Guidelines for the Implementation of

Reduced Lighting on Roadways 

PUBLICATION NO. FHWA-HRT-14-050 JUNE 2014

Research, Development, and Technology

Turner-Fairbank Highway Research Center

6300 Georgetown Pike

McLean, VA 22101-2296
FOREWORD

The Federal Highway Administration’s Office of Safety Research and Development serves the 

highway safety community by conducting research that advances safety goals while 

accommodating practical considerations. The development of methodologies and tools that result 

from this research can assist practitioners who are looking to make safety-based decisions in the 

real world. The guidelines presented in this report address the need to maintain the safety effects 

of roadway lighting while alleviating the budgetary strains associated with the maintenance of 

the lighting infrastructure. 

This report establishes a new set of criteria for practitioners to apply to their roadway 

environment that will identify appropriate lighting levels for given roadway characteristics and 

usage. Specifically, these guidelines identify the appropriate applications of adaptive lighting on 

roadways while maintaining the optimal level of safety. The methodology for applying the 

criteria is based on existing international standards that accommodate different roadway 

characteristics and usage. Therefore, practitioners will be familiar with the application of the 

results but will benefit from an enhanced data collection and statistical approaches when 

considering adaptive lighting applications.

The adaptive lighting criteria identified in this report are the first to utilize real-world lighting 

data collection and robust statistical analysis of crash histories of the associated roadways. 

Ultimately, these Guidelines will provide practitioners with the evidence-based criteria they need 

to determine the appropriate application of adaptive lighting systems in their jurisdictions. This 

allows for the unique opportunity to provide significant cost savings while maintaining the 

optimal level of safety for roadway users.

Monique R. Evans

Director, Office of Safety

Research and Development

Notice

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

in the interest of information exchange. The U.S. Government assumes no liability for the use of 

the information contained in this document. This report does not constitute a standard, 

specification, or 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.

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. 
TECHNICAL REPORT DOCUMENTATION PAGE

1. Report No.

FHWA-HRT-14-050

2. Government Accession No. 3. Recipient’s Catalog No.

4. Title and Subtitle

Guidelines for the Implementation of Reduced Lighting on 

Roadways

5. Report Date

June 2014

6. Performing Organization Code: 

7. Author(s)

Ronald Gibbons, Feng Guo, Alejandra Medina, Travis 

Terry, Jianhe Du, Paul Lutkevich, David Corkum, and Peter 

Vetere

8. Performing Organization Report No. 

9. Performing Organization Name and Address

Virginia Tech Transportation Institute

3500 Transportation Research Plaza (0536)

Blacksburg, VA 24061

10. Work Unit No.

11. Contract or Grant No.

DTFH61-13-D-00018

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

Final Report

14. Sponsoring Agency Code

15. Supplementary Notes

16. Abstract

This report provides guidelines for the implementation of an adaptive lighting system for roadway lighting. 

Based on the analysis of crashes and lighting performance, a series of criteria and the associated design levels 

have been developed to provide an approach for light level selection and the adjustability of the light level based 

on the needs of the driving environment. The application, the technology needs, the benefit cost, and the legal 

implications of adaptive lighting are also considered in this guideline document.

17. Key Words

Street Lighting, Adaptive Lighting, Energy 

Savings, Reduced Light Levels

18. Distribution Statement

No restrictions. This document is available through the 

National Technical Information Service; Springfield, VA 

22161.

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

42

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed pages authorized
ii

SI* (MODERN METRIC) CONVERSION FACTORS 

APPROXIMATE CONVERSIONS TO SI UNITS

Symbol When You Know Multiply By To Find Symbol 

LENGTH

in inches 25.4 millimeters mm 

ft feet 0.305 meters m 

yd yards 0.914 meters m 

mi miles 1.61 kilometers km 

AREA 

in2square inches 645.2 square millimeters mm2

ft2 square feet 0.093 square meters m

2

yd2 square yard 0.836 square meters m

2

ac acres 0.405 hectares ha

mi2square miles 2.59 square kilometers km2

VOLUME 

fl oz fluid ounces 29.57 milliliters mL 

gal gallons 3.785 liters L 

ft3 cubic feet 0.028 cubic meters m

3 

yd3 cubic yards 0.765 cubic meters m

3 

NOTE: volumes greater than 1000 L shall be shown in m3

MASS 

oz ounces 28.35 grams g

lb pounds 0.454 kilograms kg

T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t") 

TEMPERATURE (exact degrees) 

o

F Fahrenheit 5 (F-32)/9 Celsius oC 

or (F-32)/1.8 

ILLUMINATION 

fc foot-candles 10.76 lux lx

fl foot-Lamberts 3.426 candela/m2 cd/m2

FORCE and PRESSURE or STRESS 

lbf poundforce 4.45 newtons N 

lbf/in2poundforce per square inch 6.89 kilopascals kPa 

APPROXIMATE CONVERSIONS FROM SI UNITS 

Symbol When You Know Multiply By To Find Symbol 

LENGTH

mm millimeters 0.039 inches in 

m meters 3.28 feet ft 

m meters 1.09 yards yd 

km kilometers 0.621 miles mi 

AREA 

mm2square millimeters 0.0016 square inches in2 

m

2

square meters 10.764 square feet ft2 

m

2

square meters 1.195 square yards yd2 

ha hectares 2.47 acres ac

km2 square kilometers 0.386 square miles mi2 

VOLUME 

mL milliliters 0.034 fluid ounces fl oz 

L liters 0.264 gallons gal 

m

3 cubic meters 35.314 cubic feet ft3 

m

3 cubic meters 1.307 cubic yards yd3 

MASS 

g grams 0.035 ounces oz

kg kilograms 2.202 pounds lb

Mg (or "t") megagrams (or "metric ton") 1.103 short tons (2000 lb) T 

TEMPERATURE (exact degrees)

oC Celsius 1.8C+32 Fahrenheit o

F 

ILLUMINATION 

lx lux 0.0929 foot-candles fc 

cd/m2candela/m

2

0.2919 foot-Lamberts fl

FORCE and PRESSURE or STRESS 

N newtons 0.225 poundforce lbf 

kPa kilopascals 0.145 poundforce per square inch lbf/in2

*SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. 

