Evaluation of Best Practices in Traffic Operation and Safety: Phase I: Flashing LED Stop Sign and Optical Speed Bars

In a previous extensive review of overseas literature, researchers identified 42 traffic operations and safety technologies and practices that were not currently deployed in Virginia. These were evaluated for their potential application in Virginia, and 12 measures were determined to be good candidates for piloting. Two of the measures, a flashing light emitting diode (LED) stop sign and optical speed bars (two patterns) were installed at three locations in Virginia for before and after evaluations.

The flashing LED stop sign was installed at a T-intersection in western Albemarle County, Virginia, where the number of crashes was higher than expected. The measures of effectiveness for the sign were average speed of drivers approaching the sign and compliance with the sign. Average speeds decreased significantly (statistically) after the sign was installed, but only by 1 to 3 mph. Speeds decreased more during the night than during the day. The results of the compliance study were inconclusive Optical speed bars were installed on the centerline and edge line on both approaches to a short section of two-lane roadway in Fairfax County, Virginia. The section of roadway is hazardous, as it has inadequate vertical and horizontal alignment, narrow lanes, and reduced shoulders. A number of crashes had occurred on the section over the years, including a recent fatality. Average speeds both decreased and increased after installation, and the decreases were statistically significant right before and in the middle of the section. The decreases ranged from 1 to 3 mph.

Optical speed bars were also installed across lanes on a major, four-lane undivided highway, at two approaches to a reduced speed limit zone in the town of Zuni, Virginia. Average speeds both decreased and increased after installation. The decreases were statistically significant at the beginning of the 45 mph speed zone on each end of town. The decreases ranged from 3 to 10 mph.

Given the general positive results of the installations, the report recommends that flashing LED stop signs and optical speed bars be considered as safety countermeasures at appropriate locations where the numbers of crashes or crash rates are higher than expected or where excessive speeding occurs.

A costs and benefits assessment indicated that, generally, the benefits in terms of reduced crashes exceeded the costs of the installed measures if only one crash was prevented.