BACKGROUND

Alternative intersection designs, including the Displaced Left Turn (DLT), Median U-Turn (MUT), and Restricted Crossing U-Turn (RCUT), have been implemented nationwide to reduce congestion, crash frequency, and crash severity. The reduced number of traffic signal phases and conflict points at these intersections can improve traffic operations and safety. Much research has been conducted to develop safety performance functions (SPFs) and crash modification factors (CMFs) for various intersection designs and control types as well as conversions of traditional intersections to other forms including roundabouts. Other studies have been conducted to evaluate the safety benefits of different intersection designs.

The use of alternative intersections in the United States has increased substantially in recent years, including combinations of alternative intersection elements at different approaches to the same intersection. The operational benefits of alternative intersections compared with conventional intersections are well established. The reduced number of conflict points for alternative intersections has demonstrated safety advantages over conventional intersections. Studies show significantly lower crash rates with MUTs and RCUTs for both corridor-wide and intersection-related data. Lower crash rates for DLTs are also supported by intersection data following DLT installation; however, potential safety concerns have been expressed, especially for older drivers and those unfamiliar with alternative intersections.

Research is needed to develop quantitative safety analysis methodologies for certain types of alternative intersections that are not currently available in resources such as the AASHTO Highway Safety Manual and CMF Clearinghouse. The research would inform transportation agencies, industry, and the public of the safety benefits of alternative intersections by quantifying the predicted reduction in crash frequency and severity resulting from conversion of conventional intersections to DLT, MUT, RCUT, or other alternative intersections. Ultimately, it would help transportation professionals evaluate alternative intersection strategies in terms of safety benefits and support progress towards Vision Zero goals across the United States.

OBJECTIVES

The objectives of this research are the following: 

1. Determine the current knowledge and research gaps in quantitative crash prediction methodologies for alternative intersections, which include but are not limited to DLT, MUT, and RCUT.

2. Develop, modify, and statistically validate crash predictive methodologies such as SPFs, CMFs, and crash severity distributions to quantify the safety effects of these alternative intersections.

3. Where development of quantitative methodologies may not be possible, identify risk factors, proxies, or surrogates for vulnerable road users consistent with these methodologies.

TASKS 

Task 1. Review literature and design practitioner survey.

Task 1a. Review literature on quantitative safety prediction modeling for alternative intersections. The review shall include related research in progress and identify possible research gaps on alternative intersections themselves as well as configurations that combine elements of two or more alternative intersections.

Task 1b: Design practitioner survey. The survey shall include but not be limited to DLT, MUT, and RCUT configurations and may also include grade-separated configurations. The goals of the survey should include (1) prioritizing development of quantitative analysis models for alternative intersection designs and combinations thereof; (2) where multiple CMFs/SPFs are available for an intersection design or combination, identifying which ones that practitioners have chosen to use; (3) identifying before-after studies on SPFs/CMFs that practitioners have performed; and (4) identifying potential data collection sites.

Submit a technical memorandum summarizing the findings from Tasks 1a and 1b. Following NCHRP review, the memorandum shall be discussed via conference call. NCHRP approval of the memorandum is required before work may begin on Task 2.

Task 2. Conduct practitioner survey and develop a list of intersection designs to study.

Task 2a. Conduct practitioner survey. The survey shall initially be conducted electronically, with follow-up contacts by phone as necessary. The survey shall be sent to all pertinent personnel within an agency. Potential data collection sites and parameters shall be determined from the survey.

Task 2b. Develop a prioritized list of alternative intersection designs for study. Evaluate the sufficiency of available data for preparing SPFs, CMFs, and severity distributions for these designs and identify multimodal issues, if present. Ensure that potential study results are applicable nationwide, even if these designs are not yet widely used.

Submit a technical memorandum summarizing the results of Task 2a for NCHRP review. NCHRP approval of the memorandum must be received before work on Task 2b is finalized.

Task 3. Submit Interim Report. The report shall summarize the findings from Tasks 1-2 and include a research plan that updates the Amplified Research Plan to reflect the list of intersection types and parameters for study and potential data collection sites obtained from Task 2. Following NCHRP review, the report shall be discussed at a meeting of the NCHRP project panel and the research team, in-person if possible, at the TRB offices in Washington, D.C. NCHRP will be responsible for panel members' travel costs. NCHRP approval of the interim report is required before proceeding with Task 4.

Task 4. Conduct data collection and analysis.

Task 4a. Conduct data collection for prioritized intersection designs. Data collected from field or provided by other agencies may be used. Multimodal data should be included to the extent possible. Determine the significant factors influencing safety performance for the intersection designs studied.

Task 4b: Analyze field data. Determine findings, data limitations, and items requiring further study, e.g., influential factors such as rural/urban, multimodal, and geometric considerations.

Submit a technical memorandum summarizing the results of Task 4 for NCHRP review. NCHRP approval of the memorandum is required before work may begin on Task 5.

Task 5. Obtain feedback on the data collection results from practitioners familiar with intersection safety analysis. Coordinate with the panel to identify appropriate practitioners to participate. The practitioner feedback on the presentation may be obtained via web conference or peer exchange. Submit a technical memorandum summarizing the results of the presentation for NCHRP review, including comments on Task 4 work and work to be done in Task 6. NCHRP approval of the memorandum is required before work may begin on Task 6.

Task 6. Complete remaining data collection and analysis. Develop (1) new or modified quantitative safety prediction methodologies, and (2) tool(s) for possible incorporation into the AASHTO Highway Safety Manual, state DOT manuals and guidelines, and the CMF Clearinghouse. Ensure that findings from this task can be used to improve tools besides these three resources. If certain aspects of the methodologies can ultimately not be quantified, alternate approaches should be recommended and outlined, e.g., in appendices.

Task 7. Submit final report and project deliverables. Project deliverables shall include the safety prediction methodologies, tool(s) with user instructions, implementation memorandum, slide summary, and a conduct of research report documenting the entire research effort.

Note: Following receipt of the draft final deliverables, the remaining 3 months shall be for NCHRP review and comment and for research agency preparation of the final deliverables.

STATUS: Research in progress.