure that it can protect users against the latest cyber threats. 
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8 SUMMARY

A properly designed lighting system can enhance safety while balancing the need to minimize the 

impacts on roadway users, the surrounding environment, wildlife and the night sky. Other elements that

should be considered include equity and diversity and the societal impact of lighting. The handbook 

focuses on how best to apply roadway lighting in various applications and is therefore educational in 

nature. The handbook is also intended to further clarify and enhance elements discussed in the 

mentioned publications. However, this document does not reproduce the lighting level 

recommendations found in other publications. Any lighting level recommendation tables are cited but 

not included.

The purpose of this handbook is to provide recommendations to lighting designers and State, city, and 

town officials to improve the design and application of roadway lighting. It is not intended to be a 

detailed design guide. It is a resource for policy makers and the design and construction community to 

evaluate potential needs, benefits, and applicable references when considering a roadway or street 

lighting system. 

It is important to note that lighting is an evolving science. Research is continually enhancing our 

knowledge and understanding of lighting applications, and technological advancements continue to 

evolve our lighting capabilities. This handbook is a snapshot in time of the current best practices for 

roadway lighting application. It is important that the designer continues to be involved in the everevolving science to ensure that their projects fully utilize the latest available technologies. 

As defined in this handbook and other documents referenced, roadway lighting has significant safety 

benefit to road users. However, simply providing lighting without following the most current design 

practices will often lead to reduced benefit. The way lighting is designed can have significant impact on 

the level of visibility it provides, thus impacting the safety benefits. In considering this, it is important to 

note lighting technologies have evolved since the previous 2012 Handbook. This has led to research and 

enhanced design considerations, which are included in this handbook. The technical information 

provided in this part of the handbook has been laid out to provide the lighting designer and policy 

makers with information and methods to enhance their designs and provide a lighted environment that 

enhances safety while also considering all other benefits and impacts of the lighting system. The proper 

application of roadway lighting can improve safety and mobility. The principles discussed in this 

document can help designers achieve these benefits while considering and where possible reducing any 

the negative impacts of lighting. 

Documents available from organizations such as the American Association of State Highway and 

Transportation Officials (AASHTO), the Illuminating Engineering Society (IES), the Transportation 

Association of Canada (TAC), and the Commission Internationale de l’Eclairage (CIE) offer 

recommendations on lighting levels, lighting configurations, and other considerations and are therefore 

not repeated. This handbook directs users to that information where applicable and provides 

supplemental information on topics not addressed in those documents.

The use of these design criteria from the above organizations, such as AASHTO, IES, TAC and CIE, is not 

required under Federal Law or regulation. 
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The examples in Part II of this document are an important aspect of the handbook because they 

demonstrate the application of the technical knowledge provided in Part I to real-life design efforts. 
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PART II – Design Examples 

Part II of this document includes design examples to highlight key focus areas on various street and 

roadway types. These examples have been selected to highlight the more common areas of the roadway 

and are not meant to be a comprehensive list. It is expected that the information applied in these 

examples will be applied to other areas as needed. The examples illustrate the different design 

recommendations applicable to the areas being studied and highlight the key safety elements that 

should be considered. The examples also include new and emerging research and approaches that the 

designer may want to consider.

The two most applicable design recommendations used in these examples are AASHTO GL-7, Roadway 

Lighting Design Guide, and IES RP-8-21, Recommended Practice Lighting Roadway and Parking Facilities.

These documents generally agree but do contain some differences. The examples here include elements 

and topics that pertain to typical situations, while the reference documents contain significant 

information on specifics and details. The reference documents should be referenced when performing 

lighting design, and the authority responsible for the design can choose which document should take 

precedence. The use of these design criteria is not required under Federal Law or regulation. 

The lighting design elements discussed address four broad groups: surface types; conflict zones; 

surroundings; and strategic aspects. Roadways, bike lanes, and walkways are the surfaces being traveled 

and are lighted to provide visibility of that surface to the traveler. Crosswalks, intersections, 

interchanges, driveways, and work zones are conflict areas, where two streams of traffic might use the 

same space. Surroundings describe the walls in tunnels and the surround ratio for suitable roadways, 

providing guidance to travelers. Strategic aspects discussed in these examples are partial (beacon) 

lighting, light trespass, adaptive lighting, and color of light. These examples are almost all for continuous 

lighting, but situations occur where partial (beacon) lighting may be appropriate instead, such as an atgrade railway crossing. Similarly, adaptive lighting is a strategic option that may be appropriate for some 

projects. 

In every lighting project, the topics of color of light and light trespass are important. Color of light is a 

significant issue in some situations such as high-speed roadways or environmentally sensitive areas. 

Light trespass is also a consideration in every project, influenced by the unique features of the situation. 

These universal design elements are discussed below as general topics. A range of aspects of lighting 

design that are relevant to particular projects are discussed in these various examples, but not all 

combinations of situations are covered. Table 22 shows the breakdown of topics covered in each of the 

examples.
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Table 22. Examples listed by topics covered.

Topic

General ConsiderationsUrban StreetRural RoadExpresswayFreeway, UrbanFreeway, SuburbanFreeway, RuralRoundaboutWalkway / BikewayShort TunnelTunnelUnderpassAt-grade Railway Crossing

1 2 3 4 5 6 7 8 9 

10 11 12 13 

Roadways Y Y Y Y Y Y Y Y Y Y Y Y 

Crosswalks Y Y Y 

Sidewalks Y Y Y Y 

Bike Lanes Y 

Intersections Y Y Y Y 

Interchanges Y 

Driveways Y 

Work Zones Y Y Y 

Surround Ratio Y Y Y Y 

Partial Beacon Y Y 

Walls Y Y Y 

Adaptive Lighting Y 

At Grade Rail Crossings Y 

Color of Light Y Y Y Y Y Y Y Y Y Y Y 

Light Trespass Y Y Y Y Y Y Y Y Y Y 

Each of the relevant topics are identified by an icon chart. 
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Table of Contents

1 General Considerations.................................................................................................................. 121

1.1 Color of Light .............................................................................................................................. 121

1.2 Light Trespass............................................................................................................................. 122

2 Urban Street Lighting Example....................................................................................................... 125

2.1 The Roadway .............................................................................................................................. 126

2.2 Crosswalks.................................................................................................................................. 127

2.3 Sidewalks .................................................................................................................................... 129

2.4 Bike Lanes................................................................................................................................... 130

2.5 Intersections............................................................................................................................... 131

2.6 Adaptive Lighting........................................................................................................................ 133

2.7 Criteria Values Applicable to this Example................................................................................. 134

3 Rural Road Lighting Example .......................................................................................................... 137

3.1 The Roadway .............................................................................................................................. 138

3.2 Surround Ratio............................................................................................................................ 139

3.3 Partial or Beacon Lighting........................................................................................................... 140

3.4 Criteria Values Applicable to this Example................................................................................. 140

4 Expressway Lighting Example......................................................................................................... 143

4.1 The Roadway .............................................................................................................................. 144

4.2 Crosswalks.................................................................................................................................. 145

4.3 Sidewalks .................................................................................................................................... 147

4.4 Driveways................................................................................................................................... 148

4.5 Work Zones................................................................................................................................ 149

4.6 Criteria Values Applicable to this Example................................................................................. 151

5 Urban Freeway Lighting Example................................................................................................... 154

5.1 The Roadway .............................................................................................................................. 154

5.2 Interchanges............................................................................................................................... 155

5.3 Surround Ratio............................................................................................................................ 157

5.4 Criteria Values Applicable to this Example................................................................................. 158

6 Suburban Freeway Lighting Example ............................................................................................. 160

6.1 The Roadway .............................................................................................................................. 161

6.2 Interchanges............................................................................................................................... 162

6.3 Surround Ratio............................................................................................................................ 164

6.4 Work Zones................................................................................................................................ 165

6.5 Criteria Values Applicable to this Example................................................................................. 167

7 Rural Freeway Lighting Example..................................................................................................... 169
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7.1 The Roadway .............................................................................................................................. 170

7.2 Interchanges .............................................................................................................................. 171

7.3 Work Zones................................................................................................................................ 173

7.4 Surround Ratio............................................................................................................................ 175

7.5 Partial or Beacon Lighting........................................................................................................... 176

7.6 Criteria Values Applicable to this Example................................................................................. 176

8 Roundabout Lighting Example........................................................................................................ 178

8.1 Roundabout................................................................................................................................ 179

8.2 Crosswalks.................................................................................................................................. 180

8.3 Sidewalks .................................................................................................................................... 182

8.4 Criteria Values Applicable to this Example................................................................................. 183

9 Walkway & Bikeway Lighting Example........................................................................................... 185

9.1 Walkway / Bikeway .................................................................................................................... 186

9.2 Criteria Values Applicable to this Example................................................................................. 187

10 Short Tunnels Lighting Example ..................................................................................................... 189

10.1 The Roadway........................................................................................................................... 190

10.2 The Walls................................................................................................................................. 192

10.3 Criteria Values Applicable to this Example ............................................................................. 193

11 Long Tunnel Lighting Example........................................................................................................ 195

11.1 Tunnel Roadway, Daytime ...................................................................................................... 198

11.2 Tunnel Walls ........................................................................................................................... 200

11.3 Emergency Lighting................................................................................................................. 201

11.4 Nighttime Lighting .................................................................................................................. 202

11.5 Criteria Values Applicable to this Example .............................................................................203

12 Underpass Lighting Example .......................................................................................................... 210

12.1 The Roadway........................................................................................................................... 211

12.2 Sidewalks ................................................................................................................................ 214

12.3 Walls ....................................................................................................................................... 215

12.4 Criteria Values Applicable to this Example ............................................................................. 216

13 At-grade Railway Crossing Lighting Example.................................................................................. 219

13.1 At-grade Railway Crossing ...................................................................................................... 220

13.2 Criteria Values Applicable to this Example ............................................................................. 221
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1 General Considerations 

Two topics, color of light and light trespass, have applications in multiple categories and are considered 

here due to the importance of their design considerations. 

1.1 Color of Light

1.1.1 Currently Available Design Recommendations

The spectral content of a light source affects visibility. Basic object detection is often discussed in terms 

of luminance contrast (essentially, how bright the object is compared to how bright the background is).

In addition to luminance contrast, there is also color contrast to consider. For example, a red object 

against a gray background will be more easily detected than a gray object against a gray background. 

Based on the spectral content of the light source, lighting can either enhance or detract from the color 

contrast of an object. With LED lighting systems, the ability to change the spectral content is less 

daunting than with older technologies.

Although the spectral content indicated by the SPD of a source is a more precise metric, CCT can be used 

as an approximate metric to compare similar technologies (e.g., a white LED comprised of a base blue 

LED with a phosphor coating to achieve a white source).

1.1.2 Emerging Research

Several aspects of the implementation of roadway lighting and spectrum are being researched, and 

several reports are being published to include these changes. The following highlights the current state 

of the research:

• NCHRP 940 evaluated the detection distances of pedestrians and targets on roadways under 

various conditions and various lighting sources and found that 4000K light sources resulted in 

longer detection distances than 3000K or 5000K sources (National Academies of Sciences 

Engineering and Medicine, 2020) . 

• The spectrum of the light source is connected to human health and melatonin levels. However, 

emerging research suggests that roadway lighting has no health impacts regardless of the CCT 

because the lighting levels (dosage) from roadway lighting are too low. 

General Considerations

Color of Light

Light Trespass

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• Although subjective preferences have been reported for lower CCT sources, this preference has 

not been validated by research, and subjective questioning performed under NCHRP 940 

showed no preference difference. 

The relative impacts of light scatter and the effects of spectral content on flora and fauna are also being 

studied. The variety of responses among flora and fauna complicates general recommendations on 

mitigating impacts. The suitability of a specific color of light depends on the situation and priorities 

involved, and designers should be aware of the implications.

1.2 Light Trespass

1.2.1 Currently Available Design Recommendations 

Light trespass should be considered for all designs (See Section 6.3 of Part I). The boundaries of light 

trespass will depend on the lighting installation and corresponding location(s) of visual receptors. For 

example, for a roadway lighting system installed on a road with few abutters, the light trespass 

evaluation might best be made at the edge of the right-of-way of the roadway. For an urban setting with 

properties and homes located on the back edge of the sidewalk, the border for light trespass might be 

the property line, building edge, or windows facing the roadway. Because the conditions vary greatly 

between roadway types and abutters, engineering judgment should be applied to determine the best 

places to gauge and mitigate impacts.

Mitigation of light trespass involves diminishing the visibility of light sources and the spread of 

illumination. When lighting is warranted, source location and aiming should keep illumination within the 

property. Luminaire output and mounting height should each be as low as is suitable, and shielding 

General Considerations

Color of Light

Light Trespass

SAFETY HIGHLIGHTS 

For the best detection distance, a CCT of 4000K light source should be used. If specific 

conditions exist related to impacts on wildlife or light scatter, they should be evaluated 

in terms of visibility, perhaps by changing CCT but increasing light levels. 

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should be applied as appropriate. Management of these system characteristics can help reduce light 

trespass.

Light trespass does have various considerations depending on the roadway surroundings. For urban 

streets, the height of poles should be managed to reduce light trespass into upper floors. For urban 

freeways and expressways, the issue of light trespass arises when providing lighting in areas adjacent to 

residential properties. Multi-story buildings, freeway ramps, and frontage roads can be close to right-ofway boundaries, and high-mast lighting can be challenging to constrain. Lighting with lower mounting 

heights and appropriate shielding can help reduce light trespass.

For rural roads, the issue of light trespass arises when providing lighting in areas that have otherwise 

limited exterior illumination. In rural areas that are intrinsically dark, even limited lighting can be 

obtrusive and disturb adaptation, and it may be visible for a significant distance. Reducing lighting and 

using shielding can constrain light trespass.

For roundabouts, walkways and bikeways, and at-grade railway crossings, the issue of light trespass may 

arise when providing lighting in areas that have otherwise limited exterior illumination. Lighting of 

vertical surfaces can be challenging with lower mounting heights without increasing trespass. Pole 

location recommendations for roundabouts illustrate preferred layouts. For at-grade railway crossings, 

this is particularly true for isolated crossings that may be near residential areas. 

For all situations, local topography can be a factor in light trespass. Lighting installed upslope from 

observers will generally be more conspicuous than lighting installed below observers.

Chapter 4 of IES RP-8-21 and Chapter 11 of AASHTO GL-7 include recommendations for minimizing light 

trespass by using lighting zones to classify areas based on their level of ambient lighting (none, low, 

moderate, or high, LZ0–LZ4). Based on the classification, light trespass limits ranging from 0.5 to 15 lux 

are established for the lighting design. AASHTO uses a vertical plane located at the property line as the 

analysis area for light trespass. ANSI/IES RP-8-21 uses the same light trespass values and analysis 

method and includes additional information about the classification method used to determine the 

lighting zones.

While light trespass usually addresses the impact of lighting onto areas adjacent to the project being 

designed, the reverse may also occur, and lighting from adjacent areas may impact the proposed 

project. In general, lighting design does not account for any contributions or effects from specific 

lighting installations outside of the project because that illumination is unpredictable and unreliable. 

While accommodation to high levels of ambient illumination is appropriate, lighting design that relies on 

lighting from outside the project is not.

1.2.2 Emerging Research

Research is currently being conducted on the impacts of roadway light trespass on human health along 

with flora and fauna. Soybeans, for example, are limited in yield and bean production when the light 

level in the field exceeds 2.4 lux. There is also a push to use lower CCTs where areas adjacent to the 

roadway have a high potential for light trespass; this is an ongoing topic of research.

Adaptive lighting can mitigate light trespass by reducing illumination levels at appropriate times.
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SAFETY HIGHLIGHTS 

Safety is an important design consideration. In most cases, however, light trespass beyond 

the area included for the surround ratio can be controlled easily by correctly selecting the 

pole height and fixture optics and eliminating luminaire tilt. 

 
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2 Urban Street Lighting Example

This example consists of an urban street with bike lanes, 

parking, crosswalks, interections, and sidewalks. For this 

example, the key elements are discussed along with the 

potential criteria that can be used. The example also 

includes possible adjustments to current criteria or 

approaches expected from emerging research. These 

sections address the different traveled paths found in a 

typical urban setting and their intersections, along with 

discussions about lighting issues that arise in urban 

environments.

Urban Street

Roadways

Crosswalks

Sidewalks

Bike Lanes

Intersections 

Adaptive Lighting

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2.1 The Roadway

2.1.1 Currently Available Design Recommendations

The design for the roadway portion of this example is meant to achieve visibility for the drivers as they 

travel the roadway, allowing them to see hazards, pedestrians, and cyclists. The criteria for the roadway 

include the following: 

• Average luminance (or illuminance, which is an option in AASHTO GL-7) of the roadway

• Uniformity ratio for the roadway

• Maximum veiling luminance ratio (to limit disability glare)

The criteria given in AASHTO GL-7, Table 3-5 and ANSI/IES RP-8-21, Table 11-1 are for the travel lanes.

For this example, the criteria do not include the median with pavers, the bike lane (which is addressed 

separately), parking area, or other areas outside the travel lanes. Light for pedestrians in the median at 

crosswalk locations is included as part of the crosswalk design and analysis.

This example road has the following characteristics: 

Street or Roadway Classification: Collector 

Pedestrian Classification: Medium

Land Use Classification: Intermediate

Pavement Type: R3 Asphalt

The selection of the street or roadway classification can vary with respect to lighting. The roadway 

classifications defined by FHWA1 do not always align with the non-regulatory definitions found in IES RP1 https://www.fhwa.dot.gov/planning/processes/statewide/related/highway_functional_classifications/section03.cfm

Urban Street

Roadways

Crosswalks

Sidewalks

Bike Lanes

Intersections 

Adaptive Lighting

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8-21 and ASSHTO GL-7. For example, land use (e.g., urban vs. rural) is not defined in the GL-7 or RP-8-21 

lighting criteria selection tables; therefore, engineering judgment is required when selecting the street 

classification. Factors such as traffic volume, speed limit, and number of lanes can impact the level of 

risk. For example, an urban collector in a major city will have a very different risk factor than a rural 

collector in a small town. IES RP-8-21 uses pedestrian activity level, which is based on pedestrian 

volumes derived from judgment rather than sample counts. AASHTO uses land use classifications 

(commercial, intermediate, and residential) that are also somewhat subjective because the land use can 

vary on any given street and is subject to change over time.

2.1.2 Emerging Research 

Emerging recommendations on roadway lighting criteria and design is based on the results of safety and 

human factors research. One recent development is the inclusion of surround ratio (or edge illuminance 

ratio) as a design metric. Surround ratio has been considered in international standards for some time 

and was recently shown to be a reliable indicator of detection distance for drivers (National Academies 

of Sciences Engineering and Medicine, 2020). Surround ratio, which is the ratio of the lighting value on 

the area adjacent to the travel lane (3.6-m strip) to the lighting value for the roadway, should be at least 

0.8. Since surround ratio applies to an area that may have variable surface type, surround ratio is 

determined based on illuminance. 

In this example, the specific situation with lighted sidewalks (and parked cars) means that the 

application of surround ratio is not appropriate. There is additional discussion about surround ratio in 

some of the other examples and in RP-8-21 section 10.5.2.3.

2.2 Crosswalks

2.2.1 Currently Available Design Recommendations

Lighting should be provided for both midblock and 

intersection crosswalks. The addition of lighting in crosswalks increases the visibility of pedestrians using 

the crosswalk, allowing motorists to safely stop for the pedestrian.

Urban Street

Roadways

Crosswalks

Sidewalks

Bike Lanes

Intersections 

Adaptive Lighting

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This example of crosswalks for an urban street has the following characteristics: 

Street or Roadway Classification: Collector 

Cross-street Classification: Local

Pedestrian Classification: Medium

Land Use Classification: Intermediate

Pavement Type: R3 Asphalt

Crosswalk Location: Intersection 

AASHTO GL-7 discusses crosswalk lighting at intersections and roundabouts, including the placement of 

lighting to optimize pedestrian detection. Other lighting guides suggest that the vertical lighting level in 

the crosswalk should be equal to the horizontal lighting level recommended for the intersection or 

roundabout. IES RP-8-21 includes recommendations for crosswalk lighting at intersections, roundabouts, 

and midblock crosswalks. 

For intersections, both AASHTO GL-7 and IES RP-8-21 recommend that the average vertical lighting value 

in the crosswalk be equal to the average horizontal illuminance in the intersection. Similarly, for the 

lighting of crosswalks at roundabouts, the average vertical lighting level should also be equal to the 

average horizontal lighting level in the roundabout. The one difference in this case is that the vertical 

lighting level is in the direction of the approaching vehicle as opposed to perpendicular to the centerline 

of the crosswalk. For the lighting of midblock crosswalks, IES RP-8-21 recommends an average of vertical 

illuminance of 20, 30, and 40 lux for areas with low, medium, and high levels of pedestrian conflict, 

respectively. 

