Motorist Behavior and Safety Impacts on Bicyclists from Centerline and Shoulder Rumble Strips on High-Speed Two-Lane Highways

Shoulder and centerline rumble strips provide significant safety benefits to motorists. However, contact with rumble strips is very jarring to bicyclists, making safe riding upon them unlikely or impossible. States are increasingly installing rumble strips on roads frequented by bicyclists, particularly rural two-lane roads with speed limits over 50 miles per hour, and often with less than 4 feet of shoulder space. As a result, the bicyclist community is increasingly experiencing challenges when rumble strips are installed in rideable shoulder space and bicyclists are forced to ride in the lane with high-speed mixed traffic. The Federal Highway Safety Improvement Program (HSIP) is a major funding source for rumble strip projects. Federal law (23 USC 148(a)(4)(B)(iii)) allows HSIP use for such projects “if the rumble strips or other warning devices do not adversely affect the safety or mobility of bicyclists and pedestrians….” However, there is a lack of available research quantifying the safety effects for bicyclists with the use of rumble strips in shoulders and center lines. Another problem with rumble strips affecting bicyclist safety is the motorist behavior when passing cyclists riding on roadways with centerline rumble strips. A study by the Michigan Department of Transportation’s Traffic and Safety Division suggests that motorists are less likely to cross centerline rumble strips when passing cyclists due to vibration and noise. This may induce unsafe behaviors such as motorists passing too closely, increasing risk of a motorist-cyclist crash. At present, there are only a few studies that explore motorist and bicyclists interactions with rumble strips, and there is no research assessing the safety impacts of motorist-bicyclist interactions caused by rumble strips. In addition to public safety concerns, these impacts have repercussions for compliance with the federal law. Installing centerline and shoulder rumble strips on rural, two-lane high-speed roadways without sufficient rumble-free clear zone has an impact on the safety of bicyclists that needs to be studied. Motorists interacting with on-road bicyclists are also affected, to a lesser degree. Research into the design of rumble strips on high-speed roads and its effects on bicyclist and motorist behaviors and interactions would determine and quantify the safety impacts that may exist. The results of this research could be used to improve design and inform potential policy modifications, ensuring transportation departments are compliant with federal law when using HSIP funding for rumble strip projects. With the national rise in the number of serious injuries and fatalities for people who walk and bike, the AASHTO Council of Active Transportation has prioritized bicycle and pedestrian safety and has developed a number of goals and strategies to address risk to the most vulnerable road users. Possible presentation formats for the final deliverables include, but are not limited to, guidance or guidelines, a test method, equipment, a tool, specifications, a manual, a new or revised process, etc. The objective of this research is to determine and quantify safety impacts on bicyclists for the use of centerline and shoulder rumble strips on high-speed rural roadways. Primarily using a simulator, the researcher would compare motorist behavior passing bicyclists traveling in the same direction, using consistent rumble strip design dimensions that follow best practices for accommodating bicyclists (see Adventure Cycling's Solutions for Making Rumble Strips Safer for Bicyclists: Best Practices for Transportation Decision Makers) on 50+ mph roadways with 12-foot lanes. For roadways with no centerline rumble strips, the scenarios to be considered will include (1) bicyclist riding in the far-right of the travel lane on a roadway without paved shoulders and no rumble strip; (2) bicyclist riding in the center of a 5-foot paved shoulder with at least 4 feet of rumble-free clear zone to the right of rumble strips; and (3) bicyclist riding in the far right of the travel lane on a roadway with paved shoulders that are not usable due to rumble strips and a lack of sufficient rumble-free clear zone. For roadways with centerline rumble strips, the scenarios will include (1) bicyclist riding in the center of the 5-foot paved shoulder and (2) bicyclist in the far-right travel lane with no paved shoulder. In addition to simulation results, based on data availability, historical crash data can be used to understand crash rates for cyclists on high-speed two-lane rural roadways with shoulder and centerline rumble strips and discover possible contributing factors. The results should present the five cases’ crash rates and/or lateral passing clearance statistics as suggested. If the results warrant, guidance for Crash Modification Factors should be developed. Design recommendations should be provided for shoulder and centerline rumble strips. With the growing nationwide use of rumble strips to reduce motorist run-off-road and head-on crashes, knowledge of whether there are unintended bicyclist safety impacts from specific design policies is needed. Depending on the research’s outcome, state departments of transportation using or funding rumble strips could (1) adjust rumble strip installation and design parameters through Federal Highway Administration guidance and recommendations; (2) ensure compliance with Federal Highway Safety Improvement Program law; and (3) confidently respond to bicycle community concerns on shoulder and centerline rumble strips.


  • English


  • Status: Proposed
  • Funding: $400000
  • Contract Numbers:

    Project 17-106

  • Sponsor Organizations:

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Project Managers:

    Jawed, Inam

  • Start Date: 20210525
  • Expected Completion Date: 0
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01772201
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 17-106
  • Files: TRB, RIP
  • Created Date: May 24 2021 3:14PM