Nighttime Visibility GENERAL INFORMATION
About half of traffic fatalities occur at night, although only about one quarter of travel occurs after dark. While intoxication and fatigue contribute to the high rate of nighttime crashes, nighttime driving is inherently challenging due to decreased visibility. In dark conditions, retroreflective pavement markings and signs delineate the roadway alignment and improve the visibility of decision points such as intersections. Retroreflectivity bounces light from vehicle headlights back toward the vehicle and the driver's eyes, making the signs and markings recognizable from a greater distance. Roadway lighting is another means to increase visibility, not only for drivers, but also other roadway users.
A key to recognizing and quickly comprehending signs is to understand the meaning of the various shapes and colors. For markings, the color and pattern are important. Transportation agencies make sure appropriate signs and markings are used, and that signs are placed in highly visible locations to provide advance warning of upcoming conditions. That helps drivers make proper and timely decisions, which improves safety for all road users, especially at night. For additional information about this, please see the Manual on Uniform Traffic Control Devices (MUTCD) website.
Adequately maintained retroreflective signs and pavement markings and roadway lighting improve nighttime highway visibility and reduce the risk of crashes. For additional information about maintaining the retroreflectivity of the signs and markings, or about roadway lighting, use the links below. Additional visibility research efforts by FHWA follow.
2016 Visibility Gap Analysis
Roadway Visibility Research Needs Assessment [HTML, PDF 1.84 MB]
Following the "Breakthroughs in Vision and Visibility for Highway Safety" workshop, the FHWA Visibility team convened a ½ day of discussion with several leading Roadway Lighting and Retroreflectivity experts to identify gaps in highway visibility research, explore innovative tools and techniques to fill these gaps, and determine the role for FHWA. As a result a project was initiated to thoroughly review available information on how daytime and nighttime visibility is used in design and operation of the highway system, where gaps exist, and how those gaps may contribute to highway crashes. As part of this effort, a review of fatality data and FHWA's Office of Safety's three safety focus program areas–roadway departure safety, intersection safety, and pedestrian and bicycle safety–was conducted. The resultant report also includes an Appendix with a list of potential research problem statements for FHWA consideration.
2016 Initial stage reference search
Visual Requirements for Human Drivers and Autonomous Vehicles [HTML, PDF 1 MB]
Identification of published literature between 1995 and 2013, focusing on determining the quantity and quality of visual information needed under both driving modes (i.e., human and autonomous) to navigate the road safely, especially as it pertains to two-lane, curved, rural roads at night.
2014 Visibility workshop summary
Breakthroughs in Vision and Visibility for Highway Safety – Workshop Summary [HTML, PDF 1.73 MB]
On August 13-14, 2014, at the Turner-Fairbank Highway Research Center in McLean, VA, the Federal Highway Administration's (FHWA's) Office of Safety Research and Development and the Office of Safety, with support from the Exploratory Advanced Research Program, convened a 2-day workshop, "Breakthroughs in Vision and Visibility for Highway Safety." Investigators have previously conducted research in a variety of areas surrounding visibility issues, including efforts exploring retroreflectivity and pavement-marking signs, and legibility of fonts; however, much of this work has been tapering off. The objective of this workshop was to identify gaps in highway visibility research, explore innovative tools and techniques to fill these gaps, and determine the role for FHWA.