Evaluation of the Impact of Work Zone Traffic Control Devices on Change of Speed Using the SHRP 2 Naturalistic Driving Study

Abstract

Speeding is a major concern in work zones and a major contributor to work zone crashes. Around 71.4% of fatal work zone crashes are speeding-related compared with 30% of fatal crashes overall. Addressing speeding in work zones is therefore critical to improving work zone safety. This study utilized data from the second Strategic Highway Research Program Naturalistic Driving Study to evaluate the impact of traffic control devices (TCDs) on reducing driver speed in work zones. Time series data assessed changes in speed for 380 drivers over 104 unique work zones on four- or multilane roadways. Speed change was measured for single-point TCDs encountered in the work zones (i.e., signing, changeable message signs [CMSs]), and estimated using a linear mixed-effect model. Results indicated speeds reduced by 4.0 mph for dynamic speed feedback signs (DSFSs), 2.3 mph for speed limit signs (both regular and work zone), 2.2 mph with trailer-mounted- and 1.2 mph for active overhead CMSs, 2.8 mph for arrow boards, and up to 2 mph for other static work zone sign types. Driver characteristics (i.e., age, gender, glance location, cell phone use) were included in initial models but were not statistically significant, probably because of sample size. For instance, simple statics indicated that drivers engaged in a cell phone task had a decrease of only 1 mph when encountering a DSFS whereas drivers not engaged in a cell phone task decreased speed by over 4 mph. However, only seven drivers were engaged in a cell phone task when encountering a DSFS—probably too small to detect statistical significance.