The National Academies

NCHRP 15-40 [Final]

Design Guidance for High-Speed to Low-Speed Transition Zones for Rural Highways

  Project Data
Funds: $300,000
Research Agency: Midwest Research Institute
Principal Investigator: Darren Torbic
Effective Date: 4/22/2010
Completion Date: 6/30/2012


The objective of this research was to develop design guidance for selecting effective geometric, streetscaping, and traffic engineering techniques for transitioning from high-speed to low-speed roadways, particularly rural highways entering communities. The guidance  considers transition-zone-specific factors such as land use; community context; aesthetics; and the accommodation of trucks, parking, pedestrians, bicyclists, and public transportation services.


The following deliverables are available:
As rural and other high-speed highways approach built-up areas, there is usually a transition zone where drivers are encouraged and expected to reduce their speed to one suitable for the environment they are entering. A common example is a rural highway that passes through a small community or hamlet where 55 mph speeds are neither safe nor acceptable to the community. Design standards and policies exist for both the high-speed and low-speed environments, but differences between the two make design of the transition zone problematic. Many communities would like to use the transition zone as a gateway to the community and they often have unrealistic expectations of the magnitude of speed reduction. The design of the transition zone must attempt to meet many objectives while maintaining safety.

NCHRP Project 20-05, Synthesis Topic 40-08, Effective Speed Reduction Techniques for Rural High- to Low-Speed Transitions, is summarizing known information on speed-reduction techniques for transition zones. Publication of the synthesis report is expected in early 2010, and this project will build on that effort by (1) increasing the amount of information available on the effectiveness of those techniques and (2) developing a design process for selecting appropriate techniques.  The final draft of the synthesis will be provided to the contractor. Proposers should review other synthesis reports to understand the type of information that will be in the Topic 40-08 report.
Task 1. Review the synthesis report from NCHRP Project 20-05, Synthesis Topic 40-08 to identify geometric, streetscape, and traffic engineering techniques that demonstrate an effective and safe reduction in speed. Review international and other domestic literature to identify additional practical techniques. 

Task 2. 
Inventory and describe the practical techniques identified in Task 1. Summarize the documented effects of each technique on speed and safety. Assess the reliability of these documented effects (e.g., the robustness of the data supporting the estimates of effectiveness).

Task 3.  Develop a plan for determining the effectiveness of transition-zone techniques that appear to be practical but lack robust evidence of their effectiveness.

Task 4. 
Develop a detailed outline for design guidance, including a process for (1) assessing the transition zone, (2) setting an appropriate target speed reduction through the transition zone, (3) selecting an appropriate technique or combination of techniques for safely achieving the target speed reduction, and (4) evaluating the effectiveness of the technique(s) after implementation. The guidance should address the zone-specific factors identified in the objective statement and discuss how to incorporate early and meaningful participation by the community and relevant agencies. 

Task 5. 
Submit an interim report documenting the work accomplished in Tasks 1 through 4. Meet with the NCHRP project oversight panel to discuss the findings and receive direction concerning submitted and future work products.

Task 6. 
Carry out the Task 3 plan, as amended at the Task 5 meeting. Summarize the results in a working paper and discuss it with the panel in a web conference.

Task 7.  Develop the design guidance based on the outline developed in Task 4. When appropriate, use examples to improve the understanding of the guidance.

Task 8. 
Submit a final report that documents the entire research effort and includes the Task 7 guidance as a stand-alone document. The report should identify recommendations for text changes in the AASHTO Policy on Geometric Design of Highways and Streets and Roadside Design Guide.

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