2.2.2 Emerging Research

The current recommendations for high lighting levels in crosswalks are being discussed by technical 

committees and investigated through ongoing research. The current investigations seem to show that 

vertical lighting levels (oriented toward the vehicle) equal to horizontal lighting levels on the roadway do 

perform well from a pedestrian detection perspective. On unlit roads, however, crosswalk lighting does 

have safety benefits, and current recommendations may be higher than necessary. Lighting levels of 10 

lux on medium to high pedestrian areas and 8 lux for isolated intersections and low pedestrian areas 

appear to provide adequate lighting for visibility.

SAFETY HIGHLIGHTS 

Lighting crosswalks is a critical safety issue in areas with moderate to high pedestrian 

volumes. 

Average vertical illuminance values of at least 10 lux should be maintained in the 

crosswalk in the direction of the approaching driver. 
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2.3 Sidewalks

2.3.1 Currently Available Design Recommendations

Sidewalk (walkway) lighting within the right-of-way serves two purposes: (1) providing pedestrians with

sufficient light on the sidewalk to avoid trip hazards, allow facial recognition, and impart a sense of 

security; and (2) assisting drivers in detecting pedestrians approaching the roadway.

This example of sidewalks for an urban street has the following characteristics: 

Street or Roadway Classification: Collector 

Pedestrian Classification: Medium

Land Use Classification: Intermediate

Pavement Type: Concrete (assumed 30% reflective) 

AASHTO GL-7 recommends maintaining horizontal illuminance levels for sidewalk areas at 3 to 14 lux 

depending on the sidewalk material and whether it is in a commercial, intermediate, or residential land 

use type. AASHTO GL-7 also provides uniformity criteria for sidewalks. IES RP-8-21 recommends 

sidewalk lighting levels based on pedestrian volumes. Lighting levels are given in terms of average 

horizontal illuminance, average vertical illuminance, and uniformity across the pavement. Average 

horizontal levels can range from 2 to10 lux and up to 20 lux for rare roadway conditions where 

pedestrians and vehicles use the roadway as a common space without curbed sidewalk areas.

In general, the roadway lighting system provides lighting for the sidewalk area. There are, however, 

design issues when considering these systems. Pedestrian-scale lighting is often used to better define 

the sidewalk area and relate better in scale and feel to the pedestrians using the area. Pedestrian-scale 

lighting is often an attractive aesthetic for lighting in areas pedestrians frequent. There are, however, 

issues that can arise when trying to use pedestrian-scale lighting for lighting a street. The lumen output 

often generally needs to be significantly increased to light the roadway, which increases the amount of 

disability glare produced by the lighting system. It is also difficult to achieve high lighting levels in areas 

such as intersections and crosswalks. In areas where sidewalks use pedestrian-scale lighting, it is often 

Urban Street

Roadways

Crosswalks

Sidewalks

Bike Lanes

Intersections 

Adaptive Lighting

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recommended that a mix of higher roadway lighting poles be used in combination with lower 

pedestrian-scale poles to achieve the desired result. 

2.3.2 Emerging Research

The recommended sidewalk lighting levels are currently undergoing review. In addition, semi-cylindrical 

illuminance is being investigated as a predictive metric to replace vertical illuminance because it may 

represent a complex form like a person better than a single vertical plane.

2.4 Bike Lanes

2.4.1 Currently Available Design Recommendations

Given the high risk cyclists face, lighting bike lanes should receive high priority, specifically where motor

vehicles and pedestrians/cyclists conflict. This is discussed further in Section 3.6 of Part I. Lighting 

benefits cyclists by making them more visible to drivers and allowing the cyclists to see hazards in the 

roadway. 

This example of bike lanes for an urban street has the following characteristics: 

Street or Roadway Classification: Collector 

Pedestrian Classification: Medium

SAFETY HIGHLIGHTS 

Proper sidewalk lighting is focused on pedestrians both seeing and being seen, so lighting 

levels on the pedestrian are critical. 

Limits on light trespass need to be carefully balanced with needs for sidewalk lighting. 

Urban Street

Roadways

Crosswalks

Sidewalks

Bike Lanes

Intersections 

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Land Use Classification: Intermediate

Pavement Type: R3 Asphalt

Bile Lane Location: Adjacent to roadway

In terms of lighting, AASHTO G-7 defines the bike lane as part of the roadway. Therefore, the roadway 

lighting criteria would extend onto the bike lane. The criteria in IES RP-8-21 are based solely on where 

the bikeway is located. When the bikeway is not adjacent to the roadway, the lighting levels should 

match those for walkways. When the bikeway is adjacent to the roadway, it should be lighted based on 

the roadway illuminance, with 80% of the lighting provided for the street applied to the bike lane. This 

can be evaluated by simply defining the bike lane width and calculating the horizontal illuminance within 

the marked bike lane. The calculation grid spacing within the bike lane should be the same longitudinal 

spacing used for a street with lateral spacing of two rows to suit the lane width. Since bike lanes typically 

terminate at intersections, the intersection lighting requirements should be applied.

2.4.2 Emerging Research

Although many studies have defined the value of lighting bike lanes, more information and research are 

needed to inform lighting requirements beyond what is noted above.

2.5 Intersections

SAFETY HIGHLIGHTS 

Cyclists are vulnerable road users who face a very high risk. 

Lighting bike lanes improves visibility and thus enhances safety. 

Urban Street

Roadways

Crosswalks

Sidewalks

Bike Lanes

Intersections 

Adaptive Lighting

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2.5.1 Currently Available Design Recommendations

Intersections create a complex environment for navigation and pose challenges for lighting.

Intersections include multiple conflict points for vehicles as well as pedestrians and cyclists. During some

left- and right-hand movements of vehicles in intersections, vehicle headlamps are ineffective, and 

driver attention is divided into multiple tasks. The complexity of the environment makes it difficult to 

define key tasks and lighting criteria to improve safety and visibility.

For this urban street example, the intersection has the following characteristics: 

Street or Roadway Classification: Collector 

Cross-street Classification: Local

Pedestrian Classification: Medium

Land Use Classification: Intermediate

Pavement Type: R3 Asphalt

AASHTO GL-7 states that “intersections with high pedestrian volumes, curbs, or divisional islands may 

require somewhat higher light levels.” It also states: “Intersections of two continuously lit streets are 

typically lit to a value equal to the sum of the individual lighting level values.” IES RP-8-21 classifies 

intersections based on the categories of the intersecting streets along with the pedestrian volume (low, 

medium, or high). Intersection lighting levels range from 8 to 34 lux depending on the characteristics of 

the streets and pedestrian volumes. These lighting levels were first developed by summing the design 

illuminance values for the intersecting streets, as recommended by AASHTO. 

2.5.2 Emerging Research

Historically, lighting values for intersections have been developed from consensus rather than research 

into safety or visibility. As more research on this topic becomes available, the approach to lighting 

intersections is changing. For example, vehicle-to-vehicle conflict points are becoming less prioritized, 

while vehicle-to-pedestrian conflict points in crosswalks are becoming more important (refer to Section 

11.2 on Crosswalks). Lighting levels and where the lighting should be applied are also being fine-tuned.

One critical aspect of intersection lighting is the lighting of crosswalks, particularly those located at the 

left- or right-turn directions where both pedestrians in the crosswalk and the left-turning vehicles have 

signals that allow for potential conflict (both are permissible signals). 

SAFETY HIGHLIGHTS 

An important focus for intersection lighting is pedestrians and cyclists, who are at the 

greatest risk during vehicle movements in intersections. 

Meeting vertical lighting level requirements in the crosswalks will aid in pedestrian 

detection. 
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2.6 Adaptive Lighting

2.6.1 Currently Available Design Recommendations

Driven by the development of new lighting technologies and a nationwide push to reduce energy use 

and environmental impacts, adaptive lighting is gaining popularity. In adaptive lighting, the light output 

of a system is adjusted as traffic conditions change. More specifically, the level of lighting can be 

reduced or dimmed as follows:

• Reduce initial light output to maintained levels. Light output from a light source depreciates 

over time; therefore, roads are typically over-lit when the lighting is first installed. To maintain 

the minimum required lighting levels on the roads and sidewalks, lighting designs are based on 

the end-of-lamp life. Accordingly, the design incorporates a maintenance factor that accounts 

for this depreciation. Applying adaptive lighting technology can control the light output over 

time so the luminaires operate at a maintained level for the entire maintenance cycle, thereby 

reducing power input and saving energy. 

• Match light output to pedestrian activity levels. The amount of light required for a roadway or 

sidewalk is based on two key criteria: the classification of the roadway itself and the level of 

pedestrian activity. The classification of the roadway is based on the road designation, which is

fixed. Pedestrian activity levels do not remain constant throughout the day; in most instances, 

the number of pedestrians present in each area will be dramatically lower in the late-night and 

early-morning hours, thus requiring lower light levels.

2.6.2 Emerging Research

The FHWA report Design Criteria for Adaptive Roadway Lighting (Gibbons, Guo, Medina, Terry, Du, 

Lutkevich, & Li, 2014) includes an in-depth assessment of the effect of adaptive lighting on the overall 

safety performance of roadways. The report defines optimal times, conditions, and suitable approaches 

Urban Street

Roadways

Crosswalks

Sidewalks

Bike Lanes

Intersections 

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for reducing lighting; appropriate lighting levels for various roads and features; energy savings and 

reductions in greenhouse gases resulting from adaptive lighting; and potential legal issues. The resulting 

design methodology can be used by transportation agencies to determine whether adaptive lighting is 

appropriate for a given roadway. The methodology includes a set of criteria to help jurisdictions make 

sound, safety-based decisions when considering adaptive lighting approaches. In addition, the 

evaluation of real-world lighting data in this report provides a foundation for future analyses related to 

roadway lighting.

Notably, adaptive lighting requires a control system and “controls-ready” luminaires. Thus, to allow for 

future implementation of adaptive lighting, luminaire selection should consider controls-ready 

luminaires, even if adaptive lighting is not planned at the time of installation.

In RP-8-21, Annex K Alternative Lighting Criteria Selection Methodology includes a discussion and 

suggested process for establishing adaptive lighting levels.

2.7 Criteria Values Applicable to this Example

The characteristics of this roadway are as follows: 

Street Classification: Collector 

Cross-street Classification: Local

Pedestrian Classification: Medium

Land Use Classification: Intermediate

Pavement Type: R3 Asphalt

Sidewalk Material: Concrete (assumed 30% reflective)

Crosswalk Location: Intersection 

Bike Lane Location: Adjacent to roadway

The criteria for the lighting design could be based on either AASHTO GL-7 or IES RP-8-21. In general, the

AASHTO and IES recommendations are similar but may vary depending on the classifications used. The 

SAFETY HIGHLIGHTS 

The use of an adaptive lighting system should be considered in all aspects of exterior 

lighting. 

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choice of which recommendations to use is up to the owner and designer of the lighting system based 

on their requirements and applicability. The criteria from each for this example are listed below: 

IES RP-8-21

Roadway Lighting Level (RP-8-21, Table 11-1)

Average Luminance: >= 0.6 cd/m2

Average/minimum Uniformity Ratio: <= 3.5

Maximum/minimum Uniformity Ratio: <= 6.0

Veiling Luminance Ratio: <= 0.4

Intersection Lighting Level (RP-8-21, Table 12-1)

Average Illuminance: >= 16 lux

Average/minimum Uniformity Ratio: <= 4.0

Crosswalk Lighting Level (RP-8-21, Table 12-1)

Average Illuminance: >= 16 lux

Average Vertical Illuminance: >= 16 lux

Sidewalk Lighting Level (RP-8-21, Table 11-2)

Average Illuminance: >= 5 lux

Average/minimum Uniformity Ratio: <= 5.0

Average Vertical Illuminance: >= 2 lux

Bike Lane Lighting Level (RP-8-21)

Average Illuminance: >= 80% of roadway illuminance provided

AASHTO GL-7 

Roadway Lighting Level (Table 3-5b)

Average Luminance: >= 0.6 cd/m2

Average/minimum Uniformity Ratio: <= 3.5

Maximum/minimum Uniformity Ratio: <= 6.0

Veiling Luminance Ratio: <= 0.4

Intersection Lighting Level (Section 3.4.4 and Table 3-5b)

Average Illuminance: >= 16 lux
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Crosswalk Lighting Level (Section 3.5.6 and Table 3-5b)

Average Illuminance: >= 16 lux

Sidewalk Lighting Level (Table 3-5b)

Average Illuminance: >= 6 lux

Average/minimum Uniformity Ratio: <= 4.0

Bicycle Way Lighting Level (Table 3-5b)

Average Illuminance: >= roadway lighting level

Average/minimum Uniformity Ratio: <= 3.0

The values given above are considered maintained values; that is, they represent the level required on 

the roadway and sidewalk after system depreciation due to reductions in the lumen output of the 

luminaire, dirt accumulating on the luminaire, and other factors. The light loss factors (LLFs) are further 

discussed in RP-8-21, Section 3.1.6 and AASHTO GL-7, Section 10.2.4. For this example, an LLF of 0.8 is 

used.
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3 Rural Road Lighting Example

Most rural roadways are unlikely to have continuous 

lighting systems. More commonly, rural roads will be 

unlit or mostly unlit with partial or beacon lighting at 

higher-volume intersections. There are times, however, 

when the road usage and pedestrian volume may 

warrant continuous lighting. An example of such a case

is a rural road with frequent pedestrian or cyclist use

due to the presence of recreational areas or trailheads. 

The example discussed in this section is for a road with 

parking and hiking trail access, resulting in substantial pedestrian volumes and frequent use by cyclists. 

This example includes the following key elements:

• The Roadway

• Surround Ratio

• Partial or Beacon Lighting

Discussions about these elements cover the basics for lighting on rural roads, with additional sections 

addressing light trespass and color, which may be especially important in sensitive rural areas.

For the lighting of rural roads, mounting lights to wood utility poles is the most common solution, and

the pole locations and spacing between poles are often not ideal for lighting placement. However, given 

the variety of distributions that can be obtained from solid-state lighting components, design values can 

be met with proper equipment selection.

Rural Road

Roadways

Surround Ratio

Partial Beacon

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3.1 The Roadway

3.1.1 Currently Available Design Recommendations

The lighting design for the roadway in this example is meant to provide visibility for drivers to guide 

them as they travel along the roadway and allow them to identify hazards, pedestrians, and cyclists.

AASHTO GL-7, Table 3-5 and ANSI/IES RP-8-21, Table 11-1 provide recommendations for the lighting of 

roadways. The criteria for roadways include: 

• Average luminance (or Illuminance in AASHTO GL-7) for the roadway

• Uniformity ratios of the roadway

• Maximum veiling luminance ratio (to limit disability glare)

The criteria given in these documents are for the travel lanes and the adjoining areas. This example road 

is one lane each way with the following characteristics: 

Street or Roadway Classification: Local

Pedestrian Classification: Low (although expected volumes should be used)

Land Use Classification: Residential (Rural is not a term used in the AASHTO area 

classification) 

Pavement Type: R3 Asphalt

SAFETY HIGHLIGHTS 

The limit on disability glare is one of the most critical design elements. 

The addition of surround ratio (SR) or sidewalk lighting is helpful to increase detection 

distance. 

The presence of pedestrians and cyclists along the roadway edge increases the safety risk. 

This is the most critical consideration when determining design requirements. 

Rural Road

Roadway

Surround Ratio

Partial Beacon

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3.2 Surround Ratio

3.2.1 Currently Available Design Recommendations

Recommendations on roadway lighting criteria and design is based on the results of safety and human 

factors research. One recent development is the inclusion of surround ratio (also referred to as edge 

illuminance ratio by CIE, although with a somewhat different definition) as a design metric. Research has 

shown that the addition of lighting in areas adjacent to the travel lane of the roadway increases the 

driver’s detection distance of objects and people both on the roadway and adjacent to the roadway.

Surround ratio has been considered in international standards for some time and was recently shown to 

be a reliable indicator of detection distance for drivers (National Academies of Sciences Engineering and 

Medicine, 2020). Surround ratio is considered in both AASHTO GL-7 and ANSI/IES RP-8-21. Since 

surround ratio applies to an area that may have variable surface type, surround ratio is determined 

based on illuminance. 

The surround ratio (SR) is defined in RP-8-21 as the ratio of the average illuminance value on the area 

adjacent to the travel lane (3.6-m strip) to the average value for the edge lane of the roadway. The 

criterion for surround ratio in AASHTO GL-7 and ANSI/IES RP-8-21 is 0.8 minimum.

This value is higher than that used by CIE. For example, an average illumination on the outermost lane of 

the roadway of 0.4 fc would result in a minimum lighting level on the surround of 0.4 fc × 0.8 = 0.32 fc.

Surround ratio might not be appropriate in some situations, such as: where there is no area adjacent to 

the roadway, as on some bridges; where sidewalks are lighted; environmentally sensitive areas; and 

where additional poles might be required to meet the 0.8 minimum, thereby increasing the risk of 

collisions. More discussions about surround ratio are in Section 1.3.6 of Part I and in RP-8-21 Section 

10.5.2.3.

Rural Road

Roadways

Surround Ratio

Partial Beacon

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3.3 Partial or Beacon Lighting

As mentioned, in most rural road applications, continuous 

lighting may not be warranted. In those cases, partial or beacon intersection lighting is used primarily to 

alert the approaching driver to an upcoming intersection. Partial lighting lights the entire intersection 

area to make pedestrians or cyclists crossing the street more visible. Beacon lighting is more of an

identifier than a visibility enhancement.

AASHTO GL-7 describes this type of lighting and includes installation diagrams with pole locations but 

does not specify light levels. IES RP-8-21, Table 12-2 includes light levels for partial intersection lighting 

based on the road classification of the roadway with the most traffic volume.

3.4 Criteria Values Applicable to this Example

The classifications for the elements of this roadway would be:

Street or Roadway Classification: Local

Pedestrian Classification: Low (although expected volumes should be used)

Land Use Classification: Residential (Rural is not a term used in the AASHTO area 

classification) 

Pavement Type: R3 Asphalt

The criteria for the design of this installation could use either AASHTO GL-7 or IES RP-8-21. In general, 

the recommendations of AASHTO and IES are similar but may vary depending on the classifications used.

The choice of which recommendations to use is up to the owner and designer of the lighting system 

Rural Road

Roadways

Surround Ratio

Partial Beacon

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based on their requirements and applicability. The criteria from AASHTO GL-7 or IES RP-8-21 for this 

example are listed below: 

IES RP-8-21

Roadway Lighting Level (RP-8-21, Table 11-1)

Average Luminance: >= 0.3 cd/m2

Average/minimum Uniformity Ratio: <= 6.0

Maximum/minimum Uniformity Ratio: <= 10.0

Veiling Luminance Ratio: <= 0.4

Surround Ratio Lighting (Section 10.5.2.3)

Average Illuminance: >= 80% of illuminance provided on roadway

Partial Intersection Lighting (RP-8-21, Table 12.2)

Average Illuminance: >= 4 lux

Average/minimum Uniformity Ratio: <= 6.0

AASHTO GL-7 

Roadway Lighting Level (Table 3-5b)

Average Luminance: >= 0.3 cd/m2

Average/minimum Uniformity Ratio: <= 6.0

Maximum/minimum Uniformity Ratio: <= 10.0

Veiling Luminance Ratio: <= 0.4

Surround Illuminance: >= 3.4 lux

The surround ratio value is included in this example assuming that speeds are over 30 mph, so 

headlights are likely not sufficient, and would only apply in areas with continuous lighting. The value 

shown assumes that the travel lane has illuminance matching the design criterion and is a minimum 

average value for the surround area. If the average illuminance on the roadway were designed to be 

higher than the criterion, the average illuminance value of the surround area would need to increase 

proportionally to meet the SR criterion.

The values given above are considered maintained values; that is, they represent the level required on 

the roadway and sidewalk after system depreciation due to reductions in the lumen output of the 

luminaire, dirt accumulating on the luminaire, and other factors. The LLFs are further discussed in RP-8-

21, Section 3.1.6 and AASHTO GL-7, Section 10.2.4. For this example, an LLF of 0.8 is used.
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4 Expressway Lighting Example

Expressways are highways that have divided traffic like 

freeways, but where access is only partially controlled 

and includes at-grade intersections. This example 

includes roadway elements associated with expressways 

in urban areas, illustrating the complexity of the situation 

for drivers. Suitable nighttime illumination helps drivers 

navigate safely through these challenging environments.

This example discusses the following key elements of expressways:

• The Roadway

• Crosswalks

• Sidewalks 

• Driveways

• Work Zones

These elements are typical components of expressways, with regularly feature complex traffic patterns 

and unexpected features and hazards. Expressways have “a lot going on,” and they also may include

construction projects with work zones, too.

