Accurate traffic forecasts for highway planning and design are crucial for ensuring that public dollars are spent wisely; however, there is only a small library of empirical studies that have examined traffic forecasting accuracy in the United States. Even with limited availability, these studies are important as they address three critical benefits: insight on observed inaccuracy levels to decision makers and the public, a demonstration of the value of advanced models and data techniques, and assistance in identifying new or advanced methods to improve traffic forecasting practice. Such studies are rare because of numerous challenges, including data availability and staff turnover, and because of a lack of consistency in accepted procedures for preserving detailed information on forecasting methods and data used in the analysis. These challenges are slowly being addressed as the importance of empirical accuracy reporting has grown. The need for the demonstrated value of advanced modeling and data techniques has also grown, as these techniques require significant resources. In traffic forecasting, departments of transportation in Wisconsin, Minnesota, and Ohio have conducted targeted reviews of some traffic forecasts within the past 6 years. Other fields have demonstrated the effectiveness of such reviews, most notably the National Oceanic and Atmospheric Administration (NOAA) through their highly successful Hurricane Forecasting Improvement Program. Building on these earlier, limited reviews, especially in the context of improving technology, there is a need to expand documentation and assessment of traffic forecasting experience to improve future applications.
The objective of this study is to develop a process to analyze and improve the accuracy, reliability, and utility of project-level traffic forecasts. To meet this objective, this study will incorporate the following: (1) analysis of traffic forecasting accuracy and usefulness using information from various sources including, but not limited to, state departments of transportation (DOTs), metropolitan planning organizations (MPOs), counties, and other transportation agencies actively involved in forecasting travel demand in competitive modes; (2) assessment of transportation agency experience with respect to accuracy of various forecasting approaches; (3) identification of methods for improving flexibility and adaptability of available forecasting techniques to changing assumptions and input data; (4) consideration of risk and uncertainty in the forecasts; and (5) identification of potential methods to help the traffic forecasting industry improve forecasting usefulness and accuracy while improving their ability to communicate and explain these forecasts to affected communities. In the context of this study, the terms accuracy and reliability are meant to address how well the forecasting procedures estimate what actually occurred; utility is meant to encompass how well a particular projected outcome informs a decision; and project level is meant to include a single project or a bundle of related projects. The product of this research will provide guidance to MPOs, state DOTs, and others to improve the accuracy, reliability, and utility of traffic forecasting methods as applied to transportation planning, design, and operation efforts—both short and long term.
To meet the objectives of this study, the research plan should consider, but not be limited to, the following steps:
1. Developing metrics and processes for evaluating traffic forecasts and procedures;
2. Evaluating traffic forecast plausibility, accuracy, utility, and sensitivity across several dimensions:
a. Forecast method; e.g., travel model, linear regression, trend analysis;
b. Size and location of forecast study area;
c. Project size, design, and type, including HOV and HOT;
d. Project stage and decision points;
e. Functional class, facility type, and volume; and
f. Forecast horizon—short, medium and long term.
3. Determining under what conditions forecasting accuracy improves, including agency experience;
4. Enumerating contributors to forecast inaccuracy, and suggesting mitigation methods;
5. Evaluating methods for improving communication of forecast risk and uncertainties;
6. Exploring optional forecasting procedures or methods from other industries or institutions; and
7. Providing guidelines in support of an ongoing review of forecast accuracy, including a recommended policy for documenting and retaining models, associated analytical techniques, and sufficient data to allow replication of earlier applications.
A kick-off teleconference of the research team and NCHRP will be scheduled within 1 month of the contract’s execution. In preparation for this kick-off conference, the research team will prepare a revised scope of work, the amplified work plan (AWP), to incorporate responses to initial panel concerns expressed as an output of the contractor selection process. This AWP must be divided into two phases with tasks described in detail. Phase 1 will consist of information gathering and initial evaluation, accomplishing sufficient tasks to reach a natural decision-making point in the study. Phase 1 will conclude with submission of an interim report that describes the work completed to that point and will present a revised scope of work for Phase 2 tasks. It will also include an outline of the guidance document and the preliminary plan for disseminating and implementing the study output. Completion of Phase 1 and submission of an interim report will also coincide with a face-to-face meeting with the NCHRP panel to discuss that report (scheduled approximately 3 weeks following delivery of the interim report). No work shall be performed on Phase 2 without NCHRP panel approval. Phase 2 should include all tasks necessary to complete the analysis and development of the guidance. This phase should also include a workshop with representatives of state DOTs and other potential consumers of the final work product, together with the NCHRP panel, to review the draft guidance and implementation plan, and to finalize recommendations for the actual format of the final product. As part of the response to this RFP, the NCHRP panel is seeking insights of proposers on how they will manage the workshop and the expected outcomes. The results of this study might also be used to demonstrate the value of various forecasting techniques. Empirical evidence of the value of various techniques could significantly increase the support for continued investment in improved traffic forecasting. The output of this research should serve as guidance to state DOTs to assist in monitoring and improving the accuracy of forecasts over time. This study is expected to fill a major gap in the U.S. traffic forecasting industry by providing insights on observed levels of accuracy while identifying existing and potential challenges with traffic forecast methods and practice. Final deliverables will include but not be limited to the following: (1) a guidance document that describes best practices for assessing and improving the accuracyof forecasting methods across a variety of project types and geographic scales; (2) a final report documenting the entire project, incorporating all other specified deliverables of the research, including recommendations on priorities for additional research; (3) electronic presentation slides on the guidance material that can be tailored for specific audiences; and (4) a stand-alone technical memorandum titled, “Implementation of Research Findings and Products”. Proposers may recommend additional deliverables in support of the project objectives.
STATUS: The Draft Final Report has been received is currently under review.