Web-Based Training for FHWA Roadway Lighting Workshop

Module 4: Other Roadway Lighting Topics 
Web-Based Training for FHWA Roadway Lighting 

Workshop 

Participant Workbook 

Module 4: Other Roadway Lighting Topics 

(Other modules include: 

Module 1: Roadway Lighting Design Overview 

Module 2: Lighting Hardware and Light Source Considerations for Roadway Lighting 

Module 3: Street and Roadway Lighting Design) 

May 2018 
NOTICE 

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

Transportation in the interest of information exchange. The United States Government 

assumes no liability for its contents or the use thereof. This Report does not constitute a 

standard, specification, or regulation. 

The contents of this Report reflect the views of the contractor, who is responsible for the 

accuracy of the data presented herein. The contents do not necessarily reflect the official 

policy of the U.S. Department of Transportation. 

The United States Government does not endorse products or manufacturers named 

herein. Trade or manufacturers’ names appear herein solely because they are considered 

essential to the object of this report. 

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. 

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TECHNICAL REPORT DOCUMENTATION PAGE 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

FHWA-SA-18-036 

4. Title and Subtitle 5. Report Date 

Web-Based Training for FHWA Roadway Lighting Workshop 

Module 4: Other Roadway Lighting Topics May 2018 

6. Performing Organization Code 

7. Author(s) 8. Performing Organization Report No. 

Daniel C. Frering, John D. Bullough, Kevin Chiang, Leverson Boodlal 

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) 

KLS Lighting Research Center, 11. Contract or Grant No. 

Engineering, Rensselaer Polytechnic 

LLC (Prime), Institute (Subcontractor), 21 DTFH6116D00017, TOPR No. 16-16 

45155 Research Union Street, Troy, NY 12180 

Pl, Suite 200, 

Ashburn, VA 

20147 

12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered 

Federal Highway Administration Report (2016-2018) 

Office of Safety 

1200 New Jersey Ave. SE 14. Sponsoring Agency Code 

Washington, DC 20590 

FHWA 

15. Supplementary Notes 

Joseph Cheung from FHWA served as the Project Manager. Cathy Satterfield, George Merritt, Michelle Arnold and 

Wilmari Valentin Medina from FHWA provided helpful technical comments. 

16. Abstract 

This document serves as a participant workbook for Web-Based Training for FHWA Roadway Lighting Workshop, 

Module 4: Other Roadway Lighting Topics. Module 4 covers locations for lighting equipment, lighting for special 

locations, and the spectral effects of light. Other modules include Module 1: Roadway Lighting Design Overview, 

Module 2: Lighting Hardware and Light Source Considerations for Roadway Lighting, and Module 3: Street and 

Roadway Lighting Design. 

17. Key Words 18. Distribution Statement 

No restrictions Roadway lighting, safety, visibility, crash avoidance

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price 

Unclassified Unclassified 71 

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
List of Acronyms and Abbreviations

AASHTO American Association of State Highway and Transportation Officials 

CCT Correlated color temperature 

cd/m2 Candela per square meter 

DG Design guide 

FHWA Federal Highway Administration 

HPS High pressure sodium 

IES Illuminating Engineering Society 

K Kelvin 

LED Light emitting diode 

LRC Lighting Research Center 

MASH Manual for assessing safety hardware 

MH Metal halide 

NHTSA National Highway Traffic Safety Administration 

RDG Roadside Design Guide 

RP Recommended practice 

S/P Scotopic/photopic 

SPD Spectral power distribution 
Module 4: Other Roadway Lighting Topics 

Other Roadway Lighting Topics 

Module 4, Slide 1 

This section of the Participant Workbook will help you review the content for Module 4, 

titled Other Roadway Lighting Topics. The top of each workbook slide indicates the 

module slide title and slide number so you can locate content within the workbook that 

matches content in the online modules. 
Navigating This Course 

Module 4, Slide 2 

This slide describes how to navigate through the course module. It is similar to the 

instructions in this workbook. 
Course Objectives 

Module 4, Slide 3 

Following completion of this module, the user will be able to accomplish the following 

objectives: 

 Determine factors that influence the placement of lighting. 

 Apply appropriate lighting placement for intersections. 

 Design lighting for roundabouts, crosswalks, and other applications. 

 Estimate impacts of light source spectrum on vision. 
Table of Contents 

Module 4, Slide 4

Section 1: Lighting Equipment Location – Clear zones, curves, underpasses, 

overpasses, trees. 

Section 2: Lighting for Special Locations – Intersections, interchanges, crosswalks, 

roundabouts, tunnels. 

Section 3: Spectral Effects of Light – Mesopic vision, scene brightness and 

perception of safety, and circadian health impacts. 
Lighting Equipment Location 

Module 4, Slide 5 

This section of the module discusses issues related to the location and placement of 

lighting equipment, such as poles and luminaires. 
Lighting in Clear Zones 

Module 4, Slide 6 

A clear zone on the side of a rural highway. 

The AASHTO Roadway Design Guide (RDG) defines a clear zone as the unobstructed, 

traversable area provided beyond the edge of the through traveled way for the recovery 

of errant vehicles. The clear zone includes shoulders, bike lanes, and auxiliary lanes, 

except those auxiliary lanes that function like through lanes. 

The Clear Zone is what is available for recovery. By providing a clear recovery area, 

roadway agencies reduce the probability of a crash or mitigate the severity of a crash. 