Expressway

Roadways

Crosswalks

Sidewalks

Driveways

Work Zones

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4.1 The Roadway

4.1.1 Currently Available Design Recommendations

The roadway lighting in this example is designed to promote visibility for drivers as they travel the 

roadway. Visual tasks for the driver in these areas include navigating the vehicle while simultaneously 

recognizing features and hazards such as medians, lane markings, signs, construction zones, and other 

vehicles. AASHTO GL-7, Table 3-5 and ANSI/IES RP-8-21, Table 10-1 provide recommendations for the 

lighting of roadways. The criteria for the roadway include: 

• Average luminance (or illuminance in AASHTO GL-7) for the roadway

• Uniformity ratios for the roadway

• Maximum veiling luminance ratio (to limit disability glare)

The criteria given in AASHTO GL-7 and ANSI/IES RP-8-21 apply to the travel lanes. In this example, the 

roadway does not include medians, islands, or any other areas outside of the travel lanes.

For this expressway example, the roadway has the following characteristics: 

Street or Roadway Classification: Major (IES) or Principal Arterial (AASHTO)

Pedestrian Classification: Medium

Land Use Classification: Commercial

Pavement Type: R3 Asphalt

The selection of the street or roadway classification varies with respect to lighting. The roadway 

classifications defined by FHWA2 do not always align with those defined in IES RP-8-21 and AASHTO GL7. Land use (e.g., urban vs. rural) is not defined in the AASHTO GL-7 and IES RP-8-21 lighting criteria 

selection tables. Thus, engineering judgment is required when selecting the street classification. Factors 

such as traffic volume, speed limit, and number of lanes can affect the level of risk. For example, an 

urban collector in a major city will have a very different risk factor than a rural collector in a small town.

2 https://www.fhwa.dot.gov/planning/processes/statewide/related/highway_functional_classifications/section03.cfm

Expressway

Roadway

Crosswalks

Sidewalks

Driveways

Work Zones

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IES RP-8-21 uses a pedestrian classification based on pedestrian volumes determined by judgment

rather than sample counts. AASHTO uses land use classifications (commercial, intermediate, and 

residential) that are somewhat subjective because the land uses can vary on any given street and are 

subject to change over time.

4.1.2 Emerging Research 

Emerging recommendations on roadway lighting criteria and design is based on the results of safety and 

human factors research. One recent development is the inclusion of surround ratio (or edge illuminance 

ratio) as a design metric, as discussed in Section 1.3.6 in Part I. Since this example includes lighted 

sidewalks, surround ratio does not apply here. (Engineering & Medicine, 2020)

4.2 Crosswalks

4.2.1 Currently Available Design Recommendations

Lighting should be provided for both midblock and 

intersection crosswalks. The addition of lighting in 

crosswalks improves the visibility of pedestrians using the crosswalk, allowing motorists to safely stop 

for pedestrians. 

For this expressway example, the intersection has the following characteristics: 

SAFETY HIGHLIGHTS 

The limit on disability glare is one of the most critical design elements. 

The addition of surround ratio (SR) or sidewalk lighting is helpful to increase detection 

distance. 

The presence of pedestrians and cyclists along the roadway edge increases the safety risk. 

This is the most critical consideration when determining design requirements. 

The limit on disability glare is one of the most critical design elements. 

 

Expressway

Roadways

Crosswalks

Sidewalks

Driveways

Work Zones

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Street or Roadway Classification: Major (IES) or Principal Arterial (AASHTO)

Cross-street Classification: Collector 

Pedestrian Classification: Medium

Land Use Classification: Commercial

Pavement Type: R3 Asphalt

Crosswalk Location: Intersection 

AASHTO GL-7 discusses crosswalk lighting at intersections and roundabouts, including the placement of 

lighting to optimize pedestrian detection. Other lighting guides suggest that the vertical lighting level in 

the crosswalk should be equal to the horizontal lighting level recommended for the intersection or 

roundabout. IES RP-8-21 includes recommendations for crosswalk lighting at intersections, roundabouts, 

and midblock crosswalks. 

For the lighting of intersections, both AASHTO GL-7 and IES RP-8-21 recommend that the average 

vertical lighting value in the crosswalk be equal to the average horizontal illuminance in the intersection. 

Similarly, for the lighting of crosswalks at roundabouts, the average vertical lighting level should also be 

equal to the average horizontal lighting level in the roundabout. The one difference in this case is that 

the vertical lighting level is in the direction of the approaching vehicle as opposed to perpendicular to 

the centerline of the crosswalk. For the lighting of midblock crosswalks, ANSI/IES RP-8-21 recommends 

average vertical illuminance levels of 20, 30, and 40 lux for areas with low, medium, and high levels of 

pedestrian conflict, respectively. 

4.2.2 Emerging Research

The current recommendations for high lighting levels in crosswalks are being discussed by technical 

committees dealing with the topic and investigated through ongoing research. The current findings 

suggest that vertical lighting levels (oriented toward the vehicle) equal to horizontal lighting levels on 

the roadway perform well from the perspective of pedestrian detection. However, crosswalk lighting 

also has safety benefits on unlit roads, and current recommendations may be higher than necessary.

Lighting levels of 10 lux on areas with medium to high pedestrian volumes and 8 lux for isolated 

intersections with low pedestrian volumes appear to provide adequate lighting for visibility. Crosswalks 

in areas with medium to high pedestrian volumes along with high levels of activity and ambient 

illumination may warrant higher levels of illumination. For example, in areas near bus stops, public 

facilities, or corner-commercial locations with bright facility lighting, lighting levels of 20 lux may be 

appropriate for crosswalks.

SAFETY HIGHLIGHTS 

Lighting crosswalks is a critical safety issue in areas with moderate to high pedestrian 

volumes. 

Average vertical illuminance values of at least 10 lux should be used, with higher values in 

suitable locations. The vertical values in the crosswalk should always be in the direction of 

the approaching driver. 
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4.3 Sidewalks

4.3.1 Currently Available Design Recommendations

Sidewalk (walkway) lighting within the right-of-way serves 

two purposes: (1) providing pedestrians with sufficient 

light on the sidewalk to avoid trip hazards, allow facial 

recognition, and impart a sense of security; and (2)

assisting the driver in detecting pedestrians approaching the roadway.

This example of sidewalks for an expressway has the following characteristics: 

Street or Roadway Classification: Major (IES) or Principal Arterial (AASHTO)

Pedestrian Classification: Medium

Land Use Classification: Commercial

Pavement Type: Concrete (assumed 30% reflective)

AASHTO GL-7 recommends maintained horizontal illuminance levels for sidewalk areas from 3 to 14 lux 

depending on the sidewalk material and the land use type (commercial, intermediate, or residential). 

AASHTO GL-7 also provides uniformity criteria for sidewalks. IES RP-8-21 recommends sidewalk lighting 

levels based on pedestrian volumes; areas with low pedestrian volume are further categorized into 

medium-density, low-density, and rural locations. IES RP-8-21 provides lighting levels in terms of 

average horizontal illuminance, average vertical illuminance, and uniformity over the paved surface. The 

average horizontal lighting levels can range from 2 to 10 lux and up to 20 lux for rare roadway conditions 

where pedestrians and vehicles use the roadway as a common space without curbed sidewalk areas.

In general, the roadway lighting system provides the lighting for the sidewalk area. However, design 

considerations should be taken into account when developing these systems. Pedestrian-scale lighting is 

often used to better define the sidewalk area and relate better in scale and feel to the pedestrians using 

the area. It is often an attractive aesthetic for lighting these areas. However, issues can arise when trying 

to use pedestrian-scale lighting to light a street. The lumen output often must be significantly increased 

to light the roadway, which increases the amount of disability glare produced by the lighting system. It is 

also difficult to achieve high lighting levels in areas like intersections and crosswalks. In areas where 

sidewalks use pedestrian-scale lighting, a mixture of higher roadway lighting poles in coordination with 

lower pedestrian-scale poles is often recommended to achieve the desired result. 

Expressway

Roadways

Crosswalks

Sidewalks

Driveways

Work Zones

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4.3.2 Emerging Research

Recommendations for sidewalk lighting levels are currently undergoing review. Semi-cylindrical 

illuminance is also being investigated as a metric to replace vertical illuminance because it models a 

complex form like a person better than a single vertical plane does.

4.4 Driveways

4.4.1 Currently Available Design Recommendations

Driveways connect the travel lanes with adjacent facilities 

and typically cross sidewalks within the right-of-way.

Lighting for pedestrians should provide sufficient illumination for them to navigate the driveway and 

provide drivers with adequate light to detect pedestrians and cyclists proceeding along the sidewalk at 

the driveway.

Driveways also allow for vehicle access on and off the roadway, thereby increasing the potential for 

unexpected events. For example, drivers may encounter oncoming headlights from outside of the 

roadway as vehicles approach a driveway.

Some driveways may be highly developed, including divided roadways with medians, signage, 

landscaping, or crosswalks. When feasible, driveways should be coordinated with the lighting design. 

SAFETY HIGHLIGHTS 

Proper sidewalk lighting is focused on both the pedestrian’s ability to see and the driver’s 

ability to see pedestrians; thus, lighting levels on the pedestrian are critical. 

Limits on light trespass should be carefully balanced with needs for sidewalk lighting. 

Expressway

Roadways

Crosswalks

Sidewalks

Driveways

Work Zones

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4.4.2 Emerging Research 

The density of driveways in a section of roadway can indicate the overall level of risk along that section.

Consideration of driveway presence may be part of warranting or evaluations of roadways for adaptive 

lighting levels. 

4.5 Work Zones

4.5.1 Currently Available Design Recommendations

Work zones are elements in streets and highways 

associated with construction, maintenance, or other work that impinges on the normal ability of 

pedestrians, cyclists, and/or vehicles to travel. Work zones are inherently temporary and are described 

as mobile or having short, intermediate, or long duration. Work zones may have active work areas along 

with associated activities and lighting at night; alternatively, they may only have temporary traffic 

control equipment. All work zones should have lighting that is, at a minimum, consistent with the 

illumination of the adjacent roadway, sidewalks, etc. In some situations, additional illumination is 

appropriate, such as in areas with abrupt shifts in lanes, surface unevenness, high pedestrian activity, or 

high traffic volume. When operations in the work area occur at night, the associated illumination from 

equipment and task lighting may generate requirements for additional lighting in the work zone and 

perhaps beyond. 

AASHTO GL-7 recommends that the maintained horizontal illuminance levels for work zones meet or 

exceed the criteria shown in Table 3-5 in that document and discussed above. Considering practical 

constraints around work zones and construction, these criteria may be reasonably relaxed.

In recognition of the increase in nighttime construction activity, NCHRP Report 498: Illumination 

Guidelines for Nighttime Highway Work provides information on lighting for workers and inspectors in 

SAFETY HIGHLIGHTS 

As driveways allow vehicles to enter and exit the roadway by crossing the sidewalk, 

lighting is focused on both pedestrians seeing and being seen, with lighting levels 

measured at the potential locations of pedestrians. 

Expressway

Roadways

Crosswalks

Sidewalks

Driveways

Work Zones

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work zones as well as lighting for roadways in the work zone. Particular attention is given to providing 

temporary lighting in work zones and considering the potential for increased glare experienced by 

motorists, which may necessitate accommodation using temporary roadway lighting. In IES RP-8-21, 

glare from work zone lighting is discussed with recommendations for mitigating glare through luminaire 

aiming and shielding and increased illumination levels on the roadway. The effect of transient 

adaptation, which can prolong the visibility reductions due to glare, is also discussed, including the 

greater impact on drivers with older eyes or impaired vision. In work zones where illumination is 

significantly higher compared to adjacent areas of the roadway or sidewalk, transition lighting may be 

appropriate on the approach and departure to reduce the effect of transient adaptation.

Table 19-1 in IES RP-8-21 provides information for the lighting of long-duration work zones (those in 

place for more than three days). This table indicates which work zone roadways and activities should 

have illumination for rural highways, urban streets, and urban highways. The table indicates that the

work zone should meet the lighting criteria for the roadway, either by maintaining existing lighting or 

providing temporary lighting. IES RP-8-21 also discusses the illumination of flagger stations from above 

and in front so that flaggers are in positive contrast against their background.

4.5.2 Emerging Research

Lighting for work zones has been the subject of much discussion in recent years, and new products have 

expanded options. For example, luminous equipment has been developed for flaggers. Luminous 

paddles, signs, and attire can increase the visibility of flaggers to motorists. Additional approaches 

outside of typical illumination are being considered, and recent work has stressed glare control and 

proposed corresponding metrics. 

SAFETY HIGHLIGHTS 

Lighting for work zones should meet or exceed lighting levels for adjacent areas and be 

provided by existing equipment and temporary lighting when necessary. 

For work areas with nighttime operations; pedestrians, cyclists, and drivers may face 

additional challenges with visibility while navigating atypical conditions. 

Limits on glare from work area lighting should be consistently applied, and when glare is 

excessive, roadway lighting should be supplemented. 
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4.6 Criteria Values Applicable to this Example

The classifications for the elements of this roadway would be:

Roadway Classification: Major (IES) or Principal Arterial (AASHTO)

Cross-street Classification: Collector 

Pedestrian Classification: Medium

Land Use Classification: Commercial

Pavement Type: R3 Asphalt

Sidewalk Material: Concrete (assumed 30% reflective)

Crosswalk Location: Intersection 

The criteria for the design of the installation could be based on AASHTO GL-7 or IES RP-8-21. In general, 

the AASHTO and IES recommendations are similar but may vary depending on the classifications used. 

The choice of which recommendations to use is up to the owner and designer of the lighting system 

based on their requirements and applicability. The criteria from each for this example are listed below:

IES RP-8-21

Roadway Lighting Level (RP-8-21, Table 10-1)

Average Luminance: >= 1.0 cd/m2

Average/minimum Uniformity Ratio: <= 3.0

Maximum/minimum Uniformity Ratio: <= 5.0

Veiling Luminance Ratio: <= 0.3

Surround Ratio: >= 80% of roadway illuminance provided

Intersection Lighting (RP-8-21, Table 12-1)

Average Illuminance (Major / Collector): >= 22 lux

Average/minimum Uniformity Ratio: <= 3.0

Crosswalk Lighting Level (RP-8-21, Table 12-1)

Average Illuminance: >= 22 lux

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Average Vertical Illuminance: >= 22 lux

Sidewalk Lighting Level (RP-8-21, Table 11-2)

Average Illuminance: >= 5.0 lux

Average/minimum Uniformity Ratio: <= 5.0

Average Vertical Illuminance: >= 2.0 lux

AASHTO GL-7 

Roadway Lighting Level (Table 3-5b)

Average Luminance: >= 1.2 cd/m2

Average/minimum Uniformity Ratio: <= 3.0

Maximum/minimum Uniformity Ratio: <= 5.0

Veiling Luminance Ratio: <= 0.3

Surround Ratio: >= 14 lux

Intersection Lighting Level (Section 3.4.4 and Table 3-5b)

Average Illuminance: >= 29 lux

Crosswalk Lighting Level (Section 3.5.6 and Table 3-5b)

Average Illuminance: >= 29 lux

Sidewalk Lighting Level (Table 3-5b)

Average Illuminance: >= 10 lux

Average/minimum Uniformity Ratio: <= 3.0

The surround ratio criterion is 0.8, for the average illuminance value of the road-adjacent surround area 

divided by the value for the outside lane. If the average for the outside lane were the design criterion for 

the roadway in this example, the minimum value for the average illuminance over the surround area 

would be 1.3 footcandles. Where an expressway has a sufficiently wide median and continuous lighting, 

there are separate surround areas on each side of each direction of travel. 

Lighting criteria for work zones are not specified by AASHTO or IES based on roadway type; instead, the 

recommendation is often to maintain the existing or intended lighting levels. Some situations may 

deserve greater illumination due to sudden changes. For more information, see section 4.3.1.4 in Part 1 

and NCHRP Report 498: Illumination Guidelines for Nighttime Highway Work.
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The values given above are considered maintained values; that is, they represent the level 

recommended on the roadway and sidewalk after system depreciation due to reductions in the lumen 

output of the luminaire, dirt accumulating on the luminaire, and other factors. The LLFs are further 

discussed in IES RP-8-21, Section 3.1.6 and AASHTO GL-7, Section 10.2.4. For this example, an LLF of 0.8 

is used.
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5 Urban Freeway Lighting Example 

Freeways are highways that have divided traffic with 

controlled access. The freeway surroundings can vary 

tremendouly and thus influence the lighting design. This 

example includes the key roadway elements involved in 

lighting freeways in urban areas. Suitable nighttime 

illumination helps drivers navigate safely through these 

challenging environments.

This example discusses three key elements of urban 

freeways: 

• The Roadway

• Interchanges

• Surround Ratio 

The universal issues of light trespass and color of light are also design considerations, due to the 

importance of these aspects in suitable lighting design for the complex visual environments like urban 

freeways.

5.1 The Roadway

5.1.1 Currently Available Design Recommendations

The design of the roadway in this example is intended to provide visibility for drivers as they travel the 

roadway. Visual tasks for the driver include vehicle guidance and location as well as recognizing features 

and hazards such as medians, lane markings, signs, construction zones, and other vehicles. AASHTO GL7, Table 3-5 and ANSI/IES RP-8-21, Table 10-1 provide recommendations for the lighting of roadways.

The criteria for the roadway include:

• Average luminance (or Illuminance in AASHTO GL-7) for the roadway

• Uniformity ratios for the roadway

Freeway, Urban

Roadways

Interchanges

Surround Ratio

Freeway, Urban

Roadway

Interchanges

Surround Ratio

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• Maximum veiling luminance ratio (to limit disability glare)

The criteria given in AASHTO GL-7 and ANSI/IES RP-8-21 apply to the travel lanes. This example does not 

consider the lighting of medians, islands, or any other areas outside of the travel lanes.

This example road has the following characteristics: 

Street or Roadway Classification: Freeway A

Pavement Type: R3 Asphalt

The selection of the street or roadway classification does vary with respect to lighting. The roadway 

classifications defined by FHWA3 do not always align with those defined in IES RP-8-21 and AASHTO GL7. Land use (e.g., urban or rural) is not defined in the lighting criteria selection tables in AASHTO GL-7 or 

ANSI/IES RP-8-21. Thus, engineering judgment is required when selecting the street classification. 

Factors such as traffic volume, speed limit, and number of lanes can affect the level of risk. For example, 

an urban collector in a major city will have a very different risk factor than a rural collector in a small 

town. IES RP-8-21 uses a pedestrian classification based on pedestrian volumes determined by judgment

rather than sample counts. The land use classifications used in AASHTO GL-7 (commercial, intermediate, 

and residential) are also somewhat subjective because areas can vary on any given street and are 

subject to change over time.

5.1.2 Emerging Research 

Emerging recommendations on roadway lighting criteria and design is based on the results of safety and 

human factors research. One recent development is the inclusion of surround ratio (or edge illuminance 

ratio) as a design metric as discussed below (Engineering & Medicine, 2020). 

5.2 Interchanges

3 https://www.fhwa.dot.gov/planning/processes/statewide/related/highway_functional_classifications/section03.cfm

Freeway, Urban

Roadways

Interchanges 

Surround Ratio

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5.2.1 Currently Available Design Recommendations

Interchanges provide connections between freeways and local roads through exits from and entrances 

to the freeway linking ramps and intersections. These sections where roadways connect include conflict 

areas that deserve special design consideration. AASHTO GL-7 and ANSI/IES RP-8-21 provide 

recommendations for lighting interchanges. AASHTO GL-7, Section 3.2 includes warranting conditions 

for freeways that assist in establishing the lighting strategy for specific interchanges. 

Some situations may have no lighting requirements. Where lighting is applied, there are generally three 

different approaches: continuous freeway lighting, complete interchange lighting, and partial 

interchange lighting. As indicated in the names, these three approaches provide lighting on different 

portions of the freeway and associated interchanges: 

• Continuous freeway lighting (CFL) applies lighting to the entire freeway from the interchange to 

the intersection at the ramp terminal. 

• Complete interchange lighting (CIL) applies lighting to the complete ramp and the terminal 

intersection but not the freeway outside the interchange. 

• Partial interchange lighting (PIL) applies lighting to the ramp conflict areas at the diverge or 

merge areas and perhaps terminal intersections but not the ramps themselves or the freeway 

beyond the merge or diverge areas. 