(Revised March 2003)
iii

TABLE OF CONTENTS

INTRODUCTION......................................................................................................................... 1

PURPOSE OF THIS DOCUMENT........................................................................................ 1

ADAPTIVE LIGHTING PHILOSOPHY .............................................................................. 1

POTENTIAL BENEFITS OF ADAPTIVE LIGHTING...................................................... 2

ADAPTIVE LIGHTING SYSTEMS REQUIREMENTS .................................................... 2

CURRENT ROADWAY AND ADAPTIVE LIGHTING RECOMMENDATIONS......... 4

CHAPTER 1. ROADWAY LIGHTING LEVEL SELECTION.............................................. 7

PARAMETERS....................................................................................................................... 10

Speed..................................................................................................................................... 10

Traffic Volume...................................................................................................................... 10

Median .................................................................................................................................. 12

Intersection/Interchange Density .......................................................................................... 12

Ambient Luminance.............................................................................................................. 12

LZ0: No Ambient Lighting ................................................................................................ 12

LZ1: Low Ambient Lighting.............................................................................................. 13

LZ2: Moderate Ambient Lighting ..................................................................................... 13

LZ3: Moderately High Ambient Lighting ......................................................................... 13

LZ4: High Ambient Lighting............................................................................................. 13

Guidance ............................................................................................................................... 13

Pedestrian/Bicycle Interaction .............................................................................................. 13

Parked Vehicles .................................................................................................................... 13

Facial Recognition ................................................................................................................ 14

Conflict Areas....................................................................................................................... 15

DESIGN CRITERIA AND LUMINANCE SELECTION.................................................. 15

Design Criteria for Roadways (H-Class).............................................................................. 16

Design Criteria for Streets (S-Class)..................................................................................... 17

Design Criteria for Residential/Pedestrian Areas (P-Class) ................................................. 18

EXAMPLE OF LIGHTING DESIGN CRITERIA SELECTION..................................... 19

CHAPTER 2. ADAPTIVE LIGHTING APPLICATION ...................................................... 21

WHERE TO ADAPT LIGHTING........................................................................................ 21

WHEN TO ADAPT LIGHTING........................................................................................... 21

CHAPTER 3. LEGAL IMPLICATIONS OF ADAPTIVE LIGHTING............................... 23

JUSTIFICATION OF AGENCY DECISION...................................................................... 23

TORT LIABILITY OF AGENCY OR ENGINEER........................................................... 24

SOVEREIGN IMMUNITY.................................................................................................... 24

CHAPTER 4. COST BENEFIT ANALYSES OF ADAPTIVE LIGHTING........................ 27

FIRST STEP: QUANTIFY COSTS...................................................................................... 27

SECOND STEP: TABULATE THE COSTS....................................................................... 27

THIRD STEP: CONVERT COSTS TO PRESENT VALUE............................................. 28

CHAPTER 5. SUMMARY......................................................................................................... 31

ACKNOWLEDGEMENTS ....................................................................................................... 33

REFERENCES............................................................................................................................ 35
iv

LIST OF FIGURES

Figure 1. Illustration. General structure of a lighting control system............................................. 3

Figure 2. Photo. Roadway lighting ................................................................................................. 8

Figure 3. Photo. Street lighting....................................................................................................... 8

Figure 4. Photo. Residential/pedestrian area lighting ..................................................................... 9

Figure 5. Equation. Lighting class.................................................................................................. 9

Figure 6. Photo. Facial recognition under low lighting ................................................................ 14

Figure 7. Photo. Facial recognition under high lighting ............................................................... 15

Figure 8. Graph. Example system costs by year for standard and adaptive lighting systems...... 28

Figure 9. Equation. Present value ................................................................................................. 28

Figure 10. Graph. Example NPV for standard and adaptive lighting systems ............................. 29

LIST OF TABLES

Table 1. Street lighting levels from IESNA RP-8........................................................................... 5

Table 2. IESNA RP-8 street lighting levels for high-volume pedestrian areas.............................. 5

Table 3. IESNA RP-8 street lighting levels for medium-pedestrian areas..................................... 6

Table 4. IESNA RP-8 street lighting levels for low-pedestrian areas ............................................ 6

Table 5. Assumptions made for the LOS calculation ................................................................... 11

Table 6. Threshold traffic volume based on LOS......................................................................... 11

Table 7. Hourly traffic flow criteria for roadways........................................................................ 11

Table 8. Hourly traffic flow criteria for streets............................................................................. 12

Table 9. Hourly traffic flow criteria for residential/pedestrian roads........................................... 12

Table 10. Roadway design level selection criteria........................................................................ 16

Table 11. H-class lighting design levels....................................................................................... 16

Table 12. Street design level selection criteria ............................................................................. 17

Table 13. S-class lighting design levels........................................................................................ 17

Table 14. Residential/pedestrian design level selection criteria ................................................... 18

Table 15. P-class lighting design levels (E = illuminance)........................................................... 18

Table 16. Example lighting level selection process for a roadway facility .................................. 19

Table 17. Example lighting level selection process for a street facility ....................................... 20

Table 18. Example cost information for an adaptive lighting system .......................................... 28

Table 19. Cash flow comparison for an adaptive lighting system................................................ 29
v

LIST OF ABBREVIATIONS AND SYMBOLS

AASHTO American Association of State Highway and Transportation Officials

ADT average daily traffic

CIE Commission Internationale de L’Eclairage (International Commission on 

Illumination)

FAA Federal Aviation Administration

FTCA Federal Tort Claims Act

IESNA Illuminating Engineering Society of North America

ILE Institute of Lighting Engineers

ITS intelligent transportation system

LCC lifecycle cost

LOS level of service

LZ Lighting Zone

mcd/m2lx millicandela/meter squared lux

NPV net present value

RP-8 Recommended Practice for Roadway Lighting

TAC Transportation Association of Canada

vph vehicles per h

1

INTRODUCTION

The impact of road lighting has been well documented, and its implementation is 

overwhelmingly regarded as positive; both drivers and pedestrians recognize the safety of being 

able to detect potential hazards at night. During the energy crisis in the 1970s, which affected

metropolitan and rural areas, the removal of roadway lighting was hotly debated. Several studies 

conducted during this time assessed the impact of the presence or absence of roadway lighting. 

Other studies anticipated the installation of lighting along highways and evaluated the beforeand-after effects of the lights. The results of these studies were not surprising: the presence of 

roadway lighting makes roads generally safer, while the removal of lighting decreases safety.

However, energy concerns continue to loom today, and the expenses associated with roadway 

lighting are typically a significant component of a transportation agency budget. New lighting 

and control technologies provide the ability to adapt the output of lighting systems based on 

road-user needs. Adaptive lighting allows lighting to be turned off or reduced when few or no 

vehicles or pedestrians are using the roadway; lighting can then be turned on or increased when 

needed. This process allows a reduction in the amount of energy consumed by lighting while 

maintaining the current level of safety that lighting provides to roadway users. 

Current guidelines for roadway lighting already allow some adaptability. The Illuminating 

Engineering Society of North America (IESNA) Recommended Practice for Roadway Lighting 

(RP-8) defines the lighting level in terms of roadway type and potential for pedestrian 

interaction.(1)The Commission Internationale de L’Eclairage (CIE) provides a roadway lighting 

selection guide based on the characteristics of the roadway.

(2) These two guidelines have been 

reviewed and are incorporated into the requirements defined as part of this document.

PURPOSE OF THIS DOCUMENT

These Guidelines for the Implementation of Reduced Lighting on Roadways provide a process by 

which an agency or a lighting designer can select the required lighting level for a road or street

and implement adaptive lighting for a lighting installation or lighting retrofit. This document 

supplements existing lighting guidelines. It is expected that the reader has knowledge of lighting 

design and the issues associated with the implementation of roadway lighting.

