Iowa Local Technical Assistance Program

About the research

The objective of this project was to develop tools and procedures to identify potentially hazardous roadway locations and designs, and to demonstrate the utility of these tools by developing candidate lists of high crash locations in Iowa.

An initial task built an integrated database to facilitate the tools and procedures. The Iowa Department of Transportation (Iowa DOT) Geographic Information Management System (GIMS) and Geographic Information System Accident Analysis and Location System (GIS-ALAS) databases were integrated with available digital imagery. High crash locations and relationships between crash rates and selected roadway design characteristics were identified. Based on input from county, state and consulting engineers, the project studied five crash types: (1) crashes on horizontal curves, (2) fixed-object crashes, (3) rural four-lane expressway intersection crashes, (4) head-on crashes (due to crossing the centerline), and (5) urban four-lane undivided corridor crashes. Procedures were developed to integrate crash records and roadway characteristics (e.g., traffic volumes, number of lanes) to estimate the crash rate on any segment of the Iowa roadway network and rank high crash locations using the Iowa DOT’s conventional procedure (average ranking by frequency, rate and loss.) Statistical relationships between crash rates and roadway characteristics were then established. The resulting statistical models identify significant roadway geometric factors in causation of certain crashes. GIS-based procedures were developed to facilitate the identification and analysis of elusive roadway criteria, e.g., curve radii, which are not identified by crash records. A method was also developed for determining the most recent daily entering vehicles at intersections and for reviewing and defining extents of location specific analysis (e.g., corridors).

As highway engineering safety improvement programs are often reactive, safety countermeasures may be applied to the roadway only after high crash rates are observed. This project aimed to quantify the impact of highway geometry and design features on crash rates, enabling agencies to proactively identify and mitigate future problem areas. The project identified and analyzed roadway segments characterized by criteria that are not identified by conventional crash analysis. Methods were developed for solving intermediate problems and improving corridor analysis. Project products included a curve database for Iowa with radii and length attributes, procedures for identifying high crash locations of five types, statistical models of the relationship between geometric features and crash rates, and candidate lists (maps and tables) for improvement (Iowa top 30 lists) for five problem types.