http://safety.fhwa.dot.gov/

Roadway Visibility Research Needs Assessment
ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

ii ii

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Cover photo sources: left photo-Fotolia, top right photo-Wellesley, Massachusetts Police Department, bottom right photo-Thinkstock, 
Form DOT F 1700.7 (8-72)

1. Report No. 

FHWA-SA-17-031

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

4. Title and Subtitle 

Roadway Visibility Research Needs Assessment

5. Report Date

December 2016

6. Performing Organizations Code

7. Authors

 Travis Terry, Brad Brimley, Ronald Gibbons, and Paul J. Carlson

8. Performing Organization Report No.

9. Performing Organization Name and Address

Texas A&M Transportation Institute 

The Texas A&M University System 

College Station, Texas 77843-3135 

Virginia Tech Transportation Institute

3500 Transportation Research Plaza

Blacksburg, Virginia 24060

Leidos, Inc.

11251 Roger Bacon Drive

Reston, VA 20190

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-10-D-00024

12. Sponsoring Agency Name and Address

 Federal Highway Administration

 Office of Safety Research and Development

 6300 Georgetown Pike

 McLean, VA 22101

 Office of Safety

 1200 New Jersey Ave SE

 Washington, DC 20590

13. Type of Report and Period 

Covered

Final Report

14. Sponsoring Agency Code

 HRDS and HSA

15. Supplementary Notes

16. Abstract

This report focuses on a review of issues related to nighttime visibility and assessment of how the Federal 

Highway Administration (FHWA) Office of Safety’s three safety program areas—roadway departure 

safety, intersection safety, and pedestrian and bicycle safety—address concerns for nighttime visibility, 

as well as a review of fatality data and a gap analysis for research needs.

In addition to the assessment of the three program areas, this report summarizes a survey of practices 

and policies of highway design, traffic engineering, and highway safety that are based on daytime 

conditions and may neglect issues and concerns that arise from nighttime conditions

17. Key Words

Visibility, roadway departure, intersection, pedestrian and 

bicycle, nighttime visibility.

18. Distribution Statement 

 No restrictions This document is 

available to the public through 

the National Technical Information 

Service, Alexandria, Virginia 22312

19. Security Classif. (of this report) 

Unclassified

20. Security Classif. (of this 

page) Unclassified

21. No of Pages

 104

22. Price 

 N/A

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized.

Technical Report Documentation Page
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

in.2 square inches 645.2 square millimeters mm2

ft2 square feet 0.093 square meters m2

yd2 square yard 0.836 square meters m2

ac acres 0.405 hectares ha

mi2 square 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 m3

yd3 cubic yards 0.765 cubic meters m3

NOTE: volumes greater than 1,000 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)

°F Fahrenheit 5 (F-32)/9 or 

(F-32)/1.8 

Celsius °C

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/in.2 poundforce 

per square inch

6.89 kilopascals kPa

SI* (MODERN METRIC) CONVERSION 

*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).
APPROXIMATE CONVERSIONS TO 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

mm2 square millimeters 0.0016 square inches in.2

m2 square meters 10.764 square feet ft2

m2 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

m3 cubic meters 35.314 cubic feet ft3

m3 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)

°C Celsius 1.8C+32 Fahrenheit °F

ILLUMINATION

lx lux 0.0929 foot-candles fc

cd/m2 candela/m2 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* (MODERN METRIC) CONVERSION

*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).

ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

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TABLE OF CONTENTS

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

2. CURRENT RESEARCH AND PRACTICES......................................................................3

PRINCIPLES OF VISIBILITY.....................................................................................................................3

ROADWAY DEPARTURE SAFETY............................................................................................................4

INTERSECTION SAFETY.........................................................................................................................6

PEDESTRIAN AND BICYCLE SAFETY .....................................................................................................8

3. REVIEW OF FATAL CRASH DATA............................................................................... 11

SAFETY DATA CONSIDERED...............................................................................................................11

ROADWAY DEPARTURE BREAKDOWNS..............................................................................................13

INTERSECTION BREAKDOWN ............................................................................................................16

PEDESTRIAN AND BICYCLIST SAFETY DATA .......................................................................................19

SUMMARY OF FATALITY DATA REVIEW...............................................................................................22

4. BEST PRACTICES......................................................................................................23

5. CURRENT GAPS IN PRACTICE AND RESEARCH .......................................................25

ROADWAY DEPARTURE SAFETY..........................................................................................................25

INTERSECTION SAFETY.......................................................................................................................29

PEDESTRIAN AND BICYCLE SAFETY ...................................................................................................32

OTHER AREAS WITH NIGHTTIME VISIBILITY CONCERNS ....................................................................34

REFERENCES ................................................................................................................37

APPENDIX A. ROADWAY LIGHTING DETAILS ............................................................... 41

ASPECTS OF ROADWAY LIGHTING....................................................................................................41

LIGHTING REQUIREMENTS.................................................................................................................41

LIGHTING SELECTION ........................................................................................................................42

LIGHTING DESIGN .............................................................................................................................43

COMMON PRACTICES FOR LIGHTING ROADWAYS..........................................................................44

REFERENCES .....................................................................................................................................47

APPENDIX B. STATE PRACTICES...................................................................................49

APPENDIX C. RESEARCH PROBLEM STATEMENTS........................................................57

ROADWAY DEPARTURE SAFETY..........................................................................................................57

INTERSECTION SAFETY.......................................................................................................................70

PEDESTRIAN AND BICYCLE SAFETY ...................................................................................................77

OTHER AREAS WITH NIGHTTIME VISIBILITY CONCERNS ....................................................................83

REFERENCES ......................................................................................................................................91
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ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

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LIST OF FIGURES

Figure 1. Crash percentages by road type and lighting conditions for clear weather. 

(FARS Database, 2014) .................................................................................................................13

Figure 2. Crash percentages by road type and lighting conditions for rain. (FARS Database, 

2014) ................................................................................................................................................14

Figure 3. Crash percentages by road type, lighting condition, and weather condition. 

(FARS Database, 2014) ....................................................................................................................15

Figure 4. Crash percentages by lighting condition and age group for clear versus rain weather 

conditions. (FARS Database, 2014) .................................................................................................15

Figure 5. Crash percentages of speeding versus non-speeding by light condition. 

(FARS Database, 2014) ....................................................................................................................16

Figure 6. Crash percentages by intersection type and lighting condition. (FARS Database, 

2014) .................................................................................................................................................17

Figure 7. Crash percentages at four-way intersections by age group and lighting condition. 

(FARS Database, 2014) ....................................................................................................................17

Figure 8. Crash percentage by lighting condition and intersection control type. (FARS 

Database, 2014)...............................................................................................................................18

Figure 9. Crash percentages by lighting condition and intersection type by weather. 

(FARS Database, 2014) ....................................................................................................................19

Figure 10. Crash percentages by lighting condition and intersection type for rural roadways 

involving pedestrians and bicyclists. (FARS Database, 2014) .......................................................20

Figure 11. Total fatal crashes by lighting condition and intersection type for rural roadways 

involving pedestrians and bicyclists (FARS Database, 2014) .......................................................20

Figure 12. Crash percentages by lighting condition and intersection type for urban roadways 

involving pedestrians and bicyclists. (FARS Database, 2014) .......................................................21

Figure 13. Total fatal crashes by lighting condition and intersection type for urban roadways 

involving pedestrians and bicyclists. (FARS Database, 2014) .......................................................21

LIST OF TABLES

Table 1. Total Fatal Crashes for Lighting Condition by Traffic Control Type....................................18

Table 2. Referenced Sources for Standards and Policies for Each State.......................................49

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1. INTRODUCTION

This report focuses on a review of issues related to nighttime visibility and assessment of how the 

Federal Highway Administration (FHWA) Office of Safety’s three safety program areas—roadway 

departure safety, intersection safety, and pedestrian and bicycle safety—address concerns for 

nighttime visibility, as well as a review of fatality data and a gap analysis for research needs. 

Within the framework of the Office of Safety’s focus areas (roadway departure safety, intersection 

safety, and pedestrian and bicycle safety), the researchers identified potential ways future 

research, advancing technologies, and changes to current practices may address nighttime 

visibility concerns from a perspective of highway design, traffic operations, and highway safety. 

The strategic narratives from the roadmaps for intersection safety and roadway departure safety 

were evaluated to identify the extent to which they address nighttime conditions and issues 

of visibility, retroreflectivity, and lighting. These strategic plans were updated in February 2015. 

Information about the pedestrian and bicycle safety program was obtained from the strategic 

plan with recommended research for pedestrian safety, updated in 2010. The Office of Safety’s 

three program areas are described in detail on line (https://safety.fhwa.dot.gov/). 

In addition to the assessment of the three program areas, this task included a survey of practices 

and policies of highway design, traffic engineering, and highway safety that are based on 

daytime conditions and may neglect issues and concerns that arise from nighttime conditions. 

The topics identified are divided into the three safety program areas.

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2. CURRENT RESEARCH AND PRACTICES

PRINCIPLES OF VISIBILITY

Approximately 90 percent of the information that drivers use is visual.(1) For nighttime driving, two 

of the most important factors that affect vision are visual acuity and contrast sensitivity. Visual 

acuity is the ability for drivers to discern details at a distance. The ability to detect differences in 

luminance and discern an object from its background is contrast sensitivity.(2) 

A visual acuity of 20/20 is considered normal vision. In ideal conditions, a person with normal 

vision can read letters that subtend an angle of 5 minutes of arc. A person with 20/40 vision 

needs letters of 10 minutes of arc. A driver with poor vision must be closer to signs or roadway 

hazards to see them.(2) Contrast sensitivity is noted as being more impactful on vehicular crashes 

than is visual acuity. Regardless of a driver’s visual acuity, an object that cannot be distinguished 

from its background will not be seen. This could involve any number of roadway hazards, from 

debris to a crossing pedestrian. Drivers typically misjudge the distance at which pedestrians are 

seen,(3) which often leads to crashes. The use of lighting can increase contrast in most cases and 

make objects in the roadway more discernible.(2) 

For pedestrians and bicycles, it is important that conspicuity be increased to promote visibility. 

Lighting is one way to increase conspicuity. Although street lighting can help drivers see these 

vulnerable road users, a lack of uniformity can create dark spots, improper lighting can create 

glare, and changes in asphalt color can create areas of poor contrast.(2)

Color vision is a result of three types of color-sensitive cones in the eye. These three cones respond 

in general to red, green, and blue components of the visual spectrum. Abnormal color vision (or 

color blindness) refers to an aspect of vision where shades of color are confused by the observer. 

This is typically a result of low or missing levels of pigment in one of the cones in the retina. Color 

deficiencies can be red confusion, green confusion, or blue/yellow confusion (Protanopia, 

Deuteranopia, and Tritanopia, respectively). Color blindness occurs in approximately 8–9 percent 

of the population and mostly in males. Colorblind drivers typically use position of traffic signals 

and other clues to overcome their disability. There are new considerations in universal design 

that can overcome the limitations of color vision. These approaches are similar to a blue cross 

embedded in the red signal to aid in the signal identification.

The FHWA Lighting Handbook discusses the decline of visual function that often comes with age. 

Typical aging issues include a reduction in pupil size, which reduces the amount of light entering 

the eye; the lens losing elasticity, making focus difficult; and a general yellowing of the lens, which 

reduces both luminance and color contrast. Diseases such as glaucoma affect peripheral vision, 

and the yellowing of the ocular lens diminishes contrast sensitivity. The handbook also states 

that people over 60 have a reduced ability to detect movement of objects. Older drivers are 

also more susceptible to glare because the amount of contrast needed to overcome threshold 

contrast increases significantly. The concerns of the aging population’s vision extend beyond 
ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

4

drivers to pedestrians as well. Pedestrians, like drivers, need to accurately read sign messages 

and detect motion. Even though these concerns are known, the current roadway lighting system 

design practices are not designed with modifiers for age.(4)

ROADWAY DEPARTURE SAFETY

In the FHWA Safety Program, a roadway departure (RwD) crash is any crash in which a vehicle 

crosses an edge line, crosses a center line, or otherwise leaves the traveled way. Roadway 

departures account for over half of fatal crashes in the United States.(5) Harmful events associated 

with fatal roadway departures are fairly broad; however, the most harmful event in over 

70 percent of crashes are rollovers, collisions with other vehicles and collisions with trees. Various 

factors come into play with roadway departures, including road type, speed limit, roadway 

geometry, weather, distracted driving, and even pavement. This section contains common 

practices for lighting various roadway types and concludes with potential areas of research for 

visibility and lighting that can help prevent roadway departures.

Current Assessment of Nighttime Visibility in Program Area

The strategic narrative for the FHWA roadway departure safety roadmap focuses on the goal of 

reducing roadway departure fatalities by 50 percent by the year 2030. The principal strategy is a 

focus on data, and there are some summary statistics of characteristics of roadway departure 

fatalities. For example, 76 percent of roadway departure rollover fatalities and 70 percent of 

roadway departure opposite-direction fatalities occur in rural areas. Also, over 70 percent of fatal 

crashes occur with a posted speed limit of 50 mi/h or greater.(6)

Data for the proportion of roadway departure fatalities that occur at night are notably absent 

from the strategic narrative. It is well known that nighttime crash rates are disproportionately high, 

especially for roadway departures. Therefore, any treatment that specifically targets nighttime 

crashes has a great potential to significantly improve safety. There is little within the strategic 

narrative that emphasizes the importance of these topics.

The strategic narrative mentions improved delineation as a potential countermeasure and the 

FHWA Lighting Handbook and training as a resource for addressing roadway departure safety.(6)

There is limited information about how visibility will be integrated into the future of the roadway 

departure program area. Online, however, there is more information about retroreflectivity, lighting, 

and visibility within the current roadway departure safety program. That information relates to 

Manual on Uniform Traffic Control Devices (MUTCD) regulations, research, funding for visibility 

improvements, and other resources for implementing the objectives of the program. In general, 

however, there is not a direct link between these visibility topics and safety. Without evidence of a 

direct link, it may be difficult to persuade agencies to change their practices and policies. 

Along the same lines, the national guides have found deficiencies in design practice. The 

lighting needs for different roadways are highlighted in the American Association of State and 

Highway Transportation Officials’ (AASHTO’s) lighting guidance in A Policy on Geometric Design 

of Highways and Streets (Green Book).(7) Because fixed-source lighting tends to reduce crashes, 

and most crashes occur at critical points such as interchanges, curves, and junctions, AASHTO 
ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

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recommends lighting many urban and suburban areas. Rural lighting is rarely justified except for 

critical areas like intersections, railroad crossings, bridges, or sharp curves.(7)

There are several issues that result in a difference in design between rural and urban zones. 

Rural areas may have higher speed limits due to fewer conflicts such as intersections, curbs, and 

pedestrians. The levels in background luminance may be different since by definition rural areas 

are less populated, so there will be less surrounding illumination.(8)

Recent and Ongoing Research

Within the area of roadway departure safety, there are several research projects that have 

recently been completed or are ongoing that relate to visibility and the use of traffic control 

devices and lighting. Examples of these are described below. 

Pavement markings provide roadway alignment information that helps drivers maintain their 

position in the lane and identify upcoming features such as curves and ramps. Recent research 

conducted for the Texas Department of Transportation and FHWA has identified the benefits of 

using wider (greater than 4 inch) edge lines,(9, 10, 11) which leads to improvements in lane position, 

reductions in encroachments across the edge line, and reductions in observed crashes. A key 

finding from the work on wider edge lines is that they are shown to significantly reduce crashes 

on two-lane highways but not on multilane divided highways (which is where they are generally 

used). A pooled fund study recently showed that upgrading pavement markings so they are 

retroreflective when wet can result in significant crash reductions for multiple types of crashes, 

especially on multilane highways.(12)

In addition, there have been recent studies on how pavement marking retroreflectivity may be 

associated with nighttime crashes (see13, 14, 15,16, and 17). While there is not yet an established 

link that has been widely accepted, research has been making progress on identifying thresholds 

of pavement marking retroreflectivity where improvement in nighttime safety may be achieved. 

Complementing the research on wider and brighter pavement markings and on markings 

designed for performance in wet weather, the Texas A&M Transportation Institute (TTI) is currently 

leading a project funded through the National Cooperative Highway Research Program (NCHRP) 

on retroreflective pavement markers (RPMs). RPMs provide the most notable benefit during wet 

weather events at night because their construction and shape prevent water from accumulating 

on the marker. The objectives of the NCHRP project include addressing where RPMs should be 

used and developing specifications for spacing and maintenance (i.e., retroreflectivity and 

retention).

Regarding traffic signs that can prevent roadway departure crashes, a recently completed 

NCHRP project developed guidelines for the use of traffic control devices at changes in 

alignment.(18) Researchers evaluated the safety impacts of traditional devices used at curves 

(such as advance warning signs and chevrons) and studied how drivers respond to these 

devices. From the findings, they developed guidelines that promote the consistent use of devices 

that provide drivers the right information for safe curve negotiation.

Regarding lighting, the Virginia Tech Transportation Institute (VTTI) has recently completed 

nighttime visibility projects involving adaptive lighting, light-emitting diode (LED) sign board 
ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

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visibility in fog, and fog and rain visibility with active lane delineators. The adaptive lighting project 

produced guidelines for adaptive roadway lighting design criteria. 

The LED sign board visibility in particular was developed to determine the best color 

combinations for signs in foggy conditions. These will be used in areas where adaptive speed 

limits based on weather conditions are implemented. The results indicate that white and black 

remain the best combination. 

The active delineators have shown promise in providing information to control both speed and 

roadway position of a driver in fog. A variety of flash patterns were tested to investigate the impact 

on driver behavior. The results show that active delineators can provide lane guidance as well as 

speed control in low visibility conditions. 

Currently in progress at VTTI are research projects concerning the impact of roadside police 

vehicle and active work zone equipment lighting on visibility. These projects will produce 

recommendations for equipping vehicles with lighting that promotes traffic and worker safety. 

The Lighting Research Center and Penn State identified links between visibility and public safety 

from roadway lighting in a recent research effort. The research was prompted by a recent trend 

of municipalities removing their lighting in an effort to save money and energy. While lighting is 

expected to improve safety, little data are available to serve as a link between the two ideas. This 

research effort attempted to solidify that link and provide information on the consequences of 

removing or adding lighting to an area.

INTERSECTION SAFETY

An intersection crash is any crash where an intersection or driveway access is identified as the 

location or one of the influencing factors. Intersections vary widely depending on location, 

functional class, traffic volume, and use of channelization. While fatal crashes at intersections 

have declined in recent years, determining how and why crashes continue to occur is still a 

strong research focus. Most research shows that the addition of roadway lighting and other 

visible elements can reduce crash frequency at an intersection.

Current Assessment of Nighttime Visibility in Program Area

One of the program strategies for intersection safety is a prioritization of efforts based on data. 

While fatalities have steadily dropped in recent years, it is clear that continued improvements 

will be best realized by focusing on the conditions in which crashes occur most frequently. The 

strategic plan focuses on both signalized and unsignalized intersections, with additional emphasis 

areas categorized as vulnerable users: pedestrians, bicycles, motorcycles, and older drivers.

Some analysis has been performed for each of these emphasis areas, showing trends and 

summary statistics. There are also lists with potential treatments, projects, resources, and 

opportunities for coordination with other areas. For example, the areas for pedestrian and bicycle 

safety identify road diets and pedestrian-oriented roundabouts as potential methods to facilitate 

reductions in pedestrian and bicycle fatalities.

Of the topics and practices discussed in the strategic plan for intersection safety, there is only 

one mention of conditions related to visibility at night. Retroreflective signal backplates are 
ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

7

listed as an effective countermeasure at signalized intersections. There are other projects that 

may have a component of visibility such as the recently completed “Accelerating Roundabout 

Implementation in the US” however there are few that deal with visibility or lighting as the explicit 

research focus.

In terms of the lighting, the primary goal is to provide sufficient illuminance so drivers can see 

their entry and exit points ahead of time. Other goals of intersection lighting include alerting 

drivers of an intersection ahead of time as well as providing comfort and safety for pedestrians. 

Many policies provide information on when intersection lighting is warranted, but specifics on 

implementation can be rare. Often left out of consideration are rural intersections, which are often 

dimly lit or unlit and designed for higher speeds and typically have other confounding issues 

such as dark sky considerations and availability of utilities. Currently, guidelines for roundabout 

lighting is based on policies for signalized or all-way-stop intersections enhanced with additional 

computer based rendering simulations although roundabouts and intersections are significantly 

different in their operation and visual areas of concern. Note that some intersections are not 

controlled in any of the directions, and lighting may impact the safety at these intersections with 

noticeability of the intersection and potential conflicts.

