Date of this Version
A cost-effective means for upgrading existing barrier systems, which have deviations from standard practice (i.e., low-rail heights, antiquated end treatments, and improper installation) does not exist. As a result these systems remain on U.S. highways. Barrier systems with deviations from current practice may not perform as intended, thus resulting in fatalities and serious injuries from impacts with these safety devices. It is not plausible to eliminate fatalities and serious injuries from all guardrail impacts; but these numbers could be significantly reduced with the proper design, testing, installation, and maintenance of guardrail systems.
This report offers recommendations for upgrading W-beam guardrails based on benefit-to-cost analyses using the Roadside Safety Analysis Program (RSAP). This analyses was developed to simulate the most frequent and possible scenarios of existing W-beam barrier systems with deviations from standard practice. Before the analysis could be run, the field conditions and deviations from standard practice needed to be recognized and determined from a field investigation.
A field investigation was conducted on rural arterial highways in the state of Kansas to determine the nature of existing barrier systems with deviations from standard practice. For the study, the most prominent barrier was the strong-post, W-beam guardrail. The major deviations of the existing W-beam were low top-rail mounting-height and antiquated end treatments (i.e. turned-down and blunt-end terminals). The W-beam guardrail with low rail heights and turned-down and blunt-end terminals were the focus of the RSAP analysis.
The varying guardrail heights were modeled in RSAP by changing the level of containment of the W-beam guardrail, and the antiquated end treatments were predefined features. The roadway and roadside features including hazards (culverts and slopes) were modeled after those found in the field investigation. Finally, cost-effective safety treatments were recommended for existing W-beam guardrail with low rail height and turned-down or blunt-end terminals which shielded culverts and slopes.
Advisor: Dean L. Sicking