Four factors that are considered in determining an appropriate clear zone for any 

particular road are speed, traffic volume, roadside slope and horizontal curvature. The 

clear zone should be as wide as practical, but should meet the minimums of RDG Table 

3.1. 
Clear Zones

Module 4, Slide 7 

Light poles placed at the end of the clear zone along a highway. 

Although an unobstructed roadside is highly desirable from a roadside safety viewpoint, 

some appurtenances such as light poles must be placed near the travel way. Since 

roadway lighting is a road safety enhancement, light poles should be placed, whenever 

possible, where they are least likely to be struck by errant motor vehicles. Barriers can 

also be considered when poles are located near travel lanes, if they are likely to reduce 

crash severity, according to the AASHTO Roadside Design Guide (RDG). 

All new and replacement luminaire support poles should be selected from those that 

have been successfully crash-tested to current AASHTO MASH (manual for assessing 

safety hardware) criteria. Poles should not compromise the safety of the road user. 

Details for reducing impact severity with the use of suitable breakaway pole base design 

are included in the RDG. 
Lighting in Clear Zones 

Module 4, Slide 8

Utility poles with attached street lighting fixtures placed with a lateral offset from the 

road curb. 

For lighting on the side of the roadway, the AASHTO Roadside Design Guide (RDG) 

recommends locating the poles as far from the shoulder or clear zone edge as practical, 

including the use of breakaway poles with appropriate clearance. In urban areas with 

curbs and gutters, place poles at the back of the sidewalks (when possible, given 

locations of buildings and proper sidewalk width) to reduce the potential for being struck 

by motor vehicles. 

When poles cannot be placed behind the sidewalk, the RDG recommends that poles 

should be placed a minimum 1.5 feet back from the curb. This is a lateral offset and 

should not be confused with a clear zone. Unprotected roadway lighting poles located 

inside the clear zone or at the lateral offset, should be breakaway, unless conditions 

dictate otherwise. 
Lighting in Clear Zones (continued) 

Module 4, Slide 9 

Illustration of recommended light pole placement near clear zones. 

The AASHTO Roadway Design Guide recommends that breakaway poles be placed on 

the roadside of interstate highways at least 15 feet from the road edge. For highways 

other than interstates, also place breakaway poles on the roadside of travel lanes 15 

feet from the road edge, where practical. If sufficient right-of-way does not exist for this 

clearance, the poles may be placed just inside the right-of-way line but not closer than 

2.5 feet from the road edge. 

Whenever possible, lighting poles should not be placed in medians less than 30 feet 

wide. If they are placed in medians less than 30 feet wide, proper protections must be 

installed to prevent vehicles from crashing into lighting poles. The illustration above 

shows typical roadside side lighting of a controlled access roadway with a median less 

than 30 feet wide. If the median width were 30 feet or greater, then median lighting 

could be used for the light poles. 
Lighting for Curves 

Module 4, Slide 10

An illustration of lighting placement along curves. 

 

Where lighting is required on roadways with small radius horizontal curvature, poles 

should be positioned on the inside of the curve to reduce the potential for impacts by 

errant vehicles that overrun the entry to the curve. 

According to the 2012 FHWA Lighting Handbook, if poles cannot be positioned on the 

inside of the curve, they should be located outside of the entry overrun areas as shown 

in the illustration above. 
Underpass Lighting 

Module 4, Slide 11

A typical highway underpass that might require lighting. 

An example of a wall-pack luminaire. 

Underpass lighting generally is installed to enhance driver visibility after daylight hours. 

On highways that are not continuously lighted, consider providing underpass lighting 

where frequent nighttime pedestrian traffic exists through the underpass or where 

unusual or critical geometry exists within or on an approach to the underpass. 

Provide underpass lighting on all highways that are continuously lighted. This can be 

accomplished with pole-mounted luminaires along the side of the highway (see 

illustration on next page) or with supplemental lighting within the underpass itself. 

If lighting within the underpass is necessary, this can often be done with wall-mounted 

luminaires, often called wall packs, mounted on abutments and piers, or by pendant or 

flat luminaires, mounted over the travel lanes. 

Avoid placing these luminaires below the bottom flange of girder type bridges or other 

types of bridges that have flush bottom surfaces so as not to interfere with necessary 

clearances.
Underpass Lighting 

Module 4, Slide 12

An illustration of lighting placement within and adjacent to an underpass. Note 1: 

Position luminaire pole approximately one mounting height away from the structure 

(typically both sides). 

Favorable positioning of conventional pole-mounted highway luminaires adjacent to a 

relatively short underpass often can provide adequate illumination within the underpass 

without a need to provide supplemental lighting. If this action is considered, ensure that 

shadows cast by the conventional luminaires do not become a visibility problem within 

the underpass. 

Poles adjacent to an underpass should be located at a sufficient distance away from the 

entrance and exit point of the underpass to allow the light from the luminaire to 

penetrate the underpass. This is very important at short underpasses where 

supplemental under bridge lighting is not required. 
Trees 

Module 4, Slide 13

Trees blocking light from roadway luminaires. 

Visibility on the sidewalk and streets can be reduced if trees block the light and create 

shadows that reduce uniformity and visibility. A study titled Trees, Lighting and Safety in 

Context Sensitive Design gave some examples of how a lighting system should be 

designed to allow for the presence of trees at all stages of maturity: 

 The best design approach is to locate luminaires outside of the full growth lines 

of the species of tree along the roadway. 

 When a roadway or pedestrian lighting project includes new or existing trees in 

close proximity to the lighting, the reduction in light reaching the road caused by 

the trees can be incorporated by adding an additional light loss factor. There is 

currently insufficient research to quantify the factor with precision, but an 

additional 10 – 20 percent is reasonable. 
Trees (continued) 

Module 4, Slide 14 

An illustration of proper luminaire placement near trees. 