There may not be a need to include visibility and nighttime conditions as a separate emphasis 

area in the intersection safety strategic plan, but the typical disproportionate crash rates at night 

on all roadways justify at least identifying the resources and potential countermeasures that can 

address safety issues related to nighttime conditions for each of the emphasis areas. 

Recent and Ongoing Research

Visibility within the focus area of intersection safety can be impacted by the use of lighting and 

traffic control devices at intersections. Several recent and ongoing projects investigating these 

issues are discussed here.

One key concern for safety at intersections is communicating to drivers the presence of 

intersection control so they properly respond. While the visibility of traditional intersection control 

devices such as stop signs and traffic signals is adequate in most cases, in some cases the 

intersection control devices can be made even more visible (or conspicuous) by measures such 

as added flashing lights, with the use of either beacons or LEDs embedded in stop signs.(19, 20)

Improving the sign visibility at the intersection may be another way to obtain similar results. FHWA 

research has shown that while upgrading stop sign retroreflectivity may lead to only a modest 

reduction in crashes, the low cost of installing new stop signs produces cost-effective benefits, 

particularly at lower-volume intersections.(21)

Research completed for an NCHRP project on overhead signs showed that legibility is directly 

linked to sign luminance, whether provided from internal illumination or with retroreflective 

sheeting.(22) Increase in retroreflectivity of signs or use of internal illumination can serve to not only 

enhance legibility but also improve overall conspicuity for alerting drivers to the intersection. TTI 

is currently evaluating the safety impacts of systemically upgrading signs with a case study in 

Albuquerque, New Mexico.
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A recent study of lighting levels at isolated rural intersections was completed by the University of 

Minnesota. The study found that lighted intersections had reduced nighttime crashes compared 

to unlit intersections of comparable traffic volume and configuration. Increasing the horizontal 

illuminance is effective at reducing nighttime crash rate regardless of source, whether highpressure sodium (HPS) or LED.(23) Other recent research found lighting at intersections to reduce 

crashes by 3.6–6.5 percent.(24)

In late 2015, VTTI completed a study investigating the positioning of intersection lighting and how 

that lighting helps promote the visibility of pedestrians. The study found that lighting the box of 

the intersection provided the best results in terms of visibility with a plateau of illuminance levels 

between 8 and 12 lx. This configuration requires fewer luminaires, which may lead to an energy 

saving solution.(25)

PEDESTRIAN AND BICYCLE SAFETY

Differences in size, speed, and use of safety gear make pedestrians and cyclists the most 

vulnerable of road users. In fact, pedestrians accounted for approximately 18 percent of all traffic 

fatalities in 2014.(26) Nearly 70 percent of all pedestrian-related crashes occur at night. There are 

many policies in place for providing lighting to intersection crosswalks and midblock crosswalks, 

but typically with little regard for the differences in vehicle headlamps and surrounding 

illumination.

Current Assessment of Nighttime Visibility in Program Area

The strategic plan for the pedestrian and bicycle safety area, updated in 2010 and available 

online, discusses the proportion of nighttime fatal crashes that involve pedestrians. Sixtynine percent of those fatal crashes occur at night. Reduced visibility compared to daytime 

conditions is clearly a contributing factor in the high number of pedestrian fatalities. The issue 

of nighttime visibility is clear in the strategic plan for pedestrian and bicycle safety, which lists 

several FHWA products and topic areas that address pedestrian safety at night. Some of these 

resources include the Pedestrian Forum Newsletter, the website pedbikeinfo.org, and information 

for developers to create safe and accessible communities. Other areas of the strategic plan 

summarize research related to nighttime visibility, such as the effects of lighting on pedestrian 

crashes. 

FHWA sponsored some work assessing crosswalk lighting. In general, based on the level of 

pedestrian conflict, more lighting is required in areas where pedestrian conflict is greater. 

Crosswalks are often co-located at intersections, so intersection lighting is often designed to 

encompass sufficient lighting for crosswalks and pedestrians. Midblock crosswalks can be lit but 

are at location on a roadways in areas where vehicles do not naturally stop and therefore have 

different visibility requirements. Pedestrians are more dependent on their own judgement to keep 

them safe. Since many pedestrians do not cross strictly at marked crosswalks, some consideration 

must be made to allow for these potential conflicts.
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Recent and Ongoing Research

Pedestrian safety from a perspective of visibility focuses on the ability of drivers to see pedestrians 

and to properly respond to their crossing at an intersection or potentially anywhere in the 

roadway. In a recent study, a collaborative effort between VTTI and North Carolina State University 

studied the gaze behavior of drivers entering and exiting roundabouts. Because roundabouts 

are features that allow vehicles to pass through the intersection without stopping, the ability to see 

crossing pedestrians at the right time is critical to their safety. Information gathered from this study 

can inform where pedestrian crossings and bicycle pathways may be best implemented.(27)

New methods that help drivers identify crossing pedestrians include pedestrian hybrid beacons 

(PHBs) and rectangular rapid-flashing beacons (RRFBs). RRFBs and PHBs are user-activated 

devices that help notify drivers that pedestrians are crossing or are about to begin crossing. 

Research has shown that drivers are more likely to yield when these treatments are used.(28, 29)

Recent research evaluated drivers yielding to pedestrians when these treatments are used to 

identify the conditions for which their use may be preferable.(30)

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3. REVIEW OF FATAL CRASH DATA

The Fatality Analysis Reporting System (FARS) is a query-driven database where all vehicle 

crashes in the United States as recent as 2014 are provided for public access. Vehicle crash 

fatalities are able to be filtered by a number of different options depending on the thoroughness 

of crash reporting. The filtered options can then be univariate or cross-tabulated for comparing 

data. It is important to note that the traffic volume and roadway length are not provided in 

the FARS database and that full crash rates cannot be calculated or analyzed because the 

exposure factor cannot be assessed. It is also noteworthy that the FARS data only give information 

regarding light condition and do not consider visibility treatments associated with retroreflectivity.

These data were considered in the three areas of roadway departure, intersection, and 

pedestrian and bicycle safety. The data, however, are not consistent across the areas. These 

differences are summarized below. Additionally, other variables were considered in this analysis 

and are also listed below. 

SAFETY DATA CONSIDERED

Roadway Departure

A crash is considered a roadway departure crash when a vehicle leaves the travel lane or lanes 

by either crossing the shoulder line or the center line of a roadway. It is important to note that the 

FARS database is not confident in the detailed reports of pedestrian and bicyclist data, including 

whether the pedestrian/bicyclist was on or adjacent to the roadway when struck, which would 

also inform roadway departure crashes.

Intersections

Intersections are areas of high conflict, and crashes at intersections can be attributed to a 

number of different causes. When considering pedestrians and bicyclists at intersections, similar 

to roadway departure crashes, the details for conflicts involving pedestrian and bicyclist crashes 

are not included in the FARS database.

Pedestrians/Bicyclists

There is a lack of data regarding conflicts with vehicles and pedestrian/bicyclist fatalities. The 

FARS database does have a disclaimer that inconsistencies were identified in the pedestrian and 

bicyclist data. Thus, while some of the data are used for this analysis and the absolute numbers 

of fatalities provided in the database are said to be accurate, further qualifiers such as motorist, 

pedestrian, and bicyclist position and maneuvers are not included.
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Other Data Variables Considered

Light Condition

In an attempt to find gaps in the research surrounding lighting, the three light conditions made 

available in the FARS database were used for this research: daylight; dark, not lighted; and dark, 

lighted. The dark, not lighted and dark, lighted conditions both encompass nighttime driving 

scenarios; however, one includes artificial infrastructure lighting. Daylight is simply defined by 

when natural light is present and is not otherwise considered dawn or dusk. Dawn and dusk were 

not included in this research because it is believed that the reporting of these times of day are 

objective and apt to be misattributed.

Weather

Weather can impact several factors in a typical driving scenario, not limited to traction or visibility. 

The conditions predominantly considered were clear (as a baseline), rain, and fog/smog/

smoke. Rain is an extremely common weather type and is encountered regularly by most drivers. 

Snow, sleet, and hail were not as focused in this effort due to the available crash statistics and 

the variance not accounted for. Snow can be on the roadway or be recently cleared and on 

the shoulder and still be considered a snowy condition. While snow, sleet, and hail do have an 

impact on lighting, it is believed to not be far from the effects of rain in general. Fog/smoke/

smog are represented well in the FARS database, and these conditions have a very direct and 

noticeable impact on lighting.

Driver Age

Driver age is an important factor due to the levels of experience, cognitive factors, and visual 

ability. Younger drivers are perceived to be more risk taking and more inclined to speed, whereas 

older drivers are believed to have trouble navigating complex segments and intersections and 

react more slowly to weather or other traffic.

Speed

One of the variables believed to strongly impact all three focus areas is speeding. One-third of all 

fatalities are reported to be a result of speeding, so speed is seen as a significant threat to safety. 

Aside from lighting technology that can serve as delineators or overhead roadway smart lighting 

that can adapt to driver speed and perhaps encourage drivers to slow down, there are few 

applications in infrastructure design where lighting can serve to curb speeding behaviors. On the 

other hand, the use of retroreflective infrastructure such as markings, signing, and delineation has 

some potential to control speed. For instance, peripheral transverse markings have been shown 

to be a successful countermeasure to speed, particularly in advance of a horizontal curve.(31)
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Rural and Urban

Not only do rural and urban roadways naturally distinguish themselves by the purposes they 

serve, the driver behavior on each may also be considered different. In general, rural roads are 

higher speed, are less populated, and consume longer stretches. Typically, urban roadways are 

lower speed, are more traveled, contain more pedestrians and bicyclists, abut varying types of 

intersections, and are more commonly lit by overhead roadway lighting.

ROADWAY DEPARTURE BREAKDOWNS

Roadway Departures by Rural and Urban by Weather

Clear conditions for 2014 account for nearly 7,000 fatalities on rural roadways and just over 

4,500 for urban roadways. Shown in Figure 1, more crashes occur at night for both roadway 

types, with lighted areas consuming about half of all night crashes. Lighted areas are typically 

more complex areas or areas in which crashes are common or most likely. Due to this, results 

are somewhat skewed in their favor; however, data do not show that dark, unlighted areas may 

warrant lighting to curb the amount of crashes that take place. It is noteworthy that while there 

are some differences, most likely due to exposure (i.e., fewer rural roads have lighting) in general, 

the percentages of each of these lighting conditions are generally stable across all of the road 

types, and the percentages are also fairly evenly divided between the lighting conditions, even 

though there are typically much lower traffic volumes and exposure during the nighttime.

Figure 1. Crash percentages by road type and lighting conditions for clear weather. 

(FARS Database, 2014)
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The rate of crashes in rain conditions is far less, with only 393 occurring on rural roadways and 

270 on urban roadways (Figure 2). Despite the greater traffic on urban roadways, rural roadways 

account for more roadway departure fatalities for both clear and rainy conditions. This is likely 

due to the fact that less traffic allows drivers to increase their speed and higher speeds allow less 

opportunities for drivers to safely recover from a roadway departure, which tends to result in more 

severe crashes. Also, rural areas have much less access to timely emergency services, which 

increases the fatality rate. The other critical aspect is the change in the percentages for the dark, 

not lighted condition. While in clear conditions, the percentages were similar on many roadway 

types, the dark, not lighted condition has a higher percent contribution. This might indicate the 

importance of retroreflective performance and/or lighting in wet conditions in terms of roadway 

departure crashes.

Figure 2. Crash percentages by road type and lighting conditions for rain. (FARS Database, 2014) 

Weather Conditions and Roadway Departure

When conditions are clear or rainy, the rates of fatalities across lighting conditions are nearly 

identical. Figure 3 shows that larger differences exist during times of sleet, hail, snow, fog, and 

smoke. In general, sleet- or hail-related fatalities are very few, and only 13 total were reported in 

2014 for rural and urban roadways combined. Snow-related fatalities occur more commonly in 

daylight or lit areas of urban roadways, again likely due to exposure. For rural areas, the link is 

more difficult to assess because snow presence/condition data are less available than they are 

for urban areas. Ideally, the snow presence/condition data would be more robust and include 

details on the difference between the presence of snow on a roadway and a scraped and salted 

roadway, which may not occur as often in some rural areas, and icy roadways as a result of all 

the above.
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Figure 3. Crash percentages by road type, lighting condition, and weather condition. 

(FARS Database, 2014)

Age and Roadway Departure

Younger and middle-aged drivers perform similarly in clear and rainy conditions. Older drivers 

seem to have a higher daytime crash exposure than nighttime exposure. Again, older drivers tend 

to self-restrict their driving at night, so their exposure, particularly in the rain, is likely lower (Figure 4).

Figure 4. Crash percentages by lighting condition and age group for clear versus rain weather conditions. 

(FARS Database, 2014)
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Roadway Departure as a Result of Speeding

Because roadway departures are often linked to speeding, it is no surprise that more speedingrelated roadway departure fatalities occur at night due to the fact that drivers often out-drive 

their headlamps. In other words, headlamps span between 250 to 300 ft ahead of the car, and 

at higher speeds, the reaction time this span creates becomes smaller. The increased number of 

speed-related fatalities shown in Figure 5 for lighted areas is interesting because it is believed that 

there are many more unlighted roads and thus more opportunity for roadway departure crashes. 

However, as already mentioned, lighted roadways are often lighted because the proclivity for 

crashes is predicted to be higher in those locations. 

Figure 5. Crash percentages of speeding versus non-speeding by light condition. 

(FARS Database, 2014)

INTERSECTION BREAKDOWN

Intersection Fatalities by Light Conditions and Intersection Type

Figure 6 shows fatality crash totals for intersections. The percentages for intersections that are 

not four-way or T-intersections are perhaps too low for making statistical inferences, especially 

considering that roundabouts and five-point intersections are almost always lighted, so very 

few dark, not lighted fatalities will occur. The extent to which any of the intersections reflected in 

these data are lit is unknown. Despite some intersections being lighted already, there may be an 

opportunity to improve the lighting design. In many regards, the lighting of unique intersections, 

such as those with five or more points, may need to be considered case by case.
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Figure 6. Crash percentages by intersection type and lighting condition. (FARS Database, 2014)

Fatalities at Four-Way Intersections by Age Group 

Fatalities at four-way intersections are common among all age groups, with more older drivers 

being involved in fatal crashes during the daylight when they are likely more inclined to drive. 

Percentages in dark, unlit sections of road are consistent across all age groups, suggesting that 

unlit four-way intersections are less common and that age plays a small factor (Figure 7).

Figure 7. Crash percentages at four-way intersections by age group and lighting condition. 

(FARS Database, 2014)
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Figure 8 and Table 1 demonstrate the differences in traffic control type by lighting condition. 

The influence of these data is largely dependent on design and exposure. If the number of 

pedestrians in an area warrants a pedestrian signal, then it is also likely going to be a lighted 

area. Areas without a pedestrian signal encounter fewer fatal crashes in general and also fewer 

at night. Intersections that are controlled only by stop signs or yield signs are not as typically 

lighted, resulting in a higher rate of dark and unlighted crashes. In general, the data indicate that 

dark but lighted intersections, which typically encounter more traffic and more pedestrians, may 

require a research effort to determine opportunities for improved safety.

It is important to note, in Table 1, several traffic control devices (flashing, warning, railroad, school, 

and unknown) and lighting conditions such as dusk and dawn are not included in these tallies.

Figure 8. Crash percentage by lighting condition and intersection control type. (FARS Database, 2014)

Table 1. Total Fatal Crashes for Lighting Condition by Traffic Control Type.

Traffic Control Device Daylight

Dark—Not 

Lighted

Dark—

Lighted

Traffic control signal 275 39 70

Traffic control signal with pedestrian signal 446 20 344

Traffic control signal, pedestrian signal unknown 1,901 194 1,148

Stop sign 1,608 350 258

Yield sign 70 19 17

TOTAL 4,300 622 1,837
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Fatalities by Intersection Type and Light Condition for Clear Conditions versus Rain

Figure 9 compares intersection type for weather conditions and shows an increase in the 

percentage of crashes at unlighted four-way intersections when rain is present. However, it is 

important to note that there are far fewer reported fatalities in rain conditions compared to clear 

conditions—5,002 fatalities compared to 372. The change in the percentage when lighting is 

added is interesting in that there appears to be a potential to reduce fatalities at intersections by 

adding lighting, in particular for T-intersections

Figure 9. Crash percentages by lighting condition and intersection type by weather. 

(FARS Database, 2014)

PEDESTRIAN AND BICYCLIST SAFETY DATA

Pedestrian and Bicyclist Fatalities at Rural Intersection Types

Crash percentages (Figure 10) and total crashes (Figure 11) illustrate the major differences 

between main intersection types in rural zones. There are far fewer pedestrian- and bicyclistrelated fatalities at intersections that are not either T-intersections or four-way intersections 

based solely on exposure since there is an overwhelmingly greater number of T- and four-way 

intersections. Interestingly, unlighted T-intersections are associated with more fatalities than other 

types for other lighting conditions, perhaps indicating a need for better understanding failure 

points at T-intersections and determining a need for lighting. 
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Figure 10. Crash percentages by lighting condition and intersection type for rural roadways involving 

pedestrians and bicyclists. (FARS Database, 2014)

Figure 11. Total fatal crashes by lighting condition and intersection type for rural roadways involving 

pedestrians and bicyclists. (FARS Database, 2014)

Pedestrian and Bicyclist Fatalities at Urban Intersection Types

Crash percentages (Figure 12) and total crashes (Figure 13) illustrate the major differences 

between main intersection types in urban zones. The trends are similar to those of rural roadways; 

however, the sheer volume of incidents is much greater for urban areas, as is expected. Dark, 

lighted roadways encounter more fatal crashes involving pedestrians and bicyclists due to the 

common roadway design of having lighting placed in areas where pedestrian and bicycle traffic 

is typical.
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Figure 12. Crash percentages by lighting condition and intersection type for urban roadways involving 

pedestrians and bicyclists. (FARS Database, 2014)

Figure 13. Total fatal crashes by lighting condition and intersection type for urban roadways involving 

pedestrians and bicyclists. (FARS Database, 2014)
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SUMMARY OF FATALITY DATA REVIEW

While the FARS database provides a rich source of information for the potential causes and 

remedies for fatal crashes, the limitations in the data—in that the actual exposure cannot 

be calculated—confine the ability to perform a complete analysis of the impact of visibility 

treatments on fatalities. 

There are some initial trends in terms of the impact of lighting that can be seen when 

considering the fatalities. In terms of roadway departures, there seems to be an impact of lighting 

in bad weather. Similarly, in terms of the intersections, there is the potential to reduce fatalities at 

T intersections with the addition of lighting. There may be many other trends in the data, but they 

are likely hidden by the crash exposure rate.

One of the primary findings in the data is that there is a significant need to perform a complete 

and proper analysis of visibility treatments in terms of safety that accounts for exposure, 

retroreflectivity, and all roadway geometry impacts.
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4. BEST PRACTICES

In a review of current practices, some states and agencies emerged as leaders in the application 

of visibility treatments. A summary of the state practices for lighting is shown in Appendix B. 

In terms of lighting, many states have moved significantly forward with the application of new 

lighting technology. Many states have developed a specification for solid state luminaires, 

including Virginia DOT, Illinois DOT, and Alaska DOT. These states have been sharing their 

results, and some similarity is being found in their specifications. This is an important step in the 

implementation of the new technology because LED luminaires are significantly different in their 

applicability to the roadway than are the traditional solutions.

From a city perspective, some municipalities are implementing adaptive lighting systems. These 

include the City of Cambridge, Massachusetts, and the City of San Jose, California. In both of 

these cities, lighting is dimmed based on the time of day. This practice has been implemented 

as both a cost-saving method and as an effort to reduce the negative impacts of lighting on the 

environment and roadway users. 

Another implementation of a lighting control system is the use of the system to accurately 

provide a lighting level on the roadway regardless of the wattage and the power usage of 

the luminaire. Hawaii is using the same luminaire in all applications and then dimming to the 

appropriate lighting level. This approach significantly reduces inventory and maintenance costs 

while continuing to provide the recommended lighting levels.

Some cities, like the City of Los Angeles, are using the data-carrying capabilities of the lighting 

network to provide a backbone for connected-vehicle and smart-city applications.

