Degree Type


Date of Award


Degree Name

Master of Science


Civil, Construction, and Environmental Engineering


Civil Engineering

First Advisor

Peter T. Savolainen


Given the degree of traffic conflict inherent in their operations, intersections and driveways continue to experience a disproportionate number of traffic crashes, injuries, and fatalities. Access management strategies, such as the introduction of minimum access point spacing criteria and turning movement restrictions, are important elements to optimizing the operational and safety performance of roadway corridors. The relationship between safety and these types of access policies is a complex issue and the impacts of such features on traffic crashes is in need of further research. The purpose of this study was to identify how driveway density, type, and spacing are related to the rate of crashes among various roadways in Iowa. Data were collected for two types of facilities: (1) priority, or high-growth urban/suburban corridors; and (2) crossroad corridors, beginning at the crossroad terminal of service interchanges.

Detailed driveway information was manually collected along each corridor and integrated with traffic volume, roadway geometry, and traffic control information from the Iowa DOT. Police-reported crash data from 2010 to 2014 were also obtained from an Iowa DOT database. A series of safety performance functions (SPFs) were estimated to ascertain how crash rates change in relation to the frequency of access points observed on these corridors. The results of the study show that crash rates are strongly associated with access point density. Crash rates were higher on corridors with denser traffic signal spacing, as well as on corridors with dense commercial development. Other factors were also found to be associated with changes in crash rates, including divided roads and the posted speed limit.


Copyright Owner

Iftin Thompson



File Format


File Size

123 pages