The Impact of Relative Bridge Width on Highway Crashes in Nebraska

Authors

Mujahid Ali Bahadur, University of Nebraska-LincolnFollow

First Advisor

Aemal J. Khattak

Committee Members

Yunwoo Nam, Li Zhao

Date of this Version

11-2025

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Civil Engineering

Under the supervision of Professor Aemal J. Khattak

Lincoln, Nebraska, November 2025

Comments

Copyright 2025, Mujahid Ali Bahadur. Used by permission

Abstract

This research examines how bridge width relative to the approach roadway affects crash occurrence on Nebraska highways. The Nebraska Department of Transportation-(NDOT) Bridge Design Manual sets minimum bridge widths based on roadway classification, traffic projections, and the American Association of State Highway and Transportation Officials’ (AASHTO) Load and Resistance Factor Design (LRFD) criteria. While these guidelines ensure structural and functional adequacy, they do not incorporate safety performance analyses based on crash data. This leaves an important gap in understanding how bridge and approach roadway width decisions influence safety outcomes.

This research has four objectives: (1) evaluate crash frequency across different bridge width intervals; (2) identify variables including roadway and approach roadway widths that relate to higher crash frequencies; (3) compare bridge crash attribution results from accident report’s based “bridge switch” with those from a GIS‑based spatial matching approach; and (4) develop statistical models that account for geometric, traffic, and temporal factors in Nebraska bridge related crashes.

The study tested the hypotheses on whether narrower or wider bridges are associated with higher crash rates, and whether GIS-based methods identify more bridge-related crashes than current reporting practices. Count-based regression models were used for crash frequency analysis using three datasets that were based on how bridge related crashes were identified. The analysis was supported by additional statistical tests for comparative analyses. Narrow bridges consistently exhibited the highest crash rates in all datasets, while wide bridges maintained the lowest. GIS-based methods identified more bridge-related crashes than the current reporting practices. Analysis of the three datasets showed that bridges wider than their approaching roadways tended to experience fewer crashes. Limitations of the research include limited geographic and temporal coverage of the crash and bridge data and the non-consideration of crash severity in the analyses. However, findings from this research should be helpful to NDOT in integrating empirical safety evidence into bridge and approach roadway width decisions for new construction and rehabilitation of roadways and bridges.

Advisor: Aemal J. Khattak