Based on the assessment of the agencies, the best practices are (in order of technical 

complexity):

1. Development of a specification solid state lighting specific to the roadway types and 

needs of the lighting network.

2. Implementation of a control system where each luminaire is able to be managed from a 

central location.

3. Implementation of lighting only when and where it is needed through crash analysis and 

updated warrants.

4. Implementation of an adaptive lighting system based on the time of day. 

5. Implementation of an adaptive lighting system based on road conditions, user needs, and 

connected vehicles.

While many agencies are working on some aspect of each of these approaches, no single 

agency has achieved the highest level of implementation.

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5. CURRENT GAPS IN PRACTICE AND RESEARCH

As part of this study, researchers identified gaps in the current body of knowledge regarding the 

three areas of roadway departure, intersection, and pedestrian/bicycle safety. For each of these 

topics, an initial problem statement was developed and is presented in Appendix C.

ROADWAY DEPARTURE SAFETY

Placement of Roadway Lighting

Determining where lighting is most effective at reducing crashes could inform policy on roadway 

lighting design. Data made available in existing databases like SHRP2 can be a target of further 

research.

Geometric Considerations

Roadway departures occur on both tangents and curves. Determining the effectiveness of 

lighting a curve versus a tangent can be informative regarding how lighting can best be 

implemented. Current standards for curved roadways include instruction for pole placement to 

reduce the likelihood of a collision by an errant vehicle, but less research pertains to what areas 

of a curved roadway should be lighted to reduce departures.

Lighting and Inclement Weather

Adverse weather can reduce visibility of the roadway and pavement markings. The impact 

of lighting in adverse weather on many different road types and in combination with varying 

pavement markings and sign materials has yet to be fully explored. Policies rarely consider the 

diminished visibility caused by adverse weather conditions. 

Determining When to Use Roadway Lighting

The use of roadway lighting is often determined by levels of annual average daily traffic in 

combination with areas of conflict, municipal regulations on lighting, economic viability, 

functional class, and zoning. Most traffic, however, occurs during the daytime. If roadway lighting 

is partially determined by traffic volumes, a count of nighttime traffic should be used as a 

decision threshold because it directly matches the traffic (vehicle miles traveled [VMT] for RwD, 

entering traffic for intersections, and pedestrians/bicyclists for that focus area) that would use 

the lighting. Another determining factor is public opinion on whether an area does or does not 

warrant lighting.

LED technology is slowly replacing HPS lighting conventionally used in most roadway lighting 

applications. LEDs can be controlled to output varying intensities and color, and achieve 

particular angles to satisfy ordinances. This adaptable aspect of an LED can foster more research 

in these specific areas that has not been possible with HPS and other light sources. 
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Vehicle Lighting

Headlamps are to have a minimum height of 22 inches, with a maximum of 54 inches. Taillamps 

are to be a minimum height of 15 inches, and no higher than 72 inches.(32) These measurements 

are to be made when there are no occupants or baggage in the vehicle. The additional weight 

would reduce the height of these lights. Guidelines for the design of vertical curvature and 

passing sections are based on stopping and passing sight distances that usually assume vehicle 

headlamps and taillamps are at a height of 24 inches.(7) With the allowable taillamp height 

lower than the assumption commonly used in design (and possibly even lower when the weight 

of passengers and baggage is accounted for), there are potential safety concerns related to 

stopping sight distances involving low vehicles on crest vertical curves.

It is understood that the characteristics of all vehicles cannot be accounted for in highway 

design, but there is a disconnect between the minimum specification for the heights of vehicle 

lamps and the values commonly used in design. Another issue related to headlamps and 

vertical curvature is the shadow zone that occurs beyond the crest of a vertical curve, where 

an object in the road may not be visible until it is within the direct line of an approaching 

vehicle’s headlamps. The AASHTO Green Book suggests that with the assumed 24-inch height 

of headlamps, an object 16 inches above the roadway will be within the line of the headlamps 

at a distance equal to stopping sight distance.(7) This means drivers will typically see objects 16 

inches above the pavement in time to stop. However, this may not be true for objects less than 

16 inches high or if the headlamps are less than 24 inches high (which is currently permissible). 

Research that leads to coordination between the headlamp specifications and typical design 

assumptions is recommended.

The advent of LED headlamps has affected how drivers perceive and react to oncoming 

headlamps and glare. Research indicates that LED headlamp sources are better than halogen 

headlamps and comparable to high-intensity discharge headlamps in terms of photometric 

performance and visibility. The blue-white color produced by the headlamps does reportedly 

cause glare and discomfort to oncoming drivers.(33) Research into alternative LED colors 

and more precise beam patterns may mitigate the discomfort to other drivers and maintain 

photometric and visibility properties. Additionally, the colors produced by the different types of 

headlamps may have unique effects on sign visibility that are yet to be identified.

Vehicle headlamps are often overlooked when developing designs and policies for roadway 

lighting and signing. There are several positive safety effects of new headlamp technologies, 

such as adaptive headlamps that reduce glare for oncoming vehicles or turn in the direction 

of curves. However, these and other changes in headlamp illumination may have detrimental 

effects on visibility that should be considered in future research and policies. A new report 

by the Insurance Institute for Highway Safety (IIHS) demonstrates that most headlights need 

improvement.(34)
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Standardized Police Reporting

The implementation of lighting is partially driven by crash data obtained from on-scene crash 

reporting. Currently, there are no known standards among law enforcement agencies for 

reporting the placement and contribution of lighting for crashes. An effort to collect data on how 

different agencies interpret and apply knowledge related to lighting for crashes could improve 

how crash data are reported and be a step toward standardizing the reporting process. Currently 

the Model Minimum Uniform Crash Criteria (MMUCC) includes a field dark—lighted. 

Definition of Sight Distance

Sight distance is defined by AASHTO as the length of roadway visible to the driver. It can be 

categorized into horizontal and vertical sight distance: horizontal sight distance is limited by 

objects and the changing alignment in the horizontal plane, while vertical sight distance is limited 

by objects and the changing alignment in the vertical plane. Sight distance is generally not 

specified as being applicable to a certain time of day (daytime or nighttime). However, many of 

the assumptions used to calculate different sight distances (e.g., stopping sight distance, decision 

sight distance, passing sight distance) are based on values that may only be relevant for daytime 

conditions when daylight illuminates objects and the roadway environment.(7)

When discussing the topic of sight distance, the traditional design manuals have little mention 

of specific values or considerations for nighttime conditions. AASHTO guidelines for stopping 

sight distance (SSD), for example, are based on the provision of adequate sight distance at 

every location on a roadway such that drivers traveling at or near the design speed can see a 

stationary object in the road and stop before reaching it. The AASHTO assumptions for SSD use 

a driver eye height of 3.5 ft and an object height of 2 ft. (The 2-ft object height is one example 

where nighttime conditions are considered because most taillamps are 2 ft or higher from the 

ground. However, there is still a vulnerability from encounters with shorter objects or vehicles 

lower to the ground, as mentioned above.) There are no specifics to the shape, color, contrast, 

or reflection of the object, implying that this is a daytime design element. In general, decision 

sight distance uses the same basic models as SSD but with longer perception-reaction times, 

consequently neglecting the differences between day and night conditions.(7)

Pavement Marking Retroreflectivity

There is still some debate about the trade-off between pavement marking retroreflectivity 

levels and size of pavement markings (width). More research is needed to determine if wider 

longitudinal pavement markings (i.e., 6 inches) may provide more visibility to drivers and if 

that gain is enough to provide any relief to the proposed minimum retroreflectivity levels being 

pursued by FHWA. Also, there is a series of studies available in the last decade showing a 

consistently stronger link between pavement marking retroreflectivity and safety. However, there 

is not a general consensus on the relationship, and more work is needed to establish the link. 

Finally, since machine vision systems are becoming more common, there is a need to determine 

the pavement marking performance needs for machine drivers (compared to human drivers). 
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Research is also needed in the area of pavement markings specifically designed to maintain 

their retroreflective performance conditions under wet nighttime conditions. The crash data 

reviewed in this report indicate that roadway departure crashes under the category of the dark, 

not lighted condition were more prevalent in wet conditions compared to clear conditions. This 

finding seems to indicate the importance of retroreflective performance in wet conditions in 

terms of roadway departure crashes. However, more research is needed in this area to develop a 

better understanding of how increased wet nighttime retroreflectivity levels can mitigate roadway 

departure crashes. 

Pavement Markings for Machine Vision

There has and continues to be a fast-paced advancement in vehicle technologies that provide 

driver assistance such as lane departure warning, lane keep assistance, and automated steering. 

The primary sensor used today for these systems is a camera mounted in the windshield. These 

systems are meant to keep vehicles on the road and in their lane. They rely on the ability to detect 

edge lines and lane lines. Research is currently underway to better understand the performance 

needs of pavement markings so that the machine vision systems can reliably perform their 

intended driver assist functions. NCHRP is sponsoring the research and the objective of the 

research is to develop information on the performance characteristics of pavement markings 

that affect the ability of machine vision systems to recognize them (http://apps.trb.org/cmsfeed/

TRBNetProjectDisplay.asp?ProjectID=4004). 

Traffic Sign Visibility 

Recent research identifies conditions for which retroreflective traffic signs may be too bright.(35) 

While the MUTCD identifies minimum levels of maintained retroreflectivity, there are no guidelines 

specifying when the luminance from a sign causes glare that may be a safety hazard. The glare 

from signs reduces the distance at which drivers can see hazardous objects and also reduces 

response times.(36) The concern for glare from signs should extend to the use of digital signs as well. 

Digital signs can be loosely defined as LED-enhanced signs such as stop signs with flashing LEDs in 

the border, chevrons with flashing LEDs, or even full-color digital changeable message signs. 

The MUTCD states that the brightness of changeable message signs should be adjusted 

under varying light conditions to maintain legibility, implying a concern that they need to be 

bright enough to be read during the daytime.(37) However, there is no mention of the issue that 

changeable message signs may be a source of glare at night. This concern should be especially 

noted for full-matrix LED signs capable of very high light output. While previous sign research 

emphasized the need for legibility, the improvements in sign materials and the increasing use of 

digital infrastructure open up the possibility that these signs are too bright for driver comfort and 

safety. Future research and applications should address these concerns.

Additionally, there is a need to identify stronger relationships between the retroreflectivity levels 

of traffic signs and roadway departure crashes. Research has shown some evidence that there 

appears to be a maximum level of retroreflectivity depending on specific conditions,(35) and 

FHWA has established minimum levels based on the needs of nighttime drivers in the MUTCD. 

However, there are no established correlations between retroreflectivity and crashes. In some 
ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

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ways, having recommended guidelines for appropriate sign sheeting selections based on the 

specific conditions (e.g., roadway, traffic, roadside) would be an alternative way to address this, 

but again, these would need to be developed. 

Speed Limits

Most speed limits are set by legislative action or studies that determine the 85th percentile speed 

under free-flow conditions. When determined based on speed studies, most often the speed 

data are collected during the day, meaning that nighttime conditions are not accounted for 

in selecting speed limits. While separate speed limits are permitted at night, few agencies use 

nighttime speed limits, and there is no guidance provided in the MUTCD for establishing nighttime 

speed limits. In addition, there is the concern of over-driving headlamps at night. While no recent 

study has been completed on this topic, there is a growing concern that the new headlamp 

trends may be generating a need to take a fresh look at this somewhat controversial topic. Ongoing research may address this need (NCHRP 17-76, Guidance for Setting Speed Limits). 

Horizontal Curve Design and Curve Advisory Speeds

The design of horizontal curves is based on comfortable lateral acceleration rates derived 

during daytime studies. At night, however, reduced visibility may affect a driver’s threshold level 

of lateral acceleration where discomfort begins, thus affecting the comfortable curve advisory 

speed for the curve. While a separate advisory speed for night seems impractical, there may 

be implications related to safety if drivers are actually not comfortable adopting the advisory 

speed at night. In an exploratory analysis of unfamiliar driver data collected during both daytime 

and nighttime conditions, it was found that drivers on curves accept lower levels of lateral 

acceleration at night than during the day. However, contrasting the reduced lateral acceleration 

was a finding that driver speeds were higher at night (possibly from cutting curves with a wider 

path).(18) Further analysis of the implications of curve advisory speeds and nighttime driving 

could lead to improvements in how these advisory speeds are set and used.

INTERSECTION SAFETY

Lighting at Rural Intersections

Rural intersections vary in a number of ways, as do the policies and standards for lighting them. 

The factors involved in fatal crashes at many high-speed intersections in rural areas, whether 

signalized or not signalized, need to be explored to better inform policy for lighting.

Transient adaptation occurs when drivers travel to and from lit and unlit areas and may cause 

issues with vision for drivers as they pass through a lighted rural intersection. The general policy 

is to provide a tapering of lighting so that the transition between the two areas is gradual and 

comfortable. Exploring the limits of transient adaptation can better inform policies on rural 

intersection lighting as well as tunnel lighting.

As mentioned, another consideration for rural intersections are those of availability of electrical 

power, impact on flora and fauna as well as dark sky considerations. Reducing the light to a level 

that provides the safety benefits without over lighting is critical in these kinds of environments. 
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Using minimum lighting levels reduces the negative impacts of lighting, reduces consumption 

and provides the opportunity to investigate alternative power sources such as solar and wind 

generation. Determining this minimum level is another critical component of the required 

research.

Intersection Sight Distance and Gap Acceptance

A recent NCHRP project has identified the safety impacts of providing intersection sight distance 

(ISD), showing that fewer crashes occur as ISD increases.(38) Even though ISD is measured based 

on geometry, there may be issues related to nighttime visibility if the clear sight triangles needed 

for adequate ISD can be different during the night than during the day. Controls for ISD are 

based on principles of gap acceptance, which has been derived from daytime observations. A 

driver’s gap acceptance is a function of perception-reaction time, the time (and distance) used 

to make an appropriate maneuver, the speed of the conflicting vehicles, and any buffer added 

for personal preference and safety. The duration of a gap that drivers select may vary with time 

of day. At night, this may be impacted more because visibility is limited and there is potential for 

misjudging the distance of a conflicting vehicle. It is possible that what may be an acceptable 

sight distance during the day may not be adequate at night. Future research may address how 

gap acceptance changes by time of day, whether there is a need to consider how nighttime 

gap acceptance may impact ISD and intersection safety, and whether or not intersection 

lighting would mitigate these effects.

Selecting Phasing for Left Turns

The second edition of the Signal Timing Manual (NCHRP Report 813) provides national guidance 

on the selection of left-turn phasing modes at signalized intersections. Practitioners select 

protected or permissive phasing based on criteria such as the number of left and through lanes, 

sight distance, turning volumes, speeds, and crash history.(39) There is no specific consideration 

for nighttime conditions. These guidelines can be improved by including special circumstances 

for nighttime conditions (for example, appropriate thresholds for nighttime crashes rather than 

total crashes only or turning volumes at night rather than peak-hour volumes). This is a classic 

example of where reviews of national policies is needed with a focus on nighttime considerations. 

Review teams would include a nighttime visibility expert along with a team of relevant subject 

matter experts. A review should also include more than just left phasing, for instance, right urn 

phasing, right turn on red, and protected/permission phasing. 

Skewed Intersections: Visibility of Pedestrians or Bicycles at Night

Intersections with large skew angles are potential safety concerns at night for pedestrians 

and bicycles approaching the intersection from a conflicting direction. Because a vehicle’s 

headlamps are directed forward, with only a small amount of illumination distributed away from 

the center, there may be conditions where drivers are unlikely to see pedestrians or bicycles from 

some directions, depending on the use of lighting. At night, the visual attention of drivers tends to 

be concentrated in a smaller area than during the day, meaning that drivers are additionally less 

likely to search for those approaching pedestrians and bicycles. This concern can be addressed 
ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

31

by evaluating the illuminance patterns of headlamps and whether or not the light distributed 

horizontally at wide angles is enough for a driver to see pedestrians and bicycles.

Signal Warrants

Most of the warrants for determining whether a signal should be considered at an intersection 

focus on conditions experienced during the daytime. The heaviest traffic in most places tends 

to occur during morning and afternoon/evening peak hours, so it is reasonable that the listed 

warrants encourage the engineer to focus on those times of the day. However, special nighttime 

conditions may exist that warrant the use of a signal at an intersection. Examples may include 

reduced visibility or an unexpected peak in traffic due to a particular traffic generator. In fact, 

visibility appears to not be a concern in any signal warrant except indirectly as part of the crash 

warrant.

Alternative Interchanges and Intersections

Innovations in interchange and intersection design can promote large increases in efficiency, 

with some intersections (such as roundabouts) providing for the free flow of vehicles. Diverging 

diamond interchanges and displaced left-turn or continuous-flow intersections are recent 

concepts specifically designed to address conflicts with turning vehicles. The proper use of 

lighting and signage at these types of intersections is critical because they are very different from 

typical stop-controlled or signalized intersections. Pedestrian safety is also a critical component of 

determining the lighting and signage needs..

Traffic Signs

There is a need to establish recommendations for traffic sign retroreflectivity (materials) 

and possibly pavement markings. Depending on the type of environment and intersection 

control (rural versus urban, or stop sign versus signal), there could be justification for different 

performance levels. In fact, there are no national recommendations or guidelines that a 

practitioner can use to select the appropriate retroreflective product or performance level for a 

specific scenario. This is particularly needed for signing at intersections but it is also a general 

need that extends beyond intersections. 

Automation and Controls

With the advent of solid state lighting, controlling where the lighting can be turned on and off as 

well as dimmed is becoming more important. This technology provides the opportunity to adjust 

lighting levels and to react to the presence of vehicles and pedestrians. The investigation of the 

possible options of this type of technology is general for all lighting in the roadway.
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PEDESTRIAN AND BICYCLE SAFETY

Lighting for Pedestrians

Lighting is commonly designed for vehicles and not for pedestrians. Providing a standard of 

lighting that meets the criteria for both is a key interest. Lighting for pedestrians is believed to 

be more crucial in providing the greatest safety benefit at conflict points. Gap acceptances for 

pedestrians and the perception pedestrians have of how visible they are to drivers are research 

topics that have been explored in the past and can be re-explored with the advent of modern 

in-roadway lighting, crosswalk lighting, vehicle headlamps, and education.

Vertical illuminance is among the most important factors for determining the contrast and 

visibility for a crossing pedestrian. Methods for achieving the required vertical illuminance may 

need to be explored because current standards are often believed to be difficult to achieve. The 

amount of vertical illuminance required may vary depending on an array of variables including 

environmental lighting, intersection lighting, crosswalk size, and crosswalk geometry.

In-roadway lighting is becoming an important area of interest as more agencies adopt it as a 

method of promoting safety and reducing energy. In-roadway lighting at crosswalks is believed 

to be a benefit for drivers to visualize crosswalks ahead of time and for pedestrians to have a lit 

path. However, installations of in-roadway are difficult to maintain and can be very expensive. As a 

result, the effects of in-roadway lighting in combination with area signage, overhead lighting, and 

retroreflective markings need be explored along with a benefit and cost assessment to better 

inform policy.

Newer technology for modern roadway lighting has led to more precise output from luminaires. 

This results in less light spilling over to sidewalks since higher-quality optics provide adequate 

lighting for the roadway but not for pedestrians. Investigating the impact of newer technologies, 

such as the Nadir Dump and other luminaire types, may inform future roadway lighting design 

with sidewalks and crosswalks in mind.

Seasonal Fluctuations in Daylight Hours and Effects of Daylight Savings Time

The change in when daylight occurs because of the changing seasons and the adjustments 

that occur with the use of Daylight Savings Time (DST) mean that there are periods when road 

users may be accustomed to daylight but experience darkness. In some locations and during 

certain times of the year, peak traffic volumes may occur at night. With DST, the sudden change in 

whether or not a commute occurs during daylight has significant safety implications, especially 

on pedestrians and cyclists.(40) These road users are often poorly visible due to an absence of 

lighting. If agencies provide street lighting, it may be valuable to investigate how they address DST 

changes and gradual seasonal daylight changes, whether with automatic lighting or with timers. 

