Analysis of Policies for Safety Improvements on Low-Volume Rural Roadways,1994

In order to determine the adequacy with which safety problems on low-volume rural roadways were addressed by the four states of Federal Region VII (Iowa, Kansas, Missouri, and Nebraska), a review was made of the states' safety policies. After reviewing literature dealing with the identification of hazardous locations, evaluation methodologies, and system-wide safety improvements, a survey of the states' safety policies was conducted. An official from each state was questioned about the various aspects and procedures dealing with safety improvements. After analyzing and comparing the remarkably diverse policies, recommendations were made in the form of a model safety program. This program included special modifications that would help remediate hazards on low-volume rural roadways. Especially encouraged is a system-wide approach to improvement which would cover all parts of the highway system, not just urban and high-volume roadways.

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

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.