Access management and highway safety
The top 10 locations of the most promising segments for access management (full size view with a legend identifying the streets and segments--116 kb).
Nearly 10 percent of all crashes in Iowa occur at commercial driveways, primarily on city arterial streets. About a quarter of these crashes occurred in the Des Moines metro area in recent years, making it a prime candidate for improved access management.
The Des Moines Area Metropolitan Planning Organization (Des Moines Area MPO) and CTRE joined forces to develop a comprehensive access management plan.
Choosing where to improve access management
The first step was to decide which routes in the Des Moines metro area were the best candidates for improving access management.
Using the Iowa crash database, CTRE analyzed crash records from 1997–2000 (the most recent available at the time of the study) on the principal and minor arterials in the Des Moines metro area. There were 29,810 crashes along those corridors during that period.
Researchers identified a total of 18,089 crashes that were probably access-related. They chose several specific crash types:
- broadside
- rear-end collision
- rear-end/right-turn collision
- rear-end/collision
- broadside/right angle collision
- broadside/right entering collision
- broadside/left entering collision
The corridors were divided into 180 study segments. For each segment, three calculations were made:
- crash rate for the probable access-related crashes
- crash severity for the probable access-related crashes
- commercial driveway density
A statistical analysis revealed that these three measures are somewhat interchangeable in their ability to predict corridors needing access management improvement.
Nine percent of the study corridors (16 segments) had more than 250 access-related crashes. Nineteen percent (34 segments) are responsible for almost 50 percent of the access-related crash severity. This indicates that access-related crashes are concentrated along a few corridors. This is likely to be true in other metro areas as well.
Researchers identified the 20 most promising segments for access management improvement. Most of the segments are four-lane, undivided arterials in older parts of Des Moines.
Using the problem identification results
The Des Moines Area MPO plans to use the results of the crash analysis in its long-range transportation plan and transportation improvement program. The results will help the MPO identify the most important projects requesting federal funding.
Educating local officials about access management
For technical audiences, the Access Management Handbook and the access management section of the Iowa Statewide Urban Design Standards Manual, Chapter 5I 1-8, are useful materials (see www.ctre.iastate. edu/pubs/).
For non-technical audiences like elected officials and business groups, CTRE pre-pared a brief presentation called "Access Management 101." The presentation can be customized for including information about specific corridors and may include information about crash frequency, crash rate, crash type, driveway density, etc.
For more information
For more information about this project, contact David Plazak at CTRE, 515-296-0814, dplazak@iastate.edu, or Tom Kane at the Des Moines Area MPO, 515-334-0075, tjkane@dmampo.org.
A free access management workshop is being offered this fall.