ADAPTIVE LIGHTING PHILOSOPHY

The objective of adaptive lighting is to use lighting only when it is required and at the

appropriate level to provide for the safety of roadway users. Streets and roads are often

overlighted, meaning that more light is used than the road users require. The reasons are 

threefold:

 The output from a luminaire is quantized based on the wattage of the light source. As a 

result, the minimum-wattage criterion for a light source design may cause the luminaire 

to produce more light than the application requires.

 Lighting designs are intended to maintain given levels of illumination. During the design

process, lighting levels are calculated to account for depreciation factors such as dirt and 

age. Consequently, a new installation provides greater illumination than is needed based 
2

on the design criteria. As the system ages, the output will fall off until it reaches the 

design value. This could take a significant amount of time.

 Roadway lighting design levels are selected based on worst-case scenarios. The current 

method for selecting a lighting design level uses the maximum requirements for the 

roadway. For example, in a retail district, the lighting level is selected and designed for

times when there are high pedestrian volumes. Without an adaptive system, the lighting 

level remains the same even after the retail activities have closed for the night.

The philosophy behind adaptive lighting is to provide lighting only when and where it is needed,

essentially managing the roadway lighting level as an asset. The light level on a roadway can be 

managed and controlled in two ways.

The first approach is to reduce the light output from the luminaire to the level required by the 

lighting design. This approach, typically referred to as “right sizing,” avoids the output 

quantization problem by selecting a light source of appropriate size for the application. It is 

noteworthy that a right-sizing application typically includes a light level monitoring system to 

provide feedback for the control of the luminaire. This approach mitigates some of the 

maintenance issues by monitoring the light output over time and responding to deprecations in 

luminaire performance from dirt or lamp depreciation. 

The second method is to adjust the light level based on current road conditions, which may 

include use of criteria such as traffic volume, vehicle mix, pedestrian activity, and weather. This 

document provides guidance on how to implement an adaptive lighting design, because it is 

more responsive to roadway user needs and provides greater efficiencies for the system owner/

operator. 

POTENTIAL BENEFITS OF ADAPTIVE LIGHTING

The obvious and primary benefit of adaptive lighting is the reduction of energy use, which has 

been shown to be between 20 and 40 percent with adaptive lighting.

(3)

The other potential 

benefits of adaptive lighting are reductions in the following:

 Maintenance costs.

 Lamp and driver replacement cost as a result of extended luminaire performance.

 Traffic and travel interruptions due to maintenance operations.

 Possibility of tort issues resulting from system maintenance issues.

 Over-lighting.

 Light trespass.

 Skyglow.

 Glare from roadway lighting installations.

ADAPTIVE LIGHTING SYSTEMS REQUIREMENTS

For an adaptive lighting solution to produce a financial benefit, the lighting system must have the 

following components:
3

 Control system, either central or localized on each luminaire.

 Dimmable-controls-ready luminaire.

 Localized metering or a negotiated adaptive lighting electricity rate.

The control systems are the primary component of the adaptive lighting methodology and are 

generally monitored and managed from a central location. A general outline of a lighting control 

system is shown in figure 1. Here, each individual luminaire is controlled from a central hub. 

Generally, each luminaire has an addressable control module that turns the luminaire on and off 

and manages any dimming requirements. This module communicates to a node controller that 

may manage as many as 2,000 or more luminaires. The node controllers then communicate with 

a central management system. The method of communication can be wired, via a power line 

carrier, or wireless. Wireless communication is a popular method, particularly for retrofits, 

because it does not rely on a formal network but can be created using self-healing mesh network 

techniques. Other sensors, such as weather detectors and ambient light monitors, may also be 

linked into the system to provide additional data for lighting management. This approach to 

lighting management falls under the general description of Electrical and Lighting Management 

Systems, and the National Transportation Communications for Intelligent Transportation System

Protocol 1213 has been developed to provide commonality among the control systems.

(4) It is 

also important to note that these systems may be part of the intelligent transportation system 

(ITS) of an agency and may need to comply with Federal requirements found in 23 Code of 

Federal Regulations 940.

Figure 1. Illustration. General structure of a lighting control system.

The second aspect of the adaptive system is the luminaire itself. The luminaire must be able to 

respond to the output of the control system and provide dimming. Dimming is the recommended 

method for adaptive lighting. In the past, reduced lighting on roadways has been accomplished 

through switching or “half-code” lighting, in which every other luminaire or the luminaires on 

Lighting Management System

Luminaire 

Node Controller

Luminaire Node 

Controller

Luminaire Node 

Controller

Interface

Individual 

Luminaire

Individual 

Luminaire

Ambient 

Condition 

Sensor
4

one side of the roadway are turned off or removed. It is not possible to meet all of the existing 

design criteria for uniformity and glare control using half-code lighting scenarios. By contrast, 

dimming a luminaire allows the light level to be adjusted without upsetting the other design 

criteria. Dimming luminaires are typically capable of dimming from 100-percent output to 

anywhere between 50 and 10 percent of maximum output, depending on the light source 

technology. A controls-ready luminaire is one that is typically equipped with a driver that can be

dimmed through a standard controller connection. The typical dimming control for a luminaire is 

a 0–10-volt control input that adjusts the light output based on the input voltage. Recently 

developed technologies can provide dimming and luminaire control to the individual luminaire 

via a module attached through the photo-control receptacle on the luminaire.

The final component of the adaptive system involves negotiation with the electrical utility. Most 

lighting systems are either owned by the electrical utility or are charged at a flat rate to the 

roadway agency when connected to an unmetered source such as the utility secondary feeders. 

To reap the financial benefits of an adaptive lighting system, the roadway agency must negotiate 

with the utility for a reduced rate or a rate based on metering of the electrical usage by the 

lighting system. Some control systems provide utility-grade metering that can be used for this 

purpose. However, it is vital that this aspect of the adaptive lighting system be negotiated before 

the system is implemented.

CURRENT ROADWAY AND ADAPTIVE LIGHTING RECOMMENDATIONS

Several methods of classifying roadways and recommended lighting performance are available 

throughout the world. In addition to the IESNA, examples include the Transportation 

Association of Canada (TAC), the Institute of Lighting Engineers (ILE) in the United Kingdom, 

and the CIE. 

The typical method for selecting a lighting level has been to first choose the road classification 

and then the potential for conflict. The IESNA RP-8 provides tables for this methodology of 

light-level selection; TAC has a similar system and levels. However, the applicability of this 

method to adaptive lighting on high-speed roads is limited, because the criteria that establish the 

potential for conflict do not change with time of day. 

