Crash Analysis

Five Percent Safety Program - Background

Iowa's 5 Percent Safety Report
Section 1401 of the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU) amended Section 148 of Title 23 USC to create a new Highway Safety Improvement Program (HSIP) as a "core" Federal Highway Administration program with separate funding. The purpose of the HSIP is to reduce traffic fatalities and serious injuries on public roads. As part of the new HSIP, states are required to submit an annual report describing not less than 5 percent of their highway locations exhibiting the most severe safety needs. The intent of this provision is to raise the public awareness of the highway safety needs and challenges in the states.

This report must include an assessment of:
  • Potential remedies to hazardous locations identified.
  • Estimated costs associated with remedies.
  • Impediments to implementation other than cost.


Roadway designHighway crashes are very complex. Contributing factors can include a roadway's design, pavement conditions (e.g., rain, snow, ice), a vehicle's mechanical condition (e.g., tires, brakes, lights), a driver's behavior (e.g. speeding, inattentiveness and seat belt usage), as well as the driver's condition (e.g., alcohol use, age-related conditions, physical impairment). In fact, the driver's behavior and condition factors are the primary cause in an estimated 67 percent of highway crashes and a contributing factor in an estimated 95 percent of all crashes.

As such, highway safety needs go beyond just physical improvements to a specific roadway or intersection, and include changes to driver behavior. These are best addressed with a
multidisciplinary approach using engineering, enforcement, emergency response, and education strategies.

Iowa's most severe safety needs

Based on an analysis of Iowa's 2001�2009 fatal and major injury crashes, Iowa's most severe safety needs are related to crashes involving:
  • Single vehicles running off the road.
  • Vehicles crossing the centerline on two-lane highways.
  • Vehicles crossing the medians on freeways.
  • Horizontal curves.
  • Intersections.
  • Unbelted drivers and passengers.
  • Impaired drivers.
  • Speeding.
The analysis following this discussion identifies the 5 percent of Iowa's most severe safety needs in each of the areas listed above.

Historically, the Iowa DOT's intersection "Safety Candidate List" identified the 200 highest ranked intersections relative to crash history. Iowa's 5 percent most severe intersection safety needs are the highest 5 percent of these intersections. There are more than 100,000 miles of public roads in Iowa. Candidate roadway safety projects are the 5,000 miles of roadway with the greatest crash history. Therefore, Iowa's 5 percent most severe corridor safety needs are 5 percent of this 5,000 miles.

Office of Traffic and Safety
Ph: 515-239-1557 | Fax: 515-239-1891

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