Consistency in when lighting is provided relative to ambient light is important, especially for these 

vulnerable road users.
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Glare from Beacons, Signals, and Other Lights

Flashing beacons and lights used on signs at intersections, midblock crosswalks, and other 

locations have been shown to be effective at grabbing attention, but glare from these lights 

may have a detrimental effect on drivers’ ability to see pedestrians and marked crosswalks, 

especially at night. Some text in the MUTCD instructs that automatic dimming for traffic signals 

should be used if a signal’s indication is bright enough to cause glare.(37) There appear to be no 

specifications, however, for appropriate levels of illuminance for these lights at night. In addition 

to flashing beacons used for crosswalks, the concern regarding glare may be relevant for all 

sources of light, including all traffic signals (including PHBs), LEDs on signs, railroad gates, inroadway lights, and lane use signals.

Assumptions for Pedestrian Walking Speed

The assumed pedestrian walking speed suggested in the MUTCD is conservatively set at 3.5 

fps, with accommodation for slower walking speeds for special conditions.(37) It is likely that the 

research used to select the recommended pedestrian walking speed focused exclusively on 

daytime conditions, neglecting the behavior of pedestrians at night. Researchers in a recent 

study showed that the time of day may impact walking speeds, with pedestrians walking 

approximately 0.5 fps slower during the evening peak than during the morning peak.(41) That 

analysis, however, involved data collected only during those two time periods. Additionally, the 

data were collected in New York City (Manhattan), where the density of pedestrians tends to be 

high. Regardless, a different walking speed attributed to the time of day may justify examining the 

issue with more depth.

School Zones Marked with Word Markings

There are several instances in the MUTCD that specify that certain objects must have 

retroreflective properties.(37) There is currently no language specifying that the “SCHOOL” word 

marking informing drivers they are entering a school zone must be retroreflective. Although it is 

likely that the marking would be made of the same retroreflective material as the nearby line 

markings, there may be a question about whether the marking should be held to a standard of 

maintained retroreflectivity. If there are periods of the year during which school activities begin or 

end during dark or nighttime conditions, there may be justification to evaluate the brightness of 

the marking.

Bike Lanes 

FHWA has approved the use of green pavements to delineate bike lanes. Generally, there is no 

nighttime visibility component to the green bike lanes (adding glass beads reduces the friction). 

There is a need to develop technologies and materials that can help provide nighttime visibility 

to bike lanes so that their paths are as easily identified during dark conditions as they are during 

daytime conditions. 
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OTHER AREAS WITH NIGHTTIME VISIBILITY CONCERNS

The following research concerns do not fit within the three target program areas, but the topics 

arose in the course of identifying gaps in current practices and research related to nighttime 

visibility. Several of these research areas are a result of budding and future technologies that 

promise ways to provide cheaper and more-efficient lighting through sensors and automation. 

The effect these technologies will have is unforeseen, and research into their impacts on safety is 

warranted.

Health Effects of Roadway Lighting

In a recent document, the American Medical Association (AMA) noted that the presence of the 

blue portion of the lighting spectrum in light sources has the potential to impact the health of 

humans living close to the light source.(42) AMA recommends that the light source be no greater 

than 3000K in color temperature. Studies have, however, shown that light sources with a 4100K 

color temperature perform at a higher level in terms of the visibility of objects in the roadway.(43) It 

is vital that these issues be considered.

Energy Consumption

Energy conservation has become a focus for many precincts and agencies. Removing lighting 

from infrastructure has become a popular method of conserving energy with some disregard 

to the impact of safety. Exploring methods of conserving energy in areas while maintaining 

safety should be a focus to inform policy and prevent uninformed decisions by infrastructure 

managers. Some known methods to efficient methods of lighting that allow for reduced energy 

consumption include the use of in-roadway lighting to highlight conflict points and prevent light 

trespass. Adaptive lighting technology is also a popular method of utilizing light only when it is 

necessary to do so.

The natural extension of this would be lighting on demand. LED lighting can be implemented 

with motion sensors or through connected-vehicle technologies to have lighting respond to the 

presence of a vehicle or pedestrian. Sample projects have been implemented in a controlled 

test road environment, but wider implementation will be developed in the future.

Automation

The anticipated adoption of connected and automated vehicles allows for innovative 

approaches to lighting. On one hand, vehicle automation may reduce the need to use lighting 

because so much of what the vehicles “see” will not be with light in the visible spectrum. On the 

other hand, there will still be other road users (such as pedestrians) that are just as deserving of 

safe and efficient transportation. The concept of smart cities with connected infrastructure opens 

up opportunities to apply lighting on demand and intelligently adapt to the users’ needs.
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Lighting Uniformity

Uniformity is regarded as a desired effect of roadway lighting, though some research disputes 

this claim. There is room to explore the limits of lighting uniformity and its interaction with in 

roadway lighting, retroreflectivity, pedestrian visibility, and lighting color. The day-to-night effect 

of uniformity is important since daylight is highly uniform and roadway lighting generally strives 

to replace daylight; however, differences in source location and mount height tend to affect 

the angle of intensity of lighting. This causes severe shadows. In addition to roadway lighting, 

uniformity in intersections where light sources from other vehicles and infrastructure exist should 

be investigated.

Bridges

The AASHTO Green Book calls into question the justification of cost for lighting rural bridges. 

Whether or not rural bridges attribute to a number of conflicts and collisions that can be rectified 

by the addition or subtraction of lighting or delineators should be explored.(7)

Interaction of Overhead Lighting

The effect roadway lighting has on fauna, foliage, and crops is an aspect of lighting that is rarely 

documented in policy. Exploring the factors that benefit or harm wildlife in regard to lighting 

can provide insight on better and safer implementations. Research on this topic can also seek 

to understand the effect of environmental lighting, which is currently based on consensus 

knowledge. Adaptive lighting takes environmental effects into account, but the extent has not 

been properly researched.

Curve Design Accounting for Nighttime Line of Sight

One of the controls for the design of horizontal curvature is the line of sight cutting across 

the inside of the curve, limited by an obstruction that is offset from the road. The equation for 

calculating whether or not there is sufficient sight distance for curves is based on an assumption 

that the obstruction is the only limiting factor and the object would otherwise be visible to the 

driver. At night, however, driver vision can be restricted to the pattern of light from headlamps, 

which is mostly concentrated in a direct line in front of the vehicle. driver at night may not be 

able to see an object in the road near the end of a curve since the headlamps are only directed 

straight ahead. The limited amount of headlamp illumination that is scattered horizontally needs 

to be considered to properly judge sight distance when designing horizontal curves. Potential 

research in this area should evaluate the distribution of light from headlamps and whether 

objects would be visible at the wide viewing angles that can occur with sharp curves. 

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REFERENCES

As stated previously, this report is a snapshot of some best management practices—currently 

under real-world deployment—within agencies around the nation; it is not intended to be a 

comprehensive guide to managing roadside trees and poles. There have been a number of 

other works written about tree and pole management strategies and additional research is 

being proposed within the industry. In addition to the AASHTO Roadside Design Guide, the two 

works described and cited below are recommended reading for additional information. 

1. Hills, B.L. Vision, Visibility, and Perception in Driving. Perception, Vol. 9, 1980, pp. 183–216.

2. AASHTO. Highway Safety Manual. AASHTO, Washington, DC, 2010.

3. Allen, M.J., R.D. Hazlett, H.L. Tacker, and B.V. Graham. Actual Pedestrian Visibility and the 

Pedestrian’s Estimate of His Own Visibility. American Journal of Optometry & Archives, 

Vol. 47, 1970.

4. Lutkevich, P., D. Mclean, and J. Cheung. FHWA Lighting Handbook. FHWA-SA-11-22. Federal 

Highway Administration, Washington, DC, 2012.

5. FHWA. Roadway Departure Safety. Available at http://safety.fhwa.dot.gov/roadway_dept/.

6. FHWA. FHWA Roadway Departure (RwD) Strategic Plan. Revised 2013. Available at http://

safety.fhwa.dot.gov/roadway_dept/docs/rwd_strategic_plan_version2013.pdf.

7. AASHTO. A Policy on Geometric Design of Highways and Streets (Green Book). AASHTO, 

Washington, DC, 2004.

8. IESNA. Roadway Lighting. ANSI/IES RP-8-14. IESNA, New York, NY, 2014.

9. Carlson, P.J., E.S. Park, C. Andersen, B. Kuhn, A. Pike, J. Miles, R. Brydia, W. Ealding, and R.J. 

Porter. Pavement Marking Demonstration Project: State of Alaska and State of Tennessee—

Report to Congress. FHWA-HRT-09-039. FHWA, Washington, DC, 2010.

10. Park, E.S., P.J. Carlson, R.J. Porter, and C.K. Anderson. Safety Effects of Wider Edge Lines on 

Rural, Two-Lane Highways. Accident Analysis and Prevention, Vol. 48, 2012, pp. 317–325.

11. Miles, J.D., P.J. Carlson, R. Eurek, J. Re, and E.S. Park. Evaluation of Potential Benefits of 

Wider and Brighter Edge Line Pavement Markings. FHWA/TX-10/0-5862-1. Texas Department 

of Transportation, Austin, TX, 2010.

12. Lyon, C., B. Persaud, and K. Eccles. Safety Evaluation of Wet-Reflective Pavement Markings. 

FHWA-HRT-15-065. FHWA, Washington, DC, 2015.

13. Donnell, E.T., and S. Sathyanarayanan. Exploring the Statistical Association between 

Pavement Marking Retroreflectivity and Traffic Crash Frequency on Two- and Multilane 

Highways in North Carolina. Pennsylvania State University, University Park, August 2007.

14. Smadi, O., N.R. Hawkins, R.R. Souleyrette, and D. Ormand. Analysis of Safety-Effectiveness of 

Pavement Marking Retroreflectivity. 2008 TRB Annual Meeting, Washington, DC, 2008.
ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

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15. Carlson, P.J., E.S. Park, and D.H. Kang. Investigation of Longitudinal Pavement Marking 

Retroreflectivity and Safety. Transportation Research Record, No. 2337, Transportation 

Research Board, Washington, DC, 2013.

16. Avelar, R.E., and P.J. Carlson. Characterizing the Combined Association of Edge Line and Center 

Line Retroreflectivity to Nighttime Crashes on Michigan Two-Lane Rural Highways. Transportation 

Research Record, No. 2404, Transportation Research Board, Washington, DC, 2014.

17. Carlson, P.J., R.E. Avelar, E.S. Park, and D.H. Kang. Nighttime Safety and Pavement Marking 

Retroreflectivity on Two-Lane Highways: Revisited with North Carolina Data. Paper 15-5753, 2015 

TRB Annual Meeting, 2015.

18. Carlson, P.J., B. Brimley, G. Hawkins, S. Himes, H. McGee., and F. Gross. Traffic Control Device 

Guidelines for Curves. Final Report, NCHRP Project 03-106, April 2015. Available at http://

onlinepubs.trb.org/onlinepubs/nchrp/docs/NCHRP03-106_FR.pdf. 

19. Fitzpatrick, K., S. Chrysler, S. Sunkari, J. Cooper, B.J. Park, and L. Higgins. Modern Traffic Control 

Devices to Improve Safety at Rural Intersections. FHWA/TX-12/0-6462-1. Texas Department of 

Transportation, Austin, TX, 2011.

20. Sunkari, S.R. Improvements to Rural Intersections to Improve Motorist Compliance. FHWA/TX14/9-1529-1. Texas Department of Transportation, Austin, TX, 2014.

21. Persaud, B., C. Lyon, K. Eccles, N. Lefler, and R. Amjadi. Safety Evaluation of Increasing 

Retroreflectivity on STOP Signs. FHWA-HRT-08-041. FHWA, Washington, DC, 2007. 

22. Carlson, P.J., B. Brimley, J. Miles, S. Chrysler, R Gibbons, and T. Terry. NCHRP Report 828: Guidelines 

for Nighttime Visibility of Overhead Signs. Transportation Research Board, Washington, DC, 2016. 

23. Edwards, C. Lighting Levels for Isolated Intersections: Leading to Safety Improvements. MnDOT 

2015-05. Minnesota Department of Transportation, St. Paul, MN, 2015.

24. Obeidat, M.S., and M.J. Rys. Intersection Lighting Impacts on Nighttime Crashes Reduction 

and Safety Improvement. 2016 TRB Annual Meeting, Washington, DC, 2016.

25. Bhagavathula, R. Effects of Intersection Lighting Design on Driver Visual Performance, 

Perceived Visibility, and Glare. Dissertation, Virginia Polytechnic Institute, Blacksburg, VA, 2015.

26. National Highway Traffic Safety Administration. FARS Database Query Tool. Available at 

http://www-fars.nhtsa.dot.gov//QueryTool/QuerySection/SelectYear.aspx.

27. Findley, D., S. Searcy, K. Salamati, B. Schroeder, B. Williams, R. Bhagavathula, and L. Rodegerdts. 

Accelerating Roundabout Implementation in the United States, Volume 7: Human Factor 

Assessment of Traffic Control Device Effectiveness. FHWA-SA-15-075. FHWA, Washington, DC, 2015.

28. Fitzpatrick, K., R. Avelar, I. Potts, M. Brewer, J. Robertson, C. Fees, J. Hutton, L. Lucas, and K. Bauer. 

Investigating Improvements to Pedestrian Crossings with an Emphasis on the Rectangular 

Rapid-Flashing Beacon. FHWA-HRT-15-043. FHWA, Washington, DC, 2015.

29. Hunter, W.W., R. Srinivasan, and C.A. Martell. Evaluation of Rectangular Rapid Flash Beacon at 

Pinellas Trail Crossing in Saint Petersburg, Florida. Transportation Research Record, No. 2314, 

Transportation Research Board, Washington, DC, 2012, pp. 7–13.
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30. Fitzpatrick, K., M.A. Brewer, and R. Avelar. Driver Yielding at Traffic Control Signals, Pedestrian 

Hybrid Beacons, and Rectangular Rapid-Flashing Beacons in Texas. Transportation Research 

Record, No. 2463, Transportation Research Board, Washington, DC, 2014, pp. 46–54.

31. Katz, B. Peripheral Transverse Pavement Markings for Speed Control. Dissertation, Virginia 

Polytechnic Institute, Blacksburg, VA, 2007. 

32. Code of Federal Regulations (CFR) Title 49, Section 571.108. Federal Motor Vehicle Safety 

Standard 108. Available at https://www.gpo.gov/fdsys/pkg/CFR-2004-title49-vol5/xml/CFR2004-title49-vol5-sec571-108.xml. 

33. Kang, B., B. Yong, and K. Park. Performance Evaluations of LED Headlamps. International 

Journal of Automotive Technology, Vol. 11, No. 5, 2010, pp. 737–742.

34. Insurance Institute for Highway Safety Highway Loss Data Institute. In the Dark: New Ratings 

Show Most Headlights Need Improvement. Status Report, Vol. 51, No. 3, March 30, 2016. 

Available at http://www.iihs.org/iihs/sr/statusreport/article/51/3/1.

35. Carlson, P. Can Traffic Signs Be Too Bright on Low-Volume Roads? Transportation Research 

Record, No. 2472, Transportation Research Board, Washington, DC, 2015.

36. Oregon Department of Transportation (ODOT). Stopping Sight Distance and Decision Sight 

Distance. Discussion Paper No. 8A. ODOT, Salem, OR, 1997.

37. FHWA. Manual on Uniform Traffic Control Devices. FHWA, Washington, DC, 2009.

38. Himes, S., K. Eccles, K. Peach, C.M. Monsere, and T. Gates. Estimating the Safety Effects 

of Intersection Sight Distance at Unsignalized Intersections. 2016 TRB Annual Meeting, 

Washington, DC, 2016.

39. Urbanik, T. NCHRP Report 813: Signal Timing Manual, Second Edition. Transportation Research 

Board, Washington, DC, 2015.

40. Sullivan, J.M., and M.J. Flannagan. The Role of Ambient Light Levels in Fatal Crashes: 

Inferences from Daylight Saving Time Transitions. Accident Analysis and Prevention, Vol. 34, 

2002, pp. 487–498.

41. Peters, D., L. Kim, R. Zaman, G. Haas, J. Cheng, and S. Ahmed. Pedestrian Crossing Behavior at 

Signalized Intersections in New York City. 2015 TRB Annual Meeting, Washington, DC, 2015.

42. American Medical Association. Human and Environmental Effects of Light Emitting Diode 

(LED) Community Lighting. CSAPH Report 2-A-16. AMA, Chicago, IL, 2016.

43. North West Energy Alliance. Seattle LED Adaptive Lighting Study. North West Energy Alliance, 

Boulder, CO, 2014.

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APPENDIX A. ROADWAY LIGHTING DETAILS

ASPECTS OF ROADWAY LIGHTING

As a tool for improving visibility, there are several effects agencies should consider when 

evaluating their policies related to lighting. Two principal concerns are glare and uniformity.

Glare

Glare is a haze within the eye that reduces visibility. When light is scattered in the eye, the 

phenomenon is referred to as veiling luminance. Veiling luminance can occur with bright 

oncoming headlamps, significantly reducing driver vision and leading to discomfort. Glare is 

either classified as discomfort glare or disability glare. Discomfort glare results in a sense of pain 

or annoyance. Disability glare inhibits vision.(1)

In addition to uniformity, AASHTO states that glare is also an indicator of quality. Uniformity and 

glare both depend on factors such as height and fixture type along with placement. Discomfort 

glare and impairment to drivers should be a priority of consideration. The comfort and security of 

pedestrians should also be considered when designing lighting for an intersection or crosswalk. 

Where only intersections are lighted, and not the approach to the intersection, the lighting should 

taper, with a gradual transition from dark to light.(2)

Uniformity

Uniformity is the ratio of the maximum measured light in an area (typically illuminance) to either 

the average or minimum measured light in an area. Uniformity of lighting is indicative of quality 

and should be considered along with illumination levels.(2) The AASHTO Green Book states that 

lighting should be both continuous and energy saving, which may appear to be at odds.(2)

Signage policies included in the MUTCD for lighting include the notion of uniformity, which must 

be maintained without a decrease in visibility, legibility, or driver comprehension during either day 

or night conditions.(3)

LIGHTING REQUIREMENTS

In general, the MUTCD offers specific and often technical guides for lighting. For example, most 

regulatory, warning, and guide signs must be retroreflective or illuminated to show the same 

shape and similar color by both day and night. Sign illumination requirements cannot be met 

using lighting exterior to the sign, like highway lighting or that of a nearby business.(3)
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LED-Enhanced Signs

LEDs are a relatively new technology employed with signs. LEDs cannot be used in the 

background area of the sign, and even the size of the LEDs is prescribed by the MUTCD. 

According to the guide, LEDs should not have a diameter greater than 1⁄4 inch. For LED color, the 

MUTCD prohibits colors outside of white or red to indicate stop or yield. Regulatory signs other 

than stop or yield must use white only; guide signs must also use white only. Warning signs and 

school area signs must use white or yellow. Temporary traffic control must use white, yellow, or 

orange. The MUTCD indicates that LED units for flashing devices (that enhance conspicuity) 

should flash simultaneously at more than 50 and less than 60 times per minute.(3)

Changeable Message Signs

Changeable message signs (CMSs) have been utilized increasingly on public roadways. The 

MUTCD instructs that on roadways with speed limits of 55 mi/h and greater, the sign should be 

visible from at least a half mile under both day and night conditions. The message on the sign 

should be legible from a minimum of 600 ft for nighttime and 800 ft for daytime conditions. If 

neither of those distance recommendations can be met, the MUTCD suggests using fewer words 

on the sign or incorporating familiar symbols. CMSs should automatically adjust their brightness 

under varying light conditions to maintain legibility, while the luminance should meet certain 

criteria for day and night conditions. Luminance contrast specifically should measure between 8 

and 12 for all conditions. Contrasts on CMSs should always be positive.(3)

LIGHTING SELECTION

The FHWA Lighting Handbook offers a bulleted list of considerations when designing for lighting 

and selecting light. These considerations include photometric performance, durability, aesthetics, 

maintenance requirements, and operation costs. Specific luminaire requirements include ingress 

protection rating, lens material, housing, internal electrical components, and backlight, up-light, 

and glare (BUG) ratings.(1)

Luminaire Classification System

The Luminaire Classification System (LCS) was developed to help define luminaire distribution 

and efficiency. The LCS allows for the evaluation and comparison of outdoor luminaires. The 

primary areas for LCS are forward-light, backlight, and up-light zones. Each zone is then broken 

down further into solid angles within the area. The sum of percentages of lamp lumens within the 

three primary areas is equal to the photopic luminaire efficiency. This allows designers to find the 

best fit for their application.(1,4)

BUG Rating System

The BUG rating system existed prior to the LCS and is similar to it. Each category (backlight, uplight, and glare) consists of areas that surround the luminaire. Each region has an upper limit that 

must be met to obtain the rating. All criteria must be met for a luminaire to receive a B, U, or G 

rating.(1)
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LIGHTING DESIGN

This section highlights general policy concerning light design in terms of height, placement, and 

utilization.