For street lighting, however, IESNA RP-8 uses peak hour pedestrian counts as the criterion for 

potential conflict. A volume greater than 100 pedestrians is classified as high, a volume between 

10 and 100 pedestrians is classified as medium, and a volume of 10 or fewer pedestrians is

classified as low. Table 1 shows IESNA RP-8 recommended lighting values for various street 

classifications based on these pedestrian volumes.
5

Table 1. Street lighting levels from IESNA RP-8.

Road and Area Classification

Average

Luminance

Lavg

(cd/m2)

Maximum

Uniformity

Ratio

Lavg/Lmin

Maximum

Uniformity

Ratio

Lmax/Lmin

Maximum

Veiling

Luminance

Ratio

Road Lvmax/Lavg

Pedestrian

Area Classification

Major

High 1.2 3.0 5.0 0.3

Medium 0.9 3.0 5.0 0.3

Low 0.6 3.5 6.0 0.3

Collector

High 0.8 3.0 5.0 0.4

Medium 0.6 3.5 6.0 0.4

Low 0.4 4.0 8.0 0.4

Local

High 0.6 6.0 10.0 0.4

Medium 0.5 6.0 10.0 0.4

Low 0.3 6.0 10.0 0.4

The recommended light level for a collector road with high pedestrian volumes is 0.8 cd/m2. If 

pedestrian volumes fall into a lower category during certain times at night, the overall 

classification of the street can change. Assuming the pedestrian volumes declined to less than 

10 pedestrians per h, the lighting level on the roadway could be reduced to 0.4 cd/m2using the 

existing IES RP-8 recommendations. 

The lighting values in the American Association of State Highway and Transportation Officials 

(AASHTO) Roadway Lighting Design Guide are essentially the same as those in IESNA RP-8.(5)

Instead of using pedestrian volumes as a subcategory for selecting a light level, the AASHTO 

guide uses the land use groups of commercial, intermediate, and residential. These land use 

categories were substituted for the pedestrian volume values of IESNA RP-8, but the values were 

all derived from the same initial recommended values. Changing the land use category used in 

the AASHTO guide would be the same as changing the expected pedestrian volume used in 

IESNA RP-8. Because the land use category does not change with time of day, it is difficult to 

use the AASHTO guide as a basis for adaptive lighting recommendations.

IESNA RP-8 also includes a pedestrian-volume-based criterion for the sidewalk areas adjacent to 

the roadways. Table 2 through table 4 show the lighting levels for streets with high, medium, and 

low pedestrian usage.

Table 2. IESNA RP-8 street lighting levels for high-volume pedestrian areas.

Maintained Illuminance Values for Walkways

Units Eavg (lux/fc) EVmin (lux/fc) Eavg/Emin

Mixed Vehicle and Pedestrian 20.0/2.0 10.0/1.0 4.0

Pedestrian Only 10.0/1.0 5.0/0.5 4.0
6

Table 3. IESNA RP-8 street lighting levels for medium-pedestrian areas.

Maintained Illuminance Values for Walkways

Units Eavg (lux/fc) EVmin (lux/fc) Eavg/Emin

Pedestrian Areas 5.0/0.5 2.0/0.2 4.0

Table 4. IESNA RP-8 street lighting levels for low-pedestrian areas.

Maintained Illuminance Values for Walkways

Units Eavg (lux/fc) EVmin (lux/fc) Eavg/Emin

Rural/Semi-Rural Areas 2.0/0.2 0.6/0.06 10.0

Low-Density Residential

(2 or fewer dwelling units per acre) 3.0/0.3 0.8/0.08 6.0

Medium-Density Residential

(2.1 to 6.0 dwelling units per acre) 4.0/0.4 1.0/0.1 4.0

Adaptive lighting techniques can also be applied to these recommendations, reducing both the 

horizontal and vertical illuminance values for the sidewalk based on expected pedestrian 

volumes. This method of determining lighting levels to be applied in adaptive technology is 

somewhat useful, but it is limited by its simplistic classification of roadways and street types.
7

CHAPTER 1. ROADWAY LIGHTING LEVEL SELECTION

Regardless of the adaptability of a lighting system, the selection of the appropriate lighting level 

for the given roadway is the key component for the implementation of the system. This 

document provides a new method for the selection of a lighting level based on the relationship 

between lighting and safety.

A more complete classification system than that of the IESNA and AASHTO is needed to obtain 

the benefits of adaptive lighting for all types of roadways. The AASHTO and IESNA lighting 

guides do not provide methods to calculate changes to the recommended light levels for highspeed roads in response to changes in the driving environment. The classification methods used 

by the ILE and CIE evaluate such factors as traffic volume and geometry in addition to

pedestrian volumes. After evaluating these classification systems and the data from the current 

research, a new methodology has been developed based on an analysis of vehicle crashes and 

lighting levels. The proposed methodology is a modification of the method currently recorded in 

CIE Document 115.

(2)

This proposed approach has been developed from the results of an analysis of crashes and 

lighting levels on the roadway. For this analysis, lighting data were measured in situ on a variety 

of roadways in seven different states. Crash data were then used to determine the relationship of 

the lighting data to the crash rate. From these results, 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 design approaches and relevant literature.

An accompanying document, Design Criteria for Adaptive Roadway Lighting, provides more 

detail on the criteria listed here.(6)

For the proposed methodology, three different selection criteria based on the IESNA approach

are used to determine the lighting level. The IESNA separates design criteria for the following 

facilities: roadways, streets, and residential/pedestrian:

 Roadway lighting is provided for freeways; expressways; limited-access roadways; 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

detection of obstacles within and beyond the range of vehicle headlamps (figure 2).
8

Figure 2. Photo. Roadway lighting.

 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 3).

Figure 3. Photo. Street lighting.
9

 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/h (40 km/h), where vehicle headlights provide adequate lighting for 

drivers (figure 4). 

Figure 4. Photo. Residential/pedestrian area lighting.

Because these three facility types—roadway, street, and residential/pedestrian—form the basis 

for the lighting requirement selection methodology, each is characterized as an H (roadway), S

(street), or P (residential/pedestrian) class. Each of these classes has a specific set of criteria for 

the selection of the lighting requirements.

As with the method in CIE Document 115, 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 for the lighting design class is shown in

figure 5.

Figure 5. Equation. Lighting class.

The base value changes depending on the facility type; the sum of the weighting values is then 

subtracted from this base value. This result determines the lighting class. The lighting level is 

then determined from the lighting class. If the result is not a whole number, the next lower 

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 because they 

have the highest lighting requirements). Similarly, numbers resulting in a class lower than the 

Lighting Class = Base Value − Weighting Values
10

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, which determines a different lighting class and,

therefore, a different required design level.

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.

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 speed of 

vehicles, can be used instead.

