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                Colorado Uses GIS to Implement Level of Service of Safety
**Publication Year:** 
            2016
    
        Summary from: Roadway Safety Data Program | Colorado’s Implementation of Level of Service of Safety: Strategies For Using GIS to Advance Highway Safety | FHWA-SA-16-027

Background

Design engineers at the Colorado Department of Transportation (CDOT) developed the LOSS method as an alternative to using crash rates for evaluating safety. The LOSS method compares a roadway segment’s observed crash frequency and severity to the crash frequencies and severities predicted by Safety Performance Functions (SPFs). Relying on crash rates alone to identify safety deficiencies is problematic because crash rates imply a linear relationship between exposure and safety. However, the number of crashes fluctuates based on traffic volume.

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 functional classification. Once transportation engineers and planners develop the SPFs, they 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. For intersections, it is necessary for analysts to use some special context to link intersecting roadways, as a tabular dataset cannot use GIS to link intersecting roads.

Read the Case Study Colorado’s Implementation of Level of Service of Safety: Strategies For Using GIS to Advance Highway Safety for more detailed information. U.S. DEPARTMENT OF TRANSPORTATION

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