The criteria for the warranting conditions in AASHTO GL-7 differ for the three levels of lighting and 

include the following:

• AADT (Annual Average Daily Traffic) of the freeway and surround conditions: urban / suburban / 

rural

• AADT of the ramp traffic and surround conditions: urban / suburban / rural

• AADT of the cross road and surround conditions: urban / suburban / rural

• Lighting extends along the cross roadway or in adjacent commercial or industrial areas

• Ratio of nighttime to daytime crash rates sufficiently exceeds the Statewide average for 

unlighted similar sections along with a supporting study

This example road has the following characteristics: 

Surrounding conditions: Urban 

ADT of the freeway: Over 50,000

Surrounding lighting: Urban commercial-industrial

Interchange separation: Under 1.5 miles

After the extent of the lighting is established, typical equipment layouts can be applied and suitable 

transitions considered. For lighting entire interchanges, low-mast and high-mast lighting may be 

merged. For ramps, poles should be on the insides of curves. For PIL, “four in the gore” (meaning four 

luminaires located around the exit gore point) is a typical pattern at ramp exits and entrances to cover 

the conflict areas, with local modifications able to be made as necessary. 

The selected lighting strategy indicates the extent of the lighting but does not define the level of lighting 

to be provided. The selected lighting strategy does not modify the criteria defined in IES RP-8-21 and 

AASHTO GL-7 for roadway lighting in terms of average maintained values, uniformity ratios, or veiling 
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luminance ratios when proper evaluations can be made. However, proper luminance calculations are 

not feasible in some situations, and illuminance criteria should be applied. When “four in the gore” is 

not long enough to determine the proper luminance and veiling luminance values, these values would 

not be part of the criteria; however, the illuminance average and uniformity criteria would apply over 

the lighted area. 

5.2.2 Emerging Research 

Emerging recommendations on roadway lighting criteria and design approach indicate that human visual 

performance and aging should be considered. The application of lighting can cause glare that reduces 

visual performance after exposure to the lighting. These transient adaptation effects are enhanced with 

age. For intermittent lighting, transition sections may be appropriate to reduce the effects of glare. 

5.3 Surround Ratio

5.3.1 Currently Available Design Recommendations

Research has shown that the addition of lighting in areas 

adjacent to the travel lane of the roadway increases the 

driver’s detection distance of objects and people both on 

the roadway and adjacent to the roadway. Surround ratio 

has been considered in international standards for some 

time and was recently shown to be a reliable indicator of 

detection distance for drivers (National Academies of 

Sciences Engineering and Medicine, 2020). Surround ratio 

(also referred to as edge illuminance ratio by CIE, although with a somewhat different definition) is 

considered in both AASHTO GL-7 and ANSI/IES RP-8-21. Since surround ratio applies to an area that may 

have variable surface type, surround ratio is determined based on illuminance. 

The surround ratio (SR) is defined as the ratio of the illuminance value on the area adjacent to the travel 

lane (3.6-m strip) to the value for the edge lane of the roadway. The criterion for surround ratio in 

AASHTO GL-7 and ANSI/IES RP-8-21 is 0.8. 

This value is higher than that used by CIE. For example, an average illumination on the outside lane of 

the roadway of 0.4 fc would result in a minimum lighting level on the surround of 0.4 fc × 0.8 = 0.32 fc.

Surround ratio might not be appropriate in some situations, such as: where there is no area adjacent to 

the roadway, as on some bridges; areas where speeds are low and pedestrian volumes are low, so 

headlights provide adequate detection distance; where sidewalks are lighted; environmentally sensitive 

areas; and where additional poles might be required, increasing the risk of collisions. These 

considerations are discussed further in RP-8-21 section 10.5.2.3.

Freeway, Urban

Roadways

Interchanges 

Surround Ratio
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5.4 Criteria Values Applicable to this Example

The classification for the elements of this roadway is: 

Roadway Classification: Freeway A

The criteria for the design of the installation could be based on either AASHTO GL-7 or IES RP-8-21. In 

general, the AASHTO and IES recommendations are similar but may vary depending on the 

classifications used. The choice of which recommendations to use is up to the owner and designer of the 

lighting system based on their requirements and applicability. The criteria from each for this example 

are listed below:

IES RP-8-21

Roadway Lighting Level (RP-8-21, Table 10-1)

Average Luminance: >= 0.6 cd/m2

Average/minimum Uniformity Ratio: <= 3.5

Maximum/minimum Uniformity Ratio: <= 6.0Veiling Luminance Ratio: <= 0.3

Surround Ratio: >= 80% of illuminance provided on roadway

AASHTO GL-7 

Roadway Lighting Level (Table 3-5)

Average Luminance: >= 0.4 cd/m2

SAFETY HIGHLIGHTS 

Limits on disability glare are one of the most critical design elements. 

Increasing the surround ratio is helpful to increasing detection distance. 

Credit: FHWA
2023 FHWA LIGHTING HANDBOOK

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Average/minimum Uniformity Ratio: <= 3.5

Maximum/minimum Uniformity Ratio: <= 6.0

Veiling Luminance Ratio: <= 0.3

Surround Ratio: >= 5.4 lux

The surround ratio criterion is 0.8, for the average illuminance value of the road-adjacent area divided 

by the value for the outside lane. If the average for the outside lane were the design criterion for the 

roadway in this example, the minimum value for the average illuminance over the surround area would 

be 0.5 footcandles. For divided highways where the median is sufficiently wide, there are separate 

surround areas on each side of each direction of travel.

The values given above are considered maintained values; that is, they represent the level 

recommended on the roadway and sidewalk after system depreciation due to reductions in the lumen 

output of the luminaire, dirt accumulating on the luminaire, and other factors. The LLFs are further 

discussed in RP-8-21, Section 3.1.6 and AASHTO GL-7, Section 10.2.4. For this example, an LLF of 0.8 is 

used.
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6 Suburban Freeway Lighting Example

Freeways are highways that have divided traffic with 

controlled access. The freeway surroundings can vary 

tremendouly, thereby affecting the lighting design. This 

example includes the key roadway elements involved in 

lighting freeways in suburban areas. Suitable nighttime 

illumination helps drivers navigate safely while respecting 

those living adjacent to the freeway.

This example discusses the following key elements of rural 

freeways:

• The Roadway

• Interchanges

• Surround Ratio

• Work Zones

Suburban freeways are comprised of roadways and interchanges next to commercial and residential 

areas, often with the presence of construction and work zones. The following sections discuss lighting 

for these transportation heavyweights.

Freeway, Suburban

Roadway

Interchanges

Work Zones

Surround Ratio

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6.1 The Roadway

6.1.1 Currently Available Design Recommendations

The design of the roadway lighting system in this example is intended to provide visibility for drivers as 

they travel the highway. Visual tasks for the driver include vehicle guidance and current vehicle location

along with the recognition of features and hazards such as medians, lane markings, signs, construction 

zones, and other vehicles. AASHTO GL-7, Table 3-5 and ANSI/IES RP-8-21, Table 10-1 provide 

recommendations for the lighting of roadways, including the following criteria: 

• Average luminance (or illuminance in AASHTO GL-7) for the roadway

• Uniformity ratios for the roadway

• Maximum veiling luminance ratio (to limit disability glare)

The criteria given in AASHTO GL-7 and ANSI/IES RP-8-21 apply to the travel lanes. This example does not 

include the lighting of any medians, islands, or other areas outside of the travel lanes.

This example road has the following characteristics: 

Street or Roadway Classification: Freeway B

Pavement Type: R1 concrete

The selection of the street or roadway classification can vary with respect to lighting. The roadway 

classifications defined by FHWA4 do not always align with those defined in IES RP-8-21 and AASHTO GL7. For example, land use (e.g., urban vs. rural) is not defined in the GL-7 or RP-8-21 lighting criteria 

selection tables; therefore, engineering judgment is required when selecting the street classification. 

Factors such as traffic volume, speed limit, and number of lanes can impact the level of risk. For 

example, an urban collector in a major city will have a very different risk factor than a rural collector in a 

small town. IES RP-8-21 uses pedestrian activity level, which is based on pedestrian volumes derived 

from judgment rather than sample counts. AASHTO uses land use classifications (commercial, 

4 https://www.fhwa.dot.gov/planning/processes/statewide/related/highway_functional_classifications/section03.cfm

Freeway, Suburban

Roadway

Interchanges

Work Zones

Surround Ratio

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intermediate, and residential) that are also somewhat subjective because the land use can vary on any 

given street and is subject to change over time.

6.1.2 Emerging Research 

Emerging recommendations on roadway lighting criteria and design is based on the results of safety and 

human factors research. One recent development is the inclusion of surround ratio (or edge illuminance 

ratio) as a possible design metric (Engineering & Medicine, 2020).

6.2 Interchanges

6.2.1 Currently Available Design Recommendations

Interchanges provide connections between freeways and local roads through exits from and entrances 

to the freeway linking ramps and intersections. These sections where roadways connect include conflict 

areas that deserve special design consideration. AASHTO GL-7 and ANSI/IES RP-8-21 provide 

recommendations for lighting interchanges. The information contained in AASHTO GL-7, Section 3.2 

includes warranting conditions for freeways that assist in establishing the lighting strategies for specific 

interchanges. 

Some situations have no lighting requirements. Where lighting is applied, there are generally three 

different approaches: continuous freeway lighting, complete interchange lighting, and partial 

interchange lighting. As indicated in the names, these three approaches provide lighting on different 

portions of the freeway and associated interchanges: 

• Continuous freeway lighting (CFL) applies lighting to the entire freeway from the interchange to 

the intersection at the ramp terminal. 

• Complete interchange lighting (CIL) applies lighting to the complete ramp and the terminal 

intersection but not the freeway outside the interchange. 

SAFETY HIGHLIGHTS 

Limits on disability glare are one of the most critical design elements. 

Increasing the surround ratio is helpful to increasing detection distance. 

Freeway, Suburban

Roadway

Interchanges 

Work Zones

Surround Ratio

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• Partial interchange lighting (PIL) applies lighting to the ramp conflict areas at the diverge or 

merge areas and perhaps terminal intersections but not the ramps themselves or the freeway 

beyond the merge or diverge areas.

The criteria for the warranting conditions in AASHTO GL-7 differ for the three levels of lighting and 

include the following:

• ADT of the freeway and surround conditions: urban / suburban / rural

• ADT of the ramp traffic and surround conditions: urban / suburban / rural

• ADT of the cross road and surround conditions: urban / suburban / rural

• Lighting extends along the cross roadway or in adjacent commercial or industrial areas

• Ratio of nighttime to daytime crash rates sufficiently exceeds the Statewide average for 

unlighted similar sections, along with a supporting study

This example road has the following characteristics: 

Surrounding conditions: Rural 

ADT of the freeway: Over 77,000

ADT of the ramps: Under 1,000

ADT of the crossroad: Under 4,000

Surrounding lighting: None

After the extent of the lighting is established, typical equipment layouts can be applied and suitable 

transitions considered. For lighting entire interchanges, low-mast and high-mast lighting may be 

merged. For ramps, poles should be on the insides of curves. For PIL, “four in the gore” (meaning four 

luminaires aligned at the exit gore point) is a typical pattern at ramp exits and entrances to cover the 

conflict areas, with local modifications where applicable. 

The selected lighting strategy indicates the extent of the lighting but does not define the level of lighting 

to be provided. The selected lighting strategy does not modify the criteria defined in IES RP-8-21 and 

AASHTO GL-7 for roadway lighting in terms of average maintained values, uniformity ratios, or veiling 

luminance ratios when proper evaluations can be made. However, proper luminance calculations are 

not feasible in some situations, and illuminance criteria should be applied. When “four in the gore” is 

not long enough to determine the proper luminance and veiling luminance values, these values would 

not be part of the criteria; however, the illuminance average and uniformity criteria would apply over 

the lighted area. 

6.2.2 Emerging Research 

Emerging recommendations on roadway lighting criteria and lighting design indicates that human visual 

performance and aging should be considered. The application of lighting can cause glare that reduces 

visual performance after exposure to the lighting. These transient adaptation effects are enhanced with 

age. When intermittent lighting is considered, transition sections may be appropriate to reduce the 

effects of glare. 
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6.3 Surround Ratio

6.3.1 Currently Available Design Recommendations

Research has shown that the addition of lighting in areas adjacent to the travel lane of the roadway 

increases the driver’s detection distance of objects and people both on the roadway and adjacent to the 

roadway. Surround ratio has been considered in international standards for some time and was recently 

shown to be a reliable indicator of detection distance for drivers (National Academies of Sciences 

Engineering and Medicine, 2020). Surround ratio (also referred to as edge illuminance ratio by CIE, 

although with a somewhat different definition) is considered in both AASHTO GL-7 and ANSI/IES RP-8-

21. Since surround ratio applies to an area that may have variable surface type, surround ratio is 

determined based on illuminance. 

The surround ratio (SR) is defined as the ratio of the illuminance value on the area adjacent to the travel 

lane (3.6-m strip) to the value for the outside lane of the roadway. The criterion for surround ratio in 

AASHTO GL-7 and ANSI/IES RP-8-21 is 0.8. 

This value is higher than that used by CIE. For example, an average illumination on the outside lane of 

the roadway of 0.4 fc would result in a minimum lighting level on the surround of 0.4 fc × 0.8 = 0.32 fc.

For divided highways with sufficiently wide medians, there are separate surround areas on each side of 

each direction of the highway.

SAFETY HIGHLIGHTS 

When lighting is applied, it should cover all conflict areas where roads connect. 

Increasing the surround ratio is helpful to increasing detection distance. 

Limits on disability glare are one of the most critical design elements. 

 

Freeway, Suburban

Roadway

Interchanges

Work Zones

Surround Ratio

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165

Surround ratio might not be appropriate in some situations, such as: where there is no area adjacent to 

the roadway, as on some bridges; areas where speeds are low and pedestrian volumes are low, so 

headlights provide adequate detection distance; where sidewalks are lighted; environmentally sensitive 

areas; and where additional poles might be required, increasing the risk of collisions. These 

considerations are discussed further in RP-8-21, section 10.5.2.3.

6.4 Work Zones

6.4.1 Currently Available Design Recommendations

Work zones are elements in streets and highways associated with construction, maintenance, or other 

work that impinges on the normal ability of pedestrians, cyclists, and/or vehicles to travel. Work zones 

are inherently temporary and are described as mobile or having short, intermediate, or long duration.

Work zones may have active work areas along with associated activities and lighting at night; 

alternatively, they may only have temporary traffic control equipment. All work zones should have 

lighting that is, at a minimum, consistent with the illumination of the adjacent roadway, sidewalks, etc.

In some situations, additional illumination is appropriate, such as in areas with abrupt shifts in lanes, 

surface unevenness, high pedestrian activity, or high traffic volume. When operations in the work area 

occur at night, the associated illumination from equipment and task lighting may generate requirements 

for additional lighting in the work zone and perhaps beyond. 

AASHTO GL-7 recommends that the maintained horizontal illuminance levels for work zones meet or 

exceed the criteria shown in Table 3-5 in that document and discussed above. Considering practical 

constraints around work zones and construction, these criteria may be reasonably relaxed.

In recognition of the increase in nighttime construction activity, NCHRP Report 498: Illumination 

Guidelines for Nighttime Highway Work provides information on lighting for workers and inspectors in 

SAFETY HIGHLIGHTS 

Safety is an important design requirement. In most cases, light trespass beyond the area 

included for the surround ratio can be easily controlled by the appropriate selection of pole 

height and fixture optics and the elimination of luminaire tilt. 

Freeway, Suburban

Roadway

Interchanges

Work Zones

Surround Ratio

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work zones as well as lighting for roadways in the work zone. Particular attention is given to providing 

temporary lighting in work zones and considering the potential for increased glare experienced by 

motorists, which may necessitate accommodation using temporary roadway lighting. In IES RP-8-21, 

glare from work zone lighting is discussed along with recommendations for mitigating glare through 

luminaire aiming and shielding as well as increased illumination levels on the roadway. IES RP-8-21 also 

discusses the effect of transient adaptation, which can prolong the visibility reductions caused by glare, 

including the greater impact on drivers with older eyes or impaired vision. In work zones where 

illumination is significantly higher compared to adjacent areas of the roadway or sidewalk, transition 

lighting may be appropriate on the approach and departure to reduce the effect of transient adaptation.

Table 19-1 in IES RP-8-21 provides recommendations for the lighting of long-duration work zones (those 

in place for more than three days). This table indicates where it would be useful for work zone roadways 

and activities to have illumination for rural highways, urban streets, and urban highways. The table 

indicates the importance for the work zone to meet the lighting criteria for the roadway, either by 

maintaining existing lighting or providing temporary lighting. IES RP-8-21 also discusses the illumination 

of flagger stations from above and in front so that flaggers are in positive contrast against their 

background. 

6.4.2 Emerging Research

Lighting for work zones has been the subject of much discussion in recent years, and new products have 

expanded options. For example, luminous equipment has been developed for flaggers. Luminous 

paddles, signs, and attire can increase the visibility of flaggers to motorists. Additional approaches 

outside of typical illumination are being considered, and recent work has stressed glare control and 

proposed corresponding metrics. 

SAFETY HIGHLIGHTS 

Lighting for work zones should meet or exceed lighting levels for adjacent areas, provided 

by existing equipment and temporary lighting when necessary. 

For work areas with nighttime operations, pedestrians, cyclists, and drivers may face 

additional challenges with visibility while navigating atypical conditions. 

Limits on glare from work area lighting should be consistently applied, and excessive glare 

and excessive roadway lighting should be supplemented. 
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6.5 Criteria Values Applicable to this Example

The classification for the elements of this roadway is as follows: 

Roadway Classification: Freeway B

The criteria for the design of the installation could be based on either AASHTO GL-7 or IES RP-8-21. In 

general, the AASHTO and IES recommendations are similar but may vary depending on the 

classifications used. The choice of which recommendations to use is up to the owner and designer of the 

lighting system based on their requirements and applicability. The criteria from each for this example 

are listed below:

IES RP-8-21

Roadway Lighting Level (RP-8-21, Table 10-1)

Average Luminance: >= 0.4 cd/m2

Average/minimum Uniformity Ratio: <= 3.5

Maximum/minimum Uniformity Ratio: <= 6.0

Veiling Luminance Ratio: <= 0.3

Surround Ratio: >= 80% of illuminance provided on roadway

AASHTO GL-7 

Roadway Lighting Level (Table 3-5b)

Average Luminance: >= 0.4 cd/m2

Average/minimum Uniformity Ratio: <= 3.5

Maximum/minimum Uniformity Ratio: <= 6.0

Veiling Luminance Ratio: <= 0.3

Surround Ratio: >= 5.4 lux

The surround ratio criterion is 0.8, for the average illuminance value of the road-adjacent surround area 

divided by the value for the edge lane. If the average illuminance for the outside lane were the design 

Credit: FHWA
2023 FHWA LIGHTING HANDBOOK

168

criterion for the roadway in this example, the minimum value for the average illuminance over the

surround area would be 0.5 footcandles. For divided highways where the median is sufficiently wide, 

there are separate surround areas on each side of each direction of travel.

Lighting criteria for work zones are not specified by AASHTO or IES based on roadway type; instead, the 

requirement is often to maintain the existing or intended lighting levels. Some situations may deserve 

greater illumination due to sudden changes. For more information, see section 4.3.1.4 in Part 1 and 

NCHRP Report 498: Illumination Guidelines for Nighttime Highway Work.

The values given above are considered maintained values; that is, they represent the level required on 

the roadway and sidewalk after system depreciation due to reductions in the lumen output of the 

luminaire, dirt accumulating on the luminaire, and other factors. The LLFs are further discussed in RP-8-

21, Section 3.1.6 and AASHTO GL-7, Section 10.2.4. For this example, an LLF of 0.8 is used.
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7 Rural Freeway Lighting Example

Freeways are highways that have divided traffic with 

controlled access. The freeway surroundings can vary 

tremendouly and thus influence the lighting design. This 

example includes the key roadway elements involved in 

lighting freeways in rural areas. Suitable nighttime 

illumination helps drivers navigate safely while respecting 

the freeway’s suroundings.

This example discusses the following key elements of rural 

freeways: 

• The Roadway

• Interchanges

• Work Zones

• Surround Ratio

• Partial (Beacon) Lighting

Most freeway is rural, and lighting design should provide appropriate illumination with minimal impacts. 

The elements covered here include the basic elements and their connections along with the discussions 

above about light trespass and color of light, which can be particularly important in rural settings.

Freeway, Rural

Roadways

Interchanges

Work Zones

Surround Ratio

Partial Beacon

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7.1 The Roadway 

7.1.1 Currently Available Design Recommendations

The design of the roadway lighting system in this example 

is intended to provide visibility for drivers as they travel 

the highway. Visual tasks include vehicle guidance and current vehicle location as well as recognizing 

features and hazards such as medians, lane markings, signs, construction zones, and other vehicles.