Layouts and Spacing

Lighting pole layouts typically follow one of four formats: one-sided lighting, opposite lighting, 

staggered lighting, and median lighting. In a one-sided layout, all of the luminaires are on one 

side of the road. In an opposite lighting layout, the lighting is on direct opposite sides of the 

roadway. The staggered layout is like the opposite layout except the luminaires are offset from 

each other and do not directly face each other. Median lighting requires a divided roadway 

where the luminaires are placed in a single row along the median.(1)

High Mast 

In addition to typical luminaire pole spacing, the FHWA Lighting Handbook also details spacing 

designs for high mast poles that are typically found at freeway interchanges. These designs are 

more intricate and involve the consideration of a number of factors, including the height, number 

of luminaires for each pole, optics and orientation, wattage, source, and photometrics.(1)

High mast installations are generally regarded as being more visually comfortable. The height 

of the light source keeps it out of the typical viewing angle of drivers, but the amount of light 

provides illumination around a large corridor. Because more luminaires are attached to a single 

pole, there are fewer poles in the area, thus reducing the probability of one being struck in a 

roadway departure.(4)

Adaptive Lighting

Adaptive lighting was born from the idea of reducing power consumption by controlling light 

levels in off-peak hours. It is believed that a significant amount of power can be saved by varying 

the levels of lighting when traffic volumes change,(1) resulting in an energy savings of up to 

50 percent. Light levels are originally established by applying criteria based on the road type, 

conflict levels, pedestrian levels, and traffic volume. The current design practice is to design 

based on the highest pedestrian conflict level for an area and to establish minimum lighting 

levels based around that. Once that minimum is established, lighting systems provide that level 

of lighting throughout all hours of darkness. While traffic levels and pedestrian levels taper at later 

hours, lights have traditionally provided the same output.(1)

It is not recommended to reduce lighting levels or implement adaptive lighting near signalized 

intersections, midblock crosswalks, roundabouts, rail crossings, or the canopy area of toll plazas.

(1,4) Before designing for adaptive lighting, it is recommended that the Illuminating Engineering 

Society of North America’s (IESNA’s) RP-8 be reviewed.(1) The recommendations of the RP-8-14 

suggest adjusting the fluctuation of adaptive lighting based on the existing classifications for 

pedestrian conflict. A major roadway with high pedestrian conflict would require 1.2 cd/m¬2, but 

when pedestrian numbers drop in later hours to a low classification, the lighting can be allowed 

to reduce to 0.6 cd/m2.(4)
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COMMON PRACTICES FOR LIGHTING ROADWAYS

Street and Freeway Lighting

The AASHTO Green Book provides some separate policies on lighting streets, highways, and 

freeways in both urban and rural areas. The functional classification of the roadway typically 

factors into the decision to light it. Other factors include pedestrian and cyclist presence; night-today crash ratios; geometry of the roadway; and number of lanes, curves, and intersections.(2)

Streets and roadways often have roadside infrastructure not pertinent to the roadway, such as 

power poles. Even light poles that are necessary for hoisting the luminaires that light the roadway 

must be carefully placed to minimize a potential hazard.(1,2) For the varying street classifications 

in the RP-8-14 roadway lighting guide, specifications for average luminance and uniformity 

as well as maximum uniformity and glare are detailed. Further specifications exist for each 

classification by the level of pedestrian conflict—either high, medium, or low. In general, the lower 

the classification of street, the less average luminance and uniformity prescribed.(4)

Freeways do not contain pedestrians or roadside entrances, so many conflict points typically 

found on streets and roadways are not found along freeways. However, freeways have higher 

speed limits and merging lanes. The RP-8-14 details the lighting design criteria for roadways. There 

are different specifications for average luminance, average uniformity ratio, maximum uniformity 

ratio, and glare depending on roadway class.(4)

Interchange Lighting

Fixed-source lighting is essential at interchanges so that drivers can clearly discern the roadway 

ahead, the possible paths to be followed, and all other vehicles in enough time to make correct 

decisions. The AASHTO Green Book states that an unlit interchange decreases its usefulness 

because cars would inherently slow down as drivers approach with less certainty. It is important that 

retroreflective devices are also used so that drivers can make out grade separators such as curbs, 

piers, and abutments. In general, lighting becomes more useful as traffic volume increases.(2)

Arterials

Lighting on arterials is assumed to reduce sudden braking and swerving. The policy mentions 

that older drivers specifically benefit from well-lit arterials, which perhaps welcomes the idea of 

lighting based on area demographics. An excerpt from the AASHTO Green Book claims, “A safely 

designed, adequate lighting system is more important to optimum operation of an urban arterial 

than for any other type of city street.”(2)

Other Lighted Infrastructure Types

Miscellaneous roadway segments such as railroad crossings, tunnels, toll plazas, overpasses and 

underpasses, and bridges have less mention in the AASHTO guidance. 

For railroad crossings, the AASHTO guidance mentions the use of floodlighting or highway 

lighting, with little other documentation(2); however, RP-8-14 recommends lighting the conflict area 

30 m before and after the crossing as well as providing auxiliary lighting to highlight the sides of 

the passing train cars.(4)
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Railroad-highway grade crossings consist of either passive or active preemptive warnings for 

drivers. Passive signals include signing and pavement markings, whereas active signals include 

flashing beacons, gates, and bells. There is no quantitative information about the crash effects of 

illumination at railroad crossings.(5)

The AASHTO guidance brings to question the justification of cost for lighting rural bridges.(2)

Toll plazas have four distinct areas according to IESNA: approach/departure zones, queuing 

areas, toll collection islands, and infield.(4) There are also two recognized types of toll plaza types: 

in-line and off-line. In-line plazas require all vehicles to stop or slow down and pay a toll before 

continuing. Off-line plazas only require vehicles to stop and pay when they want to enter or exit 

a road. The lighting principles for each are similar, though the key difference is that the in-line 

plaza does not contain any ramps leading to or away from it. The RP-8-14 details specifics in 

terms of illumination for each of the four zones and two types of toll plazas, including luminaire 

placement, glare requirements, illumination level, and controls.

For underpasses and overpasses, the consideration for day and nighttime needs must be 

assessed. Nighttime underpass lighting should follow the same requirements as roadway lighting 

for that section. Daytime lighting must follow requirements suggested by American National 

Standards Institute (ANSI) RP-22-11, which provides recommendations on tunnel lighting.(4)

Tunnel lighting is dependent on grade and length and how much natural light can enter the 

portal. Lighting expenses are typically greater near portals since special consideration must be 

given so that drivers do not endure optical shock from traveling between natural and artificial 

lighting. The finish to the walls must also be given special consideration so that the surfaces 

increase reflectivity to enhance brightness and uniformity. Road design should avoid the need for 

guide signs inside tunnels.

Road Geometry

Steep grades and curves cause a visual problem for drivers and often require more lighting. The 

steeper the grade or sharper the curve is, the closer the luminaires should be spaced. Careful 

orientation of luminaires in these scenarios is required to maximize uniformity.(4)

Intersection Lighting

Intersections often have a concentration of pedestrians and roadside interference. Fixed-source 

lighting in these areas tends to reduce crashes. Rural intersections require more justification in 

terms of traffic volume, planned geometrics, and peak-time congestion.(2,3) For the benefit of nonlocal highway users, the lighting of a rural intersection is desirable to aid the driver in ascertaining 

sign messages during non-daylight hours. 

In general, the warrant for lighting an intersection must provide evidence of excessive delay, 

congestion, unfavorable approach conditions, or surrounding conditions that cause driver 

confusion.(3) The FHWA Lighting Handbook details a point scale developed by the Transportation 

Association of Canada that assists engineers and planners in deciding if an intersection warrants 

lighting and how much to provide. The scale uses a point system to decide whether to fully light, 

partially light, only light certain areas, or not use any lighting at the intersection. There are other 

warranting systems in existence, many of which simply rely on traffic volume as a determinant.(1)
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Rural at-grade intersections are lit depending on the layout and traffic volumes. Intersections 

without channelization, or multi-roads and turning lanes, are often left unlighted. However, broadscale, multi-road intersections are often lighted in rural areas. Sharper curves, limited ability of 

headlamps for wide turning radii, and presence of pedestrians often justify fixed lighting. The fixed 

lighting can also serve as an indication for drivers to adjust their speed on approach.(2)

IESNA details six types of intersections based on the convergence of three different road types: 

major, collector, and local. In general, the functional classification of the intersections ranked 

busiest to least busy in terms of traffic and pedestrian conflict are lit accordingly, with more light 

being required for major-to-major intersections and less lighting being required for local-to-local 

intersections. The need for uniformity also lessens with lower functional classifications.(4)

Roundabouts

The two main purposes for lighting roundabouts are the same as those for lighting an 

intersection: provide visibility from afar for users of the roundabout and provide visibility in key 

conflict areas to improve navigation. In general, the illumination should be designed to create 

a break in the continuous path of the roadway and emphasize the circular aspect of the 

roundabout.(4, 6)

Like intersections, the overall illumination of the roundabout should be approximately equal to the 

sum of the illumination levels of intersecting roadways. If continuous roadway lighting leading up 

to the roundabout is not present, transition lighting should be provided for the driver to taper in 

and out of the lighted section of the roundabout. In general, adequate illumination needs to be 

provided on the approach, at all conflict areas where traffic is entering the stream of cars in the 

roundabout, and at all places where cars break away to exit the roundabout.(6)

Illumination of a roundabout is beneficial when one or more approaches are illuminated 

and heavy traffic including pedestrians and cyclists is anticipated. Unlike intersections, it is 

encouraged that all roundabouts, independent of traffic volume, be illuminated.(6)

Crosswalks and Pedestrians

There are three classifications for pedestrian conflict, each dependent upon the type of abutting 

land use. High conflict areas expect pedestrians to be on sidewalks or crossings during hours 

of darkness. Areas near theaters and stadiums are examples where pedestrian conflict can be 

high. Where pedestrians are expected to be fewer at night but are still a factor during the day are 

considered medium conflict areas. Areas and blocks adjacent to office buildings, industrial parks, 

and libraries fit the description. Low areas have few pedestrians during night or day and may be 

in residential areas or rural zones.(4)

Crosswalks are often collocated at intersections but may be considered more dangerous at 

midblock locations. At an intersection crosswalk, it is important to light the crosswalk to stand out 

from the intersection in the background. Midblock crosswalks do not always have surrounding 

light sources, so lights may need to be placed specifically at certain points in the midblock in 

order to provide sufficient illumination to the crosswalk and pedestrians.(7)
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An FHWA publication regarding the design for crosswalk lighting concluded that a vertical 

illuminance level of 20 lx measured at 5 ft from the road service allowed drivers to detect 

pedestrians more easily at midblock crossings. A high level of vertical illuminance such as this 

may be required for crosswalks when there is a possibility of continuous glare from opposing 

vehicles, the crosswalk is located in an area of high ambient light levels, or the crosswalk is 

located in a lighted intersection.(7)

Lighting designed specifically for pedestrians is often lower to the ground. A pole height of 3 to 

6 m (10 to 25 ft) is more common for pedestrian-heavy zones than are typical roadway lighting 

systems, which are mounted often twice that high.(4)

In addition to lighting, other safety measures include automated pedestrian detectors that allow 

for adjusting the countdown timer on a crosswalk to the speed and volume of pedestrians 

crossing. This implementation appears to reduce pedestrian-vehicle conflicts as well as reduce 

the number of pedestrians who choose to cross during the “Don’t Walk” phase.(5)

REFERENCES 

1. Lutkevich, P., D. Mclean, and J. Cheung. FHWA Lighting Handbook. FHWA-SA-11-22. Federal 

Highway Administration, Washington, DC, 2012.

2. AASHTO. A Policy on Geometric Design of Highways and Streets (Green Book). AASHTO, 

Washington, DC, 2004.

3. FHWA. Manual on Uniform Traffic Control Devices. FHWA, Washington, DC, 2009.

4. IESNA. Roadway Lighting. ANSI/IES RP-8-14. IESNA, New York, NY, 2014.

5. AASHTO. Highway Safety Manual. AASHTO, Washington, DC, 2010.

6. Rodegerdts, L., et al. NCHRP Report 672: Roundabouts: An Informational Guide—Second 

Edition. Transportation Research Board, Washington, DC, 2010.

7. Gibbons, R., C. Edwards, and B. Williams. FHWA Informational Report on Lighting Design for 

Midblock Crosswalks. FHWA, Washington, DC, 2008.

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APPENDIX B. STATE PRACTICES

Below is a table of referenced sources on the standards and policies for each state. The 

information here consists of what was made available on the Internet through sources such as 

the MUTCD and state DOT websites. Hyperlinks to relevant sources are provided.

Table 2. Referenced Sources for Standards and Policies for Each State.

Source MUTCD

StateSupplemented 

MUTCD

State 

MUTCD RP-8

FHWA 

Lighting 

Handbook

Highway 

Safety 

Manual

AASHTO 

Green 

Book

AASHTO 

Roadway 

Lighting 

Design 

Guide

Alabama X X X

Alaska X

Arizona X

Arkansas X

California X

Colorado X X

Connecticut X

Delaware X X X

Florida X X

Georgia X X X X X

Hawaii X X

Idaho X

Illinois X X X X X

Indiana X X X X X

Iowa X X X

Kansas X

Kentucky X X X

Louisiana X X

Maine X X

Maryland X X X

Massachusetts X X

Michigan X X

Minnesota X X X

Mississippi X X X

Missouri X X

Montana X X X X X

Nebraska X X

Nevada X X X
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Source MUTCD

StateSupplemented 

MUTCD

State 

MUTCD RP-8

FHWA 

Lighting 

Handbook

Highway 

Safety 

Manual

AASHTO 

Green 

Book

AASHTO 

Roadway 

Lighting 

Design 

Guide

New Hampshire X X X X

New Jersey X X X X

New Mexico X X

New York X X X X

North Carolina X X

North Dakota X X

Ohio X X X

Oklahoma X

Oregon X X X X

Pennsylvania X X X

Rhode Island X X

South Carolina X X X

South Dakota X X

Tennessee X X X X X

Texas X X X X

Utah X X

Vermont X X X X X

Virginia X X X X

Washington X X X X X

West Virginia X

Wisconsin X X X

Wyoming X X

In addition to the resources used by the states as listed above, the following states include 

citations to these additional references:

• Illinois:

o National Electrical Code, National Fire Protection Association.

o National Electrical Safety Code, American National Standards Institute/Institute of Electrical 

and Electronics Engineers.

o Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic 

Signals, AASHTO.

o Structural Supports for Highway Signs, Luminaires, and Traffic Signals, NCHRP Report No. 411, 

TRB (TRB).

o Standard Specifications for Road and Bridge Construction, Illinois DOT.

o Supplemental Specifications and Recurring Special Provisions, Illinois DOT.

o BDE Special Provisions, Illinois DOT.

o Highway Standards, Illinois DOT.
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o Warrants for Highway Lighting, NCHRP Report No. 152, TRB.

o Partial Lighting of Interchanges, NCHRP Report No. 256, TRB.

o American National Standard Practice for Tunnel Lighting, ANSI/IESNA RP-22, ANSI/IESNA.

o Recommended Practice for Roadway Sign Lighting, IESNA RP-19, IESNA.

o Design Guide for Roundabout Lighting, IESNA DG-19, IESNA.

o Luminaire Classification System for Outdoor Luminaires, IESNA TM-15, IESNA.

o US Coast Guard Bridge Administration Manual COMDTINST M16590.5C, Bridge Lighting 

and Other Signals.

o CFR Title 33, Part 118.

o Federal Aviation Administration Advisory Circular AC 70/74602J, Proposed Construction or 

Alteration of Objects That May Affect the Navigable Airspace.

o The Lighting Handbook, Illuminating Engineering Society.

• Tennessee:

o 2006 Lighting Software Directory, IESNA Computer Committee.

o Highway Lighting, Chapter 56, Illinois DOT.

o Highway Lighting Systems, Section 11, New Jersey DOT (NJDOT).

o Nashville Downtown Streetscape Elements Design Guidelines, Metropolitan Development 

and Housing Agency.

o National Electrical Code, National Electrical Code Committee of ANSI, sponsored by the 

National Fire Protection Association (NFPA).

o National Electrical Safety Code, American National Standards Institute/Institute of Electrical 

and Electronics Engineers.

o Partial Lighting of Interchanges, NCHRP Report No. 256, TRB.

o Roadside Design Guide, AASHTO.

o Roadway and Structure Lighting Specifications, Section 714, Tennessee DOT.

o Roadway Lighting Handbook, U.S. Department of Transportation, FHWA, Offices of Research 

and Development, Office of Traffic Operations.

o Rules and Regulations for Accommodating Utilities within Highway Rights-of-Way, Chapter 

1680-06-01, Tennessee DOT.

o Standard English Drawings, Tennessee DOT.

o Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic 

Signals, AASHTO.

o Street Light Design Manual, Nashville Electric Service.

o Structural Supports for Highway Signs, Luminaires, and Traffic Signals, NCHRP Report No. 411, 

TRB.

o Warrants for Highway Lighting, NCHRP Report No. 152, TRB.

o Traffic Engineering Design Manual 2006, Section V, Chapter 2—Engineering. 
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• Virginia:

o IESNA Recommended Practices for Tunnel Lighting, IESNA PR-22 (the most current edition of 

this document is RP-22-11). 

o IESNA Recommended Practices for Sign Lighting, IESNA PR-19.

o The National Electric Code (NEC), NFPA. (Latest adopted NFPA 70/NEC by Virginia DOT).

• Oregon:

o FHWA Rules and Guidelines.

o CFR Title 23, Sub-Chapter G.

o Federal Aviation Administration’s “Obstruction Marking and Lighting” advisory circular.

o Local agency agreements, League of Oregon Cities and Association of Oregon Counties 

“Guidelines and Working Agreements for Local Government Programs” (pp. 32–33).

o Local Officials Advisory Committee (local design standards).

• Indiana:

o NCHRP Report No. 152, Warrants for Highway Lighting, TRB (not used on an Indiana DOT 

[INDOT] project).

o NCHRP Report No. 256, Partial Lighting of Interchanges, TRB (not used on an INDOT project).

o Chapter 49, “Roadside Safety,” Indiana Design Manual, INDOT.

o INDOT Standard Drawings, INDOT.

o INDOT Standard Specifications, INDOT.

o National Electrical Code.

o National Electric Safety Code.

• Delaware:

o Delaware State Code, Title 7, Chapter 71A.

o Functional Classification Maps, Delaware DOT.

o Road Design Manual, Delaware DOT.

o Standard Construction Details, Delaware DOT.

o Lighting for Parking Facilities (RP-20-98), IESNA.

• Iowa:

o Roadway Lighting Design Manual, Minnesota DOT, 2003.

o IES Lighting Handbook, 9th Edition, IESNA.

o Iowa Administrative Codes, 2011.

• Montana:

o Recommended Practice for Tunnel Lighting, IESNA.

o Recommended Lighting for Walkways and Class 1 Bikeways, IESNA.

o Standard Specifications of Structural Supports for Highway Signs, Luminaires and Traffic 

Signals, AASHTO.
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o Standard Specifications for Road and Bridge Construction, Montana Department of 

Transportation (MDT).

o MDT Detailed Drawing, MDT.

o MDT Electrical Detailed Drawing, MDT.

o Chapter 6, Roadside Safety, MDT Traffic Engineering Manual.

o Chapter 14, Roadside Safety, MDT Road Design Manual.

o Chapter 8, Project Development Process, MDT Traffic Engineering Manual.

o Chapter 9, Project Coordination, MDT Traffic Engineering Manual.

o Chapter 10, Plan Preparation, MDT Traffic Engineering Manual.

o ALADAN—A GE Lighting Application Design and Analysis Computer Program, General 

Electric Lighting Systems. 

o Lighting Design Guide for Use with ALADAN, General Electric Lighting Systems.

o Warrants for Highway Lighting, NCHRP Report No. 152, TRB.

o Partial Lighting of Interchanges, NCHRP Report No. 256, TRB.

o A Guide to Standardized Highway Lighting Pole Hardware, AASHTO.

o National, state, and local electrical codes.

