The National Academies

NCHRP 17-118 [Pending]

Understanding the Impacts of Operational Changes on Safety Performance

  Project Data
Funds: $450,000
Contract Time: 24 months
Staff Responsibility: Richard A. Retting


Mobility and safety are often identified in transportation agency mission statements as core values. State departments of transportation and local agencies are progressively incorporating the Safe System approach that works by building and reinforcing multiple layers of protection to prevent crashes from happening in the first place and minimize the harm caused to those involved when crashes do occur. At the same time, many operational changes are being implemented to reduce delays and improve traffic flow, some of which could have unintended negative effects on safety. The goals of safety and mobility must be balanced and better understood.

Roadway and intersection configurations, vehicle speed, and multimodal level of service are examples of metrics that can be used to understand operational improvements and help predict changes in crash outcomes. In addition, systemwide changes in factors related to use of the roadway network, such as land development, traffic volume, speed limit, and mode choice can affect the safety performance of the system and of individual facilities.

Studies of corridor and intersection operational improvements show mixed effects on safety outcomes, leaving agencies with an incomplete understanding of the relationship between operational changes and safety performance. Transportation agencies need tools to support decisions concerning tradeoffs between mobility, capacity, and crash severity. Providing a better understanding of these conflicts supports implementation of the Safe System approach.


The objectives of this research are to develop a guide and an associated quantitative analysis procedure to improve the understanding of how operational changes in different design and developmental contexts can impact safety performance. Results of this research will provide transportation agencies and other practitioners with means to better understand anticipated safety implications associated with implementing changes operational changes.


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 how the proposer intends to satisfy the project objective; (3) be divided logically into detailed tasks necessary to fulfill the research objective and include appropriate milestones and interim deliverables; and (4) incorporate opportunities for the project panel to review, comment on, and approve milestone deliverables. 

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


Phase I ─ Planning

Task 1. Compile existing research findings regarding the relationship between operational changes and safety performance measures.

Task 2. Identify gaps within the existing research and develop a data collection and analysis plan for conducting new research in Phase II. 

Task 3. Propose an approach for developing a quantitative analysis procedure to understand tradeoffs between operational changes and resulting changes in crash frequency and/or severity. Identify potential opportunities and/or sample projects to assess the methodology across a range of conditions.

Task 4. Propose a preliminary outline for the guide based on the proposed methodology. The guide should identify types of operational changes that measurably increase or decrease crash frequency and/or crash severity.

Task 5. Prepare Interim Report No. 1 that documents the work completed in Tasks 1 through 4. Update the work proposed for Phases II and III.


Phase II – Methodology Development

Task 6. Collect data to investigate how crash outcomes are affected by various types of operational changes, and produce a model exhibiting the findings.

Task 7. Develop a quantitative analysis procedure to understand tradeoffs between operational changes and resulting changes in crash outcomes for different environmental and temporal conditions (e.g., roadway and intersection type/configuration, land use, time of day, seasonal).

Task 8. Produce an operational and safety performance measure correlation model to be used by practitioners as a decision-making and countermeasure prioritization tool.

Task 9. Run hypothetical sample projects, as identified in Phase I and approved by NCHRP, to develop examples/instructions.

Task 10. Prepare Interim Report No. 2 that documents the results of Tasks 6 through 9 and provides an updated work plan for the remainder of the project. The updated plan must describe the work proposed for Phase III.

Phase III ─ Guide Development and Final Deliverables

Task 11. Develop the draft guide according to the approved Interim Report No. 2. The draft guide shall be submitted for NCHRP review 4 months before the contract end date.

Task 12. Prepare a final deliverable that documents the entire research effort. Final deliverables should include, at a minimum (1) a final research report documenting the entire research effort and findings; (2) the guide and associated quantitative analysis procedure as a stand-alone document; (3) outreach materials to support practitioners’ understanding and use of the guide and associated quantitative analysis procedure, including examples or case studies; (4) prioritized recommendations for future research; (5) presentation material; and (6) technical memorandum on implementation.


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


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