AASHTO GL-7, Table 3-5 and ANSI/IES RP-8-21, Table 10-1 provide recommendations for the lighting of 

roadways, including the following criteria:

• Average luminance (or illuminance in AASHTO) for the roadway

• Uniformity ratios for the roadway

• Maximum veiling luminance ratio (to limit disability glare)

The criteria given in these documents apply to the travel lanes. This example does not include the 

lighting of any medians, islands, or other areas outside of the travel lanes.

This example road has the following characteristics: 

Street or Roadway Classification: Freeway B

Pavement Type: R3 Asphalt

The selection of the street or roadway classification can vary with respect to lighting. The roadway 

classifications defined by FHWA5 do not always align with those defined in IES RP-8-21 and AASHTO GL7. For example, land use (e.g., urban vs. rural) is not defined in the GL-7 or RP-8-21 lighting criteria

selection tables; therefore, engineering judgment is required when selecting the street classification.

Factors such as traffic volume, speed limit, and number of lanes can impact the level of risk. For

example, an urban collector in a major city will have a very different risk factor than a rural collector in a

small town. IES RP-8-21 uses pedestrian activity level, which is based on pedestrian volumes derived

5 https://www.fhwa.dot.gov/planning/processes/statewide/related/highway_functional_classifications/section03.cfm

Freeway, Rural

Roadways

Interchanges

Work Zones

Surround Ratio

Partial Beacon

Credit: Google Maps. google.com/maps
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171

from judgment rather than sample counts. AASHTO uses land use classifications (commercial, 

intermediate, and residential) that are also somewhat subjective because the land use can vary on any 

given street and is subject to change over time. 

7.1.2 Emerging Research 

Emerging recommendations on roadway lighting criteria and design is based on the results of safety and 

human factors research. One recent development is the inclusion of surround ratio (or edge illuminance 

ratio) as a design metric. Surround ratio has been considered in international standards for some time 

and was recently shown to be a reliable indicator of detection distance for drivers (Engineering & 

Medicine, 2020). Surround ratio, which is the ratio of the lighting value on the area adjacent to the 

travel lane (3.6-m strip) to the lighting value for the roadway, should be at least 0.8. Since surround ratio 

applies to an area that may have variable surface type, surround ratio is determined based on

illuminance. 

7.2 Interchanges 

7.2.1 Currently Available Design Recommendations

Interchanges provide connections between freeways and local 

roads through exits from and entrances to the freeway linking ramps and intersections. These sections 

where roadways connect include conflict areas that deserve special design consideration. AASHTO GL-7 

and ANSI/IES RP-8-21 provide recommendations for lighting interchanges. The information contained in 

AASHTO GL-7, Section 3.2 includes warranting conditions for freeways that assist in establishing the 

lighting strategy for specific interchanges. 

Freeway, Rural

Roadways

Interchanges 

Work Zones 

Surround Ratio

Partial Beacon

SAFETY HIGHLIGHTS 

Limits on disability glare are one of the most critical design elements. 

Increasing the surround ratio of lighting is helpful for increased detection distance. 

Credit: Google Maps. google.com/maps
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172

Some situations have no lighting requirements. Where lighting is applied, there are generally three 

different approaches: continuous freeway lighting, complete interchange lighting, and partial 

interchange lighting. As indicated in the names, these three approaches provide lighting on different 

portions of the freeway and associated interchanges: 

• Continuous freeway lighting (CFL) applies lighting to the entire freeway from the 

interchange to the intersection at the ramp terminal. 

• Complete interchange lighting (CIL) applies lighting to the complete ramp and the terminal 

intersection but not the freeway outside the interchange.

• Partial interchange lighting (PIL) applies lighting to the ramp conflict areas at the diverge or 

merge areas and perhaps terminal intersections but not the ramps themselves or the 

freeway beyond the merge or diverge areas. 

The criteria in AASHTO GL-7 for the warranting conditions differ for the three levels of lighting and 

include the following:

• ADT of the freeway and surround conditions: urban / suburban / rural

• ADT of the ramp traffic and surround conditions: urban / suburban / rural

• ADT of the cross road and surround conditions: urban / suburban / rural

• Lighting extends along the cross roadway or in adjacent commercial or industrial areas

• Ratio of nighttime to daytime crash rates sufficiently exceeds the Statewide average for 

unlighted similar sections, along with a supporting study

This example road has the following characteristics: 

Surrounding conditions: Rural 

ADT of the freeway: Over 77,000

ADT of the ramps: Under 1,000

ADT of the crossroad: Under 4,000

Surrounding lighting: None

After the extent of the lighting is established, typical equipment layouts can be applied and suitable 

transitions considered. For lighting entire interchanges, low-mast and high-mast lighting may be 

merged. For ramps, poles should be on the insides of curves. For PIL, “four in the gore” is a typical 

pattern at ramp exits and entrances to cover the conflict areas, with local modifications. 

The selected lighting strategy indicates the extent of the lighting but does not define the level of lighting 

to be provided. The selected lighting strategy does not modify the criteria defined in IES RP-8-21 and 

AASHTO GL-7 for roadway lighting in terms of average maintained values, uniformity ratios, or veiling 

luminance ratios when proper evaluations can be made. However, proper luminance calculations are 

not feasible in some situations, and illuminance criteria should be applied. When “four in the gore” is 

not long enough to determine the proper luminance and veiling luminance values, these values would 

not be part of the criteria; however, the illuminance average and uniformity criteria would apply over 

the lighted area. 
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7.2.2 Emerging Research 

Emerging recommendations on roadway lighting criteria and design suggests that human visual 

performance and aging should be considered. The application of lighting can cause glare that reduces 

visual performance after exposure to the lighting. These transient adaptation effects are enhanced with 

age. When intermittent lighting is considered, transition sections may be appropriate to reduce the 

effects of glare.

7.3 Work Zones

7.3.1 Currently Available Design Recommendations

Work zones are elements in streets and highways 

associated with construction, maintenance, or other work 

that impinges on the normal ability of pedestrians, 

cyclists, and/or vehicles to travel. Work zones are inherently temporary and are described as mobile or 

having short, intermediate, or long duration. Work zones may have active work areas along with 

associated activities and lighting at night; alternatively, they may only have temporary traffic control 

equipment. All work zones should have lighting that is, at a minimum, consistent with the illumination 

for the adjacent roadway, sidewalks, etc. In some situations, additional illumination is appropriate, such 

as in areas with abrupt shifts in lanes, surface unevenness, high pedestrian activity, or high traffic 

volume. When operations in the work area occur at night, the associated illumination from equipment 

and task lighting may generate requirements for additional lighting in the work zone and perhaps 

beyond. 

AASHTO GL-7 recommends that the maintained horizontal illuminance levels for work zones meet or 

exceed the criteria shown in Table 3-5 in that document and discussed above. Considering practical 

constraints around work zones and construction, these criteria may be reasonably relaxed.

Freeway, Rural

Roadways

Interchanges

Work Zones

Surround Ratio

Partial Beacon

SAFETY HIGHLIGHTS 

When lighting is applied, it should cover all conflict areas where roads connect. 

Increasing the surround ratio is important to increasing detection distance. 

Limits on disability glare are one of the most critical design elements. 

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In recognition of the increase in nighttime construction activity, NCHRP Report 498: Illumination 

Guidelines for Nighttime Highway Work provides guidance on lighting for workers and inspectors in 

work zones as well as lighting for roadways in the work zone. Particular attention is given to providing 

temporary lighting in work zones and considering the potential for increased glare experienced by 

motorists, which may necessitate accommodation using temporary roadway lighting. In IES RP-8-21, 

glare from work zone lighting is discussed along with recommendations for mitigating glare through 

luminaire aiming and shielding and increased illumination levels on the roadway. The effect of transient 

adaptation, which can prolong the visibility reductions due to glare, is also discussed, including the 

greater impact on drivers with older eyes or impaired vision. In work zones where illumination is 

significantly higher compared to adjacent areas of the roadway or sidewalk, transition lighting may be 

appropriate on the approach and departure to reduce the effect of transient adaptation.

Table 19-1 in IES RP-8-21 provides recommendations for the lighting of long-duration work zones (those 

in place for more than three days). This table indicates which work zone roadways and activities should 

have illumination for rural highways, urban streets, and urban highways. The table indicates the 

importance for the work zone to meet the lighting criteria for the roadway, either by maintaining 

existing lighting or providing temporary lighting. IES RP-8-21 also discusses the illumination of flagger 

stations from above and in front so that flaggers are in positive contrast against their background. 

7.3.2 Emerging Research

Lighting for work zones has been the subject of much discussion in recent years, and new products have 

expanded options. For example, luminous equipment has been developed for flaggers. Luminous 

paddles, signs, and attire can increase the visibility of flaggers to motorists. Additional approaches 

outside of typical illumination are being considered, and recent work has stressed glare control and 

proposed corresponding metrics. 

SAFETY HIGHLIGHTS 

Lighting for work zones, including lighting provided by equipment and temporary lighting, 

should meet, or exceed lighting levels for adjacent areas. 

For work areas with nighttime operations, pedestrians, cyclists, and drivers may face 

additional challenges with visibility while navigating atypical conditions. 

Limits on glare from work area lighting should be consistently applied. Excessive glare may 

require roadway lighting to be supplemented. 

 
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7.4 Surround Ratio

7.4.1 Currently Available Design Recommendations

Research has shown that the addition of lighting in areas adjacent to the travel lane of the roadway 

increases the driver’s detection distance of objects and people both on the roadway and adjacent to the 

roadway. Surround ratio has been considered in international standards for some time and was recently 

shown to be a reliable indicator of detection distance for drivers (National Academies of Sciences 

Engineering and Medicine, 2020). Surround ratio (also referred to as edge illuminance ratio by CIE, 

although with a somewhat different definition) is considered in both AASHTO GL-7 and ANSI/IES RP-8-

21. Since surround ratio applies to an area that may have variable surface type, surround ratio is 

determined based on illuminance. 

The surround ratio (SR) is defined as the ratio of the illuminance value on the area adjacent to the travel 

lane (3.6-m strip) to the value for the outside lane of the roadway. The criterion for surround ratio in 

AASHTO GL-7 and ANSI/IES RP-8-21 is 0.8. 

This value is higher than that used by CIE. For example, an average illumination on the outside lane of 

the roadway of 0.4 fc would result in a minimum lighting level on the surround of 0.4 fc × 0.8 = 0.32 fc.

For divided highways with sufficiently wide medians, there are separate surround areas on each side of 

each direction of the highway.

Surround ratio might not be appropriate in some situations, such as: where there is no area adjacent to 

the roadway, as on some bridges; areas where speeds are low and pedestrian volumes are low, so 

headlights provide adequate detection distance; where sidewalks are lighted; environmentally sensitive 

areas; and where additional poles might be required, increasing the risk of collisions. These 

considerations are discussed further in RP-8-21, section 10.5.2.3.

Freeway, Rural

Roadways

Interchanges

Work Zones

Surround Ratio

Partial Beacon

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7.5 Partial or Beacon Lighting

Rural freeways often have partial interchange lighting 

(PIL), covering the exit and entry conflict areas on the 

freeway. In those cases, the ends of the entrance and 

exit ramps may connect with rural roads in 

intersections that have either partial or beacon 

lighting. Beacon intersection lighting is used primarily 

to alert the approaching driver to an upcoming 

intersection. Partial lighting does light the entire 

intersection area to make pedestrians or cyclists 

crossing the street more visible. Beacon lighting is 

more of an identifier than a visibility enhancement.

AASHTO GL-7 describes this type of lighting and 

includes installation diagrams with pole locations but 

does not specify light levels. IES RP-8-21, Table 12-2 

includes light levels for partial intersection lighting based on the road classification of the highestvolume roadway.

7.6 Criteria Values Applicable to this Example

The classification for the elements of this roadway is: 

Roadway Classification: Freeway B

The criteria for the design of the installation could be based on either AASHTO GL-7 or IES RP-8-21. In 

general, the AASHTO and IES recommendations are similar but may vary depending on the 

SAFETY HIGHLIGHTS 

Safety is an important design requirement. In most cases, light trespass beyond the area 

included for the surround ratio can be easily controlled by the appropriate selection of pole 

height and fixture optics and the elimination of luminaire tilt. 

 

Freeway, Rural

Roadways

Interchanges

Work Zones

Surround Ratio

Partial Beacon

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classifications used. The choice of which recommendations to use is up to the owner and designer of the 

lighting system based on their requirements and applicability. The criteria from each for this example 

are listed below:

IES RP-8-21

Roadway Lighting Level (RP-8-21, Table 10-1)

Average Luminance: >= 0.4 cd/m2

Average/minimum Uniformity Ratio: <= 3.5

Maximum/minimum Uniformity Ratio: <= 6.0

Veiling Luminance Ratio: <= 0.3

Surround Ratio: >= 80% of illuminance provided on roadway

AASHTO GL-7 

Roadway Lighting Level (Table 3-5b)

Average Luminance: >= 0.4 cd/m2

Average/minimum Uniformity Ratio: <= 3.5

Maximum/minimum Uniformity Ratio: <= 6.0

Veiling Luminance Ratio: <= 0.3

Surround Ratio: >= 5.4 footcandles

The surround ratio criterion is 0.8, for the average illuminance value of the road-adjacent area divided 

by the value for the outside lane. If the average for the outside lane matched the design criterion for the 

roadway in this example, the minimum value for the average illuminance over the surround area would 

be 0.5 footcandles. For divided highways where the median is sufficiently wide, there are separate 

surround areas on each side of each direction of travel.

Lighting criteria for work zones are not specified by AASHTO or IES based on roadway type; instead, the 

requirement is often to maintain the existing or intended lighting levels. Some situations may deserve 

greater illumination due to sudden changes. For more information, see section 4.3.1.4 in Part 1 and 

NCHRP Report 498: Illumination Guidelines for Nighttime Highway Work. 

The values given above are considered maintained values; that is, they represent the level required on 

the roadway and sidewalk after system depreciation due to reductions in the lumen output of the 

luminaire, dirt accumulating on the luminaire, and other factors. The LLFs are further discussed in RP-8-

21, Section 3.1.6 and AASHTO GL-7, Section 10.2.4. For this example, an LLF of 0.8 is used.
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8 Roundabout Lighting Example

This example consists of an urban roundabout connecting 

multiple streets with crosswalks, intersections, and 

sidewalks. These key elements provide the traveled ways 

for vehicles, pedestrians, and others moving through the 

roundabout at their own speeds and directions. Lighting to 

promote safety is discussed and the potential criteria that 

can be used are identified. The example also considers 

possible adjustmets to current criteria or approaches 

expected from emerging research.

This example includes three key elements: 

• The Roundabout Roadway

• Crosswalks

• Sidewalks 

Roundabout

Crosswalks

Sidewalks

Intersections 

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8.1 Roundabout

8.1.1 Currently Available Design Recommendations

The lighting design for the roundabout in this example is meant to provide guidance and visibility for the 

drivers, pedestrians, and cyclists as they travel the roundabout, allowing them to see hazards including 

other drivers, pedestrians, and cyclists. AASHTO GL-7, Table 3-5 and ANSI/IES RP-8-21, Table 12-4 

provide recommendations for the lighting of roundabouts. In the AASHTO guide, the separate tables are 

for different categories of roundabouts as defined by FHWA. The criteria for roundabout illumination

include: 

• Average illuminance for the pavement

• Uniformity ratio for the pavement

• Minimum vertical illuminance at 1.5 m above the crosswalk facing approaching traffic 

The criteria given in AASHTO GL-7 and ANSI/IES RP-8-21 are for the roundabout, crosswalks, and 

approaches. This example does not include the roundabout’s center island, splitter islands, or other 

areas.

The example roundabout has the following characteristics: 

Street or Roadway Classifications: Major / Collector

Pavement Type: R3 Asphalt

Pedestrian Classification: Medium

The selection of the street or roadway classification can vary with respect to lighting. The roadway 

classifications defined by FHWA6 do not always align with those defined in IES RP-8-21 and AASHTO GL7. For example, land use (e.g., urban vs. rural) is not defined in the GL-7 or RP-8-21 lighting criteria 

selection tables; therefore, engineering judgment is required when selecting the street classification. 

6 https://www.fhwa.dot.gov/planning/processes/statewide/related/highway_functional_classifications/section03.cfm

Roundabout

Crosswalks

Sidewalks

Intersections 

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Factors such as traffic volume, speed limit, and number of lanes can impact the level of risk. For 

example, an urban collector in a major city will have a very different risk factor than a rural collector in a 

small town. IES RP-8-21 uses pedestrian activity level, which is based on pedestrian volumes derived 

from judgment rather than sample counts. AASHTO uses land use classifications (commercial, 

intermediate, and residential) that are also somewhat subjective because the land use can vary on any 

given street and is subject to change over time. 

8.1.2 Emerging Research 

Emerging recommendations on roadway lighting criteria and design approach is based on the results of 

safety and human factors research. One recent development is the inclusion of surround ratio (or edge 

illuminance ratio) as a design metric. Surround ratio is not applied when the area includes lighted 

sidewalks, like in this example. If there were no lighted sidewalks, surround ratio would be an additional 

design criterion.

8.2 Crosswalks

8.2.1 Currently Available Design Recommendations

Lighting should be provided for both midblock and intersection crosswalks. The addition of lighting in 

crosswalks assists in the visibility of pedestrians using the crosswalk, allowing motorists to safely stop for 

pedestrians. 

The crosswalks for this example roundabout have the following characteristics: 

SAFETY HIGHLIGHTS 

Limits on disability glare are one of the most critical design elements. 

The presence of pedestrians and cyclists increases safety risk. This is an important 

consideration when determining design requirements. 

Roundabout

Crosswalks

Sidewalks

Intersections 

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Street or Roadway Classification: Major / Collector

Pedestrian Activity Level: Medium

Pavement Type: R3 Asphalt 

AASHTO GL-7 discusses crosswalk lighting at intersections and roundabouts, including the placement of 

lighting to optimize pedestrian detection. Other lighting guides suggest that the vertical lighting level in 

the crosswalk should be equal to the horizontal lighting level recommended for the intersection or 

roundabout. IES RP-8-21 includes recommendations for crosswalk lighting at intersections, roundabouts, 

and midblock crosswalks. 

For intersections, both AASHTO GL-7 and IES RP-8-21 recommend that the average vertical lighting value 

in the crosswalk be equal to the average horizontal illuminance in the intersection. Similarly, for the 

lighting of crosswalks at roundabouts, the average vertical lighting level should also be equal to the 

average horizontal lighting level in the roundabout. The one difference in this case is that the vertical 

lighting level is in the direction of the approaching vehicle as opposed to perpendicular to the centerline 

of the crosswalk. For the lighting of midblock crosswalks, IES RP-8-21 recommends an average vertical 

Illuminance level of 20, 30, and 40 lux for areas with low, medium, and high levels of pedestrian conflict, 

respectively. 

8.2.2 Emerging Research

The current recommendations for high lighting levels in crosswalks are being discussed by technical 

committees dealing with the topic and investigated through ongoing research. The current findings 

suggest that vertical lighting levels (oriented toward the vehicle) equal to horizontal lighting levels on 

the roadway perform well from the perspective of pedestrian detection. However, crosswalk lighting 

also has safety benefits on unlit roads, and current recommendations may be higher than necessary.

Lighting levels of 10 lux on areas with medium to high pedestrian volumes and 8 lux for isolated 

intersections with low pedestrian volumes appear to provide adequate lighting for visibility. Crosswalks 

in areas with medium to high pedestrian volumes along with high levels of activity and ambient 

illumination may warrant higher levels of illumination. For example, in areas near bus stops, public 

facilities, or corner-commercial locations with bright facility lighting, lighting levels of 20 lux may be 

appropriate for crosswalks. 

SAFETY HIGHLIGHTS 

Lighting crosswalks is a critical safety issue in areas with moderate to high pedestrian 

volumes. 

Average vertical values of at least 10 lux maintained average vertical illuminance should 

be used, with higher values in suitable locations. Vertical values in the crosswalk should 

always be in the direction of the approaching driver. 
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8.3 Sidewalks

8.3.1 Currently Available Design Recommendations

Sidewalk (walkway) lighting within the right-of-way serves two purposes: (1) providing pedestrians with 

sufficient light on the sidewalk to avoid trip hazards, allow facial recognition, and impart a sense of 

security; and (2) assisting drivers in detecting pedestrians approaching the roadway.

The sidewalk for this example roundabout has the following characteristics:

Street or Roadway Classification: Major / Collector

Pedestrian Activity Level: Medium

Land Use Classification: Intermediate

Pavement Type: Concrete (assumed 30% reflective)

AASHTO GL-7 recommends maintaining horizontal illuminance levels for sidewalk areas at 3 to 14 lux 

depending on the sidewalk material and whether it is in a commercial, intermediate, or residential land 

use type. AASHTO GL-7 also provides uniformity criteria for sidewalks. IES RP-8-21 recommends 

sidewalk lighting levels based on pedestrian volumes. Lighting levels are given in terms of average 

horizontal illuminance, average vertical illuminance, and uniformity over the paved surface. Average 

horizontal levels can range from 2 to 10 lux and up to 20 lux for rare roadway conditions where 

pedestrians and vehicles use the roadway as a common space without curbed sidewalk areas.