Traffic Volume

The traffic volume parameter typically used in the selection of a roadway lighting level is 

average daily traffic (ADT). While this is an effective parameter for selection of a basic lighting 

level, it is not practical for application of adaptive lighting. Actual traffic volumes vary by day of 

the week and hour of the day, which limits 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, is

used to determine the traffic flow level criteria for the adaptive lighting level.(7)

The capacity of a roadway is determined by the roadway speed, the number of lanes, the 

percentage of trucks, and a factor for the geometry of the roadway. This capacity is then 

characterized by an LOS grouping (i.e., Levels A through F, with A being low-traffic volume 

and F being high-traffic volume). The LOS of the roadway is determined by the density of the 

vehicles per lane. The Highway Capacity Manual should be referenced for additional 

information.

(7)

For the three roadway types used for these guidelines (i.e., roadway, street, and 

residential/pedestrian), the LOS calculations were based on the assumptions in table 5. 
11

Table 5. Assumptions made for the LOS calculation.

Variable Roadway Street Residential

Speed (mph) 65 45 25

Number of Lanes per Direction 2 2 1

Percentage of Trucks (%) 5 3 0

Terrain Effects11.5 1.5 1.5

1This value accounts for speed and capacity changes resulting from the impact of hills 

and curves.

The resulting calculations for the threshold traffic volume based on the LOS are shown in 

table 6.

Table 6. Threshold traffic volume based on LOS. 

LOS

Threshold 

Density Roadway Street Residential

A to B 11 1,310 900 N/A

B to C 18 2,150 1,520 N/A

C to D 26 2,990 2,200 290

D to E 35 3,730 2,910 760

E to F 45 4,320 3,560 990

N/A = not applicable.

As a result of these calculations, the criteria to be used for an hourly adjustment of the lighting 

level based on traffic volume are shown for roadways, streets, and residential/pedestrian areas in 

table 7, table 8, and table 9, respectively. These values are rounded values based on the transition 

from LOS B to C and the transition from LOS C to D. These levels were selected because they 

represent when the road reaches maximum free flow (B to C) and when crash rates begin to 

increase (C to D).

(8) Note that the traffic volume values listed in the tables are for single-direction 

travel. Thus, the values would have to be doubled when applied to undivided roads.

Table 7. Hourly traffic flow criteria for roadways.

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
12

Table 8. 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 9. 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 its specific roadway conditions.

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 must have a barrier or be 

designed such that the light from opposing headlamps is limited and not visible to drivers 

approaching each other. The AASHTO Roadside Design Guide defines a median width of 49.2 ft 

(15 m) where a barrier is not required in a roadway, and this median width is suitable to limit 

glare between vehicles.(9) Median widths between 32.8 to 49.2 ft (10 to 15 m) require a design 

review with engineering judgment.

Intersection/Interchange Density

The intersection/interchange density parameter refers to the number of intersections and 

entrances into the roadway per mi or km. This parameter represents the possibility of vehicles 

interacting in the roadway. It includes not only other roadways but driveways and other entrance 

areas.

Ambient Luminance

The brightness and amount of light in the surrounding area affects 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 (LZ) describing different ambient 

lighting conditions.

(10)

LZ0: No Ambient Lighting

LZ0 represents areas where the natural environment will be seriously and adversely affected by 

lighting. Effects include disturbing the biological cycles of flora and fauna and detracting from 

human enjoyment and appreciation of the natural environment, although human activity is
13

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 used in an LZ0 condition.

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.

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.

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.

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.

Guidance 

The guidance parameter refers to the presence and quality of the other non-lighting-related 

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 

millicandela/meter squared lux (mcd/m2lx).

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.

Parked Vehicles 

The parked vehicles parameter refers to the presence of parked vehicles along the side of the 

roadway.
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 6 and

figure 7). This function is related to the feeling of safety and security of the roadway users. 

Typically, facial recognition can be expected to always be an important aspect of the roadway 

environment.

Figure 6. Photo. Facial recognition under low lighting.
15

Figure 7. Photo. Facial recognition under high lighting.

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 these 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 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, then the lighting level of the intersection, in turn, will also 

be reduced.

DESIGN CRITERIA AND LUMINANCE SELECTION

The parameters described above are used to determine the lighting level. Table 10, table 12, and 

table 14 show the weighting parameters, while table 11, table 13, and table 15 show the 

recommended lighting design levels (based on the lighting class) for roadway, street, and 

residential/pedestrian facilities, respectively. The base values for each of the facility types are 

also provided for each classification. It is important to note that the lighting design criteria 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;
16

therefore, the lighting level requirements may change as well. This is particularly critical with 

respect to the traffic volume and pedestrian levels.

Design Criteria for Roadways (H-Class)

Base value for class: 5

Table 10. Roadway design level selection criteria.

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 No median present 1

Yes Must be glare blocking 0

Intersection/ 

Interchange Density 

High < 1.5 mi between intersections 

(2.5 km) 1

Moderate 1.5–4 mi (2.5–6.5 km)

between intersections 0

Low > 4 mi (6.5 km) between 

intersections -1

Ambient Luminance 

High LZ3 and LZ4 1

Moderate LZ2 0

Low LZ1 -1

Guidance Good > 100 mcd/m2

lx 0

Poor < 100 mcd/m2lx 0.5

Table 11. H-class lighting design levels.

Class

Average 

Luminance

(cd/m2)

Maximum

Uniformity 

Ratio 

(avg/min)

Maximum

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
17

Design Criteria for Streets (S-Class)

Base value for class: 6

Table 12. Street design level selection criteria.

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 No median present 1

Yes (or one-way) Must be glare blocking 0

Intersection/ 

Interchange Density 

High > 5 per mi (1.6 km) 1

Moderate 1–5 per mi (1.6 km) 0

Low < 1 per mi (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/m2lx 0.5

Pedestrian/Bicycle 

Interaction 

High > 100 pedestrians per h 2

Moderate 10–100 pedestrians per h 1

Low < 10 pedestrians per h 0

Parked Vehicles Yes Parked vehicles present 1

No Parked vehicles not present 0

Table 13. S-class lighting design levels.

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
18

Design Criteria for Residential/Pedestrian Areas (P-Class)

Base value for class: 6

Table 14. Residential/pedestrian design level selection criteria.

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 mi (1.6 km) 1

Moderate 1–5 per mi (1.6 km) 0

Low < 1 per mi (1.6 km) -1

Ambient Luminance 

High LZ3 and LZ4 1

Moderate LZ2 0

Low LZ1 -1

Pedestrian/Bicycle

Interaction

High > 100 pedestrians per h 1

Moderate 10-100 pedestrians per h .5

Low < 10 pedestrians per h 0

Parked Vehicles Yes Parked vehicles present .5

No Parked vehicles not present 0

Facial Recognition 

Required Facial recognition is required 1

Not Required Facial recognition is not 

required 0

Table 15. P-class lighting design levels (E = illuminance).

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
19

EXAMPLE OF LIGHTING DESIGN CRITERIA SELECTION

The following example illustrates how to select a roadway lighting class. The parameters are the 

following: 

 Speed limit of 70 mi (113 km).

 Equivalent of 35,000 ADT.

 39-ft (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 16.

Table 16. Example lighting level selection process for a roadway facility. 

