U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
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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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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. Â 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.
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.
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.
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.
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.
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)
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.
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.
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.
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.
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.
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.
There are currently no existing widespread efforts to standardize police reporting techniques.
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.
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)
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)
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The outcome of this research would inform policy for changeable message signs in guides such as the MUTCD.
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.
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.
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.
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).
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.
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.
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.
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.
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 human-subject research based on visibility as well as a survey of areas that currently employ night-specific speed limits.
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.
A survey of current trends in roadway design and speed limits should be followed by a human-subject 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.
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.
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.
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.
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)
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.
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.
Due to the high rate of crashes associated with rural intersections at night, lighted and non-lighted, 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.
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.
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.
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.
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.
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.
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.
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)
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.
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)
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.
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.
The current recommendations do not specifically address nighttime gap acceptance, but crashes of this type are common during nighttime conditions.
The research for this would be similar to the day versus night gap acceptance research described above.
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 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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, stop-controlled, or signalized intersections.
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.
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)
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Results of this survey would serve as a step toward forming guidelines that may improve lighting for pedestrians in some areas.
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.
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.
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)
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.
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.
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.
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.
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)
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Observational studies before and after the treatment of visible bike lane materials would be needed.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Vehicle automation is on the horizon, and very little consideration has been given to existing infrastructure in the wake of this movement.
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.
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.
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.
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.
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.
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.
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.
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)
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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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