In general, the roadway lighting system provides the lighting for the sidewalk area. There are, however, 

design considerations to consider when designing these systems. Pedestrian-scale lighting is often used 

to better define the sidewalk area and relate better in scale and feel to the pedestrians using the area. 

Pedestrian-scale lighting is often an attractive aesthetic for lighting in areas where pedestrians frequent. 

There are, however, issues that can arise when trying to use pedestrian-scale lighting for lighting a 

street. The lumen output often must be significantly increased to light the roadway, which increases the 

amount of disability glare produced by the lighting system. It is also difficult to achieve high lighting 

levels in areas like intersections and crosswalks. In areas where sidewalks utilize pedestrian-scale 

lighting, it is often recommended that a mix of higher roadway lighting poles be used in combination 

with lower pedestrian-scale poles to achieve the desired result. 

Roundabout

Crosswalks

Sidewalks

Intersections 

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8.3.2 Emerging Research

The recommended sidewalk lighting levels are currently undergoing some changes. IES is replacing the 

minimum vertical lighting level with an average vertical lighting level while maintaining the 

recommended light levels and eliminating the mixed pedestrian/vehicle recommendation. In addition, 

semi-cylindrical illuminance is being investigated as a predictive metric to replace vertical illuminance 

because it can analyze a complex form like a person instead of just a single vertical plane.

8.4 Criteria Values Applicable to this Example

The classifications for the elements of this roadway are as follows: 

Street Classification: Roundabout

Functional Classification: Major / Collector

Pedestrian Activity Level: High 

Land Use Classification: Intermediate

Pavement Type: R3 asphalt

Sidewalk Material: Concrete (assumed 30% reflective)

Crosswalk Location: Intersection 

The criteria for the design of the installation could be based on either AASHTO GL-7 or IES RP-8-21. In 

general, the AASHTO and IES recommendations are similar but may vary depending on the 

classifications used. The choice of which recommendations to use is up to the owner and designer of the 

lighting system based on their requirements and applicability. The criteria from each for this example 

are listed below:

IES RP-8-21

SAFETY HIGHLIGHTS 

Lighting for sidewalks includes providing visibility of the pedestrian and for the pedestrian. 

Facial recognition and detection of trip and fall hazards are critical. Providing both vertical 

and horizontal illuminance are important. 

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Roundabout Lighting Level (RP-8-21, Table 12-4)

Average Illuminance: >= 29 lux

Average/minimum Uniformity Ratio: <= 3.0

Crosswalk Lighting Level (RP-8-21, Table 12-4)

Average Illuminance: >= 29 lux

Average Vertical illuminance: >= 29 lux

Sidewalk Lighting Level (RP-8-21, Table 11-2)

Average Illuminance: >= 10 lux

Average/minimum Uniformity Ratio: <= 5.0

Average Vertical illuminance: >= 5 lux

AASHTO GL-7 

Roundabout Lighting Level (Table 3-5b per section 6.3)

Average Illuminance: 19 to 26 lux

Average/minimum Uniformity Ratio: <= 3.0

Crosswalk Lighting Level (Section 3.5.6 and Table 3-5b)

Average Illuminance: 19 to 26 lux

Average Vertical Illuminance: 19 to 26 lux

Sidewalk Lighting Level (Table 3-5b)

Average Illuminance: >= 6 lux

Average/minimum Uniformity Ratio: <= 4.0

The values given above are considered maintained values; that is, they represent the level required on 

the roadway and sidewalk after system depreciation due to reductions in the lumen output of the 

luminaire, dirt accumulating on the luminaire, and other factors. The LLFs are further discussed in RP-8-

21, Section 3.1.6 and AASHTO GL-7, Section 10.2.4. For this example, an LLF of 0.8 is used.
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9 Walkway & Bikeway Lighting Example

This example consists of an urban walkway and bikeway 

connecting with crosswalks, intersections, and sidewalks

(see Section 2 Urban Street Lighting Example for additional 

information). Walkways and bikeways may be together, 

adjacent, or separate; when overlapping, they combine 

movement at very different speeds. This section discusses 

the key aspects involved in an urban walkway/bikeway 

and identifies the potential criteria that can be used. The 

example also considers possible adjustments to current criteria or approaches expected from emerging 

research.

Walkway / Bikeway

Sidewalks

Bike Lanes

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9.1 Walkway / Bikeway

9.1.1 Currently Available Design Recommendations

The lighting design for the pavement portion of this example is meant to provide guidance and visibility 

for the pedestrians and cyclists as they travel the path, allowing them to see hazards, including other 

pedestrians and cyclists. AASHTO GL-7, Table 3-5 and ANSI/IES RP-8-21, Table 11-2 provide 

recommendations for the lighting of pathways. The separate tables in ANSI/IES RP-8-21 correspond to 

different pedestrian activity levels and underpasses. The criteria for walkway/bikeway illumination 

include: 

• Average illuminance for the pavement

• Uniformity ratio for the pavement

• Minimum vertical illuminance at 1.5 m above the pathway facing along the direction of travel 

The criteria given in these documents is for the pathway. For this example, it would not include any 

other areas outside of the pathway.

The example pathway has the following characteristics: 

Street or Roadway Classification: Pedestrian way / Bicycle way

Pavement Type: R3 Asphalt

Pedestrian Activity Level: High 

Identification of pedestrian ways or bicycle ways has a set level of lighting. This classification of roadway 

(Pedestrian way / Bicycle way) as defined by FHWA may not align with those defined in the AASHTO GL7 or IES RP-8-21. Land use (e.g., urban vs. rural) is not included in the lighting criteria tables of AASHTO 

GL-7 or IES RP-8-21; thus, engineering judgment is required when selecting the pedestrian activity level.

Factors such as traffic volume, speed limit, and number of intersections can affect the level of risk. For 

example, an urban pathway in a major city will have a very different risk factor than a rural pathway in a 

small town. Since the lighting criteria are for a pathway that may have curves and variable surface types, 

illuminance is used as the metric.

Walkway / Bikeway

Sidewalks

Bike Lanes

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9.1.2 Emerging Research 

Emerging recommendations on pathway lighting criteria and approach is based on the results of safety 

and human factors research. One topic being investigated is an alternative metric for evaluating vertical 

surface illumination. Semi-cylindrical illuminance may provide a better representation of the visibility of 

other pedestrians and cyclists as compared to vertical illuminance. 

9.2 Criteria Values Applicable to this Example

The classifications for the elements of this roadway would be:

Street Classification: Pedestrian way & Bicycle way (AASHTO) or

Walkway / Bikeway (IES)

Pedestrian Activity Level: High 

Pedestrian Only: Yes

Pavement Type: R3 Asphalt

The criteria for the design of the installation could be based on either AASHTO GL-7 or IES RP-8-21. In 

general, the AASHTO and IES recommendations are similar but may vary depending on the 

classifications used. The choice of which recommendations to use is up to the owner and designer of the 

lighting system based on their requirements and applicability. The criteria from each for this example 

are listed below:

IES RP-8-21

Walkway / Bikeway Lighting Level (RP-8-21, Table 11-2)

SAFETY HIGHLIGHTS 

Limits on disability glare are one of the most critical design elements. 

The presence of pedestrians and cyclists increases the safety risk, which is an important 

consideration when determining design requirements. 

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Average Illuminance: >= 10 lux

Average/minimum Uniformity Ratio: <= 5.0

Average Vertical illuminance: >= 5 lux

AASHTO GL-7 

Pedestrian way and Bicycle way Lighting Level (Table 3-5b)

Average Illuminance: >= 22 lux

Average/minimum Uniformity Ratio: <= 3.0

The values given above are considered maintained values; that is, they represent the level required on 

the roadway and sidewalk after system depreciation due to reductions in the lumen output of the 

luminaire, dirt accumulating on the luminaire, and other factors. The LLFs are further discussed in RP-8-

21, Section 3.1.6 and AASHTO GL-7, Section 10.2.4. For this example, an LLF of 0.8 is used.
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10 Short Tunnels Lighting Example

Short tunnels are different from underpasses and long 

tunnels, although the distinctions can be subtle. An 

underpass (e.g., a road under a highway bridge) is a 

structure that has no effect on driver visibility. Short 

tunnels are usually defined by length (e.g., under 400 ft 

from portal to portal) and should be treated differently 

than long tunnels. The most significant factor in 

determining how a short tunnel should be lighted is how 

big the exit portal is in an approaching driver’s view. This may even be the basis for describing a tunnel 

as short. Additional factors are the presence of pedestrians or cyclists, whether the tunnel is undivided 

with bi-directional traffic, and traffic speed and volume.

This example discusses the following two key elements of short tunnels: 

• The Roadway

• Walls 

Short Tunnel

Roadway

Walls

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10.1 The Roadway

10.1.1 Currently Available Design Recommendations

Tunnel roadway lighting is provided in the daytime to allow drivers to see into the tunnel ahead, which 

is relatively dark compared to the daytime conditions in which drivers have been. Accordingly, some 

design metrics and aspects differ from those for the lighting of other roadways, although the objective is 

the same: to provide sufficiently bright roadway lighting. 

For short tunnels, the lighting situation is complicated by the appearance of the bright exit portal at the 

same time as the darker tunnel interior. The brightness of the exit portal reduces or prevents the 

adaptation of a driver’s visual system from the exterior conditions to the darker surroundings of the 

tunnel.

Tunnels that do not have the exit portal in view during the approach should be designed as long tunnels, 

with the provision of supplemental daytime lighting at the tunnel threshold to support driver adaptation 

when entering the tunnel. 

When the exit portal is in the view of approaching drivers, the tunnel interior typically appears as a 

“black frame” around the brightness of the exit. While approaching the tunnel, the driver’s visual 

adaptation level does not change significantly (it would decrease if the exit portal were not as much in 

view, as in a long tunnel). As a result, any object with reduced visual task size might be entirely “within 

the black frame” and would be much less visible. Smaller objects, such as a box on the side of the 

roadway, might not be detected. Larger objects with greater task size that extend out of the black frame 

are seen silhouetted against the exit portal brightness and so are more easily detected. Cyclists or small 

vehicles are typically large enough to be visible against the exit portal, but in some conditions this may 

not occur.

IES RP-8-21 discusses tunnels (as does the following example on long tunnels), providing 

recommendations on adjusting the tunnel threshold illumination based on various considerations shown 

in Table 14-2. Using this approach, the tunnel threshold luminance values determined by the Lseq 

method may be reduced because less illumination is necessary for some short tunnels.

The quantity of supplemental illumination can be determined using the Lseq method (RP-8-21, section 

14.6.1.2), which evaluates the exterior view of the tunnel approach to establish an appropriate 

threshold luminance level. The traffic speed and threshold level are used to define lengths and 

luminance levels for sequential zones along the tunnel. These transitional zones have sequentially 

reduced roadway luminance requirements and extend until traffic reaches the interior zone or exit 

Short Tunnel

Roadway

Walls

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portal. The overall length for all transition zones together is roughly two to three times the SSSD. For 

short tunnels, the entire length is probably all transitional zones.

Typically, daytime supplemental lighting is not extended the full length of a tunnel since daylight is 

considered to provide adequate illumination for a distance of roughly 25 feet from the entry portal into 

the tunnel, and 50 feet from the exit portal. Any remaining length may merit illumination.

Most short tunnels are unlikely to have supplemental daytime lighting through the entire tunnel. More 

commonly, a short tunnel will be unlit or lit along a part of its length. Possible exceptions to this are 

short tunnels that have frequent pedestrian or cyclist presence, or those with curvature so the exit 

portal is not in the view of approaching drivers. 

The criteria for the short tunnel roadway include the following items: 

• Average luminance for the roadway

• Uniformity ratios for the roadway

• Maximum veiling luminance ratio (limits disability glare)

The criteria given in these documents is for the travel lanes. For this example, it would not include any 

other areas outside of the travel lanes.

This example of short tunnel roadway has the following characteristics: 

Tunnel length: < 200 ft

Traffic flow: undivided

Traffic volume (AADT): < 2,500

Traffic speed: 35 mph

Safe stopping sight distance (SSSD): 250 ft on level

Pedestrians and/or cyclists: Yes

Portal height: 20 ft

Daylight penetration: Good

Pavement type: R3 Asphalt

For this example, the SSSD exceeds the length of the short tunnel, so if supplemental lighting is 

provided, the entire tunnel would be in the threshold zone (excluding 25-foot insets from each portal).

10.1.2 Emerging Research

The current recommendations for high lighting levels in short tunnels are being discussed by technical 

committees dealing with the topic as well as being investigated with ongoing research. The current 

investigations indicate that there are three significant areas for consideration: task visibility; tunnel 

characteristics; and traffic.

Task visibility is the goal for all illumination. It is directly related to task size and corresponds with 

detection distance. As task size increases, from small targets (9-inch square) to pedestrians or cyclists (3 

by 6 feet) to vehicles (9 by 6 feet), a driver’s ability to discern the task improves tremendously under all 

conditions.
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Tunnel characteristics have several aspects. The primary aspect for short tunnels is the approaching 

driver’s view of the exit portal. Another element is the proportion of tunnel enclosure, such as solid 

walls or piers or open sides, which has a significant effect on daytime illumination within the tunnel. For 

fully enclosed tunnels such as culverts, the lighting requirements may be significant, while tunnels with 

one or two open sides, such as under highway bridges, may not need any supplemental daytime lighting.

Additional considerations include tunnel orientation, local weather conditions and surfaces’ reflectance.

Traffic aspects include whether the tunnel is divided or undivided, along with speed, volume, and 

complexity of situation. The suitability of supplemental lighting increases as any one of these aspects 

increases, and even more when multiple aspects occur. 

One of the most significant aspect of traffic is the presence of pedestrians or cyclists in the roadway, as 

demonstrated by the significance shown in RP-8-21, Table 14-2. In short tunnels, detecting pedestrians 

and cyclists who do not appear in silhouette against the exit portal may be challenging.

Accordingly, when visual task size is reduced—from vehicles to pedestrians or cyclists—the benefits 

from supplemental lighting increase. 

For relatively flat straight short tunnels, one of the primary issues considers if the presence of

supplemental daytime illumination is needed. A simplified evaluation can be based on daylight 

penetration extending from the portals into the tunnel. Using a “rule of thumb” that daylight sufficient 

to support driver visibility extends into the tunnel 1.5 times the average height of the opening in from 

the entrance portal, and 3 times “portal height” from the exit, this approach indicates that short tunnels 

with length under 5 times “the portal height” would not need lighting. For portals that are each 18 feet 

high on average, the corresponding length would be 90 feet. 

When supplemental lighting is provided, partial lighting limited to the “second quarter” of the tunnel

may be sufficient. For a 120-foot tunnel, the “second quarter” would cover the section from 30 to 60 

feet in from the entrance portal. Supplemental daytime illumination provided in the “second quarter” 

provides partial illumination into the adjacent areas to enhance visibility for the entire tunnel length. For 

“longer short tunnels,” the illuminated section may become a greater extent of the short tunnel while 

keeping consistent insets from the portals.

10.2 The Walls

Short Tunnel

Roadway

Walls

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10.2.1 Currently Available Design Recommendations

Lighting design for tunnels includes a recommendation, in RP-8-21 section 14.4.4, that the wall 

illuminance be at least 40% of the adjacent roadway illuminance. This provides visibility of the 

surroundings for drivers entering and driving through the tunnel.

10.2.2 Emerging Research

A recommended approach for improving visibility in short tunnels is to raise the brightness of some of 

the tunnel walls, creating at least a partial silhouette for predominately-vertical objects that otherwise 

are entirely within the black frame. This can be achieved by instructing drivers to turn on headlights, as 

well as painting walls white or adding reflectors. More active approaches include installing horizontal 

bands or patterns of light sources. These bands do not need to be continuous, as long as an approaching 

driver would see pedestrians or cyclists in partial silhouette. The objective is to promote detection, 

without necessarily providing recognition.

Another technique to improve detection of pedestrians and cyclists is to inform drivers that pedestrians 

or cyclists are present using signage or beacon lighting.

10.3 Criteria Values Applicable to this Example

The criteria for the design of the installation could be based on either AASHTO GL-7 or IES RP-8-21. In 

general, the AASHTO and IES recommendations are similar but may vary depending on the 

SAFETY HIGHLIGHTS 

A driver’s view of the exit portal is an important element for determining if and how to 

light short tunnels. 

Wall and roadway brightness are key for increased detection distance. 

More pedestrians and cyclists present a greater safety risk. This is a critical consideration 

when determining design requirements. 

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classifications used. The choice of which recommendations to use is up to the owner and designer of the 

lighting system based on their requirements and applicability. The criteria from each for this example 

are listed below:

IES RP-8-21

Roadway Lighting Requirement (RP-8-21, Table 14-2 and Lseq evaluations)

Tunnel length: < 200 ft

Traffic flow: undivided

Traffic volume (AADT): < 2,500

Traffic speed: 35 mph

Safe stopping sight distance (SSSD): 250 ft on level

Pedestrians and/or cyclists: Yes

Portal height: 20 feet

Daylight penetration: Good

Pavement type: R3 Asphalt

Roadway Lighting Level (RP-8-21 Chapter 14)

Threshold luminance (Lth) from Lseq evaluations of each portal

Average Luminance: varies by zones

Average/minimum Uniformity Ratio: <= 2.0

Maximum/minimum Uniformity Ratio: <= 3.5

Veiling Luminance Ratio: <= 0.3

Wall Illuminance Level (RP-8-21, Section 14.4.4)

Avg Wall Illuminance / Avg Road Illuminance: >= 0.40

Average/minimum Uniformity Ratio : <= 3.0

The values given above are considered maintained values; that is, they represent the level required on 

the roadway and sidewalk after system depreciation due to reductions in the lumen output of the 

luminaire, dirt accumulating on the luminaire, and other factors. The LLFs are further discussed in RP-8-

21, Section 3.1.6 and AASHTO GL-7, Section 10.2.4. For this example, an LLF of 0.5 is used.
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11 Long Tunnel Lighting Example

Lighting long tunnels involves providing nighttime

illumination as well as supplemental daytime lighting at 

high levels to support drivers’ visual adaptation when 

entering a tunnel at speed.

Long tunnels are different from underpasses and short 

tunnels, although the distinctions can be subtle. An underpass is considered a structure that has minimal 

effect on driver visibility, such as roads under highway bridges. Short tunnels are regularly defined by 

length, e.g., under 400 ft from portal to portal, or by how visible the exit is during approach and have 

distinct design issues. When the exit portal is in view during the driver’s approach to a tunnel and the 

length is under 400 ft, short tunnel design considerations can be applied. IES RP-6-21, Table 14-2 has 

recommendations for lighting required in short tunnels (i.e., 80'-410'). 

Tunnel roadway lighting should be provided at night and during the day. At night, tunnel lighting is 

provided to promote guidance within the structure. In the daytime, supplemental lighting is provided to 

enable drivers to see into the relatively dark tunnel ahead, despite the comparatively bright daytime 

conditions that drivers have been experiencing. Accordingly, tunnel lighting has some metrics and design 

Tunnel

Roadways

Walls

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aspects that differ from other roadway lighting, while the common objective is to make the roadway 

sufficiently bright during hours of darkness. 

For nighttime tunnel lighting, the design criteria address roadway luminance quantity and roadway and 

wall uniformity, maximum veiling luminance, wall brightness, and flicker. These apply over the entire 

length of the tunnel at night. For daytime supplemental lighting, these same design criteria apply but 

with variations along the length of the tunnel to accommodate eye adaptation. For emergency lighting, 

the design criteria address illuminance on the tunnel floor (roadway and walkways) for average

illuminance, minimum illuminance, and illuminance uniformity.

A significant factor in tunnel lighting for daytime is how bright the surroundings (scene) are in an 

approaching driver’s view. This provides the basis for lighting levels in the threshold and transition zones 

inside the portal. Additional significant factors are the presence of pedestrians or cyclists in the 

roadway, whether the tunnel is undivided, tunnel curvature where the exit is not visible from one SSSD, 

having traffic in both directions, and traffic complexity.

For tunnels that do not have existing portals, the design requires greater assumptions. Renderings of the 

approach can be used in place of photographic images and luminance values established from 

measurements in the area of the anticipated surroundings.

Evaluation of solar positions over the year for drivers approaching the tunnel is also recommended. An 

example is shown in Figure 66. In the example, the sun position relative to the tunnel can be defined 

based on the GPS location, and the sun position throughout the day can be tracked. The sun is typically 

at its highest point in the horizon at summer solstice and at its lowest point at winter solstice. 

