01664980

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Low visibility conditions can inhibit a driver’s ability to perceive appropriate operating speeds, particularly during foggy conditions where the characteristics of the fog can vary spatiotemporally. Numerous agencies have installed countermeasures like weather advisory systems and variable speed limits (VSLs) to mitigate these conditions, but not many studies have quantitatively analyzed the results of these projects. This paper assesses how the I-77 fog VSL system in Fancy Gap, Virginia affected driver speeds since its activation in October 2016. Prior to the installation of the VSL, drivers frequently drove much faster than the safe speed based on the stopping sight distance during fog. The VSL system sought to get drivers to travel closer to the safe speed based on available visibility by posting appropriate reduced speed limits. The results showed statistically significant reductions in mean speeds after the VSL was activated, and drivers drove closer to the safe speed based on available visibility. Trends in speed by posted speed limit were examined across the corridor, and it was found that compliance generally improved once drivers encountered reduced visibilities. Speeds did not change as much in transition areas leading into the area where the fog was present, however. The results of this VSL implementation may serve as a reference for other agencies contemplating alternatives to improve safety at fog-prone areas, and indicate that the countermeasure did have a positive effect.

This paper was sponsored by TRB committee AHB50 Standing Committee on Traffic Control Devices.

18-03222

English

18p

2018

Transportation Research Board 97th Annual Meeting

Digital/other

Figures; Maps; Photos; References; Tables

Countermeasures; Drivers; Fog; Highway safety; Variable speed limits; Visibility

Fancy Gap (Virginia)

Highways; Operations and Traffic Management; Safety and Human Factors

Transportation Research Board Annual Meeting 2018 Paper #18-03222

TRIS, TRB, ATRI

Jan 8 2018 10:47AM