Parameter Options Criteria

Weighting 

Value

Speed Very High > 60 mi/h (97 km/h) 1

Traffic Volume High > 30,000 ADT 1

Median No No median present 1

Intersection/Interchange Density Moderate 1.5–4 mi (2.4–6.4 km) 

between intersections 0

Ambient Luminance High LZ3 and LZ4 1

Guidance Good > 100 mcd/m2lx 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, maximum-to-minimum uniformity ratio of 5, and 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 to 15,000 ADT, the weighting value of traffic volume would decrease from 1to 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 10 and table 11).

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 h (vph), the weighting value would 

be 1 (table 7). This would still result in an H1 class, assuming the same variables listed in table 

16 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 17.

Here, a change in the number of pedestrians per h could result in a change in the recommended 

lighting level. 
20

Table 17. Example lighting level selection process for a street facility.

Parameter Options Criteria

Weighting 

Value

Speed Moderate > 35 mi/h (55 km/h) 0.5

Traffic Volume High > 15,000 ADT 1

Median Yes Must be glare blocking 0

Intersection/Interchange Density High > 5 per mi (1.6 km) 1

Ambient Luminance Moderate LZ2 0

Guidance Poor < 100 mcd/m2lx 0.5

Pedestrian/Bicycle Interaction High > 100 pedestrians per h 2

Parked Vehicles Yes Parked vehicles present 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 infer the use of the lighting class S1

(table 13). If the traffic volume changed to less than 5,000 vehicles per day and the pedestrian 

volume changed from more than 100 pedestrians per h to less than 10 per h, the sum would 

change from 6 to 4, allowing for a reduction in light levels at the S2 class.
21

CHAPTER 2. ADAPTIVE LIGHTING APPLICATION

The approach taken for adaptive lighting affects where the lighting system should be controlled 

and when it should be controlled. This section applies specifically to active adaptive systems. 

WHERE TO ADAPT LIGHTING

It is believed that adaptive lighting can be used in most roadway scenarios. However, in certain 

areas, 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. Responsible designers 

of adaptive policies must 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 consistent throughout the night (e.g., a hospital or other service facility). It 

is also important that adaptive policies not be used to replace other responsible lighting activities,

such as luminaire maintenance and tree trimming.

Another consideration in implementing adaptive lighting is the size of the area covered by the 

lighting system. Dimming a roadway lighting system can occur broadly over all of the roadways 

in the area, or it can occur section by section on each of the roadways being dimmed, depending

on nighttime use and driver needs. 

In general, dimming a large area maintains 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.

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 a one-level change in the lighting class per mi 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. 

WHEN TO ADAPT LIGHTING

The optimal approach to selecting the timing of the adaptive lighting is to continually monitor 

the roadway and the environment. As an example, ITSs can provide traffic and pedestrian counts 

as inputs to an algorithm that establishes the lighting level in real time. 

When ITSs are not available, such as 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:

(11)
22

 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, providing an agency with 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 affected by dimming of luminaires.

(12)

Further investigations are 

under way.
23

CHAPTER 3. LEGAL IMPLICATIONS OF ADAPTIVE LIGHTING

The parties most concerned with the legal implications of an adaptive lighting system are the 

owners and designers of the system. The owner is likely the government agency responsible for 

drafting the regulations defining the system and for implementing it. The designers include the 

engineers and design professionals working for the owner or agency. The legal concerns range 

from the agency justification for implementing such a system to the legal liability of the owners 

and designers in the event of a personal injury lawsuit attributed to the adaptive lighting system.

JUSTIFICATION OF AGENCY DECISION

The implementation of an adaptive lighting system likely require the promulgation or revision of 

highway safety regulations and the exercise of agency decisionmaking procedures. Such agency 

action is typically regulated by a statute outlining administrative procedures. (See, for example,

5 U.S.C. 553, informal rulemaking procedures of the Federal Administrative Procedures Act, and

Wash. Rev. Code § 34.05.510, judicial review of agency action under State of Washington 

Administrative Procedure Act.)

(13,14)

The action of an agency in promulgating or revising highway safety standards may be challenged 

if it can be shown to be “arbitrary, capricious, an abuse of discretion, or otherwise not in 

accordance with law.” (See Motor Vehicle Mfrs. Ass’n of U.S., Inc. v. State Farm Mut. Auto. Ins. 

Co., 463 U.S. 29, 41 [1983], reviewing order of National Highway Traffic Safety Administration 

rescinding crash protection requirements of the Federal motor vehicle safety standard.)

(15)

In the 

Motor Vehicle Mfrs. case, the decision of the agency was challenged because it failed to present 

an adequate basis and explanation for rescinding certain requirements relating to the use of 

seatbelts and airbags in motor vehicle passive restraint systems under its regulations.

(15)

The U.S. 

Supreme Court stated the following:

There are no findings and no analysis here to justify the choice made, no indication of the 

basis on which the [agency] exercised its expert discretion. . . . Expert discretion is the 

lifeblood of the administrative process, but ‘unless we make the requirements for 

administrative action strict and demanding, expertise, the strength of modern 

government, can become a monster which rules with no practical limits on its discretion.’ 

(Id. at 48, quoting New York v. United States, 342 U.S. 882, 884 [1951], Black, J., 

dissenting)(15)

Most important is that the agency “cogently explain[s] why it has exercised its discretion in a 

given manner.”

(15)

For the agency implementing an adaptive lighting system, demonstrating the basis for the 

application of its expert discretion is crucial if the regulations are to survive. Supporting the 

decision with empirical data strengthens the case for needing the system, as does adherence to 

industry-accepted guidelines during the design of the system. A narrative explanation of the 

reasons the agency decided to implement the system—written or endorsed by the engineers with 

the particular expertise required—leaves little doubt regarding the basis for the new system. A 

well-supported agency decision will receive substantial deference from a reviewing court.
24

TORT LIABILITY OF AGENCY OR ENGINEER

An agency implementing an adaptive lighting system, or the engineer designing such a system, 

may face tort liability for personal injury resulting from such a system on the theory of negligent 

design.

Negligence is “conduct which falls below the standard established by law for the protection of 

others against unreasonable risk of harm” (Restatement [Second] of Torts, § 282).

(16)

Engineers 

and other design professionals must act according to the standard of care set by their particular 

profession:

Architects, doctors, engineers, attorneys, and others deal in somewhat inexact sciences 

and are continually called upon to exercise their skilled judgment in order to anticipate 

and provide for random factors which are incapable of precise measurement. The

indeterminable nature of these factors makes it impossible for professional service people 

to gauge them with complete accuracy in every instance. . . . Because of the inescapable 

possibility of error which inheres in these services, the law has traditionally required, not 

perfect results, but rather the exercise of that skill and judgment which can be reasonably 

expected from similarly situated professionals. (Klein v. Catalano, 386 Mass. 701, 

718–19 [1982], citing Mounds View v. Walijarvi, 263 N.W.2d 420, 424 [Minn. 1978]; 

Trustees of Union College v. Kennerly, Slomanson & Smith, 167 N.J. Super. 311, 318 

[1979]; and Broyles v. Brown Eng'r Co., 275 Ala. 35, 39 [1963]).