It is best to locate luminaires beyond the tree canopy so that the trees do not interfere 

with the light distribution of the luminaire. 

However, even when roadway lighting and tree installations are carefully planned, tree 

pruning will be required over time. 

The illustration at right shows how to determine which tree branches should be trimmed. 

If you stand 15 meters back from a low mounted luminaire (top illustration) or 30 meters 

back from a high mounted luminaire, you should remove all of the tree branches below 

the line of sight. 

This will help to ensure that the light from luminaires is not being blocked by the 

branches of adjacent trees. 
Knowledge Check 

Module 4, Slide 15

True or False:

If luminaire poles cannot be positioned on the inside of a curve, they should be located 

outside of the entry overrun areas. 

□ A) True 

□ B) False 

The correct answer is on the next page. 
Knowledge Check Answer 

Module 4, Slide 16

Illustration of lighting on curves. 

The correct answer is True. 

As shown in the illustration from Module 4, Slide 10, lighting should be positioned so as 

not to interfere with the overrun area. 
Lighting for Special Locations 

Module 4, Slide 17

This section discusses lighting for special situations such as intersections, interchanges, 

crosswalks, roundabouts and tunnels.
Lighting Intersections 

Module 4, Slide 18

An example of lighting at a signalized intersection. 

Unlike lighting standards for straight sections of roadways, which are written in terms of 

luminance (candelas per square meter); lighting for intersections is specified in terms of 

illuminance (lux). Lux tells us the amount of light (in lumens) that is falling on the 

roadway surface per a unit area, in this case, per square meter. 

For example, if you measure 30 lux on the roadway surface of an intersection, you have 

30 lumens per square meter on that surface. 
Lighting Intersections (continued) 

Module 4, Slide 19 

Many vehicle-to-vehicle and vehicle-to-pedestrian conflicts occur at intersections, so 

even when the intersecting roadways are not lighted, lighting intersections may be 

warranted. In Module 1 a method for intersection lighting warranting is given. AASHTO 

recommends that signalized intersections always be lighted. High priority may also be 

given to intersection lighting when the busier road at the intersection has the traffic 

volume characteristics shown in the chart below. Designers may also want to consider 

the number of pedestrians or cyclists using the intersection. 
Types of Intersection Lighting 

Module 4, Slide 20

A signalized intersection that should be illuminated with full lighting. 

There are three primary types of lighting system that can be installed along an 

intersection: 

Full lighting: The intersection conflict areas (where the roads overlap) and approaching 

legs of the intersecting roads are illuminated. 

Partial lighting: Only the primary intersection conflict areas are illuminated. 

Beacon or delineation lighting: Only one or two luminaires are provided to demarcate 

the intersection location. 
Full Intersection Lighting 

Module 4, Slide 21

Examples of full intersection lighting layouts. Lighting fixtures are shown in black. 

Full intersection lighting covers an intersection and related areas in a uniform manner 

over the traveled portion of the roadway. It is installed whenever the intersecting roads 

are continuously illuminated, and when the intersection is signalized. As examples, 

typical layouts for intersections with and without a right-turn bypass lane are shown 

above. 
Partial Intersection Lighting 

Module 4, Slide 22

Top: Partial intersection lighting layout for an intersection with a right-turn bypass lane. 

Bottom: Typical partial intersection lighting layout. Lighting fixtures are shown in black.

Partial intersection lighting illuminates key decision areas and conflict points at the 

intersection. As examples, typical layouts for intersections with and without a right-turn 

bypass lane are shown. 
Beacon Lighting for Intersections 

Module 4, Slide 23

 

Examples of beacon lighting at rural intersections. 

Beacon lighting denotes the use of one or two luminaires at an intersection. It is 

sometimes installed at rural intersections, as the accompanying photographs show. 

Beacon lighting helps identify the location of a potential conflict to approaching drivers. 

Lower light output levels are suggested to reduce the potential for glare. 
Knowledge Check 

Module 4, Slide 24

Full lighting at intersections is recommended when: 

□ A) An intersection is unsignalized 

□ B) Whenever the intersecting roads are continuously illuminated 

□ C) The intersection is located in a rural area 

□ D) None of the above 

The correct answer is on the following page. 

 
Knowledge Check Answer 

Module 4, Slide 25

An example of a full intersection lighting layout. 

The correct answer is B. Full lighting at intersections is installed whenever the 

intersecting roads are continuously illuminated. (See Module 4, Slide 21.)
Lighting for Interchanges 

Module 4, Slide 26

 

This section discusses lighting techniques for highway interchanges. 
Interchange Lighting 

Module 4, Slide 27

Examples of types of freeway interchanges. 

Interchanges, where freeways intersect, can be lighted if conditions warrant it. Module 1 

describes the warranting procedure for determining the type of interchange lighting 

needed: 

Complete interchange lighting involves illuminating all roadways in the intersection 

(ramps, approaching legs) with continuous lighting. 

Partial interchange lighting illuminates only the key decision-making locations for road 

users along the interchange (ramp exits/entrances, and service road intersections). 
Interchange Lighting Layouts 

Module 4, Slide 28

 

Examples of partial lighting layouts for interchanges. Lighting fixtures are shown in 

black. 

Typical partial interchange lighting layouts are shown in these diagrams. Only the key 

decision-making locations (merging and diverging points and conflict areas) along the 

interchange are illuminated. 

