BACKGROUND

The American Association of State Highway and Transportation Officials (AASHTO) Highway Safety Manual (HSM) has crash prediction methods for multilane roadway facilities, but only a few of the available methods address the safety performance of these facilities with long-duration work zones (defined as work zones with temporary traffic control [TTC] devices that remain in place for extended time periods [i.e., multiple weeks or months]) in place. As a result, state departments of transportation (DOTs) and other highway agencies rely on judgment and experience rather than quantitative safety analysis in developing TTC plans for long-duration work zones.

Research is needed to better understand the quantitative safety performance, including crash frequency and crash severity measures, of a variety of work zone TTC characteristics. These characteristics include speed limit, lane closures, lane shifts, shoulder closures, median crossovers, lane width, shoulder width, horizontal curvature, offsets from the traveled way to traffic barriers, breakdown bay (i.e., emergency pull-off area), and construction access points. New knowledge on these topics should be assembled into quantitative crash prediction methods that can be used by state DOTs and other highway agencies in developing TTC plans. 

OBJECTIVE

The objective of this project is to develop crash prediction methods and supporting spreadsheet tools for state DOTs and other highway agencies to plan and design TTC for long-duration work zones on high-speed (45 mph or higher) multilane roadway facilities. 

The crash prediction methods should be capable of comparing the expected safety performance of different work zone design options to assist in planning work zone configurations and project phasing. These crash prediction methods should have a similar structure to existing HSM crash prediction methods, with safety performance functions and crash modification factors. The research may adapt these approaches as needed to provide an effective procedure and structure for the models to provide crash frequency and severity estimates. These crash prediction methods should be suitable for incorporation in future editions of the AASHTO HSM. 

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

RESEARCH PLAN

The research plan should build in appropriate checkpoints with the NCHRP project panel, including, at a minimum, (1) a kick-off teleconference meeting to be held within 1 month of the contract’s execution date and (2) one face-to-face interim deliverable review meeting and web-enabled teleconferences tied to panel review and/or NCHRP approval of the interim deliverables, including the expenses in the budget. The cost of teleconferences, the in-person meeting venue, and NCHRP panel member travel will be paid by the NCHRP.

At a minimum, the proposed tasks should be accomplished.

Phase I

Task 1. Conduct a critical review of the road safety literature and a survey of the state of the practice at state and other agencies to identify factors associated with the performance of work zone TTC characteristics. The review should summarize the factors considered, discuss related modeling efforts, and identify gaps in the current state of knowledge and practice on the research topic.

Task 2. Identify data currently used and other public data that could help develop exposure and crash prediction models for use in long-duration work zones. Develop a comprehensive data collection, management, and validation plan. The plan should include metadata for raw and processed data, data ownership information, data restrictions (if applicable), and recommendations for data archiving.

Task 3. Prepare a detailed methodological framework for developing crash prediction models. Examine key factors for evaluating the performance of long-duration work zone TTC characteristics.

For the crash prediction modeling task, the methodological framework shall, at a minimum, include:

• Methods for multisource data integration/fusion;
• A 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;
• A validation approach for the methodology and tool; and
• Development of a spreadsheet tool.

The methods for the prediction of crash frequency and severity for long-duration work zones should be repeatable, capable of evaluating existing and future conditions, and practical and readily implementable by state and other transportation agencies of all sizes to help evaluate the potential performance of a long-duration work zone at a given location.

Task 4. Prepare an interim report documenting the results of Tasks 1 through 3 and provide a work plan for Phase II no later than 8 months after the contract is awarded. 

Phase II

Task 5. Execute the work plan based on the approved interim report. Prepare a technical memo with the research findings.

The Task 5 technical memo shall include detailed discussions on the impact of the significant variables, including sign of impact (i.e., positive or negative), magnitude, and elasticities (or marginal effects), with the purpose of improving the scientific understanding of the performance of long-duration work zone TTC characteristics. The documentation for model development should include:

• Detailed methodology;
• Data summary and descriptive statistics by facility type and work zone with TTC characteristics;
• Validated models and results, including variable importance ranking, and elasticities (or marginal effects) of analyses by facility type and work zone with TTC characteristics;
• Metrics used for assessing the quality of statistical models and results of the quantitative analyses; and
• Tables and graphs showing relationships between crash frequency/severity and key independent variables.

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).

Task 6. Develop a user-friendly, updatable, and easy-to-maintain spreadsheet tool and user manual with example applications that can be used by practitioners of state and other transportation agencies to quantify the performance of long-duration work zones. The development of the spreadsheet tool should use commonly available software and avoid the use of third-party software components.

Task 7. Refine and update the spreadsheet tool and user manual based on comments from the NCHRP. 

Task 8. Prepare draft language for consideration by AASHTO to incorporate the research results into the next update of the AASHTO HSM (herein called the AASHTO Deliverable). Include sample problems, assumptions, data limitations, and other constraints (e.g., range for valid input fields, conditions that cannot be assessed with the methodologies).

Task 9. Present the research findings in-person or virtually to appropriate AASHTO technical committees for comments and propose any revisions to the NCHRP. The research team should anticipate making at least two presentations during the research process to appropriate technical committees at the meetings of the AASHTO Committees on Safety, Construction, Traffic Engineering, Design, or other technical committees with the NCHRP’s approval. Revise the AASHTO Deliverable after consideration of the review comments and NCHRP approval.   

Task 10. Prepare the final deliverables, including:

1. A final research report documenting the entire research effort; 
2. The AASHTO Deliverable;
3. All raw, cleaned, and processed data collected and used in the research (data should be provided in as close to its raw form as possible based on contractual or legal restrictions), input data sets, fused and integrated research data sets, data dictionaries, data models, and so forth;
4. The spreadsheet tool (including annotated spreadsheet macro code, if any), user manual, and any other spreadsheet tool documentation;
5. Media and communication material [e.g., presentations, two-page executive-level flyer, graphics, graphic interchange formats, press releases]; and
6. A stand-alone technical memorandum titled “Implementation of Research Findings and Products”.

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