About the research
This research will expand upon previous studies and provide comprehensive guidance as to access management strategies that are appropriate across various road types and geographic settings in consideration of important local factors. This guidance will be developed on the basis of a quantitative risk assessment that relates crash rates to traffic volumes and access management strategies. The results of this analysis will help to inform development of a revised access management policy, as well as associated guidelines that assist the Iowa Department of Transportation (DOT) in implementing consistent, research-based guidance as a part of its continuing access management program.
Phase I included a review of the existing research literature, as well as an assessment of available data. Phase II has involved a quantitative risk assessment aimed at quantifying crash risk as a function of access point spacing while controlling for the effects of other important factors (average annual daily traffic/AADT, segment length, number of through and auxiliary lanes, etc.). The results of these analyses provide an important Iowa-specific supplement to existing access management safety research. This will allow for the determination of thresholds for various access management policies. This will address issues such as the minimum spacing between freeway off-ramps and the first side-street driveway (full movement, three-quarter movement, right-in/right-out, etc.), the minimum spacing between on-ramps and the first at-grade intersection on expressway facilities, and other access management characteristics of interest to the Iowa DOT.
The objective of Phase III will be to establish a new and more functional access program framework within the DOT that incorporates modern access management strategies and is supportive of DOT goals to support the economic vitality of the State, preserve the functional integrity of the public’s capital investment in the highway system and help ensure that the traveling public are provided with safe roads.
The Institute for Transportation (InTrans) will work in cooperation with the Iowa DOT and a select group of national experts on the development of an administrative access permitting rule and an internal access management engineering, agency practices, and procedures manual.