Abstract
Traffic volume forecasts are fundamental to policymaking; yet, the impacts of forecast errors are rarely considered. Accordingly, traffic forecasts in 39 studies were compared to observed volumes after the forecast year had elapsed, yielding a mean error of 40%. To evaluate the effect of forecast accuracy, five case studies examined how forecast error affected investment decisions. Because errors of 11%, 12%, 20%, 33%, and 34% can alter investment decisions, the respective observed errors of 20%, 38%, 64%, 6%, and 52% meant the forecast error was potentially large enough to alter the investment decision based on each study’s stated criterion. Although striving for more accurate forecasts is laudable, the results from the 39 studies showed that only a quarter of the variation in study accuracy is not attributable to random variation. Accordingly, until highly accurate forecasts become the norm, an interim recommendation for planners is to use empirical decision intervals, as shown herein, indicating the magnitude of error can alter investment decisions.
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Data Availability Statement
Some or all data, models, or code generated or used during the study are available from the corresponding author by request (data for the 39 studies used in Models 1–4 and data for the 1,159 links).
Acknowledgments
This research benefited from insights, data, and suggestions from Paul Agnello, Gloryah Allen, Ed Azimi, Deven Barkley, Angela Biney, Linda Evans, Scott Gagnon, Bill Guiher, Paul Hinson, Ralph Jones, Jaesup Lee, Ling Li, Olivia Lippincott, Raleigh Matteo, Dan Painter, Chuck Proctor, Tom Schinkel, Sharon Smidler, Eric Stringfield, Andre’ Surles, Ron Svejkovsky, Rick Tambellini, Chad Tucker, Ramkumar Venkatanarayana, Mike Vorburger, Laura Walton, and two anonymous reviewers. The authors alone are responsible for any errors herein.
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ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil Engineering
Volume 6 • Issue 2 • June 2020
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©2020 American Society of Civil Engineers.
History
Received: Apr 1, 2019
Accepted: Oct 9, 2019
Published online: Jan 29, 2020
Published in print: Jun 1, 2020
Discussion open until: Jun 29, 2020
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