In-Service Performance Evaluation of Single-Post, Circular Aluminum Sign Supports with Frangible-Base and Slip-Base Designs

Authors

• Nitesh Adhikari, University of Nebraska-LincolnFollow

First Advisor

Joshua S. Steelman

Committee Members

Ronald Faller, Cody Stolle

Date of this Version

7-2026

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 Joshua S. Steelman

Lincoln, Nebraska, July 2026

Comments

Copyright 2026, Nitesh Adhikari. Used by permission

Abstract

Single-post, circular aluminum sign supports with frangible-base or slip-base designs are widely used on Florida highways. Full-scale crash tests and LS-DYNA simulations sponsored by the Florida Department of Transportation identified performance concerns, including occupant-compartment penetration that violated Manual for Assessing Safety Hardware (MASH) criteria and simulation predictions that diverged from physical tests. Because no in-service performance evaluation existed for this hardware family, this thesis evaluated their field performance using police-reported crash data. In total, 429 Florida crashes coded with Traffic Sign Support as the First Harmful Event were drawn from the Signal4Analytics database: 248 fatal and incapacitating-injury (K+A) crashes (2022-2024) and 181 non-incapacitating-injury crashes (2024). Each case was reviewed using crash narratives, scene diagrams, and roadway imagery to identify the support type, classify the harmful-event sequence, and assign a likelihood (Likely, Uncertain, or Unlikely) that the sign impact caused the reported injury. Sign type was identified in 63-66% of cases. Among 152 identified K+A crashes, 28 (18.4%) were Likely, and 70-77% involved multi-impact sequences in which the sign was not the most harmful event. Frangible-base posts were most prevalent (34-41%) but produced a modest Likely rate (16.7%), while unidirectional slip-base posts yielded zero Likely classifications among 11 cases. These results indicate that most sign supports are small contributors to statewide severe-crash totals, and that slip-base supports may pose lower field risk than frangible-base designs, though findings are constrained by identification and evidentiary limitations. The study establishes a reproducible sign-identification and likelihood-assessment methodology and recommends a statewide sign inventory.

Advisor: Joshua S. Steelman