Figure 66. Line graph. Evaluation of solar positions visible to drivers relative to tunnel over one year.(Image Credit: 

Sunearthetools.com) 

Where the sun is in direct view of drivers entering the tunnel, it is important to note no tunnel lighting 

system can allow a driver to adapt to the direct view of the sun. Therefore, seasonal tracking of the sun 

can indicate if higher threshold luminance or mitigation measures may be appropriate. Mitigation 

measures may include blocking of the sun from the drivers view. The direct view of the sun is most 
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prevalent when the tunnel is oriented in the east–west direction and the sun is low in the horizon at 

sunrise or sunset and a significant amount of sky is prevalent. 

ANSI/IES RP-8-21 divides a tunnel into four sequential adaptation zones and an exit zone as follows:

1 Approach zone 

2 Threshold zone Transition zone

3 Interior zone

4 Exit zone

The approach zone is the area of open road immediately prior to the entry portal. The length of this 

zone is one SSSD. The phenomenon of pre-adaptation begins here. As the portal increasingly fills the

driver’s field of view, the eye begins to adapt from the luminance of the wider general view to the 

significantly lower luminance within the approaching threshold. The point where the portal structure 

completely fills the field of view is called the adaptation point and is considered the start of the 

threshold zone. The threshold zone extends one SSSD from the adaptation point into the tunnel and is 

followed by the transition zone(s) with decreasing luminance levels until the interior zone level—or the 

exit portal—is reached.

For each zone in the tunnel, the length and associated lighting recommendations vary with the vehicle 

speed and associated SSSD, exterior daylight conditions, and driver’s current adapted state. 

The pavement luminance produced by the lighting system in each zone also depends on the reflectance

of the materials used for the road and structure. 

The length of these threshold and transition zones and associated daytime lighting level are based on 

design criteria and the human eye’s adaptation rate to darkness. 

It is important to note that different luminance levels are used for the interior zone during daytime and 

nighttime operations unless the tunnel is bi-directional, where daytime levels can be used at night. 

Because human adaptation to higher brightness is practically instantaneous and adaptation to lower 

levels is time dependent, standard practice does not require increases in luminance levels in the exit 

zone. However, transitional nighttime roadway lighting is typically recommended for the approach and 

exterior zones.

This example discusses the key elements for lighting tunnels, based on the design elements that form 

overlapping operational systems within the tunnel:

• Daytime supplemental lighting

o approach

o Lseq evaluation 

o luminance levels for various zones

• Emergency lighting

• Nighttime lighting 

• Lighting control system
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11.1 Tunnel Roadway, Daytime

11.1.1 Currently Available Design Recommendations

The lighting zones are defined in Figure 67 from RP-8-21. The lighting design for the threshold zone just 

inside the entry includes the potential to provide very high roadway luminance to support visibility as 

drivers adapt from daylight conditions. Sequential zones inside the tunnel provide decreasing levels of 

roadway luminance until the interior zone or the exit portal is reached. Lighting for the exit zone at the 

end of the tunnel may also be provided to prepare drivers who are adapted to the tunnel interior to 

enter daytime conditions. 

Figure 67. The primary external and internal areas associated with and affected by tunnel lighting design (RP-8-21).

The quantity of supplemental daytime illumination can be determined using the Lseq method (RP-8-21, 

section 14.6.1.2), which evaluates the exterior view of the tunnel approach to establish an appropriate 

threshold luminance level. This value is the design criterion for the threshold zone inside the entry 

portal and can be the starting point for determining the luminance levels for the remaining transition 

zones. The final design of tunnel lighting systems may be performed through an Lseq analysis. Key 

measures to perform an Lseq analysis include:

Tunnel

Roadways

Walls

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Luminance readings during the day of the approach conditions for the tunnel. These include sky 

luminance, roadway luminance, luminance of natural features around the portal such as vegetation or 

rocks, and luminance of the structural portal.

If the tunnel is a new tunnel, the same readings are taken at the proposed location of the tunnel for sky 

and natural features. Typical luminance readings are also taken on surfaces like roadways in the area 

with approximately the same orientation as the new roadway for the new tunnel.

The luminance readings gathered need to be adjusted for the time of year and conditions when they are 

made and when the highest brightness conditions are expected to occur. For example, if lighting levels 

are taken in January and peak brightness would be expected in July, then the readings should be 

factored to those peak condition. Methods of making those adjustments vary, but typical sky and 

surface brightness values from daylight analysis data and factors generally can be developed with those.

It is also recommended that readings be done on clear sky days, at peak hour or throughout the day.

Factors can be derived for clear versus overcast skies but are much more complex and variable.

The factored readings are then used to determine the Lseq value as outlined in IES RP-8-21, Chapter 14. 

For transition zones, the traffic speed and threshold level can be used to define lengths and luminance 

levels for the transitional zones along the tunnel. These transitional zones typically have sequentially 

reduced roadway luminance requirements and extend until traffic reaches the interior zone or exit 

portal. The overall length for all transition zones together is roughly two to three times the SSSD. IES RP8-21 offers two methods for determining transition zone levels and lengths. These include the stepdown method or the curve method. Either can be used, but the curve method generally provides a 

better analysis of human eye adaptation because it uses the research formulas for determining the 

reductions.

The criteria for the tunnel roadway include the following items: 

• Average luminance for the roadway

• Uniformity ratios for the roadway

• Maximum veiling luminance ratio (limits disability glare)

The criteria given in these documents is for the travel lanes. For this example, it would not include any 

other areas outside the travel lanes except for marked bike lanes, which should be included as part of 

the roadway.

The recommendations for tunnel wall illumination apply during daytime to promote guidance within the 

structure. As discussed in RP-8-21, section 14.4.4, the lower area of the walls is evaluated, up to 6.6 ft 

above the roadway shoulder. The ratio of roadway-to-wall illuminances should be no more than 2.5. In 

other words, the average wall illuminance should be at least 40% of the average illuminance on the 

adjacent traveled lanes of the roadway.

This example tunnel roadway has the following characteristics: 

Posted speed: 35 mph (56.4 km/h) = 51 ft/sec 

Length: 873 feet (along Baseline)

Portal height: 23 ft 

Orientation: entry portal faces SSE 
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Longitude: 83deg31’6” West 

Latitude: 35deg44’40” North

Traffic volume: 25,000 Average Annual Daily Traffic (AADT) 

30,000 Seasonally Adjusted Daily Traffic (SADT) 

Safe-sight stopping distance (SSSD): 250 ft (not considering grade) 

Structure surfaces: Poured concrete (= 30%)

Roadway surface: Portland cement, (R1), Qo=10% 

11.2 Tunnel Walls

11.2.1 Currently Available Design Recommendations

Lighting design for tunnels includes a recommendation, in RP-8-21, section 14.4.4, that the wall 

illuminance be at least 40 % of the adjacent roadway illuminance. This provides visibility of the 

surroundings for drivers entering and driving through the tunnel.

Tunnel

Roadways

Walls

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11.3 Emergency Lighting

11.3.1 Currently Available Design 

Recommendations

Lighting design for tunnels includes a 

recommendation, in RP-8-21 section 14.4.10, that the 

emergency illumination be consistent with NFPA 502, 

Standard for Road Tunnels, Bridges, and Other 

Limited Access Highways. Generally, this system is to 

provide visibility of the tunnel during emergency 

situations to assist escape along the path of egress

when power fails. 

Following NFPA 502, the illuminance onto the 

roadway and walkway surfaces should have an 

average value of at least 10 lux maintained, with a minimum at any point of at least 1 lux maintained.

The overall uniformity ratio of maximum-to-minimum should be no more than 40:1. This should be done

from portal to portal.

Emergency lighting has power supplied through protected conduits and wiring, to be automatically 

switched on when regular power fails or lights otherwise go out. Note that, because emergency lighting 

needs to remain operational during conditions like fires within tunnels, the electrical system to support 

their operation should be 2-hour fire rated with specific testing and operational functions defined in 

NFPA 502.

Also to be considered in the design is egress lighting consisting of illuminated markers mounted to be 

seen in smoke conditions leading to exits that also have added lighting. Additional information can be 

found in NFPA 502.

11.3.2 Emerging Research

The emergency lighting in tunnels is intended to provide visibility of the structure and guidance along 

the egress path when the lighting has otherwise failed. In such conditions, visibility may be significantly 

reduced, e.g., smoke and people may be agitated, so the emergency illumination should be sufficiently 

robust to show how to proceed from any location toward an exit.

Additional fire safety measures may also be applied and should be coordinated with the emergency 

lighting, including cross-passage doors, Distance-to-Exit signage, and emergency communications 

equipment.

For designers, starting luminaire layouts using a regular pattern of emergency-capable equipment that 

supports the emergency requirements assures compliance after higher lighting levels from nonemergency luminaries are included.

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11.4 Nighttime Lighting

11.4.1 Currently Available Design Recommendations 

Lighting design for tunnels includes a recommendation, in RP-8-21, section 14.4.3, that the nighttime

luminance be at least 2.5 cd/m2 for divided tunnels (this will vary depending on the posted speed). This 

level is more than recommended roadway luminance levels to provide visibility of the tunnel structure 

consistent with the adjacent roadway for drivers entering and driving through the tunnel at night.

When the tunnel is undivided, with bi-directional traffic, then the nighttime roadway luminance should 

be the same as the daytime interior level. This should assist drivers in such higher-conflict situations. 

Following these recommendations, the tunnel at night probably has higher roadway luminance than the 

exterior roadway. For such situations, RP-8-21, section 14.4.3 includes recommendations that for a 

distance of at least one SSSD before and beyond the portals, the roadway luminance should be at least 

one third of the tunnel nighttime luminance. This applies even when the roadway is not otherwise 

lighted. For example, based on an anticipated nighttime interior lighting level of 2.5 cd/m2

, the approach 

zone and exterior exit zone roadways should be illuminated to a minimum average pavement luminance 

of 0.8 cd/m2

. 

The recommendations for tunnel wall illumination apply at night to promote guidance within the 

structure. As discussed in RP-8-21, section 14.4.4, the lower area of the walls is evaluated up to 6.6 ft 

above the roadway shoulder. The ratio of roadway-to-wall illuminances should be no more than 2.5. In 

other words, the average wall illuminance should be at least 40% of the average illuminance on the 

adjacent traveled lanes of the roadway. 

The recommendations concerning flicker from tunnel lighting apply at night, as discussed in RP-8-21, 

section 14.4.8. The effect is considered minimal for any duration under 20 seconds, or for frequencies 

under 2.5 Hz or over 15 Hz. Exposure for more than 20 seconds to frequencies between 4 Hz and 11 Hz 

should be avoided. For example, at 60 mph (88 fps) the spacings between 22 and 8 feet on center 

should be avoided for sections over 1,700 feet in extension.

Flicker is not usually an issue when linear luminaires are used or regular spacings do not extend beyond 

20 seconds of exposure. At night, when a luminaire pattern could extend from portal to portal, a 

Tunnel

Roadways

Walls

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recurring spacing pattern should be evaluated for flicker. In addition, when lighting levels are increased 

by operating additional luminaires at the midpoint of longer spacings, the frequency will double, so 

luminaire layouts and control strategies may need to be adjusted accordingly.

11.4.2 Emerging Research

The nighttime lighting in tunnels is brighter than the general roadway to enhance visibility of the 

structure and guidance along the roadway. Driver challenges at night are not necessarily the same as 

during the day, and designers should be aware of the nighttime surroundings of the tunnel.

For existing tunnels, comparison of nighttime crash rates between “the combined approach and exit 

roadways” to “inside the tunnel” can provide information about how well the nighttime illumination 

meets drivers needs.

11.5 Criteria Values Applicable to this Example

The criteria for the design of this installation would be found in IES RP-8-21 Chapter 14, Tunnel Lighting. 

The choice of whether to use these recommendations or which one to use is up to the owner and 

designer of the lighting system based on their requirements and applicability. The criteria for this 

example are below:

IES RP-8-21

Roadway Lighting Requirement (RP-8-21, Table 14-2 and Lseq evaluations)

SAFETY HIGHLIGHTS 

Brightness surrounding the driver’s view of the portal is the most important element for 

determining how to light tunnels. 

Wall and roadway brightness are key for increased detection distance. 

More pedestrians and cyclists present a greater safety risk. This is a critical consideration 

when determining design requirements. 

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Tunnel length: 873 ft

Traffic flow: divided 

Traffic volume (AADT): 25,000

Traffic speed: 35 mph (51 fps)

Safe stopping sight distance (SSSD): 257 ft on 3% down grade

Portal height: 23 feet

Pavement type: R3 Asphalt

Roadway Lighting Level (RP-8-21 Chapter 14)

Daytime

Threshold luminance (Lth) from Lseq evaluations of each portal

Average Luminance: >= 121 cd/m2

Average/minimum Uniformity Ratio: <= 2.0

Maximum/minimum Uniformity Ratio: <= 3.5

Veiling Luminance Ratio: <= 0.3

Nighttime

Average Luminance: >= 2.5 cd/m2 for divided tunnel

Average/minimum Uniformity Ratio: <= 2.0

Maximum/minimum Uniformity Ratio: <= 3.5

Veiling Luminance Ratio: <= 0.3

Wall Illuminance Level (RP-8-21, Section 14.4.4)

Avg Wall Illuminance / Avg Road Illuminance: >= 0.40

Average/minimum Uniformity Ratio: <= 3.0

Emergency Lighting (NFPA 502)

Average floor illuminance: >= 1.0 fc

Minimum-at-any-point illuminance: >= 0.1 fc

Maximum/minimum Uniformity Ratio: >= 40

The values given above are considered maintained values. This means they represent the level required 

on the roadway and walls after depreciation of the system occurs due to reductions in the lumen output 

of the luminaires, dirt accumulating on the luminaire, and other factors. LLFs are further discussed in RP8-21, Section 3.1.6 as well as AASHTO GL-7, Section 10.2.4. For this example, an LLF of 0.5 is often used. 

It is important to base the luminaire dirt deprecation that is part of the LLF on the tunnel cleaning and 

washing schedule. There is no exact formula for linking the dirt deprecation to the cleaning schedule, 

but it is recommended that cleaning be undertaken every 3 to 6 months. Sensors can be considered in 

the tunnel to measure light levels and access the degradation via the reduction in light output. 

For emergency lighting, recommendations come from NFPA 502, for 1 fc average over the entire tunnel 

floor, including roadway and shoulders and walkways, with at least 0.1 fc at any point and uniformity 

over the tunnel as maximum-to-minimum limited to 40:1.
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For nighttime lighting, the recommended luminance level extends from portal to portal, with uniformity 

limits of 2.0 for average-to-minimum and 3.5 for maximum-to-minimum. The pavement average 

depends on the tunnel traffic as divided or undivided, as discussed in RP-8-21, section 14.4.3. For this 

example, with one-way divided traffic, the average maintained luminance for nighttime is 2.5 cd/m2

, 

from portal to portal. Therefore, adjacent roadway lighting should be at least 0.8 cd/m2 for at least one 

SSSD from each portal.

For daytime supplemental lighting, the design is intended to provide sufficient lighting during the 

transition from the exterior conditions through the threshold zone to the interior zone. The level for the 

threshold zone, Lth, is consistent with the driver’s adaptation level approaching the portal, as 

determined using the Lseq method. The interior zone daytime level is established from RP-8-21, section 

14.6.3. For a tunnel with 35 mph speed and over 24,000 AADT, the recommended nighttime pavement 

luminance is 5 cd/m2 based on extrapolation in Table 14-7. The lighting is designed to transition from 

the driver’s adaptation from Lth to the interior level, since this tunnel is that long.

The length of the total threshold zone should be equal to one SSSD, which at 35 mph is approximately 

250 feet, minus the pre-adaptation distance. When using the reduction curve, the first half—called 

Threshold Zone 1 (TH1)—should be illuminated to the full threshold pavement luminance (Lth), while 

the second half—Threshold Zone 2 (TH2)—should begin reducing to the calculated value of the first 

transition zone (TZ1). Based on the height of the portal, the adaptation distance for the tunnel is 43 feet, 

so the first section of the threshold zone should be 159 feet long and the second half should be 54 feet 

long. 

Typically, daytime lighting is not provided for a distance into the tunnel from either portal corresponding 

to roughly 1.5 times the portal height due to daylight contribution. For portals approximately 16 feet 

high, this distance would be 25 feet in accordance with ANSI/IES RP-8-21. This inset only applies to 

daytime lighting, as nighttime lighting should be extending to the roadways outside the portals and 

emergency lighting is intended to cover the entire tunnel floor.

Figure 68. Tunnel entrance luminance evaluation polar diagram (Image Credit: WSP).
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The required values for Lth in the threshold zone(s) depend on the design speed, structure orientation, 

ambient daylight conditions, and the visual environment immediately surrounding the structure portal. 

The current standard practice, RP-8-21, states that the threshold luminance is determined by using the 

Equivalent Veiling Luminance Method, also called the Lseq Method. 

The Lseq value is determined using an image of the portal taken at one SSSD from the portal, with the 

Lseq polar graph overlayed (Figure 68). The Lseq figure is specified in RP-8-21, Table 14-4 and in CIE 88-

2004, with concentric rings divided into 12 sectors so each 4-sided area has an equivalent spatial 

contribution to the driver’s view. With this diagram, the sum of the luminance values from each area 

corresponds to the veiling luminance for drivers approaching the tunnel under such conditions.

EXTERIOR LUMINANCE SITE READINGS @ ENTRY PORTAL AREA

A B C D E F G H I 

SKY ROAD ROCK-DK TREE PORTAL GRASS WALL-INT WALL-EXT ROAD-SH

cd/m2 2750 3649 1840 1422 1902 3098 72 3200 437 

cd/m2 1902 3200 392 1594 2838 2463 94 

cd/m2 2770 

cd/m2 4540 

avg kcd/m2 2.99 3.42 1.12 1.51 2.37 2.78 0.08 3.20 0.44 

READINGS TAKEN AT 11:40AM ON APRIL 28, 2021 UNDER A CLEAR SKY

APPROACH ROAD IS R3, TUNNEL ROAD FROM PORTAL TO PORTAL IS R1

Figure 69. Tunnel entrance luminance evaluation example points (Image Credit: WSP).

The 12 sectors are numbered starting from zenith and increasing clockwise. Each sector has eight or 

nine rings outside the center circle. The diameter of the center circle corresponds to the 2-degree field 

of central vision and is determined by the length of the SSSD and 1 degree angle that represents the 

center circle’s radius. The circle should be filled by an area of the tunnel to be illuminated to the level 

being determined by the Lseq method.
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Figure 70. Tunnel entrance luminance example assignments polar diagram (Image Credit: WSP).

The luminous elements in the image are grouped together and assigned luminance values based on site 

evaluations. For example, roadway surface luminance values may be measured on site and averaged to 

establish the luminance used for roadway surface in the Lseq calculation. For this example, the defined 

elements are shown in Figure 69. The luminance readings collected for sky, portals, roads, and 

vegetation at the entrance of the tunnel are also dependent on the time of year and conditions at that 

time. There are daylighting factors that would need to be applied if readings are taken during a time of 

the year with reduced ambient light levels and what would be considered the peak ambient light levels. 

Information of daylighting of the sky and surfaces for different latitudes can be found in the IES 

Handbook and other daylighting references.

For each sector-ring area, the contribution from the surroundings is determined by area-weighting the 

luminance values in view in that area. For example, the detail in Figure 70 shows the area for sector 9 

ring 8, which clearly includes different defined luminous elements. This area’s area-weighted luminance 

has 20% road, 40% grass, and 40% trees, and the value is 2.4 kcd/m2 with the defined luminance for 

these elements. 

The calculated luminance values from the sector-ring areas are summed and multiplied by a factor to 

determine the value of Lseq. The Lseq is combined with the specified design factor, typically 4.7, that 

corresponds to a level of visual contrast that would be effective for detection if the Lth is produced in 

the center circle. For the design factor 4.7, that contrast level is 0.301, and the corresponding ratio for 

Lth/Lseq is 1.26.

This method accounts for the complete visual field around the portal. For this example, using all 

luminance within the visual field and for the contrast visibility recommended, the resultant design 

threshold luminance (Lth) is 121 cd/m2

. 
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An additional factor may be applied to the Lth value for adjustment of the luminance values from those 

measured during a site visit to values that represent the highest anticipated brightness for the situation.

Because the calculation of Lseq is simple arithmetic, any multiplier to the set of luminance values used 

in the Lseq calculation can be applied at this stage of the calculation. In CIE 88-04 (6.2.b), the 

recommendation is to represent the 75 hours per year with the brightest conditions. For example, if site 

readings were taken in April under cloudy skies, it may be appropriate to adjust those luminance values 

to be consistent with a June day with partly cloudy skies, which typically corresponds to the brightest 

conditions. Orientation of the approach should determine which hours of the day are most significant.