• Nevada:

o Standard Plans for Road and Bridge Construction, Nevada DOT, 2010.

o NEC, NFPA, 2011.

o Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic 

Signals, AASHTO, 2002 and Interims.

o Photometric Measurement of Roadway Lighting Installations—LM-50-99, IESNA.

o Design Guide for Roadway Lighting Maintenance—DG-4-03, IESNA.

o Addressing Obtrusive Light in Conjunction with Roadway Lighting—TM-10-00, IESNA.

o Accessible Rights of Way: A Design Guide, U.S. Access Board.

• New Hampshire:

o Manual on Uniform Traffic Control Devices, FHWA, 2007.

o Minnesota Manual on Uniform Traffic Control Devices, Minnesota DOT, December 2001.

o Roadway Lighting Design Manual, Minnesota DOT, 2006.

o Indiana Manual on Traffic Control Devices, Indiana DOT, 2008.

o Specifier Bulletin for Dark Sky Applications—Volume 2: Issue 1, International Dark Sky 

Association, 2009.

o Holophane Product Catalogue, September 2001.

o Highway Design Manual, New Hampshire DOT, 2007.

• New Jersey:

o Standard Specifications for Road and Bridge Construction, NJDOT.
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o Supplemental Specifications, NJDOT.

o Special Provisions, NJDOT.

o Standard Electrical Details, NJDOT.

o Electrical Material Specifications, NJDOT.

o NFPA NEC.

o Sample Plans, NJDOT.

o CADD Manual, NJDOT.

• New York:

o Policy on Highway Lighting, Traffic Engineering and Safety Division, New York State 

Department of Transportation (NYSDOT), 1979.

o Roadway Lighting Handbook, Addendum to Chapter 6, U.S. Department of Transportation, 

FHWA, September 1983.

o American National Standard Practice for Roadway Lighting, IESNA, July 1983.

o Americans With Disabilities Act Accessibility Guidelines for Buildings and Facilities (ADAAG), 

Landscape Architecture Bureau, NYSDOT, December 1993.

o Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic 

Signals, AASHTO, 1994.

o American National Standard Practice for Tunnel Lighting, IESNA, 1987.

o Guide for the Design of Park-and-Ride Facilities, AASHTO, 1992.

o Geometric Design Policy for Bridges, Structures Design and Construction Division, NYSDOT, 

1993.

o Recommended Practice for Roadway Sign Lighting, IESNA, 1983.

• Pennsylvania:

o Publication 408, Specifications, and associated changes, Pennsylvania DOT. 

o Current Publication 72M, Roadway Construction Standards, Highway Lighting Drawings, RC80M, RC-81M, RC-82M, RC-83M and RC-84M. 

o Current Publication 219M, Standards for Bridge Construction, BC-721M and BC-722M. 

o Publication 10, Design Manual, Part 1, Transportation Program Development and Project 

Delivery Process.

o Publication 10C, Design Manual, Part 1C, Transportation Engineering Procedures.

o Publication 10X, Design Manual, Part 1X, Appendices to Design Manuals 1, 1A, 1B, and 1C.

o Publication 14M, Design Manual, Part 3, Plans Presentation.

o Publication 15M, Design Manual, Part 4, Structures.

• Texas:

o Standard Specifications for Construction of Highways, Streets, and Bridges, Texas 

Department of Transportation (TxDOT).

o Traffic Operations Standard Plans, TxDOT.
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o Texas Manual on Uniform Traffic Control Devices, TxDOT.

o Other TxDOT manuals.

o National Electrical Code Handbook, NFPA.

o Lighting Handbook: Reference and Application (HB-9-00), IESNA.

o Recommended Practices for Tunnel Lighting (RP-22-96), IESNA.

o Nomenclature and Definitions for Illuminating Engineering (RP-16-96), IESNA.

o Other IESNA publications.

• Vermont:

o RP-22 Standard Practice for Tunnel Lighting, ANSI/IES. 

o DG-19 Design Guide for Roundabout Lighting, IES.

o RSDG-3 Roadside Design Guide, AASHTO.

o A Policy on Geometric Design of Highways and Streets, AASHTO. 

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APPENDIX C. RESEARCH PROBLEM STATEMENTS

ROADWAY DEPARTURE SAFETY

Placement of Roadway Lighting and Geometric Considerations

The placement of roadway lighting is typically left to city planners. Planners establish a need for 

lighting based on crash data and existing criteria, but the exact placement of lighting is often 

determined by spacing or convenience. Determining where lighting is most effective at reducing 

crashes could inform policy on roadway lighting design. This research would differ from most 

previous research, which focuses on lighting output or the visibility provided by the light output, 

by focusing on physical placement of luminaires in conventional circumstances such as areas 

with geometric considerations.

Statement of Urgency

Roadway departures occur on both tangents and curves. Determining the effectiveness of 

lighting a curve versus a tangent can be informative regarding how lighting can best be 

implemented. Current standards for curved roadways include instruction for pole placement to 

reduce the likelihood of a collision by an errant vehicle, but less research pertains to what areas 

of a curved roadway should be lighted to reduce departures.

Project Objective

The outcome of this research would include a report detailing any statistical differences found 

in the physical placement of luminaires in areas such as intersections, horizontal and vertical 

curves, and merge points. The data may be acquired from literature and case study research, 

the SHRP2 database, or an experimental driving study that incorporates alternative lighting 

placement as a variable. 

Relationship to Existing Body of Knowledge

Data made available by existing databases like SHRP2 can be a target of further research. In 

addition, mapped data of lighting output combined with crash data can inform best practices. 

Results of this research can serve to validate existing practices or to provide information on 

better means of placing luminaires, specifically in areas where roadway departures are more 

problematic.

Anticipated Work Tasks

An effort to gather information on current policies and trends on lighting placement should 

be conducted and analyzed. This would determine conventional methods as well as newer 

techniques that can be leveraged in an experiment.
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The design of this research should incorporate a variety of geometric instances of vertical and 

horizontal curves with the ability to manipulate lighting placement on the roadway. In general, 

the results of the study would determine if there is a difference in speed adjustment and lane 

keeping among the variations. It may also be beneficial to track eye movements of drivers in 

these scenarios to better understand where drivers fixate and gaze to and from while driving in 

lighting curves.
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Lighting and Inclement Weather

Adverse weather can reduce visibility of the roadway and pavement markings. The impact 

of lighting in adverse weather on many different road types and in combination with varying 

pavement markings and sign materials has yet to be fully explored. Policies rarely consider the 

diminished visibility caused by adverse weather conditions. 

Statement of Urgency

Improving driving in inclement weather, specifically at night when vision is already diminished, 

is key to improving overall safety and driver confidence in these conditions. As it stands, there is 

very little research regarding the interaction of lighting and inclement weather, such as rain, snow, 

sleet, and hail. Lighting may have the ability to improve lane keeping in these conditions and 

prevent roadway departure crashes from occurring.

Project Objective

The outcome of this research would be a report of experimental analysis of varying lighting 

techniques employed in an experiment with the consideration of varying weather effects 

such as rain, sleet, snow, hail, and fog. The resulting findings should provide guidelines and 

recommendations for lighting in these conditions in terms of roadway visibility.

Relationship to Existing Body of Knowledge

Lighting has been researched thoroughly in clear night conditions. Typically, inclement weather 

visibility focuses on the visibility of pavement markings as they relate to retroreflection and 

headlamps or the use of actively lighted delineators. Roadway lighting and its effects with 

inclement weather activity has been understudied.

Anticipated Work Tasks

The research tasks associated with this effort must focus on evaluating the impact of varying 

weather conditions in combination with conventional roadway lighting on visibility. This would 

inform standards and policy regarding lighting during periods of inclement weather. An improved 

lighting policy focused on inclement weather may cause drivers to meet appropriate speeds 

sooner, anticipate events more quickly, and avoid roadway departure crashes more often.
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Determining When to Use Roadway Lighting

The use of roadway lighting is often determined by levels of annual average daily traffic in 

combination with areas of conflict, municipal regulations on lighting, economic viability, 

functional class, and zoning. Most traffic, however, occurs during the daytime. If roadway 

lighting is partially determined by traffic volumes, a count of nighttime traffic should be used 

as a decision threshold because it directly matches the traffic (VMT for RwD, entering traffic for 

intersections, and pedestrians/bicyclists for that focus area) that would use the lighting. Another 

determining factor is public opinion on whether an area does or does not warrant lighting.

Statement of Urgency

LED technology is slowly replacing HPS lighting conventionally used in most roadway lighting 

applications. LEDs can be controlled to output varying intensities and color, and achieve 

particular angles to satisfy ordinances. This adaptable aspect of an LED can foster more research 

in these specific areas that has not been possible with HPS and other light sources. As LEDs 

become the preferred and adopted lighting technology, research should begin focusing on LED 

capabilities in terms of energy consumption and cost savings.

Project Objective

The outcome of this research can inform many municipalities about a method of reducing costs 

and conserving energy while maintaining their current level of safety. In addition, this research 

may find a need for more LED lighting with controlled output in areas where roadway departure 

is most common.

Relationship to Existing Body of Knowledge

Adaptive lighting is a trending topic in research. Moving forward, the topic would benefit from 

a better understanding of when lighting is most and least important for safety. In addition, 

techniques for managing the lighting in adaptive areas, such as dimming by certain amounts 

over time or sensing the presence of vehicles and traffic, are topics that can be expanded on.

Anticipated Work Tasks

A research effort should determine any viable opportunities to reduce lighting at night in 

locations where traffic and pedestrian activity is significantly reduced. Traffic behavior in areas 

will differ depending on several factors including location, time zone, and proximity to residential 

and commercial areas. Observing a variety of locations that have the opportunity to decrease 

lighting output would form guidelines for when to reduce lighting and the rate at which the 

lighting should be reduced in order to maintain current levels of safety and safety perception.
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Vehicle Lighting Height and Considerations 

Headlamps are to have a minimum height of 22 inches, with a maximum of 54 inches. Taillamps 

are to be a minimum height of 15 inches, and no higher than 72 inches.(1) These measurements 

are to be made when there are no occupants or baggage in the vehicle. The additional weight 

would reduce the height of these lights. Guidelines for the design of vertical curvature and 

passing sections are based on stopping and passing sight distances that usually assume vehicle 

headlamps and taillamps are at a height of 24 inches.(2) With the allowable taillamp height 

lower than the assumption commonly used in design (and possibly even lower when the weight 

of passengers and baggage is accounted for), there are potential safety concerns related to 

stopping sight distances involving low vehicles on crest vertical curves.

Statement of Urgency

It is understood that the characteristics of all vehicles cannot be accounted for in highway 

design, but there is a disconnect between the minimum specification for the heights of vehicle 

lamps and the values commonly used in design. Another issue related to headlamps and 

vertical curvature is the shadow zone that occurs beyond the crest of a vertical curve, where 

an object in the road may not be visible until it is within the direct line of an approaching 

vehicle’s headlamps. The AASHTO Green Book suggests that with the assumed 24-inch height of 

headlamps, an object 16 inches above the roadway will be within the line of the headlamps at 

a distance equal to stopping sight distance.(2) This means drivers will typically see objects 16 

inches above the pavement in time to stop. However, this may not be true for objects less than 

16 inches high or if the headlamps are less than 24 inches high (which is currently permissible). 

Research that leads to coordination between the headlamp specifications and typical design 

assumptions is recommended.

Project Objective

Results from this project would inform auto manufacturers and policy makers about how vehicle 

headlamp height differences impact the visibility of roadway objects at night. Better visibility due 

to headlamps and less glare caused by them may reduce roadway departure crashes.

Relationship to Existing Body of Knowledge

There is plenty of literature surrounding the height of headlamps and visibility, but very little 

information exists on how they can be improved in regard to highway design. It is believed that 

the current guides, such as the AASHTO Green Book, could be updated to current trends in 

headlamp technology.

Anticipated Work Tasks

Research on this problem would require a variety of vehicle heights and headlamp types to be 

tested against standard visibility measures. In addition to examining how headlamp height has 

an effect on forward visibility, it is also important to determine the impact of glare produced by 

different sized vehicles. Human subjects must test the ability of the vehicle headlamps to promote 

visibility but reduce offensive glare from an oncoming source.
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62

LED Vehicle Headlamp Considerations

The advent of LED headlamps has affected how drivers perceive and react to oncoming 

headlamps and glare. Research indicates that LED headlamp sources are better than halogen 

headlamps and comparable to high-intensity discharge headlamps in terms of photometric 

performance and visibility. The blue-white color produced by the headlamps does reportedly 

cause glare and discomfort to oncoming drivers.(3) Research into alternative LED colors and more 

precise beam patterns may mitigate the discomfort to other drivers and maintain photometric 

and visibility properties. Additionally, the colors produced by the different types of headlamps 

may have unique effects on sign visibility that are yet to be identified.

Statement of Urgency

Vehicle headlamps are often overlooked when developing designs and policies for roadway 

lighting and signing. There are several positive safety effects of new headlamp technologies, 

such as adaptive headlamps that reduce glare for oncoming vehicles or turn in the direction 

of curves. However, these and other changes in headlamp illumination may have detrimental 

effects on visibility that should be considered in future research and policies. A new report by IIHS 

demonstrates that most headlights need improvement.(4) 

Project Objective

The outcome of this type of research would inform auto manufacturers about the glare and 

perception of vehicle headlamps. Improvements in these areas could result in a reduction of 

roadway departure crashes.

Relationship to Existing Body of Knowledge

Research related to this topic has been conducted in the past; however, headlamp technology is 

constantly changing. In addition, a complete survey of existing LED headlamps and their effects 

on drivers in terms of depth perception, visibility, glare, and preference has not been conducted.

Anticipated Work Tasks

To determine the improvement needs of headlamps, a strong literature review of the current state 

of headlamps must be completed. The amount of glare produced by newer technologies should 

be assessed and compared to conventional headlamp technology. In addition, the visibility 

produced by varying headlamp technologies should be tested and compared using human 

subjects in a controlled environment.
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63

Standardized Police Reporting

The implementation of lighting is partially driven by crash data obtained from on-scene crash 

reporting. Currently, there are no known standards among law enforcement agencies for 

reporting the placement and contribution of lighting for crashes. An effort to collect data on how 

different agencies interpret and apply knowledge related to lighting for crashes could improve 

how crash data are reported and be a step toward standardizing the reporting process.

Statement of Urgency

Much of what is determined as a need to be researched or improved stems from fatal crash 

reporting provided by on-scene law enforcement when a crash has occurred. The methods for 

reporting a crash and the details surrounding it differ agency to agency, state to state. There are 

no standard definitions or guidelines to establish criteria for law enforcement when submitting a 

report.

Project Objective

The objective of this research would be to determine the differences in reporting fatal crashes 

among many different agencies and levels. In addition, a guideline or recommendation for 

revising fatal crash reporting methods and systems should be made.

Relationship to Existing Body of Knowledge

There are currently no existing widespread efforts to standardize police reporting techniques.

Anticipated Work Tasks

A research effort should involve reviewing as many crash reporting methods as can be made 

available. This effort may not result in forming a universal crash reporting system but would inform 

researchers and practitioners on some of the differences that may affect the crash data. A next 

step would be to attempt to establish a common guide to be used across agencies.
ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

64

Definition of Sight Distance

Sight distance is defined by AASHTO as the length of roadway visible to the driver. It can be 

categorized into horizontal and vertical sight distance: horizontal sight distance is limited by 

objects and the changing alignment in the horizontal plane, while vertical sight distance is 

limited by objects and the changing alignment in the vertical plane. Sight distance is generally 

not specified as being applicable to a certain time of day (daytime or nighttime). However, many 

of the assumptions used to calculate different sight distances (e.g., stopping sight distance, 

decision sight distance, passing sight distance) are based on values that may only be relevant 

for daytime conditions when daylight illuminates objects and the roadway environment.(2)

Statement of Urgency

When discussing the topic of sight distance, the traditional design manuals have little mention 

of specific values or considerations for nighttime conditions. AASHTO guidelines for SSD, for 

example, are based on the provision of adequate sight distance at every location on a roadway 

such that drivers traveling at or near the design speed can see a stationary object in the road 

and stop before reaching it. The AASHTO assumptions for SSD use a driver eye height of 3.5 ft 

and an object height of 2 ft. (The 2-ft object height is one example where nighttime conditions 

are considered because most taillamps are 2 ft or higher from the ground. However, there 

is still a vulnerability from encounters with shorter objects or vehicles lower to the ground, as 

mentioned above.) There are no specifics to the shape, color, contrast, or reflection of the object, 

implying that this is a daytime design element. In general, decision sight distance uses the same 

basic models as SSD but with longer perception-reaction times, consequently neglecting the 

differences between day and night conditions.(2)

Project Objective

The outcome of this work would directly influence policy on speed limits in areas that are 

unlighted or have increased crash risks due to geometry or wildlife presence. Improvement in 

these areas can reduce roadway departure crashes that are a result of excessive speeding, 

dodging wildlife, or failure to adjust to a curve.

Relationship to Existing Body of Knowledge

Results from this effort would influence guides such as AASHTO’s Green Book and IESNA’s RP-8 to 

include night-specific design criteria for roadways.

Anticipated Work Tasks

A research effort on this topic must incorporate closed-course testing of sight distance at different 

times of day including twilight and night with headlamps.
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65

Pavement Marking Width and Retroreflectivity 

There is still some debate about the trade-off between pavement marking retroreflectivity 

levels and size of pavement markings (width). More research is needed to determine if wider 

longitudinal pavement markings (i.e., 6 inches) may provide more visibility to drivers and if 

that gain is enough to provide any relief to the proposed minimum retroreflectivity levels being 

pursued by FHWA. Also, there is a series of studies available in the last decade showing a 

consistently stronger link between pavement marking retroreflectivity and safety. However, there 

is not a general consensus on the relationship, and more work is needed to establish the link. 

Finally, since machine vision systems are becoming more common, there is a need to determine 

the pavement marking performance needs for machine drivers (compared to human drivers). 

Research is also needed in the area of pavement markings specifically designed to maintain 

their retroreflective performance conditions under wet nighttime conditions. The crash data 

reviewed in this report indicate that roadway departure crashes under the category of the dark, 

not lighted condition were more prevalent in wet conditions compared to clear conditions. This 

finding seems to indicate the importance of retroreflective performance in wet conditions in 

terms of roadway departure crashes. However, more research is needed in this area to develop a 

better understanding of how increased wet nighttime retroreflectivity levels can mitigate roadway 

departure crashes. 

Statement of Urgency

To better understand how improvements to pavement markings, whether by width or 

maintenance schedules, can reduce the likelihood of roadway departures, research in this area 

is the necessary first step.

Project Objective

Results of this effort would inform policy on pavement marking design and placement as well as 

improve safety and perhaps reduce the rate of roadway departure crashes.

Relationship to Existing Body of Knowledge

Regarding nighttime continuous roadway delineation, agencies have two factors within their 

control: pavement marking width and pavement marking brightness. There is not a good 

understanding of how these two interact and/or how an emphasis on either one provides more 

benefit. Both have been studied independently, but this work would be focused on developing a 

better understanding of how they interact. 

Anticipated Work Tasks

Weather simulation and a test track with a means for applying a variety of pavement markings 

for testing are essential to this research. A human subjects test for visibility of pavement markings 

of varying width, materials, and weather conditions is recommended. 
ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

66

LED Sign Brightness

Recent research identifies conditions for which retroreflective traffic signs may be too bright.(5)

While the MUTCD identifies minimum levels of maintained retroreflectivity, there are no guidelines 

specifying when the luminance from a sign causes glare that may be a safety hazard. The glare 

from signs reduces the distance at which drivers can see hazardous objects and also reduces 

response times.(6) The concern for glare from signs should extend to the use of digital signs as well. 

Digital signs can be loosely defined as LED-enhanced signs such as stop signs with flashing LEDs in 

the border, chevrons with flashing LEDs, or even full-color digital changeable message signs. 

Statement of Urgency

The MUTCD states that the brightness of changeable message signs should be adjusted 

under varying light conditions to maintain legibility, implying a concern that they need to be 

bright enough to be read during the daytime.(7) However, there is no mention of the issue that 

changeable message signs may be a source of glare at night. This concern should be especially 

noted for full-matrix LED signs capable of very high light output. While previous sign research 

emphasized the need for legibility, the improvements in sign materials and the increasing use of 

digital infrastructure open up the possibility that these signs are too bright for driver comfort and 

safety. Future research and applications should address these concerns.

Project Objective

The outcome of this research would inform policy for changeable message signs in guides such 

as the MUTCD.

