The National Academies

NCHRP 17-26 [Completed]

Methodology to Predict the Safety Performance of Urban and Suburban Arterials

  Project Data
Funds: $1,096,403
Research Agency: Midwest Reseach Institute
Principal Investigator: Doug Harwood
Effective Date: 6/2/2003
Completion Date: 3/31/2008


There is a significant need and opportunity for improving the explicit consideration of highway safety in making decisions on roadway planning, design, and operations. The Transportation Research Board (TRB) Joint Subcommittee for the Highway Safety Manual (HSM) has identified the need to take advantage of a number of recent technical advances and to synthesize new research on highway safety into a HSM. The purpose of an HSM is to provide the best factual information and tools, in a useful and widely accepted form, in order to facilitate roadway planning, design, and operational decisions, based upon explicit consideration of their safety consequences. This manual will greatly strengthen the role of safety in road planning, design, and operational decisions.

The transportation agencies that are responsible for road systems do not currently have useful tools for considering safety in their decisions. The result is that when difficult choices must be made, greater confidence is often placed in predictions of factors such as cost, operational impacts, and environmental impacts. Therefore, an effective resource is urgently needed that predicts the safety performance of the variety of elements considered in road planning, design, and operation.

NCHRP Project 17-18(4), Improved Guidelines for Median Safety, developed a draft outline and chapter for 2-lane rural roads for the HSM. Project 17-26 will develop models similar to those in the 2-lane rural roads chapter for the safety performance of elements of urban and suburban arterials. Establishing models for urban and suburban highways is expected to require extensive effort. Separate model sets may be required for the analysis of arterial segments and intersections.

The HSM is targeted primarily at those on the front line of daily decision making within state DOTs and local organizations such as MPOs. These include analysts studying impacts of proposed road improvements on users and conducting studies at the planning, design, or operations levels. The development of the models for urban and suburban arterials will provide the basis for a significant chapter in the HSM.


The objective of this project is to develop a methodology that predicts the safety performance of the various elements (e.g., lane width, shoulder width, use of curbs) considered in planning, design, and operation of non-limited-access urban and suburban arterials.

Accomplishment of the project objective(s) will require at least the following tasks.

TASKS (1.) Conduct a review of completed and ongoing research, including the draft outline and chapter of the HSM, to identify existing accident modification factors and models relevant to urban and suburban arterials. (2.) Identify the candidate model inputs and design a survey to compile existing accident modification factors, models, and sources of available data. The survey shall also identify high-priority planning, design, and operational safety issues. (3.) Survey transportation agencies to determine available data and conduct follow up interviews, as necessary. (4.) Based on the findings of Tasks 1 through 3, propose the transportation elements to be analyzed and the methodology to predict the safety performance for non-limited-access urban and suburban arterials. Separate model sets may be required for analysis of arterial segments and intersections. The methodology should identify the different modeling approaches to be taken for each set. (5.) Develop a work plan (including a data collection plan) addressing model development, validation, and application of the models to practical examples. The work plan does not need to be restricted to the funds available for this project. If the total cost exceeds the funds available for this project, the plan shall include a prioritization scheme that considers high-priority safety needs and available data for what can be achieved with the available funds. (6.) Submit an interim report summarizing the findings of Tasks 1 through 5. (7.) Meet with the NCHRP panel to review the Task 6 interim report approximately 1 month after its submittal. Submit a revised interim report addressing the panel's review comments. (8.) Execute the approved revised work plan. (9.) Submit a final report documenting the entire research effort. The final report shall describe how the project was conducted, identify areas for further research, and include as an appendix the methodology in a format suitable for incorporation in the HSM.

Status: The contractor has submitted the draft final reports for all phases and the revised Chapter 10 for the Highway Safety Manual. The Phase I and II, and Phase III draft final reports have been posted on the TRB website as Web Document 129.  The draft HSM Chapter 10 has been provided to the HSM production contractor (NCHRP Project 17-36).

Product Availability: Draft final reports for Phases I and II (NCHRP Web-Only Document 129, Phases I and II), and III (NCHRP Web-Only Document 129, Phase III).

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