Center for Transportation Research and Education

About the research

When access via driveways and minor public roads from arterial and collector roadways to land development is not effectively managed, the result is often increased accident rates, increased congestion, and increased delays for motorists. The most common access management problem in Iowa involves allowing a high density of direct driveway access via private driveways to commercial properties located alongside arterial highways, roads, and streets. Although access management is often thought of as an urban problem, some of the most difficult access management issues occur in areas at and just beyond the urban fringe. Like most other states, Iowa is becoming more urbanized, with large urban centers accounting for more and more employment and inbound commuting from rural hinterlands. This research project is intended to produce a strategy for addressing current and future access management problems on state highway routes located just outside urban areas that serve as major routes for commuting into and out of major employment centers in Iowa.

There were two basic goals for the project: (1) to develop a ranking system for identifying high-priority segments for access management treatments on primary highways outside metro and urban areas and (2) to focus efforts on routes that are major commuting routes at present and in the future. The project focused on four-lane expressways and two-lane arterials most likely to serve extensive commuter traffic.

Available spatial and statistical data were used to identify existing and possible future problem corridors with respect to access management. The research team developed a scheme for ranking commuter routes based on their need for attention to access management.

This project was able to produce rankings for corridors based on a variety of factors, including proportion of crashes that appear to be access-related, severity of those crashes, and potential for improvement along corridors. Frequency and loss were found to be highly rank correlated. Most of the highest ranked routes are on two-lane rural cross sections, but a few are four-lane expressways with at-grade private driveways and public road intersections. The most important conclusion of the ranking system is that many of the poor-performing corridors are located in a single Iowa Department of Transportation district near two urban areas: Des Moines and Ames.