Evaluation of Alternative Messages and Sign Locations on Driver Response to a Dynamic Speed Feedback Sign on a Freeway Interchange Ramp

Abstract

Research was undertaken to determine effective messaging strategies and sign positions for dynamic speed feedback signs (DSFS) when used for speed management at freeway ramp curves. A field evaluation was performed in this setting to assess the impacts of a DSFS on driver speed selection and braking characteristics while approaching and entering the curve. Three feedback messaging strategies were evaluated at three sign positions in advance of the curve. Compared with the existing site (without the DSFS), the DSFS reduced curve entry speeds and improved brake response across all test conditions, particularly for heavy trucks. Overall, considering the combination of both sign position and feedback messaging strategy, the greatest benefits to driver behavior were attained when the DSFS was positioned 255 ft upstream of the curve and the feedback message included the speed number alternating with a SLOW DOWN message. The inclusion of an advisory speed panel with the DSFS did not have a substantive impact on driver behavior. Based on the findings, the continued use of DSFS as a speed reduction treatment at freeway ramp curves is recommended. Specifically, the sign should be positioned to provide adequate time for drivers to perceive and react to the message, such that comfortable braking can be accommodated while approaching the curve. However, the sign should not be placed too far in advance of the curve, as drivers may be more likely to disregard such a premature warning message. Further evaluation of DSFS under various alternative ramp configurations is recommended.

Driver Response to a Dynamic Speed Feedback Sign on Freeway Exit Ramps Based on Sign Location, Interchange Type, and Time of Day

“…It is also worth noting that the DSFS had a similar effect on driver response across all vehicle categories. These results are aligned with prior findings associated with DSFS use in similar freeway ramp settings ( 8 ).…”

“…The DSFS had no significant effect on reducing excessive curve entry speeds or improving brake response at this particular site. These results are consistent with earlier phases of the research at an alternative ramp location, which found the DSFS to be less effective when positioned 400 ft upstream of the curve ( 8 ). One possible reason for the diminishing effectiveness at increasing advance warning distances is that drivers may be more likely to disregard warning messages that are provided too far in advance of a hazard.…”

“…A standard advisory speed panel was also installed with the DSFS at Site 1. However, the use of an advisory speed panel was not found to affect the effectiveness of the DSFS during the initial field study ( 8 ).…”

“…The message that the DSFS displays can also affect a driver’s behavior. Full-matrix displays that are able to provide messages such as “Slow Down” when the driver is exceeding a certain speed threshold have been found to outperform signs that simply display the driver’s speed ( 7 – 9 , 11 , 14 , 19 ).…”

“…Thus, the effectiveness of the signs in such settings is not well established. A recent study by Gates et al presented a before-and-after field evaluation at a freeway interchange ramp using various DSFS messaging and positioning strategies ( 8 ). The study found a significant reduction in curve entry speeds when the DSFS was positioned near or at the point of curvature and when the speed number display alternated with a “Slow Down” message.…”