Establishing Speed Limits on Unpaved Roads

Abstract

The lack of national standards for establishing speed limits on unpaved roads has put pressure on local governments to make judgment calls about their road networks. Unpaved roads have unique characteristics that differ from those of paved roads. They usually are very low volume and were not necessarily designed by engineers. This study was conducted to determine the necessary standards and guidelines for establishing speed limits on unpaved roads in Wyoming. The process used national standards and state practices to ensure that a comprehensive methodology was followed. A focus group composed of traffic and safety engineers was formed to find an efficient process for establishing speed limits on unpaved roads. The group examined four main aspects for establishing speed limits: data collection requirements, roadway safety, determination of the appropriate speed limit, and declaration of the speed limit. Once the standards and guidelines were developed, five groups were asked to provide feedback to ensure that all stakeholders had an opportunity to review them. The Wyoming Technology Transfer Center–Local Technical Assistance Program developed and offered several training options for local jurisdictions to start their own speed limit programs. These options allowed for the standards and guidelines to be implemented by local jurisdictions in Wyoming. The findings of this study will provide states and counties with established standards for setting speed limits on unpaved roads as well as with a guide to different options for establishing speed limit programs.

Factors Contributing to Crashes on Low-Volume Unpaved Roads

“…Roadway departures were associated with a 22% increase in crashes on unpaved roads. Because multivehicle crashes are rare on unpaved roads ( 7 ), most of the crashes on this type of road involve a single vehicle, and single-vehicle crashes are more likely to be roadway departures. Along with common contributors to crashes (horizontal curve, speeding, impaired driving), as far as roadway departure is concerned, several other factors such as loose gravel, reduced vehicle traction, and blown dust causing visibility issues could contribute to crashes at this location.…”

“…Traffic characteristics on unpaved roads are different from paved roads. Jones and Ksaibati ( 7 ) conducted a study at 76 locations on eight county roads in Wyoming to investigate the differences in traffic characteristics between unpaved roads and paved roads using a t -test. The results showed higher percentages of trucks on local roads because they serve the mining and oil industries.…”

“…Because of the low traffic volume, the occurrence of multivehicle crashes is significantly lower on unpaved roads in comparison with paved roads ( 7 ). A study in Wyoming found that the injury crash rate per million vehicle miles of travel (MVMT) on Albany County unpaved roads was nearly six times higher than all Wyoming crashes ( 8 ).…”