Driver Night Visibility Needs
Approximately half of the fatal crashes on the nation's highways occur at night, despite the fact that travel at night is significantly less than during the daytime. Figure 1 shows the breakdown of annual fatalities since 1978 by lighting conditions. Figure 2 shows the relative rate of day versus night crashes. There has been a significant decrease in the nighttime crash rate, but the rate of night fatalities is still three times higher than that for daytime. There is also correspondingly higher number of injuries and more property damage resulting from night crashes. Consequently, the FHWA is interested in finding ways to remedy the nighttime safety problem. There are many alternative solutions, but it is believed that delineation treatments may represent the most highly cost effective approach.
There is a need to implement measures to improve driver visibility to address the night safety problem. Information from the Fatal Accident Reporting System provided the most comprehensive national summary of highway safety. Figures 1 and 2 show the trends in nighttime fatal crashes since 1978.
Figure 2 – Trends in day and Night Crash Rates
The data indicate that:
- For the last 25 years, 50% or more of the fatal crashes have occurred at night despite the lower volumes of traffic at night.
- Overall annual fatalities on US highways have declined from about 50,331 in 1978 to a plateau around 42,000 by the late 1990's, and in 2003 was 42,643.
- Crashes under dark conditions are higher than under dark conditions with lighting owing to the fact that there are many more miles of unlit road.
- Crashes during dawn and dusk are relatively a small portion of the fatal crashes that has remained fairly constant.
- There has been a drop in night fatalities, with a more pronounced decrease for the “dark” condition.
- Despite a long-term downward trend, the night crash rate is about three times higher than that during the day.
Other factors contribute to the nighttime safety problem. These include:
- There are likely to be more fatigued and intoxicated drivers during the nighttime periods.
- Visual cues that delineate the roadway alignment are greatly reduced at night, even when there is street lighting.
- Regulatory, warning, and guidance information provided by traffic control devices is compromised under dark conditions or when headlight illumination is less than optimal.
- Glare from opposing traffic can adversely affect the driver's ability to detect changes in the road alignment or to see traffic control devices.
- Adverse weather (e.g., rain, snow, fog) further reduces night visibility of the road, other traffic (including pedestrians & bicyclist), and TCDs.
- The driving population is aging and it is well known that visual acuity decreases as a person ages. Older drivers are therefore less able to see the road, traffic control devices, and other traffic at night.
All of these reasons can be addressed, at least partially, if TCDs are appropriately visible to drivers at night. While the need for TCDs that are visible at night is considered intuitively obvious, it has not been possible to establish quantitative measures of the benefits associated because of the many factors that affect night driving for a diverse population.