Relationship to Existing Body of Knowledge

The MUTCD is the primary guide for sign implementation. Currently, there are no standards or 

guides in relation to LED signs or their brightness as there are for retroreflective signs. This is true 

despite the increasing number of LED sign installations on highways.

Anticipated Work Tasks

Research on this problem should incorporate an LED sign capable of very high light output and 

have human subjects rate the glare for different messages at different levels of brightness. In 

addition, visibility tests should be conducted using human subjects in the vicinity of the message 

boards to ensure the signs are not inhibiting drivers from attending to potential roadway hazards. 
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67

Retroreflectivity Levels of Traffic Signs

There is a need to identify stronger relationships between the retroreflectivity levels of traffic 

signs and roadway departure crashes. Research has shown some evidence that there appears 

to be a maximum level of retroreflectivity depending on specific conditions,(8) and FHWA has 

established minimum levels based on the needs of nighttime drivers in the MUTCD. However, 

there are no established correlations between retroreflectivity and crashes. In some ways, having 

recommended guidelines for appropriate sign sheeting selections based on the specific 

conditions (e.g., roadway, traffic, roadside) would be an alternative way to address this, but 

again, these would need to be developed. 

Statement of Urgency

Nighttime fatality rates are approximately three times higher than daytime fatality rates. While 

various factors are involved, sign visibility is one factor that can be designed, specified, and 

maintained so that it is not a contributor to the increased fatality rate at night. Developing the 

data needed to support the appropriate safety-derived levels of retroreflectivity would be useful 

information that agencies can use to select the appropriate materials and maintain their signs 

to the appropriate retroreflectivity levels (the current retroreflectivity levels are based on legibility 

needs). 

Projective Objective

The aim of this research would be to develop correlations between sign brightness 

(retroreflectivity) and nighttime crash rates. This should include roadway departure crashes as 

well as intersection crashes. 

Relationship to Existing Body of Knowledge

Safety-derived retroreflectivity recommendations have been researched and partly developed for 

pavement markings. This work would be similar in nature but focused on traffic signs. 

Anticipated Work Tasks

The research that would be beneficial here is to develop a database of signs and their 

retroreflectivity levels (measured or carefully estimated) along roadways where the geometric 

characteristics, as well as the traffic levels and mix, are known. This information would be 

combined with multiple years of nighttime crash information so that the appropriate statistical 

analyses could be performed to determine how sign retroreflectivity levels impact nighttime 

crashes. An alternative to tracking or modeling sign retroreflectivity would be to identify agencies 

that have upgraded their signing. Knowing when signs were upgraded would allow agencies to 

theoretically obtain before and after crash data (preferably at least 3 years of both before and 

after data) to analyze the impacts of the new signs. The specific areas where this research may 

pay off is horizontal curves, which are overrepresented in RwD crashes. 
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68

Speed Limits at Night

Most speed limits are set by legislative action or studies that determine the 85th percentile speed 

under free-flow conditions. When determined based on speed studies, most often the speed 

data are collected during the day, meaning that nighttime conditions are not accounted for in 

selecting speed limits. 

Statement of Urgency

While separate speed limits are permitted at night, few agencies use nighttime speed limits, 

and there is no guidance provided in the MUTCD for establishing nighttime speed limits. In 

addition, there is the concern of over-driving headlamps at night. While no recent study has been 

completed on this topic, there is a growing concern that the new headlamp trends may be 

generating a need to take a fresh look at this somewhat controversial topic. 

Project Objective

The findings of this research should be used to determine the necessary conditions for 

implementing a night-specific speed limit to a roadway. This may be completed by humansubject research based on visibility as well as a survey of areas that currently employ nightspecific speed limits.

Relationship to Existing Body of Knowledge

This research can add to the headlamp research opportunities previously mentioned with a 

focus on speed limits and areas where speed limits may need to be altered at night versus day 

to prevent roadway departures.

Anticipated Work Tasks

A survey of current trends in roadway design and speed limits should be followed by a humansubject test to determine, in combination with sight distance and headlamps, if speed limits 

should be reduced in certain situations. The reduction of speed limits in some areas where 

roadway departures are most common may mitigate crashes. 
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69

Horizontal Curve Design and Curve Advisory Speeds

The design of horizontal curves is based on comfortable lateral acceleration rates derived 

during daytime studies. At night, however, reduced visibility may affect a driver’s threshold level 

of lateral acceleration where discomfort begins, thus affecting the comfortable curve advisory 

speed for the curve. While a separate advisory speed for night seems impractical, there may be 

implications related to safety if drivers are actually not comfortable adopting the advisory speed 

at night. 

Statement of Urgency

Further analysis of the implications of curve advisory speeds and nighttime driving could 

lead to improvements in how these advisory speeds are set and used. There is currently very 

little consideration of curve advisory speeds for nighttime visibility. Sight distance at night and 

especially around curves where headlamps are not angled to illuminate is greatly diminished. 

Progress on this topic can result in fewer roadway departure crashes due to speeding in curves.

Project Objective

Increased knowledge about curves with higher rates of roadway departure crashes would 

allow policy makers to establish criteria for advisory speeds. Results of this effort should provide 

recommendations for implementing advisory speed systems based on curve design.

Relationship to Existing Body of Knowledge

In an exploratory analysis of unfamiliar driver data collected during both daytime and nighttime 

conditions, it was found that drivers on curves accept lower levels of lateral acceleration at night 

than during the day. However, contrasting the reduced lateral acceleration was a finding that 

driver speeds were higher at night (possibly from cutting curves with a wider path).(9)

Anticipated Work Tasks

A survey of policies around curve design and horizontal curve speed limits should first be 

conducted. It is perhaps not practical to test multiple curves and speeds with human subjects, 

but a survey of areas with increased crash data may suggest some trends in design. The survey 

should incorporate lighting, pavement marking design, material, width, roadway design speed 

and advisory speed, location, and guardrail presence. 
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70

INTERSECTION SAFETY

Lighting at Rural Intersections

Rural intersections vary in a number of ways, as do the policies and standards for lighting them. 

The factors involved in fatal crashes at many high-speed intersections in rural areas, whether 

signalized or not signalized, need to be explored to better inform policy for lighting.

Transient adaptation occurs when drivers travel to and from lit and unlit areas and may cause 

issues with vision for drivers as they pass through a lighted rural intersection. The general policy 

is to provide a tapering of lighting so that the transition between the two areas is gradual and 

comfortable. 

Statement of Urgency

Due to the high rate of crashes associated with rural intersections at night, lighted and nonlighted, findings from this effort can increase understanding of potential causational factors 

associated with crashes. A focus on transient adaptation, its effects, and methods of limiting this 

effect at rural intersections would benefit intersection design and safety.

Project Objective

This project should explore the limits of transient adaptation and general safety concerns of rural 

intersections. The results of the project should progress policy to include lighting techniques and 

standards to improve safety at rural intersections.

Relationship to Existing Body of Knowledge

Existing research has explored the best methods to lighting intersections in terms of visibility inside 

the box where points of conflict mostly occur. This research should build on that existing research 

as well as determine visibility issues, if any, that exist around the intersection due to the lighting.

Anticipated Work Tasks

To explore the limits of transient adaptation, human subjects should perform visibility tasks in 

various intersection lighting setups. A survey of conventional lighting methods in addition to 

alternative methods should be explored in this way.
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71

Intersection Sight Distance and Gap Acceptance

A recent NCHRP project has identified the safety impacts of providing ISD, showing that fewer 

crashes occur as ISD increases.(10) Even though ISD is measured based on geometry, there may 

be issues related to nighttime visibility if the clear sight triangles needed for adequate ISD can 

be different during the night than during the day. Controls for ISD are based on principles of gap 

acceptance, which has been derived from daytime observations. A driver’s gap acceptance is 

a function of perception-reaction time, the time (and distance) used to make an appropriate 

maneuver, the speed of the conflicting vehicles, and any buffer added for personal preference 

and safety. 

Statement of Urgency

The duration of a gap that drivers select may vary with time of day. At night, this may be 

impacted more because visibility is limited and there is potential for misjudging the distance of a 

conflicting vehicle. It is possible that what may be an acceptable sight distance during the day 

may not be adequate at night. Future research may address how gap acceptance changes by 

time of day, whether there is a need to consider how nighttime gap acceptance may impact ISD 

and intersection safety, and whether or not intersection lighting would mitigate these effects.

Project Objective

Research to support this issue would be focused on how daytime versus nighttime drivers judge 

the speed and distance of approaching vehicles in terms of gap acceptance. If nighttime gap 

acceptance differs from daytime gap acceptance, then changes to policies to accommodate 

the difference may lower certain types of intersection-related crashes.

Relationship to Existing Body of Knowledge

There is limited research on this topic. The research that is available is focused on gap 

acceptance (day versus night) at two-way stop-controlled intersections and shows a statistically 

significant difference in gap acceptance capabilities for older drivers (they need significantly 

larger gaps during nighttime conditions).(11)

Anticipated Work Tasks

The research might start with simulator work, but definitive research would involve actual studies 

of gap acceptance under similar conditions except time of day. These could be observation 

studies under the correct scenarios and/or closed-course studies. 
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72

Selecting Phasing for Left Turns

The second edition of the Signal Timing Manual (NCHRP Report 813) provides national guidance 

on the selection of left-turn phasing modes at signalized intersections. Practitioners are to select 

protected or permissive phasing based on criteria such as the number of left and through lanes, 

sight distance, turning volumes, speeds, and crash history.(12) 

Statement of Urgency

There is no specific consideration for nighttime conditions. These guidelines can be improved by 

including special circumstances for nighttime conditions (for example, appropriate thresholds 

for nighttime crashes rather than total crashes only or turning volumes at night rather than 

peak-hour volumes). This is a classic example of where a nighttime review of national policies 

is needed, including nighttime visibility, especially with a collaborative team of relevant subject 

matter experts. 

Project Objective

The application of the results would be applied to the current guidelines for converting 

permissive left turns to protected left turns. The results from this research could reduce left-turn 

crashes at night under permissive control conditions. 

Relationship to Existing Body of Knowledge

The current recommendations do not specifically address nighttime gap acceptance, but 

crashes of this type are common during nighttime conditions.

Anticipated Work Tasks

The research for this would be similar to the day versus night gap acceptance research 

described above. 
ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

73

Skewed Intersections: Visibility of Pedestrians or Bicycles at Night

Intersections with large skew angles are potential safety concerns at night for pedestrians 

and bicycles approaching the intersection from a conflicting direction. Because a vehicle’s 

headlamps are directed forward, with only a small amount of illumination distributed away from 

the center, there may be conditions where drivers are unlikely to see pedestrians or bicycles from 

some directions, depending on the use of lighting. 

Statement of Urgency

At night, the visual attention of drivers tends to be concentrated in a smaller area than during 

the day, meaning that drivers are additionally less likely to search for those approaching 

pedestrians and bicycles. This concern can be addressed by evaluating the illuminance patterns 

of headlamps and whether or not the light distributed horizontally at wide angles is enough for a 

driver to see pedestrians and bicycles.

Project Objective

The objectives of this research would be to determine the extent of off-axis pedestrian lighting 

that exists from conventional headlamps and determine those limits, as well as to compare the 

capabilities of those headlamps to angles produced by skewed intersections and determine 

safety implications at those intersections. The results of this effort would support pedestrian safety 

and visibility and inform municipalities of when additional visibility aids such as lighting need to 

be implemented in skewed intersections.

Relationship to Existing Body of Knowledge

Research on this topic would progress existing research related to headlamp and pedestrian 

safety. Curve-adapted headlamp technologies need to be researched to better understand how 

they address existing corner cases. In addition, alternative intersection angles are understudied 

in terms of pedestrian safety.

Anticipated Work Tasks

This research would include an assessment of how much light conventional and contemporary 

headlamps provide for pedestrian detection off-axis of the vehicle direction. Mapping the 

beam pattern onto nonconventional intersection designs (such as skewed intersections 

and roundabouts) would be a unique way to compare current sight distance and visibility 

assessment techniques with relevant data. This technique would also be a useful way to optimize 

the location of intersection lighting, with respect to pedestrian visibility at an intersection of 

interest. 
ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

74

Free-Flow Interchanges and Intersections

Innovations in interchange and intersection design can promote large increases in efficiency, 

with some intersections (such as roundabouts) providing for the free flow of vehicles. Diverging 

diamond interchanges and displaced left-turn or continuous-flow intersections are recent 

concepts specifically designed to address conflicts with turning vehicles. The proper use of 

lighting and signage at these types of intersections is critical because they are very different from 

typical stop-controlled or signalized intersections. 

Statement of Urgency

There may be visibility issues at night that are not obvious during the day, especially for 

roundabouts, where drivers are not expecting to stop unless they see another vehicle. This makes 

pedestrians even more vulnerable at roundabouts and other free-flow intersections where speeds 

are typically higher than traditional intersections. Lighting and signage in these spaces need to 

be designed and implemented to ensure pedestrian safety.

Project Objective

The primary objective would be to identify critical points in free-flow interchanges and 

intersections and evaluate the effect of lighting and signage at those points. 

Relationship to Existing Body of Knowledge

This research would expand on existing research centered on roundabout and free-flow 

interchange gaze behavior. Many of the current observations are based on daytime research, 

and evaluating nighttime driving may point to different critical aspects. A better understanding 

of nighttime driver behavior would inform the proper implementation of signage and lighting in 

free-flow type intersections.

Anticipated Work Tasks

This research would include an assessment of how much light conventional and contemporary 

headlamps provide for pedestrian detection off-axis of the vehicle direction. Mapping the 

beam pattern onto nonconventional intersection designs (such as skewed intersections 

and roundabouts) would be a unique way to compare current sight distance and visibility 

assessment techniques with relevant data. This technique would also be a useful way to optimize 

the location of intersection lighting, with respect to pedestrian visibility at an intersection of 

interest. 
ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

75

Traffic Signs

There is a need to establish recommendations for traffic sign retroreflectivity (materials) 

and possibly pavement markings. Depending on the type of environment and intersection 

control (rural versus urban, or stop sign versus signal), there could be justification for different 

performance levels. In fact, there are no national recommendations or guidelines that a 

practitioner can use to select the best retroreflective product or performance level for a specific 

scenario. This is a general need that extends beyond intersections. 

The MUTCD contains requirements for minimum levels of traffic sign retroreflectivity.(7) These 

requirements are based on research conditions that represent dark rural highways. As shown in 

the recent NCHRP Report 828, nighttime sign brightness must increase to offset increasing levels 

of background visual complexity.(13) Intersections generally have more background complexity 

than a random section of highway, particularly urban signalized intersections. 

Statement of Urgency

There is a need to evaluate shoulder-mounted sign visibility in areas with more visual complexity 

than a dark rural highway. Increased retroreflectivity levels for these types of intersections would 

make the signs more visible and may lead to fewer nighttime intersection-related crashes. 

Project Objective

The primary focus of this effort would be to create recommendations for retroreflective materials 

based on the evaluations of performance levels in specific scenarios such as rural, urban, stopcontrolled, or signalized intersections.

Relationship to Existing Body of Knowledge

NCHRP Report 828 provides the most relevant demonstration that this research is needed. In 

NCHRP Report 828, overhead sign performance levels were developed based on the background 

complexity.(13) Similar work would be needed for ground-mounted signs in different environmental 

conditions. 

Anticipated Work Tasks

This work could be similar to the work that was performed for NCHRP Report 828, which included 

closed-course legibility studies as well as open-road recognition studies.(13)
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76

Roadway Lighting Automation and Controls

With the advent of solid state lighting, controlling where the lighting can be turned on and off as 

well as dimmed is becoming more important. This technology provides the opportunity to adjust 

lighting levels and to react to the presence of vehicles and pedestrians. 

Statement of Urgency

As more agencies adopt solid state lighting, the need to establish guides for automation and 

controls grows. A survey of current trends and capabilities of the technology is important for 

developing policies.

Project Objective

Results of this effort would provide municipalities and policy makers with information for deciding 

to use an automated lighting system. Automated lighting has impacts on energy consumption 

and can produce an economic benefit.

Relationship to Existing Body of Knowledge

There has been recent research utilizing programmable solid state lighting, but these studies 

have been isolated. A full-scope evaluation of the systems should include a wide variety of road 

types and consider multiple regions.

Associated Work Tasks

Research would require a survey of the solid state lighting control systems currently available. 

Experiments should focus on reliability, network reach, and usability of controls. In addition, 

research should take into account any limitations the systems have in terms of interference or 

delay.
ROADWAY VISIBILITY RESEARCH NEEDS ASSESSMENT

77

PEDESTRIAN AND BICYCLE SAFETY

Lighting for Pedestrians

Lighting is commonly designed for vehicles and not for pedestrians. Providing a standard of 

lighting that meets the criteria for both is a key interest. Lighting for pedestrians is believed to 

be more crucial in providing the greatest safety benefit at conflict points. Gap acceptances for 

pedestrians and the perception pedestrians have of how visible they are to drivers are research 

topics that have been explored in the past and can be re-explored with the advent of modern 

in-roadway lighting, crosswalk lighting, vehicle headlamps, and education.

Vertical illuminance is among the most important factors for determining the contrast and 

visibility for a crossing pedestrian. Methods for achieving the required vertical illuminance may 

need to be explored because current standards are often believed to be difficult to achieve. The 

amount of vertical illuminance required may vary depending on an array of variables including 

environmental lighting, intersection lighting, crosswalk size, and crosswalk geometry.

In-roadway lighting is becoming an important area of interest as more agencies adopt it as a 

method of promoting safety and reducing energy. In-roadway lighting at crosswalks is believed 

to be a benefit for drivers to visualize crosswalks ahead of time and for pedestrians to have a lit 

path. The effects of in-roadway lighting in combination with area signage, overhead lighting, and 

retroreflective markings need be explored to better inform policy.

Statement of Urgency

Newer technology for modern roadway lighting has led to more precise output from luminaires. 

This results in less light spilling over to sidewalks since higher-quality optics provide adequate 

lighting for the roadway but not for pedestrians. Investigating the impact of newer technologies, 

such as the Nadir Dump and other luminaire types, may inform future roadway lighting design 

with sidewalks and crosswalks in mind.

Project Objective

The purpose of this project would be to develop a cost-efficient plan for lighting pedestrians that 

promotes safety. The results of this project would inform policy on lighting crosswalks and other 

critical pedestrian conflict points.

Relationship to Existing Body of Knowledge

Pedestrian visibility has been evaluated in a number of ways. The primary focus is typically either 

the use of roadway lighting to spill light onto pedestrian walkways or crosswalk-specific lighting. This 

research would build onto that existing body of knowledge by considering alternative methods.

Associated Work Tasks

First, a survey of all available pedestrian- and crosswalk-related technologies must be considered. 

Then, an experimental design that involves human subjects detecting the presence of 

pedestrians under varying lighting technologies could determine the best methods for lighting 

pedestrians. The environments of sidewalks and crosswalks can vary in ambient lighting, which 

may impact visibility and thus should also be explored.
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78

Seasonal Fluctuations in Daylight Hours and Effects of Daylight Savings Time

The change in when daylight occurs because of the changing seasons and the adjustments that 

occur with the use of Daylight Savings Time mean that there are periods when road users may be 

accustomed to daylight but experience darkness. In some locations and during certain times of 

the year, peak traffic volumes may occur at night. With DST, the sudden change in whether or not 

a commute occurs during daylight has significant safety implications, especially on pedestrians 

and cyclists.(14) These road users are often poorly visible due to an absence of lighting. 

Statement of Urgency

If agencies provide street lighting, it may be valuable to investigate how they address DST 

changes and gradual seasonal daylight changes, whether with automatic lighting or with timers. 

Consistency in when lighting is provided relative to ambient light is important, especially for these 

vulnerable road users.

Project Objective

Results of this survey would serve as a step toward forming guidelines that may improve lighting 

for pedestrians in some areas. 

Relationship to Existing Body of Knowledge

DST-related issues are an understudied aspect of roadway lighting and visibility. There is a link 

between DST and pedestrian-related crashes. This research would explore that link and attempt 

to establish recommendations regarding pedestrian safety at those times.

