Estimating the Crash Reduction and Vehicle Dynamics Effects of Flashing LED Stop Signs

Project summary:

Previous work in Minnesota indicated that the installation of overhead warning flashing beacons at stop signs showed no clear safety benefit. In addition, there was potential for drivers to confuse overhead warning flashers with flashing signal indications. This research project conducted an empirical Bayes before/after evaluation to estimate the crash reduction effect of LED stop signs (stop signs to which LEDs have been added on the sign corners) and a field study involving collection and analysis of data on driver behavior at stop-controlled intersection approaches, with and without LED stop signs.

The before/after hierarchical Bayes observational study found an estimated reduction of about 41.5% in right-angle crashes, but with 95% confidence this reduction could be anywhere between 0% and 70.8%. In a field study, portable video equipment was used to record vehicle approaches at an intersection before and after installation of flashing LED stop signs. After installing the flashing stop signs, there was no change in the relative proportion of clear stops to clear non-stops when minor-approach drivers did not face opposing traffic, but the relative proportion of clear stops increased for drivers who did encounter opposing traffic. Random samples of 60 minor-approach vehicles, and speeds for these vehicles when about 500 feet from the intersection, were selected before and after installation of flashing LED stop signs, and average deceleration rates over the final 500 feet were estimated using trajectory-based methods. Average approach speeds tended to be highest in June, somewhat lower in July, and lower yet in September and November, with September and November having roughly equal average speeds. The average deceleration rates showed a similar pattern.

• OST-R summary report for this project (PDF)