The National Academies

NCHRP 22-49 [Pending]

The Effect of Vehicle Mix on Crash Frequency and Crash Severity

  Project Data
Funds: $400,000
Contract Time: 30 months
Staff Responsibility: Camille Crichton-Sumners



The American Association of State Highway and Transportation Officials (AASHTO) Highway Safety Manual (HSM) has become a key safety management and evaluation toolbox for state and local highway agencies, metropolitan planning organizations, planning, safety, design, and operations communities. Current HSM tools include predictive methods for a wide variety of highway facility types and site conditions. The current methods account for traffic volumes and other roadway characteristics but not for vehicle mix or distribution of vehicle types.


Recent studies suggest that truck traffic adversely impacts roadway safety performance. These studies indicate that the consideration of vehicle mix would improve predictive methods for crash frequency and severity. Improved methods will result in better use of the limited funds and resources available for improving the safety of the highway system and support performance-based approaches.




The objectives of this research are to (1) develop and validate a statistically valid predictive methodology to quantify the effect of vehicle mix on crash frequency and severity for various facility types; and (2) develop a spreadsheet tool for practitioners to quantify the effect of vehicle mix on safety performance across the range of highway activities including planning, design, operations, and safety management.




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.


The research plan should: (1) include a kick-off teleconference with the research team and NCHRP convened within 1 month of the contract’s execution; (2) address the manner in which the proposer intends to satisfy the project objectives; (3) be divided logically into at least two phases that detail tasks necessary to fulfill the research objectives; (4) include appropriate milestones and interim deliverables; and (5) incorporate opportunities for the project panel to review, comment, and approve milestone deliverables.


Accomplishment of the project objectives will require at least the following tasks.




Task 1.  Prepare a technical report that:

  • Summarizes information from relevant literature on the effect of vehicle mix on crash frequency and severity;  
  • Identifies sources and assesses the adequacy (e.g., time frame) of new and existing data needed for the development and implementation of the predictive methodology;  
  • Discusses and evaluates analytical approaches and robust statistical techniques to establish the relationship between vehicle mix and crash frequency and severity;  
  • Includes consideration for how each approach and their respective results may be incorporated into future editions of the HSM;  
  • Recommends an approach for development and implementation of methodology consistent with the guiding principles established for HSM development—found in the Federal Highway Administration’s HSM Implementation Guide for Managers; and  
  • Identifies characteristics for assessing the effect of vehicle mix on crash frequency and severity for selected facility types. At a minimum, consider various roadway and roadside geometrics and operational conditions.


Note: The Task 1 report shall be submitted within 3 months of contract execution and also presented to NCHRP during a teleconference meeting.


Task 2. Based on the results of Task 1, propose a detailed Phase II work plan for developing and validating predictive methodology to quantify the effects of vehicle mix on safety performance. Include, at a minimum:

  • Specific sources of data planned for analysis;
  • Selected facility types including the rationale for their inclusion;
  • Methods for multi-source data integration/fusion;
  • Data collection, management, and distribution plan;
  • Identified tools or software to be used for data management, processing, and modeling;
  • Metrics for assessing statistical models and analysis results;
  • Validation approach for the methodology and tool; and
  • A spreadsheet tool that implements the application of the methodology.


Task 3. Submit an interim report that documents the work completed in Tasks 1 and 2 that also includes the detailed Phase II work plan.


Note: The research team shall meet with NCHRP via teleconference within 1 month of submitting the Phase I interim report. NCHRP approval of the proposed Phase 2 work plan is required prior to initiation.



 Task 4. Perform the approved work plan, analyze the results, and document the results in a Task 4 report that includes the following at a minimum.

·         Detailed methodology; 

·         Data summary and descriptive statistics by facility type;

·         Validated models and results of analyses by facility type; and

·         Metrics used for assessing the quality of statistical models and results of analyses.


Note: The Task 4 report will be discussed at a face-to-face meeting, convened at a TRB facility, with the NCHRP project panel.


Task 5. Develop a spreadsheet tool—that avoids the use of third-party software components—that will implement the validated methodology. Provide all assumptions, data limitations, and other constraints (e.g., range for valid input fields, conditions that cannot be assessed with the methodologies because the data sources, used to develop the method, did not include these conditions).