Anticipated Work Tasks

A survey of municipality ordinances on lighting, specifically during periods of DST, as well 

as pedestrian-related crash rates in these locations would serve as data for this project. It is 

important that many municipalities in varying regions be considered so that the many nuances 

in DST are reviewed. 
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Glare from Beacons, Signals, and Other Lights

Flashing beacons and lights used on signs at intersections, midblock crosswalks, and other 

locations have been shown to be effective at grabbing attention, but glare from these lights may 

have a detrimental effect on drivers’ ability to see pedestrians and marked crosswalks, especially 

at night. Some text in the MUTCD instructs that automatic dimming for traffic signals should be 

used if a signal’s indication is bright enough to cause glare.(7)

Statement of Urgency

There appear to be no specifications, however, for appropriate levels of illuminance for these 

lights at night. In addition to flashing beacons used for crosswalks, the concern regarding glare 

may be relevant for all sources of light, including all traffic signals (including PHBs), LEDs on signs, 

railroad gates, in-roadway lights, and lane use signals.

Project Objective

Results from this effort would inform policy makers on how bright beacons and lights at 

intersections and crosswalks can be while maintaining the level of visibility and safety for 

pedestrians and other road users.

Relationship to Existing Body of Knowledge

In 2008, NCHRP Report 624: Guidelines for Selection and Application of Warning Lights on 

Roadway Operations Equipment presented guidelines for selection and application of warning 

lights to improve the conspicuity and recognizability of roadway operations equipment used for 

construction, maintenance, utility work, and other similar activities.(15) Since NCHRP Report 624 

was completed, significant technology changes and pressure from increased speeds, traffic 

volumes, and distracted drivers have occurred, necessitating additional guidelines. 

Associated Work Tasks

Research on this topic should involve access to an intersection with the ability to manipulate 

lighting types and levels. A human subjects test involving the visibility of pedestrians at crosswalks 

and intersections while exposed to a variation of lighting technologies must be conducted. 
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Assumptions for Pedestrian Walking Speed

The assumed pedestrian walking speed suggested in the MUTCD is conservatively set at 3.5 fps, 

with accommodation for slower walking speeds for special conditions.(7)

Statement of Urgency

It is likely that the research used to select the recommended pedestrian walking speed focused 

exclusively on daytime conditions, neglecting the behavior of pedestrians at night. 

Project Objective

The objective of this research would be to determine if there are different nighttime walking 

speeds and then make appropriate adjustments in the signal phasing plans. The results may 

lead to fewer nighttime intersection-related crashes. 

Relationships to Existing Body of Knowledge

Researchers in a recent study showed that the time of day may impact walking speeds, with 

pedestrians walking approximately 0.5 fps slower during the evening peak than during the 

morning peak.(16) That analysis, however, involved data collected only during those two time 

periods. Additionally, the data were collected in New York City (Manhattan), where the density of 

pedestrians tends to be high. Regardless, a different walking speed attributed to the time of day 

may justify examining the issue with more depth.

Associated Work Tasks

This research would be aimed at collecting nighttime pedestrian walking speeds and comparing 

the results to the existing literature, which includes mostly, if not only, daytime pedestrian walking 

speeds. 
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School Zones Marked with Word Markings

There are several instances in the MUTCD that specify that certain objects must have 

retroreflective properties.(7) There is currently no language specifying that the “SCHOOL” word 

marking informing drivers they are entering a school zone must be retroreflective. Although it is 

likely that the marking would be made of the same retroreflective material as the nearby line 

markings, there may be a question about whether the marking should be held to a standard of 

maintained retroreflectivity. 

Statement of Urgency

If there are periods of the year during which school activities begin or end during dark or 

nighttime conditions, there may be justification to evaluate the brightness of the marking.

Project Objective

The research objectives would be to determine if there is an overlooked need to implement 

retroreflective markings in school zones and provide recommendations on how to determine 

those needs. Results of this project would influence policy makers and reduce the number of fatal 

crashes at school zones.

Relationship to Existing Body of Knowledge

Part 7 of the MUTCD includes standards for marking school zones.(7) The standards are based 

on consensus voting of agencies across the United States. However, they could be enhanced 

with research results to help agencies better understand how to make modifications to increase 

visibility and safety. 

Associated Work Tasks

This research could involve surveys of nighttime drivers who drove through areas with and without 

retroreflective school markings. If they have a better recall of the retroreflective markings, then 

there would be some merit to requiring them to be retroreflective. 
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Bike Lanes 

FHWA has approved the use of green pavements to delineate bike lanes. Generally, there is 

no nighttime visibility component to the green bike lanes (adding glass beads reduces the 

friction). Markings are retroreflective because of glass or ceramic spheres. While this adds an 

element of nighttime visibility to the markings, it can also create slippery markings, especially 

when wet. Bike lanes need to be carefully designed to avoid slippery conditions because of the 

need to balance a bike (two wheels versus four wheels). Therefore, the bike lanes do not include 

retroreflective properties, which reduces their visibility at night.

Statement of Urgency

There is a need to develop technologies and materials that can help provide nighttime visibility 

to bike lanes so that their paths are as easily identified during dark conditions as they are during 

daytime conditions. 

Project Objective

The objective of this research would be to develop a material that provides daytime color of bikes 

lanes during nighttime conditions, while maintaining a high degree of friction. The outcome of 

this research would support bicycle safety and reduce crashes between motorists and bicyclists.

Relationship to Existing Body of Knowledge

Studies to date have demonstrated that bike lanes generally improve biker safety. None of the 

existing studies have had the opportunity to examine bike lanes that provide a highly visible path 

to the nighttime bikers. 

Associated Work Tasks

Observational studies before and after the treatment of visible bike lane materials would be 

needed. 
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OTHER AREAS WITH NIGHTTIME VISIBILITY CONCERNS

The following research concerns do not fit within the three target program areas, but the topics 

arose in the course of identifying gaps in current practices and research related to nighttime 

visibility. Several of these research areas are a result of budding and future technologies that 

promise ways to provide cheaper and more-efficient lighting through sensors and automation. 

The effect these technologies will have is unforeseen, and research into their impacts on safety is 

warranted.
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Health Effects of Roadway Lighting

In a recent document, AMA noted that the presence of the blue portion of the lighting spectrum 

in light sources has the potential to impact the health of humans living close to the light source.(17)

AMA recommends that the light source be no greater than 3000K in color temperature. Studies 

have, however, shown that light sources with a 4100K color temperature perform at a higher level 

in terms of the visibility of objects in the roadway.(18) It is vital that these issues be considered.

Statement of Urgency

There is a disagreement between visibility researchers and health researchers on which light 

should be used for nighttime driving. A better understanding and consensus on this topic is vital 

for maintaining road safety and user health.

Project Objective

The purpose of this project would be to gain insight on how lighting, particularly that associated 

with driving, affects health. Insight on this topic can ensure that driver visibility and human health 

are maintained.

Relationship to Existing Body of Knowledge

There are several reports and research efforts that discuss this issue. Most of these are discussed 

in the AMA report.(17) However, these research efforts are limited in the dosage level of the light 

source. This means that the research was performed at much higher levels of light than typically 

experienced by a driver. As such, the applicability of the results and the assessment of the overall 

impact can be limited. The full impact of this effect is unknown, and this research would serve to 

fill this gap in the knowledge.

Associated Work Tasks

This research effort should begin with an extensive literature review about the effect of lighting 

on health, specifically in terms of the light spectrum. In addition, a survey of the multiple ways 

humans are exposed to different spectrums of light, not just in a roadway setting, is crucial to the 

observation.
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Energy Consumption

Energy conservation has become a focus for many precincts and agencies. Removing lighting 

from infrastructure has become a popular method of conserving energy with some disregard 

to the impact of safety. Exploring methods of conserving energy in areas while maintaining 

safety should be a focus to inform policy and prevent uninformed decisions by infrastructure 

managers. Some known methods to efficient methods of lighting that allow for reduced energy 

consumption include the use of in-roadway lighting to highlight conflict points and prevent light 

trespass. Adaptive lighting technology is also a popular method of utilizing light only when it is 

necessary to do so.

The natural extension of this would be lighting on demand. LED lighting can be implemented 

with motion sensors or through connected-vehicle technologies to have lighting respond to the 

presence of a vehicle or pedestrian. Sample projects have been implemented in a controlled 

test road environment, but wider implementation will be developed in the future.

Statement of Urgency

As mentioned previously, due to the increased focus of energy conservation, roadway and 

infrastructure lighting is being removed with little regard for safety. Alternatives to lighting that may 

alleviate economic concerns and improve energy efficiency exist. These alternatives need to be 

thoroughly explored for wider implementation to take place.

Project Objective

The project should determine the safety aspects of adaptive and on-demand lighting. The 

adoption rate and economic justifications for installation and maintenance also need to be 

considered. The implications of this research could have huge impacts on municipal budgets 

and local economies as well as reduce the overall energy consumption. 

Relationship to Existing Body of Knowledge

The technological aspects of adaptive lighting and on-demand lighting have been researched, 

as have some safety components of on-demand systems. This research would focus on energy 

conservation and economic benefits as a means of providing a more detailed breakdown of 

costs and savings to interested agencies.

Associated Work Tasks

Wider implementation would warrant testing on-demand lighting and reduced lighting 

technologies in a number of naturalistic locations. Doing so would create observable data on the 

behavior and safety of the lighting. 
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Vehicle Automation

The anticipated adoption of connected and automated vehicles allows for innovative 

approaches to lighting. On the one hand, vehicle automation may reduce the need to use 

lighting because so much of what the vehicles “see” will not be with light in the visible spectrum. 

On the other hand, there will still be other road users (such as pedestrians) that are just as 

deserving of safe and efficient transportation. The concept of smart cities with connected 

infrastructure opens up opportunities to apply lighting on demand and intelligently adapt to the 

users’ needs.

Statement of Urgency

Vehicle automation is on the horizon, and very little consideration has been given to existing 

infrastructure in the wake of this movement. 

Project Objective

Using a smart city or network of automated vehicles and infrastructure, this project would 

identify weak points and areas of consideration in terms of vehicle and user safety (e.g., 

pedestrians). The results of this research would lay the foundation for safety guidelines in relation 

to automation. 

Relationship to Existing Body of Knowledge

There have been very few opportunities for a rigorous smart city or simulation thereof to be 

conducted due to the limitations of most research facilities. These opportunities are becoming 

more plentiful, and research on this topic would keep safety ahead of the curve.

Associated Work Tasks

Research would require a smart-city simulation with vehicle and infrastructure communication 

in place. Testing would involve an evaluation of the technology’s capabilities as well as human 

interaction with it. 
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Lighting Uniformity

Uniformity is regarded as a desired effect of roadway lighting, though some research disputes this 

claim. There is room to explore the limits of lighting uniformity and its interaction with in roadway 

lighting, retroreflectivity, pedestrian visibility, and lighting color. 

Statement of Urgency

The day-to-night effect of uniformity is important since daylight is highly uniform and roadway 

lighting generally strives to replace daylight; however, differences in source location and mount 

height tend to affect the angle of intensity of lighting. This causes severe shadows. In addition 

to roadway lighting, uniformity in intersections where light sources from other vehicles and 

infrastructure exist should be investigated. 

Project Objective

The primary objective of this effort would be to compare visibility in a uniform driving environment 

versus a nonuniform environment. Results of this study could directly impact roadway design 

practices.

Relationship to Existing Body of Knowledge

Uniformity typically falls under the school of thought that more lighting at night is typically better 

for visibility; however, some recent studies have found that uniform lighting on a roadway can 

decrease contrast in some instances.

Associated Work Tasks

A research effort would require comparing small-target visibility, a metric commonly used in 

roadway visibility tests, of uniform and nonuniform roadways. A facility equipped with adjustable 

roadway lighting and the ability to perform visibility evaluations from inside a vehicle is preferred. 

The results of this study may influence lighting policy and affect the amount of lighting used on a 

roadway, which impacts the economy, energy consumption, and safety.
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Lighting on Rural Bridges

The AASHTO Green Book calls into question the justification of cost for lighting rural bridges. 

Whether or not rural bridges attribute to a number of conflicts and collisions that can be rectified 

by the addition or subtraction of lighting or delineators should be explored.(2)

Statement of Urgency

Lighting on rural bridges has been removed in some areas for cost savings; however, very little 

regard has been given to the safety implications of those removals. Bridges, particularly the 

variety of ones in rural areas, are unique and may provide visibility limitations and lack cues 

drivers need for safety.

Project Objective

The focus of this effort would be to determine the impact of lighting on rural bridges and 

establish when removal of lighting is permissible in regard to safety. The outcome of this research 

would inform policy makers and municipalities about the importance of lighting for rural bridges 

prior to a decision to remove the lighting.

Relationship to Existing Body of Knowledge

In general, providing light in rural areas improves visibility and safety; however, very little research 

has been conducted in regard to lighting on specifically rural bridges.

Associated Work Tasks

A survey of bridges and their crash rates should be conducted. In addition, innovative lighting 

solutions to rural bridges that may be less costly to implement and maintain should be 

investigated. 
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Interaction of Overhead Lighting with Fauna, Foliage, and Crops

The effect roadway lighting has on fauna, foliage, and crops is an aspect of lighting that is rarely 

documented in policy. Exploring the factors that benefit or harm wildlife in regard to lighting 

can provide insight on better and safer implementations. Research on this topic can also seek 

to understand the effect of environmental lighting, which is currently based on consensus 

knowledge. Adaptive lighting takes environmental effects into account, but the extent has not 

been properly researched.

Statement of Urgency

As the lighting inventory evolves rapidly from traditional sources to solid state LED sources, these 

issues of impact on the environment need to be considered in much greater detail. Taking 

action now to identify the issues would reduce issues later that may require a redesign or further 

retrofit of the system. As an example, there has long been an impact on the growth patterns of 

soybeans based on proximity to roadway lighting. As agencies convert to solid state sources, 

the change in the spectrum and selection of the light source may impact this soybean-to-light 

relationship. As a result, the selection of the light source today is critical to minimizing the future 

impact of the lighting system.

Project Objective

The objective of this research would be to analyze the interaction of lighting on the growth 

and behavior of fauna, foliage, and crops. The secondary mission of this research would be to 

develop alternatives that would be less impactful than the conventional lighting systems used. 

The results of this research would serve to inform specification on light trespass and lighting 

design in the roadway.

Relationship to Existing Body of Knowledge

This is a growing body of knowledge. Existing studies have shown impacts on turtle migration, bird 

flight paths, soybean maturity, and other growth. However, the development of the application 

factors for the lighting impacts and the mitigation techniques are required to fully mitigate these 

issues.

Associated Work Tasks

Research in this area would involve assessing the plant growth and studying the animal 

migratory patterns and vehicle-animal crashes in areas with roadway lighting. A variety of plant 

species and animal types should be considered since the spectral receptivity of the plants and 

animals can vary from human responses. A variety of lighting levels would also be required to 

determine the threshold of impact of the lighting.
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Curve Design Accounting for Nighttime Line of Sight

One of the controls for the design of horizontal curvature is the line of sight cutting across 

the inside of the curve, limited by an obstruction that is offset from the road. The equation for 

calculating whether or not there is sufficient sight distance for curves is based on an assumption 

that the obstruction is the only limiting factor and the object would otherwise be visible to the 

driver. At night, however, driver vision can be restricted to the pattern of light from headlamps, 

which is mostly concentrated in a direct line in front of the vehicle. 

Statement of Urgency

A driver at night may not be able to see an object in the road near the end of a curve since the 

headlamps are only directed straight ahead. The limited amount of headlamp illumination that 

is scattered horizontally needs to be considered to properly judge sight distance when designing 

horizontal curves.

Project Objective

The purpose of this research would be to evaluate headlamps and their limitations in curves. 

Results of this research would better inform policy on curve design and headlamp design. 

Solutions for protecting cyclists and other road users in areas such as this are also dependent on 

this research.

Relationship to Existing Body of Knowledge

The IIHS is currently testing curve-adapted headlamp technology with two specific radii (500 

ft and 800 ft). Readings are taken 10 inches from the ground for visibility and 3 ft 7 inches from 

the ground for glare.(19) While this testing provides some initial information, additional research is 

needed to understand the gaps in this technology and how it affects driver behavior. 

Associated Work Tasks

Potential research in this area should evaluate the distribution of light from headlamps and 

whether objects would be visible at the wide viewing angles that can occur with sharp curves. 

This research would be similar to that of skewed intersections. In addition to evaluating the 

capabilities of headlamps, the research would also benefit from better understanding the gaze 

patterns of drivers in curves at night. Eye-tracking data can provide feedback for where in curves 

drivers fixate, whether at the farthest depth their headlamps reach or at some point in the curve. 
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REFERENCES

1. Code of Federal Regulations (CFR) Title 49, Section 571.108. Federal Motor Vehicle Safety 

Standard 108. Available at https://www.gpo.gov/fdsys/pkg/CFR-2004-title49-vol5/xml/CFR2004-title49-vol5-sec571-108.xml. 

2. AASHTO. A Policy on Geometric Design of Highways and Streets (Green Book). AASHTO, 

Washington, DC, 2004.

3. Kang, B., B. Yong, and K. Park. Performance Evaluations of LED Headlamps. International 

Journal of Automotive Technology, Vol. 11, No. 5, 2010, pp. 737–742.

4. Insurance Institute for Highway Safety Highway Loss Data Institute. In the Dark: New Ratings 

Show Most Headlights Need Improvement. Status Report, Vol. 51, No. 3, March 30, 2016. 

Available at http://www.iihs.org/iihs/sr/statusreport/article/51/3/1.

5. Carlson, P. Can Traffic Signs Be Too Bright on Low-Volume Roads? Transportation Research 

Record, No. 2472, Transportation Research Board, Washington, DC, 2015.

6. Oregon Department of Transportation (ODOT). Stopping Sight Distance and Decision Sight 

Distance. Discussion Paper No. 8A. ODOT, Salem, OR, 1997.

7. FHWA. Manual on Uniform Traffic Control Devices. FHWA, Washington, DC, 2009.

8. Carlson, P. Can Traffic Signs Be Too Bright on Low-Volume Roads? Transportation Research 

Record, No. 2472, Transportation Research Board, Washington, DC, 2015.

9. Carlson, P.J., B. Brimley, G. Hawkins, S. Himes, H. McGee., and F. Gross. Traffic Control Device 

Guidelines for Curves. Final Report, NCHRP Project 03-106, April 2015. Available at http://

onlinepubs.trb.org/onlinepubs/nchrp/docs/NCHRP03-106_FR.pdf.

10. Himes, S., K. Eccles, K. Peach, C.M. Monsere, and T. Gates. Estimating the Safety Effects 

of Intersection Sight Distance at Unsignalized Intersections. 2016 TRB Annual Meeting, 

Washington, DC, 2016.

11. Dissanayake, S., J.J. Lu, and P. Yi. Driver Age Differences in Day and Night Gap Acceptance 

Capabilities. IATSS Research, Vol. 26, No. 1, 2002, pp. 71–79.

12. Urbanik, T. NCHRP Report 813: Signal Timing Manual, Second Edition. Transportation Research 

Board, Washington, DC, 2015.

13. Carlson, P.J., B. Brimley, J. Miles, S. Chrysler, R Gibbons, and T. Terry. NCHRP Report 828: Guidelines 

for Nighttime Visibility of Overhead Signs. Transportation Research Board, Washington, DC, 2016.

14. Sullivan, J.M., and M.J. Flannagan. The Role of Ambient Light Levels in Fatal Crashes: 

Inferences from Daylight Saving Time Transitions. Accident Analysis and Prevention, Vol. 34, 

2002, pp. 487–498.

15. Gibbons, R.B., S.E. Lee, B. Williams, and C.C. Miller. NCHRP Report 624: Guidelines for Selection 

and Application of Warning Lights on Roadway Operations Equipment. Transportation 

Research Board, Washington, DC, 2008.
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16. Peters, D., L. Kim, R. Zaman, G. Haas, J. Cheng, and S. Ahmed. Pedestrian Crossing Behavior at 

Signalized Intersections in New York City. 2015 TRB Annual Meeting, Washington, DC, 2015.

17. American Medical Association. Human and Environmental Effects of Light Emitting Diode 

(LED) Community Lighting. CSAPH Report 2-A-16. AMA, Chicago, IL, 2016.

18. North West Energy Alliance. Seattle LED Adaptive Lighting Study. North West Energy Alliance, 

Boulder, CO, 2014.

19. Insurance Institute for Highway Safety Highway Loss Data Institute. Headlight Evaluation: About 

Our Tests. Available at http://www.iihs.org/iihs/ratings/ratings-info/headlight-evaluation.
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FHWA-SA-17-031

December 2016

For More Information:

http://safety.fhwa.dot.gov/