Impacts of experimental advisory exit speed sign on traffic speeds for freeway exit ramp

Abstract

Many crashes occur around freeway exit ramp areas in China due to excessive speeds and large speed variances. Traditionally, a single posted ramp speed limit sign is installed around the physical gore area to manage the speed. To address this issue, the study presented in this paper proposes the use of an advisory exit speed sign (AESS), which is an additional exit speed limit sign positioned along the deceleration lane to accommodate the speed changes ahead of the physical gore. The study selected three sites with similar exit ramp configurations and two scenarios (with AESS/without AESS) to quantify the influences of the AESS on the speed of exiting vehicles. The speed profiles of 480 vehicles were obtained based on 12 hours of data collection. A t-test was applied to verify the reduction in mean speed between the two scenarios. The results show that the AESS in this study was effective in reducing the mean speed and 85th percentile speed, especially in the taper and deceleration lane. It was clearly seen that drivers began to decelerate in advance when the AESS was installed, which led to a smooth deceleration process, especially on the segment between the theoretical gore and the physical gore. The AESS was also helpful in reducing speeding to some extent. Although the effects of the AESS on speed reduction at curved ramps were not ideal, the speed fluctuation range tended to be more contracted when the AESS was installed. This paper provides useful information for researchers, managers, and engineers when considering the implementation of AESS.

Safety Evaluation of Freeway Exit Ramps with Advisory Speed Reductions

“…Widening the shoulder may also improve traffic safety, allowing drivers to have extra space in case of an emergency when traversing the ramp. Additionally, the implementation of various experimental signs such as advance advisory exit speed signs and dynamic speed feedback signs at ramp approach have also shown positive results in reducing the speed of vehicles onto ramps (32)(33)(34)(35).…”

“…However, these signs are non-regulatory in nature and essentially serve as recommendations for drivers as to safe travel speeds when traversing the ramp. Studies have shown that when advisory speed signs are present on high-risk roads (e.g., exit ramp, sharp curve, work zone), drivers tend to estimate their travel speeds better and, consequently, demonstrate safer driving behavior (8)(9)(10)(11).…”

Driver Response to a Dynamic Speed Feedback Sign at a Freeway Exit Ramp Considering the Sign Design and Installation Characteristics

“…Various traffic control strategies have been implemented to reduce speeds and improve the safety performance on freeway ramps, including chevron signs, ramp advisory speed signs, advance curve warning signs, and rumble strips. However, with the exception of rumble strips, such strategies were not found to be effective speed reduction countermeasures on ramps ( 4 , 5 ). A promising countermeasure to reduce curve entry speeds on freeway interchange ramps is the dynamic speed feedback sign (DSFS).…”

“…Exit ramps are particularly vulnerable to the effects of excessive speed, owing to the deceleration that must occur when transitioning from the mainline freeway to the ramp, which often contains substantial horizontal curvature. Several prior studies have shown that travel speeds on exit ramps often exceed the exit ramp advisory speed by 8.0 to 21.5 mph (4)(5)(6)(7)(8). A recent safety evaluation of freeway exit ramps also found crashes to increase as the speed difference between mainline and ramp speed increased (9).…”