For complete interchange lighting, all ramps and connecting roads would be illuminated 

using regularly spaced luminaires. 
High Mast Interchange Lighting 

Module 4, Slide 29

 

Left: A photograph of a high mast lighting installation. Right: Illuminance patterns from 

high mast lighting.

Complete interchange lighting can also be provided by a smaller number of high mast 

lighting units. Templates showing illuminance patterns from high mast luminaires can be 

overlaid onto an interchange plan to identify a suitable layout as shown in the illustration 

above and to the right.
Lighting for Crosswalks 

Module 4, Slide 30

An example of a mid-block crosswalk. 

An important purpose of lighting at pedestrian crosswalks is to provide illumination that 

increases the visibility of pedestrians who may be crossing the street, or about to cross 

the street. 

Crashes involving pedestrians on crosswalks are a common cause of road fatalities. 

According to the National Highway Traffic Safety Administration (NHTSA), in 2015, 

nearly 1000 pedestrians died when they were crossing the road at intersections. 

Although there are many reasons for crashes involving pedestrians (speeding, alcohol, 

etc.), inadequate lighting at or adjacent to crosswalks might increase the risk to 

pedestrians crossing the road. The nighttime fatal vehicle/pedestrian crash rate in 

unlighted areas is around three times higher than the daytime rate. 
Lighting for Crosswalks (continued) 

Module 4, Slide 31

An example of a mid-block crosswalk. 

Important considerations for crosswalk lighting include the vertical illumination levels on 

the pedestrians and the contrast between the pedestrians and the background. 

In areas where it is darker at night (less ambient lighting), such as a rural roadway, 

vertical illumination on the pedestrian can potentially be reduced, because there will be 

a good contrast between the pedestrian and the darker background against which they 

are viewed by drivers. However, on a city street, where nighttime ambient light levels 

are much higher, a higher level of vertical illuminance will be needed on pedestrians in 

crosswalks in order to provide equivalent visibility. 

A study, Informational Report on Lighting Design for Midblock Crosswalks, performed 

by the Virginia Tech Transportation Institute found that a vertical illuminance of 20 lux 

(about 2 footcandles) in a crosswalk, measured at 5 feet above the road surface, 

allowed drivers to detect pedestrians at adequate stopping distances under rural 

conditions. Higher vertical light levels, perhaps as much as 40 lux, might be needed for 

urban crosswalks. 
Mid-Block Crosswalk Lighting 

Module 4, Slide 32

Illustration of a recommended lighting layout for a mid-block crosswalk. 

Illustration of vertical illumination on a pedestrian. 

Crosswalks are typically lighted by overhead light fixtures mounted on poles. For midblock crosswalks, it is recommended that lighting be placed on each side of the 

roadway approximately 15 feet in front of the crosswalk in each direction of vehicle 

travel. Placing the light fixtures in this manner provides higher vertical illuminance on 

pedestrians, making them more visible to drivers. 
Intersection Crosswalk Lighting 

Module 4, Slide 33

An illustration of a lighting layout recommended for crosswalks at intersections. 

Lighting recommendations for crosswalks at intersections are similar to mid-block 

crosswalks in that the lighting should be placed 15 feet before the crosswalk in each 

direction of vehicle travel. This layout is shown in the figure above. 
Bollard-Based Crosswalk Lighting 

Module 4, Slide 34

An illustration (left) and computer simulation (right) of a bollard-based crosswalk lighting 

system. The images show pedestrians located throughout the crosswalk in the roadway. 

Another possible way to provide lighting for crosswalks is through the use of bollard 

lights at each end of the crosswalk. A bollard light is a type of outdoor lighting encased 

in a vertical post at ground level. Such a light provides light across an intersection at the 

pedestrian level. This is an excellent means of providing high vertical illumination on 

pedestrians as they cross the street. 

This technique may provide improved visibility for drivers, while using less light. This 

also can be a more economical solution than lighting the crosswalk from overhead light 

sources. 

An additional benefit to the use of bollards is that they act as an architectural elements 

to help direct pedestrian traffic to crosswalks, especially for mid-block applications, and 

for delineating the location of crosswalks to drivers during both daytime and nighttime. 
Bollard-Based Crosswalk Lighting (continued) 

Module 4, Slide 35

A nighttime photograph of a temporary field test of a bollard-based crosswalk lighting 

system. Bollards were placed in the roadway temporarily, only for the field test. These 

bollards would typically be mounted on the sidewalk, adjacent to the roadway, in a 

permanent installation. 

In a study (Demonstrating Urban Outdoor Lighting for Pedestrian Safety and Security) 

conducted by the Lighting Research Center (LRC), a bollard-based lighting system for 

crosswalks was judged to be promising for improving pedestrian safety. 

It was also found to be practical and acceptable by transportation, transit and public 

safety professionals. Bollard-based lighting systems have been field tested in New 

Jersey, New York, and Colorado. 

Optical (and temporal) control can minimize glare from bollard lights. Breakaway design 

(see Module 2) should be incorporated into their installation. 
Knowledge Check 

Module 4, Slide 36

Select the correct answer:

When lighting a mid-block crosswalk from overhead pole-mounted light fixtures, it is 

recommended that: 

□ A) The light poles are placed directly in line with the crosswalk 

□ B) A light pole is placed on one side of the street only 

□ C) Light poles are placed on each side of the street 15 feet in front of the crosswalk 

□ D) The lighting provides less than 10 vertical lux across the crosswalk 

The correct answer is on the next page. 
Knowledge Check Answer 

Module 4, Slide 37

An illustration of mid-block crosswalk lighting. 

The correct answer is C. 

