The emergence of Solid-State Lighting (SSL), which predominantly utilizes LED lamp technology for highway applications, created a strong incentive for transportation agencies to convert existing High Pressure Sodium (HPS) lighting systems to SSL systems. The motivation for this conversion is primarily due to substantially lower operating and maintenance costs associated with SSL over conventional HPS lighting systems. The relatively low capital costs and estimated 60-70% reduction in energy consumption and maintenance costs presents incentives for considering strategic lighting improvements at locations where the frequency and potential for severe crashes is highest. However, the current safety and operational performance research as well as documented crash modification factors (CMFs) for roadway lighting applications are based on HPS lighting systems. The “color temperature” of SSL produces light that is very different from HPS produced light and the color of light plays a significant role in a driver’s visual ability to effectively perform driving tasks at night and detect pedestrians . Recently completed FHWA research on adaptive lighting and reduced lighting levels shows that SSL technology effectively reduces the amount of light needed versus HPS lighting. Agencies considering converting from HPS to SSL will be encouraged by this research, but there remains very little understanding of how replacing HPS with SSL lighting will influence safety performance. Due to the efficiency and output potential of SSL systems, there is the potential to “over-light” locations which can degrade safety performance by creating disability glare conditions for drivers. This proposal is for a comprehensive evaluation of how SSL systems compare to the proven and significant safety benefits of HPS systems. Replacing HPS lighting with SSL technology may provide road users (especially aging road users) additional safety and driver comfort benefit by improving their ability to detect longitudinal pavement markings during darkness. Section 3A.02 of the Manual on Uniform Traffic Control Devices (MUTCD) permits the use of pavement markings that are not retroreflective “…where ambient illumination assures the marking is adequately visible.” However, the performance benefit of using lighting to enhance a driver’s ability to detect longitudinal pavement markings is largely unknown. This proposal also seeks to conduct a human factor’s evaluation to quantify how lighting source, color temperature, and illumination levels affect a driver’s ability to see longitudinal pavement markings during periods of darkness. As noted above, there are also operational benefits to lighting, particularly in areas that present multiple decision points to drivers. Crashes that result in multiple lane and freeway connector ramp closures prior to or during peak periods can cause congestion and other unintended consequences on freeways and parallel arterials for extended periods of time. Since non-recurrent congestion accounts for almost half of all congestion in metropolitan areas, a modest reduction in crashes on urban freeways before or during peak periods can produce a significant reduction in the level of congestion and a corresponding improvement in travel time reliability. SSL technology provides designers a great deal of control over what is, and is not, illuminated. This control over roadway lighting systems provides environmental advantages through the use of optics that focus light on the intended areas, which reduces the potential for impacts to species that are sensitive to light sources during time of darkness, light pollution, or trespass. Finally, the amount of reliable guidance information on SSL applications and associated performance benefits is very limited. The strategic nature of this proposal is to improve safety on our Nation’s roadways by providing Agencies with performance-related guidance on SSL applications befo

This strategic initiative will evaluate the safety benefits of Solid-State Lighting (SSL) versus High Pressure Sodium (HPS) lighting systems, and quantify the effect of these technologies on driver ability to detect pavement markings during periods of darkness. This project proposes to develop design guidelines to help Agencies take into account the performance impacts for targeted applications of SSL systems. This effort will focus on the establishing recommended design lighting levels using SSL to positively impact areas of safety and/or mobility concern including: 1. Pedestrian safety 2. Intersection safety 3. Horizontal curve safety 4. Freeways and interchange safety and operations 5. Freeways with managed lane system safety and operations Additionally, this proposed project seeks to conduct a comprehensive human factor’s evaluation to quantify the effect SSL versus HPS lighting has on driver’s ability to detect pavement marking traffic control devices.

The final report will strategically address current gaps in the state of the practice for roadway lighting by providing Agencies with the following information: 1. SSL lighting design guidelines for the locations of safety or mobility concern focused on by this research proposal; 2. The safety performance impact(s) of converting existing HPS systems to SSL by establishing Crash Modification Factors specifically associated with SSL systems; and 3. Human factors evaluation report determining the effect of SSL versus HPS on driver ability to detect pavement marking traffic control devices.

FHWA will contribute $1.125M.