Evaluating Driver Response to Speed Feedback Trailers and Digital Speed Limit Signs Positioned Near the Work Area Within Freeway Construction Work Zones

A series of field evaluations were conducted within work zone lane closures on rural freeways in Michigan to determine 1) the optimal positioning of a speed feedback trailer (SFT) approaching an active work area, 2) the effectiveness of a digital speed limit (DSL) sign for posting work zone speed limit reductions, and 3) the effectiveness of a speed feedback panel paired with a DSL. Speed trajectories were collected for vehicles traversing each work zone using a series of handheld light detection and ranging (LiDAR) guns operated by a team of technicians seated in unmarked vehicles within each lane closure. The SFT was found to be increasingly more effective at reducing speeds of vehicles approaching and entering the work area as it was positioned closer to the work area. Positioning the SFT 200 ft from the start of the work area, which was determined to be the optimal position, reduced speeds entering the work area by 3.1 mph compared with when the SFT was positioned further upstream. This SFT position helps ensure that motorists receive timely feedback within sight of the work area while providing sufficient deceleration time to maximize speed reductions as drivers enter the work area. The use of a DSL to reduce the work zone speed limit from 60 mph to 45 mph reduced vehicle speeds by 3.7 mph near DSL. Furthermore, activation of the speed feedback panel that was on the same assembly as the DSL reduced vehicle speeds by an additional 1.8 mph.