For mid-block crosswalks lighted from overhead, it is recommended that lighting be 

placed on each side of the roadway approximately 15 feet in front of the crosswalk in 

each direction of vehicle travel. (See Module 4, Slide 32)
Roundabout Lighting 

Module 4, Slide 38

 A nighttime view of a typically lighted roundabout. 

For a roundabout to operate satisfactorily, all users—drivers, pedestrians, and cyclists—

must be able to enter, navigate around, and exit the roundabout in a safe and efficient 

manner and pedestrians must be able to safely use crosswalks, during the day and at 

night. 

In its lighting design guide for roundabouts (DG-19-08) the IES (Illuminating Engineering 

Society) provides criteria to address the visibility of the roadway, pedestrians, and 

hazards through a roundabout. This guide uses a combination of horizontal illuminance 

for the roadway areas of the roundabout and vertical illuminance in the crosswalks 

areas. 

The latest edition of the Transportation Research Board's Roundabouts: An 

Informational Guide, reiterates the recommendation of IES DG-19-08. 
Roundabout Lighting (continued) 

Module 4, Slide 39

A computer rendering of recommended roundabout lighting layout. 

Illumination is recommended for all roundabouts, including those in rural environments. 

The geometry of a roundabout makes headlamps ineffective in the detection of people 

or objects in the vehicle’s path. 

Lighting of roundabouts serves two main purposes: 

1. It provides visibility from a distance for drivers approaching the roundabout. 

2. It provides visibility of the key conflict areas to improve drivers’ perception of the 

layout and visibility of other users within the roundabout. 

Lighting located around the perimeter of the roundabout provides better visibility of 

pedestrians and obstructions than lighting located in the center. 

According to IES DG-19-08, approach lighting should be used providing 20 to 40 

vertical lux in crosswalks, if present, at roundabouts. 
Roundabout Lighting (continued) 

Module 4, Slide 40

 

 Recommendations for placement of lighting within a roundabout. Light fixtures are 

shown in red. 

A roundabout may have continuous lighting on the approach roads. This lighting will 

help a driver adapt to the roundabout lighting. Where there is no lighting on the 

approach roads lighting should be added on the approach roads for a distance of 

approximately 80 m from the start of the roundabout. 

The lighting level used in a roundabout should be equivalent to the intersection lighting 

level included in IES RP-8-14, Standard Practice for Roadway Lighting. 
New Approach to Roundabout Lighting 

Module 4, Slide 41

Computer renderings of the Ecoluminance roundabout lighting layout. 

At roundabouts, pedestrian crosswalks appear in non-traditional locations as compared 

to those at intersections, and conventional overhead lighting does not enhance contrast 

of pedestrians. In a field study conducted by the Lighting Research Center, researchers 

installed bollard-based crosswalk lighting in conjunction with landscape and low-level 

overhead lighting. This resulted in a 75% energy use reduction. The bollard lighting 

enhanced visibility of pedestrians, while the landscape lighting helped to direct drivers 

through the roundabout. This design technique is referred to as Ecoluminance due to its 

use of lighting on existing ecological features within and around the roundabout. While 

not yet incorporated into national standards, this approach is being used by several 

transportation agencies. 
Lighting for Tunnels 

Module 4, Slide 42

IES Recommended Practice for Tunnel Lighting. 

Unlike roadways, which are lighted by daylight during the day, tunnels must be lighted 

both during the day and at night. 

The objectives of tunnel lighting are to: 

1. Allow traffic to enter, pass through, and exit the enclosed section of the tunnel 

safely. 

2. Do so without impeding the flow-through of traffic. 

The IES publication RP-22-11, Standard Practice for Tunnel Lighting, provides 

recommendations for the lighting of tunnels. 
Lighting for Tunnels (continued) 

Module 4, Slide 43

The entrance to a lighted tunnel. 

It is important to consider several zones when lighting a tunnel. The lighting for each 

zone will be different to allow drivers to enter the tunnel, adapt to the light levels within 

the tunnel, safely pass through the tunnel, and adapt to the light levels as they exit the 

tunnel. 

Approach Zone: The external roadway area leading to the tunnel. 

Threshold Zone: The interior area near the entrance and exit of the tunnel. 

Transition Zone: The area between the threshold zone and the interior zone. 

Interior Zone: The area within the tunnel where drivers eyes have adapted to the 

interior light levels. This is often the longest stretch of the tunnel. 
Tunnel Lighting Zones 

Module 4, Slide 44

A view of the approach zone to a tunnel. 

Approach Zone: Due to high light levels at the approach to the tunnel during the day, 

the tunnel lighting system must provide enough light to allow drivers to see inside the 

tunnel. If it does not, the tunnel will look like a black hole, which will cause drivers to 

slow down. 

Threshold Zone: A substantial amount of light must be provided in this zone to reach 

an acceptable reduction from the exterior to the interior luminance so that the eye can 

adapt. 

Transition Zone: Light levels are reduced at a rate of no more than 3 to 1 in this zone 

until the interior zone light level is reached. 

Interior Zone: The light levels for this zone will vary based on traffic volume and speed. 
Knowledge Check 

Module 4, Slide 45

Select the correct answer:

To ensure good visibility in a roundabout, is it best to provide lighting along the 

perimeter of the roundabout or lighting from the center of the roundabout? 

□ A) It is best to light the roundabout from the center 

□ B) It is best to light the roundabout from the perimeter 

The correct answer is on the following page. 
Knowledge Check Answer 

Module 4, Slide 46

A rendering of a roundabout lighted from the perimeter. 

The correct answer is B. 

