BACKGROUND

Roadside design guidance typically instructs agencies to limit fixed objects, including trees, along roadways to provide a safer recovery area for errant vehicles. On urban streets, trees are amenities that benefit pedestrians, bicyclists, residents, and others by providing shade, heat reduction, potential traffic calming and speed reductions, air and water quality benefits, and aesthetic appeal.  However, trees are fixed objects that can cause serious injury or fatality if struck by an errant vehicle.

NCHRP Project 17-82, “Proposed Guidance for Fixed Objects in the Roadside Design Guide” explored crash prediction methods and developed design guidelines regarding trees and utility poles in rural non-freeway settings. On roadways with posted speed limits of 30 mph and less, trees are generally accepted as part of the roadside environment. At posted speed limits of 55 mph and greater, facilities for non-motorized users are less likely to be present and vehicular collisions with trees have the potential to result in serious injuries or fatalities. However, research is needed for urban and suburban roadways, particularly in posted speed limit settings between 35 and 50 mph. On these roadways, vehicle collisions with trees are a significant safety concern; however, maximizing properly and sustainably designed tree placements in the roadside environment can benefit public health and community livability.

Research is needed to help state departments of transportation (DOTs) and other transportation agencies advance the knowledge on the safety effects of trees and support guidelines to inform tree planning and landscaping policies, procedures, and practices that support the needs of all roadway users.

OBJECTIVE

The objective of this research is to develop a practitioner’s guide for evaluating the safety effects of trees on urban and suburban roadways with a focus on posted speed limits of 35 to 50 mph.

The practitioner’s guide will include a framework for the sustainable placement, maintenance, removal, and replanting of trees and complementary features in roadway environments. This research will consider the needs of all users of the transportation system and support implementation of the Safe System approach.

Accomplishment of the project objective(s) will require at least the following tasks.

TASKS

PHASE I – Planning

Task 1.  Conduct a literature review of relevant research, literature, and other sources regarding trees in the roadside environment, related to the project objective, including livability and effects on all transportation system users. The review shall include published and unpublished research conducted through the NCHRP; the Federal Highway Administration (FHWA); and other national, international, state, and pooled fund sponsored research.

Task 2. Review state, county, and local tree-related policies and practices in urban and suburban settings from diverse geographic areas, climates, and contexts within the United States.

Task 3.  Conduct a critical analysis and synthesis of the Tasks 1 and 2 results and identify knowledge gaps and opportunities related to the project objective. These gaps must be addressed in the final deliverables if the budget allows or in the recommended future research. Document findings from Tasks 1 through 3 in a technical memorandum.

Task 4. Develop a method to achieve the project objective to be executed in Phases II and III. At a minimum, the method shall formulate strategies to:

• Determine what effect trees, based on their presence and characteristics (e.g., size, placement, canopy) have on vehicle operating speeds and non-motorized transportation system users (e.g., pedestrians and cyclists);
• Evaluate the safety effects, both positive and negative (e.g., crash frequency, type, and severity), related to trees in the roadside environment;
• Identify and analyze roadway context characteristics at tree crash sites that resulted in fatalities or serious injuries (e.g., presence of on-street bike facilities, lighting, roadside barriers, tree density, proximity to travel lanes);
• Identify tree characteristics (e.g., size, habit, family, canopy, maintenance) that may impact the frequency and severity of crashes;
• Evaluate the safety effects of stewardship and tree maintenance policies (e.g., pruning and inspection programs); and
• Conduct a comparative analysis of the frequency, type, and severity of crashes on roadways with trees to similar roadways without trees and identify trends and risk factors (e.g., traffic volume, intersections, curves, medians).

The method shall include the proposer’s approach to collecting and analyzing data, and if practicable, an approach for presenting research findings at posted speed limits increments within the range.

Task 5. Prepare an annotated outline of the draft practitioner’s guide.

Task 6. Prepare Interim Report No. 1, which documents Tasks 1 through 5 and provides an updated work plan for the remainder of the research.

PHASE II – Method Development

Task 7. Collect data and refine approaches for analyses. Summarize refinements and data collection processes in a technical memorandum.

Task 8. Execute methods in the approved Interim Report No. 1 and as refined in Task 7. Provide a summary of results and an approach to how the results will be incorporated into the practitioner’s guide in a technical memorandum.

Task 9. Develop the draft practitioner’s guide with supporting graphics.

Task 10. Develop an outreach plan that includes at least one in-person workshop that is 1.5 days long hosted by the contractor with at least 15 participants, including a potential attendees’ list with representatives from state DOTs and other practitioners with diverse viewpoints. The outreach plan will include workshop materials and a draft attendee list.

Task 11. Develop draft materials for a webinar suitable to explain the guide and its contents to practitioners. Include a plan for dissemination and potential participants.

Task 12. Prepare Interim Report No. 2, which documents Tasks 7 through 11 and provides an updated work plan for the remainder of the research.

PHASE III – Final Deliverables

Task 13. Execute the outreach plan in the approved Interim Report No. 2.  NCHRP will approve the final list of attendees. Summarize findings in a technical memorandum.

Task 14. Refine the draft guide based on input from outreach efforts in Task 13.

Task 15. Refine the draft webinar materials based on the results from Task 14.

Task 16. Organize, coordinate, and deliver the webinar. (The webinar’s recording and presentation with the presenter’s notes will be part of the final deliverables.) NCHRP will approve the final list of webinar attendees.

Task 17. Prepare final deliverables, including:

• A practitioner’s guide;
• A conduct of research report, including an executive summary, that documents all research and project efforts;
• A PowerPoint presentation with speaker notes that summarizes the project and distinctly illustrates for the audience how the research can be applied in their organization;
• A 90-minute recorded webinar with presentation notes; and
• A technical memorandum titled “Implementation of Research Findings and Products”.

STATUS: Proposals have been received in response to the RFP. The project panel will meet to select a contractor to perform the work.