About half of traffic fatalities occur at night, although only about one quarter of travel occurs after dark. Although intoxication and fatigue contribute to the high rate of nighttime crashes, nighttime driving is inherently hazardous because of decreased driver visibility.
Adequately maintained retroreflective signs and pavement markings improve highway safety and prevent roadway departure crashes by bouncing light from vehicle headlights back toward the vehicle and the driver's eyes, making the signs and markings appear brighter and easier to see and read. Because the retroreflective properties of traffic control devices deteriorate over time, highway agencies need to actively manage the maintenance of signs and pavement markings in order to ensure that they are clearly visible at night.
Roadway lighting is another means to increase visibility for drivers and other roadway users. Properly designed roadway lighting allows road users to quickly assess roadway conditions and creates a safe environment within the roadw ay vicinity. New technologies to reduce the long-term costs of lighting need to be balanced with understanding and addressing the needs of the road user.
Use the links below to obtain pertinent information related to these three important areas that impact nighttime visibility. The subject areas are grouped as follows:
Roadside Design: Steel Strong Post W-beam. A guidance memo was issued on May 17, 2010 on the height of guardrail for new installations. Guidance regarding existing guardrail will be developed in the next several months, in consultation with AASHTO’s Technical Committee on Roadside Safety.