Lighting located around the perimeter of the roundabout provides better visibility of 

pedestrian and obstructions than lighting located in the center. 
Spectral Effects of Lighting at Night 

Module 4, Slide 47

The following section discusses impacts of light source spectral distribution in roadway 

lighting applications. 
Mesopic Vision 

Module 4, Slide 48

An illustration of the different regions of human vision. 

The word mesopic is derived from the Greek word meso which means middle; and the 

English word optic which pertains to vision. So the word literally means “middle 

vision.” 

Mesopic vision describes the changes in the way people see under low light levels, like 

those experienced on most roadways at night. This is the area of vision between near 

total darkness (referred to a scotopic vision) and typical interior light levels (referred to 

as photopic vision). Under scotopic light levels the human eye exclusively uses its rod 

photoreceptors. Under photopic light levels, the cone photoreceptors are dominant. 
Mesopic Vision (continued) 

Module 4, Slide 49

 

On the graph above, the peak wavelength sensitivity of rods (scotopic vision) is shown 

in green. The peak sensitivity of cones (photopic vision) is shown in pink. The mesopic 

region is shown in orange. 

In the middle or mesopic region of vision, the eye relies on both the rod and cone 

photoreceptors to varying degrees. This visual region is dynamic, and changes with light 

level. The lower the light level in the mesopic region the more the rod photoreceptors 

play a role; the higher the light levels in the mesopic region the more the cone 

photoreceptors play a role. 

This is important because the spectral sensitivity of rod and cone photoreceptors are 

different. Rod photoreceptors are more sensitive to shorter wavelengths of light than 

cone photoreceptors. Therefore, as light levels decrease, the visual effectiveness of 

light sources changes. Light sources with more short wavelength content, such as most 

LEDs, become more visually effective than light sources, like high pressure sodium 

(HPS), which have more long wavelength content. 
Mesopic Vision and S/P Ratios 

Module 4, Slide 50

Spectral power distributions and S/P ratios of 2 light sources. The light source with more 

short wavelength energy (LED) has a higher S/P ratio. The SPD curves show the 

relative amount of energy produced by the light source at each wavelength, from short 

visible wavelengths (violet/blue) to long wavelengths (yellow//red). 

The first step in determining the mesopic visual efficacy of a particular light source, is to 

find the scotopic/photopic (S/P) ratio for the source. The S/P ratio provides the relative 

stimulation of the rod photoreceptors in the eye (scotopic vision) for equal photopic light 

levels. In other words, if the light source were to be used to provide very low (scotopic) 

light levels, this ratio would allow you to calculate the visual efficacy of the light source 

at that level. 

As an example, you want to compare two light sources each providing 10,000 lumens. 

These lumens are rated at photopic light levels. 

 The 1st light source has an S/P ratio of 0.5. 

 The 2nd light source has an S/P ratio of 1.5. 

Therefore at scotopic (near dark) light levels: 

 The 1st light source will provide 5,000 scotopic lumens. 

 The 2nd light source will provide 15,000 scotopic lumens. 

S/P ratios for all light sources used for outdoor lighting are available from the 

manufacturer. 
Mesopic Visual Efficacy 

Module 4, Slide 51

This graph shows response times of drivers as a function of unified luminance of the 

targets, including headlamp contributions. 

The S/P ratio allows you to calculate the visual efficacy of a light source at scotopic 

levels. But roadways are not lighted to levels that low. Therefore, you must adjust the 

S/P ratio depending upon the luminance level of the roadway you are designing. This is 

done based on a photometric system called the Unified System of Photometry. This 

system was developed by researchers doing field studies which measured reaction 

times of drivers under light sources of different S/P ratios at night. 

In these studies researchers compared drivers’ responses to a target located at the side 

of the road. This was done both under high pressure sodium (HPS) and metal halide 

(MH) light sources. HPS has a much lower S/P ratio than MH. For both acceleration 

and braking, drivers’ performance under MH at 5 lux was equivalent to their 

performance under HPS at 9 lux. This showed that MH, with the higher S/P ratio, was 

40% more visually effective than the HPS. 

Most LED sources will also have higher S/P ratios compared to HPS. 

 
Unified System of Photometry 

Module 4, Slide 52

The chart above, taken from the Outdoor Lighting: Visual Efficacy publication shown on 

the next page, compares the relative mesopic visual efficacy of HPS (the row denoted 

by S/P=0.65) with LED (the row denoted by S/P=2.05) for local residential roads 

(average luminance=0.3 cd/m2). 

The Unified System of Photometry is generally used to determine the visual 

effectiveness of a new or replacement light source, to an existing light source, for 

example, to compare an LED to an HPS you are replacing. 

If you know you want to provide the same visual effectiveness of an HPS light source 

(S/P 0.65) at a luminance of 0.3 cd/m2, with an LED light source (S/P 2.05), you first find 

the mesopic level for HPS under the 0.3 cd/m2 column for its S/P ratio. You then go to 

the S/P ratio of LED (S/P 2.05), and find approximately the same mesopic level. The 

column in which you find this level determines the luminance level to which you should 

design to provide the same visual effectiveness of the HPS light source at 0.3 cd/m2. In 

the case shown on the chart at right, you know you can design to a luminance of 0.2 

cd/m2 using the LED and your installation will provide the visual effectiveness of the 

HPS at a luminance of 0.3 cd/m2. 
Unified System of Photometry (continued) 

Module 4, Slide 53

A guide to using the Unified System of Photometry. 

