Assessing the Impact of Speed-Limit Reduction near Signalized High-Speed Intersections Equipped with Advance-Warning Flashers: Fid-Bau Portal

Assessing the Impact of Speed-Limit Reduction near Signalized High-Speed Intersections Equipped with Advance-Warning Flashers

Wang, Shefang / Sharma, Anuj

Abstract

An advance-warning flasher alerts drivers of the imminent onset of a yellow light at a signalized intersection, and it is widely used to reduce crash frequency and severity. Recently, a more-aggressive countermeasure, a speed-limit reduction, is being used at high-speed signalized intersections in addition to advance-warning flashers. In this paper, six high-speed intersection approaches in Nebraska were evaluated to assess the operational effects of no speed-limit reduction, an $8.0 km / h$ ( $5 mi / h$ ) speed-limit reduction, and a $16.1 km / h$ ( $10 mi / h$ ) speed-limit reduction in the vicinity of high-speed signalized intersections equipped with advance-warning flashers. The placement of speed-limit-reduction signs resulted in significant reductions in observed speeds only when upstream drivers were traveling at speeds higher than a comfortable range—1.8 to $4.0 km / h$ (1.1 to $2.5 mi / h$ ) higher than the regulatory speed limit. The likelihood of this condition being satisfied was higher in case of $16.1 km / h$ ( $10 mi / h$ ) drop; however, it was not found to be true when the speed limit was dropped by $8.0 km / h$ ( $5 mi / h$ ). Also, the compliance rates to the regulatory speed limit varied from 15 to 85%, highlighting the fact that ambient conditions have a much greater influence on drivers’ speed choices as compared to the regulatory speed limit. This research provides further evidence that speed-limit reductions, in conjunction with advance-warning flashers, appears to be an effective safety countermeasure; however, their effects will be dependent on the amount of speed-limit reduction and observed speeds.