(17)

In designing an adaptive lighting system, an agency or engineer does not breach this duty of care 

if the agency or engineer performs according to industry-accepted guidelines (e.g., Federal 

highway standards). That is, if the engineer does what every other engineer would do in the same 

situation, a plaintiff will be hard pressed to argue that the engineer was negligent.

SOVEREIGN IMMUNITY

Sovereign immunity is a legal doctrine by which the government cannot commit a legal wrong 

and is immune from civil suit without its consent. The government has waived its immunity in 

most States, although discretionary policy decisions of employees of Federal and State agencies

are still protected from suit. This protection does not extend to consulting engineers or other 

design professionals working on behalf of the agency.

The Federal government has waived its sovereign immunity to a limited extent under the Federal 

Tort Claims Act (FTCA, 28 U.S.C. 1346[b], 2671–2680).

(18) Under the FTCA, the United States 

is liable for the following:

... injury or loss of property, or personal injury or death caused by the negligent or 

wrongful act or omission of any employee of the government while acting within the 

scope of his office or employment, under circumstances where the United States, if a 

private person would be liable to the claimant in accordance with the law of the place 

where the act or omission occurred.(18)
25

The United States may be held liable under the FTCA for torts of employees of the executive, 

legislative, and judicial branches, but not for torts of government contractors (28 U.S.C. 

2671).

(19)

A significant exception to the FTCA immunizes the United States government from claims 

“based upon the exercise or performance or the failure to exercise or perform a discretionary 

function” (28 U.S.C. 2680[a]), even if the Federal employee acted negligently in the 

performance or nonperformance of his discretionary duty.(20)The U.S. Supreme Court has held 

that the discretion protected by the exception:

...is the discretion of the executive or administrator to act according to one’s judgment of 

the best course. ... It ... includes more than the initiation of programs and activities. It 

also includes determinations made by executives or administrators in establishing plans, 

specifications or schedules of operations. Where there is room for policy judgment and 

decision there is discretion. It necessarily follows that acts of subordinates in carrying out 

the operations of government in accordance with official directions cannot be actionable.

(Dalehite v. United States, 346 U.S. 15 [1953])

(21)

Elsewhere, the Supreme Court has stated that “[j]udicial intervention in [agency] decisionmaking

through private tort suits would require the courts to ‘second-guess’ the political, social, and 

economic judgments of an agency exercising its regulatory function” (United States v. Varig 

Airlines, 467 U.S. 797, 820 [1984]).

(22) Hence, the Court protected employees of the Federal 

Aviation Administration (FAA) from suit brought by victims of airplane accidents, alleging that 

the FAA employees had acted negligently in certifying certain airplanes for operation.

(22)

Sovereign immunity also applies at the State level. Similar to the Federal government, Alaska 

has barred tort claims against a State agency or its employees relating to the discretionary 

functions of those employees (Alaska Stat. § 09.50.250[1]).

(23) Case law distinguishes between 

“planning level” and “operational level” decisions, attaching immunity to the former but not the 

latter (Wainscott v. State, 642 P.2d 1355, 1356 [Alaska 1982]).

(24) A planning decision involves 

policy formulation, while an operational decision involves policy implementation (Alaska Dept. 

of Trans. and Pub. Facilities v. Sanders, 944 P.2d 453, 456 [1997]).

(25)

Thus, the decision of an 

agency to follow a certain policy is protected from suit, but the actual implementation of the 

policy is not protected. (See Moloso v. State, 644 P.2d 205, 218 [Alaska 1982], stating that 

“[o]nce the state decided to and did undertake the task of re-routing the highway for better road 

maintenance, travel, and safety, it was obligated to use due care in its design and 

construction.”)(26)

Texas has a similar sovereign immunity statute to that of Alaska, in which the State does not 

waive immunity for discretionary acts. (See Tex. Civ. Prac. & Rem. Code Ann. § 101.056 and

101.060.)

(27)

This protection has been specifically applied to highway design and safety features. 

(See State v. Miguel, 2 S.W.3d 249, 251 [Texas 1999], stating that “[d]ecisions about highway 

design and about what type of safety features to install are discretionary policy decisions” for 

which the government cannot be held liable.)

(28) Also as in Alaska, immunity does not extend to 

the negligent implementation of a policy decision. (See Tex. Civ. Prac. & Rem. Code Ann.

§101.021.)

(29)
26

The State of Washington also has a discretionary function exemption to sovereign immunity, but 

“its applicability is limited to high-level discretionary acts exercised at a truly executive level” 

(McCluskey v. Handorff-Sherman, 125 Wash.2d 1, 12 [1994]; see also Wash. Rev. Code

§ 4.92.090).

(30,31)

Still, decisions involving traffic or highway planning are entitled to immunity. 

(See Jenson v. Scribner, 57 Wash. App. 474 [2012], holding that collection of accident data to 

plan and prioritize highway projects at a 2-year interval is part of the planning process and is, 

therefore, protected by sovereign immunity.)

(32) However, this protection does not extend to 

negligent design and construction. (See State v. Stewart, 92 Wash.2d 285 [1979], holding that,

while the decision to construct a bridge was a policy-level decision, the State was negligent in its 

planning and design of the bridge because of the lack of lighting; also see Riley v. Burlington 

Northern, Inc., 27 Wash. App. 11, 17 [1980], holding that the angle of how a road approached a 

railroad track was a design issue, not a policy determination, and the State could not avail itself 

of sovereign immunity when sued for an accident related to the dangerous angle.)

(33,34)

Based on the foregoing, the decision of an agency to follow an adaptive lighting regime would 

likely be protected by Federal or State sovereign immunity. However, the agency would remain 

open to suit if the implementation or installation of an adaptive lighting system was negligent in 

some way. Moreover, neither the Federal exemption nor the State exemptions extend the 

immunity protection to engineers and design professionals who are not direct government 

employees but are only agents of the government. Accordingly, the engineers or design 

professionals creating an adaptive lighting system would not be protected from suit by sovereign 

immunity and would have to rely on a typical negligence defense concerning the standard 

of care.
27

CHAPTER 4. COST BENEFIT ANALYSES OF ADAPTIVE LIGHTING

To determine the financial benefits to be expected from an adaptive lighting system, a lifecycle 

cost (LCC) analysis should be considered. A simple payback method of analysis could be used,

but this method ignores operating and maintenance expenses, which are key components in 

evaluating lighting control systems and their expected benefits.

LCC is a simple calculation relating to the energy savings and the equipment required for the 

implementation of adaptive lighting. It does not consider the cost of a crash or a vehicle-caused

fatality, and it assumes that the safety level of the roadway is not affected by the changes to the 

lighting level.

