BACKGROUND
Shoulder and centerline rumble strips and stripes on roadways, whether conventional or sinusoidal, provide many safety benefits to motorists. But for bicyclists, coming in contact with them can be a very jarring experience, and riding safely upon them nearly impossible. State departments of transportation (DOTs) are increasingly installing rumble strips on roads also traveled by bicyclists, particularly rural two-lane roads with speed limits over 50 miles per hour (mph). These roads often have less than four feet of clear useable shoulder space. Bicyclists, riding on such roads with rumble strips and limited rideable shoulder space, feel increasingly challenged and may find no option but to ride in the lane with high-speed mixed traffic, increasing the likelihood of a crash with a motor vehicle.
Another safety issue of much concern to the bicyclists is the motorists’ behavior when passing them on roadways with centerline rumble strips. However, there is very little information available on the motorist-bicyclist interaction on rural roads where rumble strips decrease or eliminate the rideable shoulder space. A Michigan DOT study on motorists’ behavior on rural roads with centerline rumble strips concluded that motorists were less likely to cross centerline rumble strips when passing bicyclists to avoid vibration and noise (https://www.michigan.gov/documents/mdot/RC1627_489159_7.pdf). This would most likely make them pass too closely to the bicyclist, greatly increasing the risk of the bicyclist losing control and crashing.
Federal legislation allows federal Highway Safety Improvement Program (HSIP) projects to install rumble strips if “the rumble strips or other warning devices do not adversely affect the safety or mobility of the bicyclists and pedestrians….” However, there is little research on quantifying the effects of shoulder and centerline rumble strips on bicyclists’ safety. With growing use of rumble strips nationwide to reduce run-off-road and head-on crashes of the motorists, it is imperative that the unintended safety impacts on the bicyclists also be determined to better inform state DOTs’ design policies.
OBJECTIVES
The objectives of this research are to:
1. Determine and quantify safety impacts on bicyclists on rural high-speed two-lane roadways with centerline and shoulder rumble strips.
2. Characterize motorists’ behavior when encountering bicyclists on rural high-speed two-lane roadways with centerline and shoulder rumble strips. Aspects of motorists’ behavior to be assessed could include, among other things, lateral and longitudinal controls, reaction time, and eye movement, when passing bicyclists traveling in the same direction on such roads.
3. Develop a guide on various rumble strip applications, with a focus on their impact on bicyclists’ safety.
RESEARCH PLAN
Phase I
Task 1. Perform a critical review of the literature addressing bicyclists’ safety issues on high-speed (> 50 mph) roadways with rumble strips. The review will identify key factors associated with bicyclists’ safety as well as the behavior of the motorists on such roads in the presence of the bicyclists. Gaps in the current state of knowledge and practice on the research topic, with particular focus on the objectives of this study, should also be identified. Another element to be included in the literature review should be an updated summary of state DOTs’ practices related to the needs and safety of the bicyclists.
Task 2. Based on data availability (crash and rumble strip inventory), assess the feasibility and usefulness of crash data analysis in this research. This analysis should inform the development of the Phase II work plan.
Task 3. Develop a detailed work plan to be executed in Phase II. It is anticipated that much of the research will be based primarily on simulation studies in lieu of real-world video capture and analysis. Ideally, the simulation studies should replicate as many real-world sensory characteristics of motorists’ interactions with rumble strips as possible, including sound, vibration, and visual. These studies will compare motorists’ behavior when passing bicyclists traveling in the same direction, using rumble strip design dimensions that follow the best practices for accommodating bicyclists. Roadways, both with and without centerline rumble strips, will be considered under a variety of scenarios.
The baseline roadway characteristics should include high-speed (> 50 mph) two-lane roadways with 12-foot wide lanes, with and without centerline rumble strips. The following scenarios will be investigated, at a minimum:
1. Bicyclist riding in the far-right portion of the travel lane on a road without paved shoulders and no rumble strips.
2. Bicyclist riding in the center of a 5-foot paved shoulder with shoulder rumble strips and at least four feet of rumble strip-free useable riding shoulder to the right of the rumble strips.
3. Bicyclist riding in the far-right of the travel lane on a road with paved shoulders that are not usable due to the presence of shoulder rumble strips and insufficient rumble-free shoulder space.
Proposers are welcome to propose additional cross sections or scenarios, based on state DOTs’ practices review. Factors of interest may include, among other things, shoulder width, rumble design/placement, travel-lane width (11-12 feet), sight distance, characteristics of the bicyclists, etc.
Task 4. Prepare an interim report documenting the critical literature review and analysis, summary of state DOTs’ practices, crash analysis feasibility summary and the proposed Phase II work plan.
Phase II
Task 5. Execute Phase II work plan, as approved by the NCHRP at the end of Phase I, and analyze simulation results.
Task 6. Collect and analyze available historical crash data to understand crash characteristics for bicyclists on high-speed two-lane roadways with rumble strips and determine possible contributing factors. If feasible, crash rates and guidance for crash modification factors should also be developed and included in the final report (Task 7). Execution of this task will be based on the findings of Task 2 (Phase I).
Task 7. Prepare a final report documenting all research results, conclusions, and recommendations for improving the safety of the bicyclists on two-lane high-speed rural roads, including design recommendations for all longitudinal rumble strip applications. Also include a discussion of how changes in the road environment and users’ behaviors may impact safety outcomes for all users and how the proposed strategies can be applied to effectively address those changes.
Task 8. Conduct at least one webinar and one presentation within the contract period to disseminate the research findings and recommendations. The presentation should address a relevant audience, such as the AASHTO Safety Committee or the AASHTO Technical Committee on Non-Motorized Transportation. The NCHRP must approve the material content and the target audiences for these activities. Prepare a draft article suitable for publication in the TR News, highlighting the research findings and recommendations and their implementation strategies. However, no commitment to publish the article is implied. Information regarding TR News publication can be found on the TRB webpage via the link: https://onlinepubs.trb.org/onlinepubs/trnews/info4contributors.pdf.
DELIVERABLES
Deliverables shall include the following, at a minimum. Proposers may suggest additional deliverables, if they support the project’s objectives.
1. A virtual presentation to the NCHRP oversight panel to discuss the findings of Tasks 1 and 2.
2. Interim report documenting the literature review, summary of state practices, summary of crash analysis feasibility, and the proposed Phase II work plan.
3. A final report that documents results, summarizes findings, draws conclusions, makes recommendations, and presents implementation strategies for the study results. These strategies should include guidance on: (a) optimizing rumble strip installations and design parameters; (b) supporting compliance with the federal HSIP guidance; and (c) addressing bicycling community’s safety concerns related to rumble strips on two-lane high-speed rural roads.
4. At least one webinar and one presentation within the contract period to disseminate the research findings and recommendations. The presentation should address a relevant audience, such as the AASHTO Safety Committee or the AASHTO Technical Committee on Non-Motorized Transportation. The NCHRP must approve the material content and the target audiences for these activities.
5. A draft article suitable for publication in the TR News, highlighting the research findings and recommendations and their implementation strategies. TR News publication information is available on the TRB webpage via the link below
STATUS: Proposals have been received in response to the RFP. The project panel will meet to select a contractor to perform the work.
