As the Highway Safety Manual (HSM) continues to evolve, determining the potential crash severity at a location becomes an increasingly vital component in predicting safety performance. For safety performance functions (SPFs) to be reliable, they must be consistent. Consistency in how states apply stand-alone severity or severity with frequency based tools and estimates are a fundamental requirement for the adoption and use of the HSM and its associated tools. Consistency is a function of several factors: (1) results that are in general agreement from a multitude of analytical techniques available to practitioner; (2) availability of data sources that allow for broad state and interstate analysis; and (3) interpretability of results for policy application at the national, state, and local agency levels.
Severity analysis tools, as currently available in the HSM, do not fully meet this definition of consistency–for various reasons, but primarily originating from the fact that the analytical techniques available in the published literature are not consistent in their estimation of crash severity probabilities and frequencies. The differences in severity estimations can be significant–from the methods currently in use that adopt the observed severity ratios to emerging methods which analyze the severity aspects at multiple scales–from spot location, to corridor and network levels.
Three factors are critical to adoption of safety analysis techniques–integrity with network screening methods (Part B of the HSM), data availability and requirements, and model predictive performance (Part C of the HSM). The HSM provides methods for model calibration and qualitative guidance on the model reliability, but lacks methods to identify which crash severity levels and crash types need to be modeled to ensure consistency. The default approach recommends using observed crash severity ratios for a facility type and using those factors to obtain severity specific expected values. Data quality, crash severity reporting, and how to model crash severity level combinations are significant challenges in terms of crash prediction reliability.
Crash prediction model results are currently used to make planning and project-level decisions without complete understanding of their reliability. Specific examples include: (1) lack of understanding of confounding factors due to inaccuracy of severity estimations; (2) poor understanding of models and their limitations; (3) use of models at or near their limits; and (4) inappropriate transfer of severity ratios and severity level definitions without consideration of location specific temporal and spatial factors. Continuing the use of models in this way may lead to suboptimal design of projects, degradation of model credibility, and open concerns of liability and public trust.
The objectives of this project are to: (1) assess the current HSM approaches to severity estimation and prediction using SPFs; (2) Identify gaps and opportunities in the current severity prediction/estimation procedures within the HSM; (3) Develop and validate new severity models to address the gaps and opportunities; and (4) develop a guidance document that includes protocols for the use and application of severity based models in a format suitable for possible adoption in the HSM.
The guidance and protocols should address:
- Both the current HSM methods and any newly created models that consider, but are not limited to the following potential approaches:
- Number of crashes at each severity level by predicating total crash count and adjusting by assumed or observed crash severity distribution.
- Number of crashes at each severity level by predicting crashes for each of the individual severity categories.
- Estimated probability of crashes at each severity level.
- Number of crashes at each severity level by predicting both the total crashes and the crash severity likelihoods.
- How crash frequency and severity models would be integrated.
- New crash models shall include but are not limited to discrete choice models.
- Statistical reliability in terms of, but not limited to, spatial, temporal, and statistical specification and fit.
- Data quality and availability and how each affects the models application at both the national and local levels.
- The criteria for model development and selection.
- The use of the models for network screening (HSM Part B) and predictive methods (HSM Part C).
- How project planning and design decisions are affected by different modeling approaches.
- The performance of the models at varying AADTs, segment lengths, roadway functional classes, and contexts (e.g. roadside conditions, and speeds).
The guidance should include a number of case studies or illustrative examples that demonstrate the issues with model use and statistical reliability.
In addition, the guidelines should promote better informed planning decisions and the use of engineering judgment in the model application, greater implementation of crash prediction models, and better acceptance of model results leading to improved decision making.
The NCHRP is seeking the insights of proposers on how best to achieve the research objectives. Proposers are expected to describe research plans that can realistically be accomplished within the constraints of available funds and contract time. Proposals must present the proposers' current thinking in sufficient detail to demonstrate their understanding of the issues and the soundness of their approach to meeting the research objectives.
A kick-off web-conference call with the research team and NCHRP shall be scheduled within 1 month of the contract’s execution. The research plan proposed must be divided into tasks, with each task described in detail. The research plan must be divided into two phases.
Phase 1 will consist of information gathering and planning tasks culminating in the submittal of an interim report. The interim report will describe the work completed in the Phase 1 tasks and provide an updated research plan for the Phase 2 tasks as well as an outline of the framework and protocol at a minimum. The updated Phase 2 research plan should address the manner in which the proposer intends to use the information obtained in Phase 1 to satisfy the project objective. At the completion of Phase 1, a face-to-face meeting with NCHRP will be scheduled to discuss the interim report. Work on Phase 2 tasks will not begin until the updated research plan is approved by NCHRP. The project schedule shall include 1 month for NCHRP review and approval of the interim report.
The final deliverables will include, but not be limited to: (1) the guidance document in a format suitable for possible incorporation in a future edition of the AASHTO Highway Safety Manual; (2) a final report documenting the entire project and incorporating all other specified deliverable products of the research including the database used in the analyses and documentation sufficient for use by other research professionals; (3) an executive summary that outlines the research results; (4) a PowerPoint presentation with speaker notes describing the project background, objective, research methods, findings, and conclusions suitable for use in a webinar; and (5) a stand-alone memorandum titled “Implementation of Research Findings and Products” (see Special Note E for additional information).
The research plan may include additional deliverables as well as additional meetings with the NCHRP project panel via web-conferences. All web-conference calls will be hosted by NCHRP.