FIRST STEP: QUANTIFY COSTS

The first step in preparing an LCC is to quantify all of the costs associated with the lighting 

system. These costs include the following:

 Installation cost of the system.

 Expected reductions in energy costs (or change in rate structure offered by the electricity 

utility).

 Expected reduction or increase in maintenance costs for the lighting system, as well as 

the control equipment and support network.

 Expected life of the equipment.

 Any energy incentives that may be available for the installation.

SECOND STEP: TABULATE THE COSTS

After the initial costs have been collected, assemble a simple tabulation of costs over a period of 

time, without inflation or time-value of money elements. A fixed period of time (e.g., 20 years)

can be used, and system replacement costs can be added to the costs depending on expected 

component life. Another option is to use the expected life of the system and equipment being 

evaluated as the period of time.

For example, assume that an adaptive control system is being added to a light-emitting diode 

street lighting system already equipped with dimming drivers and an acceptable photocell 

receptacle with sufficient pins for control and power connections. The assumed equipment life is 

15 years, and the simple LCC analysis is set to that time frame. An example is shown in table 18

and figure 8.
28

Table 18. Example cost information for an adaptive lighting system.

Type of Cost

Existing System Without 

Adaptive Control Adaptive Control System Costs

Installed Cost $0 $600,000

Annual Energy Cost $841,000 $589,000

Annual Maintenance Cost $100,000 $90,000

15-year Total Cost $14,115,000 $10,785,000

w/o = without

Figure 8. Graph. Example system costs by year for standard and adaptive lighting systems.

THIRD STEP: CONVERT COSTS TO PRESENT VALUE

To obtain a better picture of the actual costs, the cost of capital and future costs should be 

brought into the present day by converting them to the present value based on the assumed 

discount rate. Figure 9 presents the formula for this conversion:

Figure 9. Equation. Present value.

For the example above, a cash flow analysis is shown in table 19 using a 5-percent interest rate.

Present Value = Future cost ∙

1

(1 + discount rate)

n
29

Table 19. Cash flow comparison for an adaptive lighting system.

Term

Street-Lighting System Without Adaptive 

Controls

Street-Lighting System With Adaptive 

Controls

Years Cash Flow Total Expense Present Value Cash Flow Total Expense Present Value

0 $0 $0 $0 $600,000 $600,000 $600,000

1 $941,000 $941,000 $896,190 $679,000 $1,279,000 $1,218,095

2 $941,000 $1,882,000 $1,707,029 $679,000 $1,958,000 $1,775,964

3 $941,000 $2,823,000 $2,438,614 $679,000 $2,637,000 $2,277,940

4 $941,000 $3,764,000 $3,096,652 $679,000 $3,316,000 $2,728,081

5 $941,000 $4,705,000 $3,686,491 $679,000 $3,995,000 $3,130,187

6 $941,000 $5,646,000 $4,213,132 $679,000 $4,674,000 $3,487,811

7 $941,000 $6,587,000 $4,681,258 $679,000 $5,353,000 $3,804,277

8 $941,000 $7,528,000 $5,095,247 $679,000 $6,032,000 $4,082,695

9 $941,000 $8,469,000 $5,459,193 $679,000 $6,711,000 $4,325,970

10 $941,000 $9,410,000 $5,776,924 $679,000 $7,390,000 $4,536,819

11 $941,000 $10,351,000 $6,052,015 $679,000 $8,069,000 $4,717,777

12 $941,000 $11,292,000 $6,287,808 $679,000 $8,748,000 $4,871,214

13 $941,000 $12,233,000 $6,487,421 $679,000 $9,427,000 $4,999,339

14 $941,000 $13,174,000 $6,653,765 $679,000 $10,106,000 $5,104,217

15 $941,000 $14,115,000 $6,789,556 $679,000 $10,785,000 $5,187,769

The net present value (NPV) is shown in figure 10. The results show that the return on 

investment for this example is less than 3 years.

Figure 10. Graph. Example NPV for standard and adaptive lighting systems.

31

CHAPTER 5. SUMMARY

These guidelines have been developed to provide a designer or a roadway agency with a 

complete review of all aspects of the implementation of adaptive lighting on roadways. Through 

the development of a relationship between crashes and lighting, criteria have been chosen that 

affect the selection of the lighting level on a roadway. A lighting level selection methodology has 

been developed with these parameters. These parameters can also be used to actively determine a 

lighting level, meaning that the lighting system could be changed to adapt to the current needs of 

the driver and the roadway. The implementation of these systems requires a lighting control 

system and dimmable luminaires.

It is expected that the application of these design methods will sustain the current safety levels on 

roadways while reducing the use of unwanted light, the waste of energy, and the overall impact 

of the lighting system on the environment.

33

ACKNOWLEDGEMENTS

The project team would like to thank the project technical representatives from FHWA, Carl 

Andersen (2011–2012) and Craig Thor (2012–2014). Many individuals also provided data for 

the traffic and lighting parameters.

35

REFERENCES

1. Illuminating Engineering Society of North America, ANSI/IESNA RP-8-00, American 

National Standard Practice for Roadway Lighting, New York, 2000, reaffirmed 2005.

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Edition, Vienna, Austria, 2010.

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13. Informational rulemaking procedures of the Federal Administrative Procedures Act, 5 U.S.C. 

553.

14. Wash. Rev. Code § 34.05.510
36

15. Motor Vehicle Mfrs. Ass’n of U.S., Inc. v. State Farm Mut. Auto. Ins. Co., 463 U.S. 29, 41 

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16. Restatement (Second) of Torts, § 282.

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167 N.J. Super. 311, 318 (1979); and Broyles v. Brown Eng'r Co., 275 Ala. 35, 39 (1963).

18. Federal Tort Claims Act, 28 U.S.C. 1346(b), 2671–2680.

19. 28 U.S.C. 2671.

20. 28 U.S.C. 2680(a).

21. Dalehite v. United States, 346 U.S. 15 (1953).

22. United States v. Varig Airlines, 467 U.S. 797, 820 (1984).

23. Alaska Stat. § 09.50.250(1).

24. Wainscott v. State, 642 P.2d 1355, 1356 (Alaska 1982).

25. Alaska Dept. of Trans. and Pub. Facilities v. Sanders, 944 P.2d 453, 456 (1997).

26. Moloso v. State, 644 P.2d 205, 218 (Alaska 1982).

27. Tex. Civ. Prac. & Rem. Code Ann. § 101.056 and 101.060.

28. State v. Miguel, 2 S.W.3d 249, 251 (Texas 1999).

29. Tex. Civ. Prac. & Rem. Code Ann. §101.021.

30. McCluskey v. Handorff-Sherman, 125 Wash.2d 1, 12 (1994).

31. Wash. Rev. Code § 4.92.090.

32. Jenson v. Scribner, 57 Wash. App. 474 (2012).

33. State v. Stewart, 92 Wash.2d 285 (1979).

34. Riley v. Burlington Northern, Inc., 27 Wash. App. 11, 17 (1980).

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