Colorado's Implementation of Level of Service of Safety: Strategies for Using GIS to Advance Highway Safety

The objective of this case study is to illustrate how Colorado uses geographic information systems (GIS) to spatially integrate roadway data with crash data, develop Safety Performance Functions (SPFs), visualize data, and implement the Level of Service of Safety (LOSS) method to assess a roadway’s safety performance. LOSS compares a roadway segment's observed crash frequency and severity to the crash frequencies predicted by SPFs. Transportation agencies that model crash frequency and severity based on annual average daily traffic (AADT) develop SPFs for public roadways, including segments and intersections. They stratify SPFs by the number of lanes, number of legs, traffic control, terrain, environment, and intersecting roadways, as a tabular dataset cannot use GIS to link intersecting roads. When analysts evaluate the magnitude of a safety problem, they assess it from two angles— frequency and severity. As such, they develop distinct SPFs, one for the total number of crashes and the other for injury and fatal crashes. With LOSS, analysts use quantitative assessment and qualitative description measures to characterize the safety of a roadway segment or an intersection and establish four levels of service safety. These levels are based on how the predicted frequency or severity of crashes deviates from observed crashes at a specific AADT. The comparison relies on the standard deviation of predicted crashes to assign a roadway segment to a particular level of safety. The four LOSS categories indicate the potential for crash reduction, from high to low. Figure 1 uses an SPF calibrated for total crashes expected on six-volume. functional classification can employ the LOSS method. While it is possible to segment roadway data in tabular form, using a Geographic Information System (GIS) greatly facilitates segmentation of these roadways. More specifically, GIS enables analysts to spatially link data describing roadway geometry with crash data.

  • Record URL:
  • Corporate Authors:


    8608 West Mountain Lane
    Littleton, CO  United States  80125

    Felsburg Holt & Ullevig

    6300 S Syracuse Way
    Englewood, CO  United States  80111

    Colorado Department of Transportation

    4201 E Arkansas Avenue
    Denver, CO  United States  80222

    Federal Highway Administration

    Office of Safety, Roadway Safety Data Program
    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • Allery, Bryan
    • Kononov, Jake
    • Johnson, William
    • Kirby, Evan
  • Publication Date: 2016-5


  • English

Media Info

  • Media Type: Digital/other
  • Edition: Case Study
  • Features: Figures; Maps; References;
  • Pagination: 13p

Subject/Index Terms

Filing Info

  • Accession Number: 01749229
  • Record Type: Publication
  • Report/Paper Numbers: FHWA-SA-16-027
  • Created Date: Aug 17 2020 11:03AM