The length of the threshold zone is one SSSD from the adaptation point, the location outside the portal 

where the tunnel fills the driver’s view. The distance from the portal to the adaptation point is 

determined using a cutoff angle between 22 and 24 degrees for the driver’s view. With the poral height 

at 23 feet and using a cutoff angle of 22 degrees, the adaptation point is 45 feet from the portal. When 

this distance is subtracted from the one SSSD length of the complete threshold zone, the length inside 

the tunnel is 212 feet. This distance is divided in two parts, with the part inside the portal at the 

threshold luminance Lth value for three quarters of the length (100%), and the remaining quarter of the 

threshold zone’s length at 70% of Lth. At the end of the threshold zone, the luminance level drops to 

41% and the transition zone begins. This portion of the luminance profile is shown at the upper left in

Figure 71. 

Tunnel (FT) 873.00 Zone Luminance Distance (FT)

Step Method

Distance (m)

Step Method

Zone Luminance

ratio

Cumm. Dur.s (s) 

Reduc. Curve

Duration (s)

Tunnel (FT) 214.30 Reduc. Curve

ft/s ec 51.33 Lth1 121 cd/ M2 161 49 Lth1 n.a. 0.0 3.1

Duration (sec) 17.01 Lth2 85 cd/ M2 54 16 Lth2 1.4 3.1 1.0

Ltr1 49 cd/ M2 103 31 Ltr1 1.7 4.2 2.0

Ltr2 18 cd/ M2 154 47 Ltr2 2.7 6.2 3.0

Ltr3 8.1 cd/ M2 205 63 Ltr3 2.2 9.2 4.0

Ltr4 NA 0 0 Ltr4 13.2

Ltr5 NA 0 0 Ltr5 - 

Int-Day 6.00 cd/ M2 197 60 Int-Day 1.3 17.0 3.8

Int-Night 2.5 cd/ M2 873 266 Total Duration: 17.0

Figure 71. Line graph and tables. Example Zone and Recommended Luminance Calculations (Image Credit: WSP). 

After the threshold zone luminance and length are determined, the remaining luminance profile can be 

established using the curve shown in RP-8-21 and CIE 88-04 and in red in Figure 71. This curve 
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represents the minimum luminance level to be provided at that position inside the tunnel, and the 

intent of the design is to stay above that curve in every zone. This is typically achieved through steps in 

pavement luminance for each zone. The profile shown in the figure in blue uses transition zone 

durations of 2, 2, and 4 seconds for those steps. 

Combined with the threshold zones’ duration of 4.1 seconds, the time from portal to the interior zone is 

12.1 seconds. This is adequate time for drivers’ adaptation to decrease from the exterior daytime 

conditions and achieve suitable adaptation for the roadway luminance in the interior zone. Many other 

choices of zone durations can be used to achieve the same overall transition.

Exit portal lighting is not provided in this example since the driver’s view out the portal will allow for 

suitable adaptation before leaving the tunnel.

The lighting calculations are performed with the luminance method with a grid located in each zone, 

typically in the first third of the zone, to capture the full effect of the lighting in that zone. Calculations 

represent maintained values, so an LLF is applied. Wall illuminance calculations should be coordinated 

with the roadway calculations to provide the averages for comparison to meet the 40% minimum level.

Flicker evaluations should be made for any section of the tunnel where the luminaire pattern remains 

the same for 20 seconds or more of travel. For example, with speed at 35 mph equal to 51 fps, 

luminaires spaced at 25 feet on center will produce a 2 Hz frequency, lower than the range of concern.

Because this tunnel is 873 feet long, the anticipated duration of 17 seconds is lower than the 20-second 

threshold for flicker concern. 
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12 Underpass Lighting Example

Underpasses (including overpasses) are different from 

short tunnels and long tunnels, although the distinctions 

can be subtle. An underpass is considered a structure like 

roads under highway bridges, which typically have 

minimal impact on a driver’s visibility. A significant factor 

in determining when and how an underpass should be 

lighted is how well daylight extends into the underpass, 

which involves the geometry and particularly the extent of 

enclosure. Additional significant factors are the presence 

of pedestrians or cyclists and whether the tunnel is 

undivided, having traffic in both directions, as well as traffic speed and volume.

This example discusses the key elements for underpasses: 

• The Roadway

• Sidewalks 

• Walls 

Underpass

Roadways

Sidewalks

Walls

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12.1 The Roadway

12.1.1 Currently Available Design Recommendations

Tunnel roadway lighting is provided in the daytime to enable drivers to see into the relatively dark road 

ahead, despite the comparatively bright daytime conditions in which drivers have been. Accordingly, it 

has some metrics and design aspects that differ from other roadway lighting, but the common objective 

is to make the roadway sufficiently bright. 

RP-8-21 discusses underpasses and tunnels and provides recommendations on adjusting threshold 

illumination based on those considerations (RP-8-21 Table 14-2). This approach modifies the tunnel 

design criteria for threshold luminance values in recognition that reduced illumination is appropriate for 

some underpasses. With this approach, supplemental daytime illumination may be provided for part or 

all of the underpass. RP-8-21, Table 14-2 does define daytime lighting as not required for a tunnel 80 ft 

or less in length. This length should not be considered absolute, as the amount of daylight penetration 

will vary greatly depending on tunnel opening size. Investigations are being performed to determine if a

four-lane and an open median underpass will have significantly more daylight penetration than a twolane structure vertical wall. Determining the need for daytime lighting should therefore require a level 

analysis and engineering judgment. 

Underpass

Roadways

Sidewalks

Walls

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The quantity of supplemental illumination can be determined using the Lseq method (RP-8-21 section 

14.6.1.2), which evaluates the exterior view of the underpass approach to establish an appropriate 

threshold luminance level. The traffic speed and threshold level are used to define lengths and 

luminance levels for sequential zones along the underpass. These transitional zones have sequentially 

reduced roadway luminance requirements and extend until traffic reaches the interior zone or exit 

portal. The overall length for all threshold and transition zones together is roughly two to three times 

the SSSD. For underpasses, the entire length is typically all within the threshold zone.

Most underpasses are unlikely to have supplemental daytime lighting throughout. More commonly, 

underpasses will be unlit or lit with partial daytime lighting. Possible exceptions to this are underpasses 

that have frequent pedestrian or cyclist presence in the roadway itself.

The criteria for the underpass roadway include the following items:

• Average luminance for the roadway

• Uniformity ratios for the roadway

• Maximum veiling luminance ratio (limits disability glare)

The criteria given in these documents is for the travel lanes. For this example, it would not include any 

other areas outside of the travel lanes.

This example of underpass roadway has the following characteristics: 

Underpass length: < 120 ft

Traffic flow: undivided

Traffic volume (AADT): unknown

Traffic speed: 35 mph

Safe stopping sight distance (SSSD): 250 ft on level

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Pedestrians and/or cyclists: Yes, on sidewalk

Portal height: 16-18 ft

Daylight penetration: Good

Pavement type: R3 Asphalt

For this example, the SSSD exceeds the length of the underpass, so if supplemental lighting is provided, 

the entire tunnel would be in the threshold zone (excluding 25-foot sections inside the tunnel at each 

entry portal and 50-foot sections approaching the exit portal for single direction underpasses).

12.1.2 Emerging Research

The current recommendations for high lighting levels in underpasses are being discussed by technical 

committees (reference IES RLC) dealing with the topic as well as being investigated with ongoing 

research. The current investigations indicate that there are generally three significant areas for 

consideration: task visibility; tunnel characteristics; and traffic.

Task visibility is the goal for all illumination, and it is directly related to task size and corresponds with 

detection distance. As task size increases, from small targets (9 inches square) to pedestrians or cyclists 

(3 by 6 feet) to vehicles (9 by 6 feet), a driver’s ability to discern the task improves tremendously under 

all conditions.

Tunnel characteristics have several aspects. The primary aspect for underpasses is the approaching 

driver’s view of the exit portal. Another element is the proportion of tunnel enclosure, such as solid 

walls or piers or open sides, which has a significant effect on daytime illumination within the underpass.

For fully enclosed roadways such as culverts, the lighting requirements may be significant, while 

underpasses with one or two open sides, such as under highway bridges, may not need any 

supplemental daytime lighting. Additional considerations include driver orientation, local weather 

conditions, and surfaces’ reflectance.

Traffic aspects include whether the underpass is divided or undivided, along with speed, volume, and 

the complexity of the situation. The suitability of supplemental lighting increases as any of these aspects 

increases individually, and more when multiple aspects combine. 

A significant aspect of traffic is the presence of pedestrians or cyclists in the roadway, as demonstrated 

by its position in RP-8-21, Table 14-2. Pedestrians and cyclists on a sidewalk adjacent to the roadway are 

less significant. When task size is reduced from vehicles to pedestrians or cyclists, the benefits from 

supplemental lighting increase. 

For relatively flat straight underpasses, an important issue is whether any supplemental daytime 

illumination is required. A simplified evaluation can be based on daylight penetration extending from 

the portals into the underpass. Using a rule of thumb that daylight sufficient to support driver visibility 

extends into the underpass 1.5 times the average height of the opening in from the entrance portal, and 

3 times portal height from the exit, this approach indicates that underpasses with length under 5 times 

the portal height would not generally need lighting. For portals that are each 18 feet high on average, 

the corresponding length would be 90 feet. 
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When supplemental lighting is provided, partial lighting limited to the second quarter of the tunnel may 

be sufficient. For a 120-foot tunnel, the second quarter would cover the section from 30 to 60 feet in 

from the entrance portal. Supplemental daytime illumination provided in the second quarter provides 

partial illumination into the adjacent areas to enhance visibility for the entire tunnel length. 

12.2 Sidewalks

12.2.1 Currently Available Design Recommendations

When sidewalks are present in tunnels, adequate illumination should be provided consistent with the 

lighting on the roadway and sidewalks outside the underpass. The objective in lighting the sidewalk 

surface is to provide safety, e.g., avoid tripping. There are also recommendations for vertical 

illumination, providing lighting for faces and hands of other pedestrians to promote personal security.

The sidewalk for this example underpass has the following characteristics: 

Street or Roadway Classification: Collector 

Pedestrian Activity Level: Medium

Land Use Classification: Intermediate

Pavement Type: Concrete (assumed 30% reflective)

AASHTO GL-7 recommends maintaining horizontal illuminance levels for sidewalk areas at 3 to 14 lux 

depending on the sidewalk material and whether it is in a commercial, intermediate, or residential land 

use type. AASHTO GL-7 also provides uniformity criteria for sidewalks. IES RP-8-21 recommends 

sidewalk lighting levels based on pedestrian volumes. Lighting levels are given in terms of average 

horizontal illuminance, average vertical illuminance, and uniformity over the paved surface. Average 

horizontal levels can range from 2 to 10 lux and up to 20 lux for rare roadway conditions where 

pedestrians and vehicles use the roadway as a common space without curbed sidewalk areas. 

In general, the roadway lighting system provides the lighting for the sidewalk area. There are, however, 

separate design considerations for these systems. In particular, the scale of the illumination and 

equipment for pedestrians may be smaller than for roadways or tunnels, so using one system to light 

Underpass

Roadways

Sidewalks

Walls

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both areas may lead to undesirable consequences such as increases in disability glare (and 

corresponding challenges meeting the veiling luminance ratio limit).

IES provides recommended values (Table 11-2 in RP-8-21), for day or night, for maintained illuminance 

values for sidewalks and corresponding uniformity criteria. An average illuminance recommendation 

applies to the horizontal sidewalk surface, and a minimum illuminance recommendation for vertical 

illuminance at 1.5 m above grade, onto surfaces facing in each direction of pedestrian traffic. The 

uniformity criteria apply to the horizontal surface, limiting the average-to-minimum ratio value.

12.2.2 Emerging Research

Sidewalk lighting levels are currently under review and subject to research. 

In particular, semi-cylindrical illuminance is being investigated as a better predictive metric compared to 

vertical illuminance because it represents a complex form such as a person better than a single vertical 

plane does.

Current IES recommendations for sidewalk areas are being reconsidered and may result in lower 

recommended values, closer to open area sidewalks.

12.3 Walls

12.3.1 Currently Available Design Recommendations

Lighting design for tunnels includes a recommendation, in RP-8-21, section 14.4.4, that the ratio of roadto-wall illuminance values be no more than 2.5. This is the same as saying that wall illuminance be at 

least 40% of the adjacent roadway illuminance. This provides visibility of the surroundings for drivers 

entering and driving through the tunnel.

For underpasses, there may not be walls to the tunnel, with piers or clear spans commonly applied.

12.3.2 Emerging Research

When the exit portal is in the view of approaching drivers, the tunnel interior typically appears as a 

“black frame” around the brightness of the exit. While approaching the tunnel, the driver’s visual 

adaptation level does not change significantly (it would decrease if the exit portal were not as much in 

view, as with long tunnels). A driver’s ability to distinguish details within the black frame is compromised 

due to visual adaptation to daylight surroundings. As a result, while objects with larger task size will 

appear in silhouette against the exit portal, different objects with smaller task size may be viewed 

entirely against the black frame and would be much less visible. Smaller objects, such as a box on the 

side of the roadway, might not be detected. Larger objects with greater task size that extend out of the 

black frame are seen silhouetted against the exit portal brightness and so are more easily detected.

Underpass

Roadways

Sidewalks

Walls

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Cyclists or small vehicles are typically large enough to be visible against the exit portal, but in some 

situations this may not occur.

The recommended approaches for improving visibility in short tunnels aim to raise the brightness of 

some of the tunnel walls, creating at least a partial silhouette for predominately vertical objects that 

otherwise are entirely within the black frame. Detection can be improved by instructing drivers to turn 

on headlights, combined with painting walls white or using tile or adding reflectors. More active 

approaches include installing horizontal bands or patterns of light sources on the roadway, thus 

reducing uniformity and improving object contrast. These bands do not need to be continuous as long as 

an approaching driver would see pedestrians or cyclists in partial silhouette. The objective is to promote 

detection without necessarily providing recognition. 

Where feasible, introducing daylight into the underpass, through a gap in the cover near the middle of 

the underpass, can provide significant improvement in visibility for approaching drivers. For example, 

projects with median in-fills of freeways could retain some open space between parallel overpasses.

Another technique to improve detection of pedestrians and cyclists is to inform drivers that pedestrians 

or cyclists are present using signage or beacon lighting.

12.4 Criteria Values Applicable to this Example

The criteria for the design of this installation would be found in IES RP-8-21, Chapter 14, Tunnel Lighting. 

The choice of whether to use these recommendations or which one to use is up to the owner and 

SAFETY HIGHLIGHTS 

A driver’s view of the exit portal is an important element for determining if and how to 

light short tunnels. 

Wall and roadway brightness are key for increased detection distance. 

More pedestrians and cyclists present a greater safety risk. This is a critical consideration 

when determining design requirements. 

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designer of the lighting system based on their requirements and applicability. The criteria for this 

example are below:

IES RP-8-21

Roadway Lighting Requirement (RP-8-21, Table 14-2 and Lseq evaluations)

Underpass length: 117 ft

Traffic flow: undivided

Traffic volume (AADT): unknown

Traffic speed: 35 mph

Safe stopping sight distance (SSSD): 250 ft on level

Pedestrians and/or cyclists: Not on Roadway / Low

Portal height: 17 feet

Daylight penetration: Good

Pavement type: R3 Asphalt

Roadway Lighting Level (RP-8-21 Chapter 14)

Threshold luminance (Lth) from Lseq evaluations of each portal

Average Luminance: 100 cd/m2

Average/minimum Uniformity Ratio: <= 2.0

Maximum/minimum Uniformity Ratio: <= 3.5

Veiling Luminance Ratio: <= 0.3

Wall Illuminance Level (RP-8-21, Section 14.4.4)

Avg Wall Illuminance / Avg Road Illuminance: >= 0.40

Average/minimum Uniformity Ratio: <= 3.0

Sidewalk Lighting Level (RP-8-21, Table 11-2)

Average Illuminance: >= 2 lux

Average/minimum Uniformity Ratio: <= 10.0

Average Vertical illuminance: >= 2 lux

The extent of illumination in the underpass is less than the overall length due to daylight, which is 

considered to extend roughly a distance of 1.5 times the height of the underpass into the underpass 

from each side. When the sides of the underpass are open and allow daylight penetration, these 

distances may be increased.

The values given above are considered maintained values; that is, they represent the level required on 

the roadway and walls after depreciation of the system occurs due to reductions in the lumen output of 
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the luminaires, dirt accumulating on the luminaire, and other factors. LLFs are further discussed in RP-8-

21, Section 3.1.6 as well as AASHTO GL-7, Section 10.2.4. 
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13 At-grade Railway Crossing Lighting Example

This example consists of a railway crossing at grade with 

isolated illumination of the roadway, a particular type of 

intersection that has unusual lighting considerations. The 

two sections include the key aspects involved in lighting 

such as a railroad crossing for drivers, pedestrians, 

cyclists, and neighbors and the criteria to be used.

The application of lighting at isolated interchanges, including at-grade railway crossings, is based on a 

safety concern that could arise from several aspects of the situation. For this example, these could 

include: nighttime train operation; limited visibility of the crossing or the trains; view under the train 

showing oncoming headlights; and crash history. 

Chapter 13 of RP-8-21 discusses at-grade railway crossings, including considerations such as pole 

characteristics and location, and provides detailed figures and specific recommendations for lighting.

At-grade Railway Crossing

At Grade Rail Crossings

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13.1 At-grade Railway Crossing

13.1.1 Currently Available Design Recommendations

The lighting design in this example is intended to provide guidance and visibility for drivers as they 

approach an at-grade railway crossing, allowing them to see hazards in general as well as other vehicles 

and trains. ANSI/IES RP-8-21 provides recommendations for the lighting of crossings in Chapter 13. The 

criteria for illumination for at-grade railway crossings address:

• Average illuminance onto the pavement

• Uniformity ratio for the pavement

• Average vertical illuminance above the outside of the tracks, facing toward approaching 

drivers 

The criteria given here are for the approaches to the crossing, for 30 m in each direction away from the 

tracks, and for the vertical calculation grids above the edge of the tracks and facing toward drivers. 

These vertical grids are located on the outsides of the track(s) and extend along the tracks a bit beyond 

the outside edges of the roadway, shoulder, sidewalk, or pathway on each side of the traveled way.

The example roadway has the following characteristics:

Street or Roadway Classification: Major

Pavement Type: R3 Asphalt

In RP-8-21, Chapter 13, there are detailed figures and descriptions of the surfaces to be evaluated, both 

real and virtual, with relevant dimensions. The recommendations for roadway illumination are based on 

the road classification, while the criterion for the virtual vertical surfaces is the same for all situations. 

For isolated interchanges, including railway crossings, the assignment of a road classification 

corresponds to a specific level of lighting. Such a classification as defined by FHWA may not align with 

those defined in the AASHTO GL-7 or IES RP-8-21. Land use (e.g., urban vs. rural) is not included in the 

lighting criteria tables of AASHTO GL-7 or IES RP-8-21; thus, engineering judgment is required when 

selecting the pedestrian activity level. Factors such as traffic volume, speed limit, and number of 

pedestrians and cyclists can affect the level of risk. For example, an urban crossing in a major city will 

have a very different risk factor than a rural crossing outside a small town. Since the lighting criteria are 

At-grade Railway Crossing

At Grade Rail Crossings 

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for crossings that typically have sloped sections and variable surface type, as well as a conceptual 

vertical surface, illuminance is the metric used.

13.2 Criteria Values Applicable to this Example

For this example of at-grade railway crossings, the classifications for the isolated interchange are:

Street or Roadway Classification: Major

Pavement Type: R3 Asphalt

The criteria for the design of the installation discussed here are from IES RP-8-21 and listed below:

IES RP-8-21 

Partial (Isolated) Intersection Lighting Level (RP-8-21, Table 12-2)

Average Pavement Illuminance: >= 9 lux

Average/minimum Uniformity Ratio: <= 3.0

Railway Crossing Lighting Level (RP-8-21 Section 13.3)

Average Vertical Illuminance: >= 10 lux

The values given above are considered maintained values; that is, they represent the level required on 

the roadway and sidewalk after system depreciation due to reductions in the lumen output of the 

luminaire, dirt accumulating on the luminaire, and other factors. The LLFs are further discussed in RP-8-

21, Section 3.1.6 and AASHTO GL-7, Section 10.2.4. 

SAFETY HIGHLIGHTS 

Identifying both the presence of a crossing and the presence of a train is critical for safety 

at at-grade railway crossings. 

The presence of pedestrians and cyclists increases the safety risk for crossing the 

embedded tracks. 
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For More Information: 

https://safety.fhwa.dot.gov/ 

FHWA – SA-23-004