Note: Include the following items, in a pre-approved format, with sufficient quality and detail that enables replication of the research: (1) all raw and cleaned data collected and used in this research: input data sets, fused and integrated research data sets, data dictionaries etc.; (2) documentation of the steps in the data fusion and integration process; (3)  annotated data management code used to fusing, integrating, and cleaning the data; (4)  annotated model development and validation code; (5) annotated spreadsheet macro code; and (6) any other spreadsheet tool documentation.


Task 6. Using practical examples, test the spreadsheet tool developed in Task 5.


Task 7. Develop a detailed, stand-alone user instruction guide, quick start guide, Frequently Asked Questions (FAQ), and comprehensive spreadsheet tool documentation in both electronic and hard copy formats.


Task 8. Host a virtual demonstration for the NCHRP panel.


Task 9. Develop a stand-alone document—for practitioners, researchers, and trainers—with language suitable for suggested modifications to a future edition of HSM. Include sample problems, assumptions, data limitations, and other constraints as described in Task 5.


Task 10.  Prepare draft final deliverables that fulfill the research objectives. 


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.


Task 11.  Prepare and submit final deliverables that fulfill the research objectives and document the entire research effort.

Final deliverables should include the following items at a minimum: (1) a final report documenting the entire research effort; (2) prioritized recommendations for future research; (3) replicable, editable, unlocked spreadsheet tool and associated documents; (4) input data sets for the research, the fused and integrated research data sets, data dictionaries, steps in the data fusion and integration process, and program code used to fuse, integrate, and analyze the data; (5) executive summary; (6) a PowerPoint-style presentation (suitable for a presentation to both the  AASHTO Committee on Safety and the TRB Highway Safety Committee meetings) that includes speaker notes, background, objectives, research approach, findings, conclusions, and a demonstration of the spreadsheet tool; (7) a stand-alone technical memorandum titled “Implementation of Research Findings and Products” (see Special Note H for additional information); (8) a stand-alone document that includes language suitable for suggested modifications to a future edition of the HSM; and (9) a draft article suitable for publication in TR News (information regarding TR News publication may be found on the TRB webpage http://onlinepubs.trb.org/onlinepubs/trnews/info4contributors.pdf).

Note: No commitment to publish a TR News article is implied.




A.  Item 4 of the proposal, the Research Plan, shall not exceed 25 pages, in 12-point Arial font or larger. Item 5 of the proposal shall be limited to 3 page of biographical information for each core staff person and 1 page of biographical information for all other team members.


B. 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.


C.  NCHRP wishes to award the contract for NCHRP Project 22-49 for a fixed price of $400,000. This amount will not be subject to any adjustment by reason of the research team’s cost experience in the performance of the contract.  In addition to providing a detailed budget, the proposer should provide a proposed schedule of project milestones, deliverables and progress payments tied to the detailed budget and schedule which will be inclusive of specific dates. For budgeting purposes, proposers should assume that (1) NCHRP will provide access to web-enabled teleconference services and (2) one in-person meeting with the NCHRP project panel will be held in Washington, DC. NCHRP will pay panel members’ travel costs for the meeting.

D. 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. Item 5 must also include which research team members have experience in performing similar scopes of work including the statistical modeling of safety data and spreadsheet tool development, testing, support, and maintenance. Include their specific role, domain experience, past performance, and process maturity of the specific project team, company subgroup, teammates, and subcontractors proposed to execute the work directly related to this research objective.

E. Item 7 in the proposal, "Other Commitments of the Research Team," must include an exhaustive list of current external and internal commitments to other work in sufficient detail to indicate that the organization and all of the individuals assigned to the proposed project will be able to meet the commitments of the proposal. Staff hour commitments and percentage of time committed to other work for each member of the proposed research team shall be specified. This shall include the names of projects and affiliation or sponsoring agency, percentage of time allocated to each effort, and the duration of each project.


F. 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) data collection, management, and sharing plan; (4) the experience, qualifications, and objectivity of the research team in the same or closely related problem area; (5) the plan for ensuring application of results; (6) how the proposer approaches inclusion and diversity in the composition of their team and research approach, including participation by certified Disadvantaged Business Enterprises; and, if relevant, (7) the adequacy of the facilities.


Note: The proposer's approach to inclusion and diversity as well as participation by Disadvantaged Business Enterprises should be incorporated in Item 12 of the proposal.


G. 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.


H. 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.


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