Note: The research plan shall include a schedule for completion of the research that includes 1 month for NCHRP panel review of the interim report. Following receipt of the draft final deliverables, the remaining 3 months shall be for NCHRP panel review and comment and for research agency preparation of the final deliverables.
A. The Research Plan, Item 4 of the proposal, shall be limited to no more than 20 pages.
B. The research team should have experience with AASHTO guidance development and writing. This also includes a working relationship or familiarity with the AASHTO Committee on Safety and the TRB Highway Safety Performance Committee (ANB25).
C. During the development of the first edition of the HSM, and continuing since its publication, the AASHTO Committee on Safety and the ANB25 have had a unique relationship that results in significant collaboration and communication on materials related to the HSM, including development of materials intended for inclusion in future editions of the HSM. When a new chapter or other material is complete or nearly complete, the TRB committee reviews materials and provides a recommendation to the AASHTO Committee on Safety’s Task Group on Technical Publications Oversight and Outreach; this is a key factor in the Task Group's recommendation to the Committee on Safety regarding readiness for balloting and therefore publication by AASHTO. The research team should anticipate making a total of at least two presentations, one during the annual meeting of the Committee on Safety and one during the mid-year meeting of ANB25. While the NCHRP panel is overseeing the project, it is recognized that these two groups can provide valuable input where appropriate and are important stakeholders in the effort. This should be included in the proposed budget.
D. Proposals should include a task-by-task breakdown of labor hours for each staff member as shown in Figure 4 in the brochure, "Information and Instructions for Preparing Proposals" (http://onlinepubs.trb.org/onlinepubs/crp/docs/ProposalPrep.pdf). Proposals also should include a breakdown of all costs (e.g., wages, indirect costs, travel, materials, and total) for each task using Figures 5 and 6 in the brochure. Please note that TRB Cooperative Research Program subawards (selected proposers are considered subawards to the National Academy of Sciences, the parent organization of TRB) must comply with 2 CFR 200 – Uniform Administrative Requirements, Cost Principles, and Audit Requirements for Federal Awards. These requirements include a provision that proposers without a "federally" Negotiated Indirect Costs Rate Agreement (NICRA) shall be subject to a maximum allowable indirect rate of 10% of Modified Total Direct Costs. Modified Total Direct Costs include all salaries and wages, applicable fringe benefits, materials and supplies, services, travel, and up to the first $25,000 of each lower-tier subaward and subcontract. Modified Total Direct Costs exclude equipment, capital expenditures, charges for patient care, rental costs, tuition remission, scholarships and fellowships, participant support costs and the portion of each lower-tier subaward and subcontract in excess of $25,000.
E. The NCHRP is a practical, applied research program that produces implementable products addressing problems faced by transportation practitioners and managers. The benefits of NCHRP research are realized only when the results are implemented in state DOTs and other agencies. Implementation of the research product must be considered throughout the process, from problem statement development to research contract and beyond completion of the research. Item 4(c), "Anticipated Research Results," must include the following: (a) the "product" expected from the research, (b) the audience or "market" for this product, (c) a realistic assessment of impediments to successful implementation, and (d) the institutions and individuals who might take leadership in deploying the research product. The project panel will develop and maintain an implementation plan throughout the life of the project. The research team will be expected to provide input to an implementation team consisting of panel members, AASHTO committee members, the NCHRP Implementation Coordinator, and others in order to meet the goals of NCHRP Active Implementation: Moving Research into Practice, available at http://onlinepubs.trb.org/onlinepubs/nchrp/docs/NCHRP_ActiveImplementation.pdf.
F. Item 5 in the proposal, "Qualifications of the Research Team," must include a section labeled "Disclosure." Information relevant to the NCHRP's need to ensure objectivity and to be aware of possible sources of significant financial or organizational conflict of interest in conducting the research must be presented in this section of the proposal. For example, under certain conditions, ownership of the proposing agency, other organizational relationships, or proprietary rights and interests could be perceived as jeopardizing an objective approach to the research effort, and proposers are asked to disclose any such circumstances and to explain how they will be accounted for in this study. If there are no issues related to objectivity, this should be stated.
G. Proposals are evaluated by the NCHRP staff and project panels consisting of individuals collectively very knowledgeable in the problem area. Selection of an agency is made by the project panel considering the following factors: (1) the proposer's demonstrated understanding of the problem; (2) the merit of the proposed research approach and experiment design; (3) the experience, qualifications, and objectivity of the research team in the same or closely related problem area; (4) the plan for ensuring application of results; (5) the proposer's plan for participation by Disadvantaged Business Enterprises--small firms owned and controlled by minorities or women; and (6) the adequacy of the facilities.
Note: The proposer's plan for participation by Disadvantaged Business Enterprises should be incorporated in Item 12 of the proposal.
H. Copyrights - All data, written materials, computer software, graphic and photographic images, and other information prepared under the contract and the copyrights therein shall be owned by the National Academies of Sciences, Engineering, and Medicine. The contractor and subcontractors will be able to publish this material for non-commercial purposes, for internal use, or to further academic research or studies with permission from TRB Cooperative Research Programs. The contractor and subcontractors will not be allowed to sell the project material without prior approval by the National Academies of Sciences, Engineering, and Medicine. By signing a contract with the National Academy of Sciences, contractors accept legal responsibility for any copyright infringement that may exist in work done for TRB. Contractors are therefore responsible for obtaining all necessary permissions for use of copyrighted material in TRB's Cooperative Research Programs publications. For guidance on TRB's policies on using copyrighted material please consult Section 5.4, "Use of Copyrighted Material," in the Procedural Manual for Contractors.