A guide to using the Unified System of Photometry including the charts used to find 

luminance equivalents of light sources with a wide variety of S/P ratios is available 

online at the following link: 

http://www.lrc.rpi.edu/programs/solidstate/assist/pdf/AR-VisualEfficacy-Jan2009.pdf

The Unified System of Photometry more accurately characterizes different light sources 

at any light level, facilitating the specification of effective lighting systems for different 

applications, including those used outdoors at night. 
Brightness Perception 

Module 4, Slide 54

A graph showing the spectral sensitivity of the human eye for brightness at night [VB2()] 

in orange, as compared to the photopic spectral sensitivity curve [V()], shown in black. 

Similarly to the way that the sensitivity of the human visual system to the spectral 

wavelengths of light changes as light levels vary at night, our eyes also perceive 

brightness differently from the photopic spectral sensitivity curve used to determine the 

lumen output of a light source. 

As shown on the graph at right, the response of our eye to brightness (shown by the 

curve in orange on the graph) is significantly different than the photopic visual sensitivity 

curve (shown in black). 

This mean that light sources that provide more spectral power under the orange curve, 

such as many LEDs, will appear brighter than their lumen output would predict. 
Brightness Perception and Sense of Security 

Module 4, Slide 55

Graphs showing the spectral power distributions of HPS (top) and LED (bottom) light 

sources with installation pictures. 

Research has shown that when people perceive an outdoor area, such as a parking lot 

or street, to be brighter at night, their sense of personal safety and security improves. 

Therefore, if one of the objectives of a lighting installation is to make people feel safe in 

an area at night, using the spectral sensitivity curve for brightness will help you to 

achieve this objective. 

Based on the spectral sensitivity of the eye for brightness perception, the illuminance 

from an LED light source would only need to produce 54 percent of the illuminance from 

an HPS source to appear equally bright. 
Summary 

Module 4, Slide 56

 

An HPS installation (left); a white light source installation (right). 

When nighttime visibility and brightness (safety/security perception) is important, 

existing “white” light sources provide equivalent (or better) performance with ~30%-40% 

less energy than sources such as HPS. 

The spectra of LED sources can be selected to provide the visual response you wish to 

achieve. 
Circadian Impacts of Roadway Lighting 

Module 4, Slide 57

Graph showing the suppression of the hormone melatonin by light sources of various 

CCTs. Melatonin suppression is a measure of the degree to which each light source can 

disrupt the normal functioning of the human circadian system. 

There have recently been some concerns expressed about the negative impacts that 

outdoor lighting, especially from LEDs, might have on people’s health. The concern is 

that outdoor lighting may disrupt the body’s biological clock, referred to as the body’s 

circadian system. Disruption of this system has been shown to have several negative 

impacts on a person’s health. 

Some organizations have recommended that roadway lighting designers select light 

sources with lower correlated color temperatures (CCTs) to help prevent this disruption. 

However CCT is not a good measure of the spectral output of a light source or its 

impact on the human circadian system. As shown on the graph at the right, a light 

source with a lower CCT (e.g., 3000 K) may actually have more of a disruptive impact 

on the circadian system than a light source with a higher CCT (e.g., 4100 K). Therefore 

CCT is not a good measure to use for this purpose. 
Circadian Impacts of Roadway Lighting (continued) 

Module 4, Slide 58

In order for light to impact our circadian system, the light needs to be at a relatively high 

level, and we need to be exposed to it for a significant period of time. In general, 

magnitudes of street lighting are too low to have substantial impacts on circadian 

rhythms in the general population. 

This is still an area where research is ongoing; however, at this time negative impacts 

on the human circadian system should probably not be a concern in the design and 

specification of roadway lighting. 

This however does not mean that lights should not be shielded or controlled in order to 

avoid light trespass or glare. 
Self-Assessment Quiz 

Module 4, Slides 59 to 69

Please answer each question. 

1. Lighting poles placed on the roadside of interstate highways should be breakaway 

and located at least ____ from the lane edge. 

□ A) 15 feet 

□ B) 10 meters 

□ C) The same distance as the mounting height of the luminaire 

□ D) 3 feet 

2. When a roadway or pedestrian lighting project includes new or existing trees in close 

proximity to the lighting, an additional light loss factor of _____ should be included in the 

design to accommodate light loss due to shading. 

□ A) an amount equal to the target illuminance on the pavement 

□ B) 50 percent 

□ C) 10 to 20 percent 

□ D) An amount equal to the mounting height of the luminaire 

3. Full intersection lighting should be installed whenever the intersecting roads are not 

illuminated. 

□ A) True 

□ B) False 

4. When specifying partial lighting for a freeway interchange ____________ should be 

lighted. 

□ A) all of the ramps 

□ B) the key decision-making locations along the interchange 

□ C) only the connecting roads 

□ D) only the entrance and exit points 

5. For mid-block crosswalks, it is recommended that lighting be placed on each side of 

the roadway approximately 15 feet in front of the crosswalk. 

□ A) True 

□ B) False 

6. Lighting located ________ of a roundabout provides better visibility of pedestrian and 

other vehicles. 

□ A) in the center 

□ B) at entry and exit points 

□ C) at the approach 

□ D) around the perimeter 
7. In the transition zone of tunnel lighting, light levels are reduced at a rate of no more 

than ______ until the interior zone light level is reached. 

□ A) 3 to 1 

□ B) 5 to 1 

□ C) 10 to 1 

8. Scotopic vision describes the way people see under typical daytime light levels. 

□ A) True 

□ B) False 

9. Correlated Color Temperature (CCT) is a good measure of the impact a light source 

will have on peoples’ circadian systems. 

