Upgrading Bridge Rails on Low-Volume Roads in Iowa, TR-679, 2016

(2016) Upgrading Bridge Rails on Low-Volume Roads in Iowa, TR-679, 2016. Transportation, Department of


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Building on previous research, the goal of this project was to identify significant influencing factors for the Iowa Department of Transportation (DOT) to consider in future updates of its Instructional Memorandum (I.M.) 3.213, which provides guidelines for determining the need for traffic barriers (guardrail and bridge rail) at secondary roadway bridges—specifically, factors that might be significant for the bridge rail rating system component of I.M. 3.213. A literature review was conducted of policies and guidelines in other states and, specifically, of studies related to traffic barrier safety countermeasures at bridges in several states. In addition, a safety impact study was conducted to evaluate possible non-driver-related behavior characteristics of crashes on secondary road structures in Iowa using road data, structure data, and crash data from 2004 to 2013. Statistical models (negative binomial regression) were used to determine which factors were significant in terms of crash volume and crash severity. The study found that crashes are somewhat more frequent on or at bridges possessing certain characteristics—traffic volume greater than 400 vehicles per day (vpd) (paved) or greater than 50 vpd (unpaved), bridge length greater than 150 ft (paved) or greater than 35 ft (unpaved), bridge width narrower than its approach (paved) or narrower than 20 ft (unpaved), and bridges older than 25 years (both paved and unpaved). No specific roadway or bridge characteristic was found to contribute to more serious crashes. The study also confirmed previous research findings that crashes with bridges on secondary roads are rare, low-severity events. Although the findings of the study support the need for appropriate use of bridge rails, it concludes that prescriptive guidelines for bridge rail use on secondary roads may not be necessary, given the limited crash expectancy and lack of differences in crash expectancy among the various combinations of explanatory characteristics.

Item Type: Departmental Report
Keywords: bridge barrier rails, bridge guardrails, crash severity mitigation, low-volume roads, safety countermeasures, secondary road bridges
Subjects: Transportation
Transportation > Bridges and tunnels
Transportation > Roads and highways
Transportation > Traffic safety
Transportation > Research
Transportation > Design and Construction
Transportation > Maintenance and preservation
ID Code: 22592
Deposited By: Iowa DOT Library
Deposited On: 04 Aug 2016 14:26
Last Modified: 04 Aug 2016 14:26
URI: https://publications.iowa.gov/id/eprint/22592