Speaker: Udaya Adhikari, Ph.D. student, Department of Civil and Architectural Engineering and Mechanics, University of Arizona
When
Join in person or online: https://arizona.zoom.us/j/87815388173?from=addon
Abstract: The City of Phoenix is upgrading aging traffic signal infrastructure and implementing targeted signal modifications/modernizations to improve visibility, operational consistency, and system reliability. Understanding the safety effects of these investments is essential for prioritizing future improvements. This collaborative project between the City of Phoenix and the University of Arizona will develop locally applicable Crash Modification Factors (CMFs) to quantify changes in crash frequency associated with signal modernizations and modifications.
The study will identify treated intersections, document their improvements and installation dates, and select comparable untreated intersections. A database will integrate three to six years of crash records with traffic volumes and geometric and operational characteristics. Treatment sites will be grouped according to the improvements implemented. Safety Performance Functions (SPFs), developed using appropriate statistical models such as negative binomial regression, will relate crash frequency to traffic exposure and intersection characteristics. An Empirical Bayes (EB) before–after evaluation will combine SPF predictions with each treatment site’s crash history to estimate the crashes expected during the after period without the improvement. Comparing these estimates with observed after-period crashes will support CMF development while accounting for regression to the mean, changes in traffic volumes, and background time trends.
Up to eight CMFs will be developed across treatment groups, crash types, and severity categories, subject to data availability. Standard errors and confidence intervals will quantify the precision of the estimates. The resulting CMFs and supporting documentation will provide the City with local evidence to evaluate signal improvements, guide future investments, and support potential submission to the FHWA CMF Clearinghouse.
Researcher's Bio: Udaya Adhikari is a third-year Ph.D. student in Civil Engineering at the University of Arizona. His research interests include transportation safety, traffic operations, intelligent transportation systems, and data-driven transportation engineering. He uses emerging data sources and statistical and analytical methods to evaluate roadway and intersection performance and assess strategies for improving transportation safety, efficiency, and reliability.