Case Study of an Alternative Merging Sign Design for Temporary Traffic Control in Work Zones

Abstract

Signage plays an important role in work zones to provide guidance to drivers under changed conditions. This study investigated the safety effect of an alternative merge sign configuration in a freeway work zone. In this alternative configuration, the graphical-only lane closed sign from the Manual on Uniform Traffic Control Devices (MUTCD) was compared against a MERGE/arrow sign on one side and a Right Lane Closed sign on the other side. Although the graphical-only MUTCD signage for work zones has been in use for several years, it is not known if the signage recommended by the MUTCD offers the highest safety for all jurisdictions. The study measured driver behavior characteristics including speeds and open lane occupancies. The measurements were taken at a work zone on Interstate 70 in Missouri. The study found that the open lane occupancy upstream of the merge sign was higher for the test sign in comparison to the MUTCD sign. The occupancy values at different distances between the merge sign and the taper were similar for both signs. The test sign had 11% more traffic in the open lane upstream of the merge sign. In terms of safety, it is desirable for vehicles to occupy the open lane as far upstream from the taper as possible to avoid conflicts due to the lane drop. The analysis of speed characteristics did not reveal substantial differences between the two sign configurations. The 85th percentile speeds with the MUTCD sign were only 1.6 and 3.2 kph (1 and 2 mph) lower than the test sign at the merge sign and taper locations, respectively. In considering all the aforementioned performance measures, the alternative sign configuration was not superior, but performed equal to the MUTCD sign configuration.