□ A) True 

□ B) False 

See the following page for the answer key to this self-assessment. 
Self-Assessment Quiz Answer Key 

Module 4, Slides 59 to 69

The correct answers for the self-assessment are provided below. 

1. Lighting poles placed on the roadside of interstate highways should be breakaway 

and located at least ____ from the lane edge. 

 A) 15 feet (see Module 4, Slide 9) 

□ B) 10 meters 

□ C) The same distance as the mounting height of the luminaire 

□ D) 3 feet 

2. When a roadway or pedestrian lighting project includes new or existing trees in close 

proximity to the lighting, an additional light loss factor of _____ should be included in the 

design to accommodate light loss due to shading. 

□ A) an amount equal to the target illuminance on the pavement 

□ B) 50 percent 

 C) 10 to 20 percent (Module 4, Slide 13) 

□ D) An amount equal to the mounting height of the luminaire 

3. Full intersection lighting should be installed whenever the intersecting roads are not 

illuminated. 

□ A) True 

 B) False (Module 4, Slide 21) 

4. When specifying partial lighting for a freeway interchange ____________ should be 

lighted. 

□ A) all of the ramps 

 B) the key decision-making locations along the interchange (Module 4, Slide 28) 

□ C) only the connecting roads 

□ D) only the entrance and exit points 

5. For mid-block crosswalks, it is recommended that lighting be placed on each side of 

the roadway approximately 15 feet in front of the crosswalk. 

 A) True (Module 4, Slide 32) 

□ B) False 

6. Lighting located ________ of a roundabout provides better visibility of pedestrian and 

other vehicles. 

□ A) in the center 

□ B) at entry and exit points 

□ C) at the approach 

 D) around the perimeter (Module 4, Slide 39) 
7. In the transition zone of tunnel lighting, light levels are reduced at a rate of no more 

than ______ until the interior zone light level is reached. 

 A) 3 to 1 (Module 4, Slide 44) 

□ B) 5 to 1 

□ C) 10 to 1 

8. Scotopic vision describes the way people see under typical daytime light levels. 

□ A) True 

 B) False (Module 4, Slide 48) 

9. Correlated Color Temperature (CCT) is a good measure of the impact a light source 

will have on peoples’ circadian systems. 

□ A) True 

 B) False (Module 4, Slide 57) 
Extended Example Problem

For the intersection shown below, circle the luminaires (shown in black) that should be 

used to ensure that pedestrians in the crosswalks will be visible. 

See the following page for the answer to this extended example problem.
Extended Example Problem (Answer Key)

For the intersection shown below, the circled luminaires would likely be used to ensure 

that pedestrians are visible to oncoming drivers. 
References and Other Resources 

Module 4, Slide 70 

Roundabouts: An Informational Guide, 2nd Edition

http://www.trb.org/publications/blurbs/164407.aspx

AASHTO Roadside Design Guide 

https://bookstore.transportation.org/collection_detail.aspx?ID=105

Informational Report on Lighting Design for Midblock Crosswalks 

https://www.fhwa.dot.gov/publications/research/safety/08053

IES Design Guide for Roundabouts, DG-19-08 

https://www.ies.org/store/design-guides/roundabout-lighting/ 

IES Standard Practice for Tunnel Lighting, RP-22-11 

https://www.ies.org/store/recommended-practices-and-ansi-standards/tunnel-lighting/

ASSIST Recommends: Outdoor Lighting – Visual Efficacy 

http://www.lrc.rpi.edu/programs/solidstate/assist/pdf/AR-VisualEfficacy-Jan2009.pdf

Mesopic Street Lighting Demonstration and Final Report 

http://www.lrc.rpi.edu/researchAreas/pdf/GrotonFinalReport.pdf

FHWA 2012 Lighting Handbook 

https://safety.fhwa.dot.gov/roadway_dept/night_visib/lighting_handbook 

Trees, Lighting and Safety in Context-Sensitive Solutions 

http://dx.doi.org/10.3141/2120-11 

Demonstrating Urban Outdoor Lighting for Pedestrian Safety and Security 

http://www.utrc2.org/sites/default/files/Final-Report-Demonstrating-Urban-OutdoorLighting-Pedestrian-Safety.pdf
Credits 

Module 4, Slide 72

Slide 6: Photograph courtesy of Virginia Tech Transportation Institute, WSP Global Inc., 

and DMD & Associates Ltd. 

Slide 9: Image courtesy of Texas Department of Transportation. 

Slide 12: Image courtesy of Virginia Tech Transportation Institute, WSP Global Inc., and 

DMD & Associates Ltd. 

Slide 14: Image courtesy of Virginia Tech Transportation Institute, WSP Global Inc., and 

DMD & Associates Ltd. 

Slide 38: Photograph courtesy of Virginia Tech Transportation Institute, WSP Global 

Inc., and DMD & Associates Ltd. 

Slide 39: Image courtesy of Virginia Tech Transportation Institute, WSP Global Inc., and 

DMD & Associates Ltd. 

Slide 40: Image courtesy of Virginia Tech Transportation Institute, WSP Global Inc., and 

DMD & Associates Ltd. 

Slide 43: Photograph courtesy of Virginia Tech Transportation Institute, WSP Global 

Inc., and DMD & Associates Ltd. 

Slide 44: Photograph courtesy of Virginia Tech Transportation Institute, WSP Global 

Inc., and DMD & Associates Ltd. 

Slide 46: Image courtesy of Virginia Tech Transportation Institute, WSP Global Inc., and 

DMD & Associates Ltd. 

All other images taken from U.S. Government publications or are released to the public 

domain by the module authors.