Roadway Safety Data Program

COLORADO’S IMPLEMENTATION OF LEVEL 

OF SERVICE OF SAFETY

STRATEGIES FOR USING GIS TO ADVANCE HIGHWAY SAFETY 

CASE STUDY

FHWA-SA-16-027

Prepared for

Federal Highway Administration

Office of Safety

Roadway Safety Data Program

http://safety.fhwa.dot.gov/rsdp/

Fewer 

Fatalities & 

Serious 

Injuries 

Better 

Targeted 

Safety 

Investment 

More 

Informed 

Decision 

Making 

Improved 

Data 

Collection 

& Analysis 

May 2016
Colorado’s Implementation of Level of Service of Safety 
Colorado’s Implementation of Level of Service of Safety 

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CASE STUDY OVERVIEW 

OBJECTIVE 

The objective of this case study is to illustrate how Colorado uses GIS to spatially integrate 

roadway data with crash data, develop SPFs, visualize data, and implement the Level of Service 

of Safety (LOSS) method to assess a roadway’s safety performance. 

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).(1) 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.(2) 

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.(1) 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.(3) 

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-
Colorado’s Implementation of Level of Service of Safety 

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lane urban freeways to illustrate the LOSS concept. Different crash severities (e.g., injuries 

versus fatalities) may have different LOSS levels, thereby generating several levels for a single 

segment or an intersection.(1) 

The AASHTO Highway Safety Manual (HSM) incorporated LOSS into the first edition. While 

LOSS lent itself well to the safety decision-making process in the DOT environment, it did not 

initially address correction for the regression to the mean (RTM) bias. By adopting an Empirical 

Bayes (EB) procedure, the latest HSM version uses the LOSS method, along with correction for 

RTM bias. The EB method combines the observed crash frequency with the predictive model 

estimate and uses a weighted adjustment factor that is based on the variance of the SPF model. 

After the adjustment, LOSS levels can be categorized with more certainty and in an intuitive 

percentile-based reporting method.(4) 

The following are the four LOSS 

categories used: 

 LOSS-I. Indicates low potential 

for crash reduction; 

 LOSS-II. Indicates low to 

moderate potential for crash 

reduction; 

 LOSS-III. Indicates moderate to 

high potential for crash 

reduction; and 

 LOSS-IV. Indicates high potential for crash reduction.(2)

LOSS provides information only on the magnitude of the safety problem; it does not specify the 

reason for the problem. CDOT uses direct diagnostics and pattern recognition techniques to 

better understand the nature of safety problems. These diagnostic methods use what are 

essentially tests of proportions: they use the binomial distribution and a set of stratified 

diagnostic norms to detect abnormalities in crash types and related characteristics. Integrating 

LOSS with diagnostic analysis provides a comprehensive analysis of the nature and magnitude of 

the safety problems on segments and intersections.(1) 

By blending quantitative assessment and qualitative description, LOSS can categorize a roadway 

segment’s or intersection’s safety performance in relation to the expected frequency and 

severity of crashes predicted by its SPF. Additionally, it facilitates effective communication about 

Figure 1: LOSS concept using SPF
Colorado’s Implementation of Level of Service of Safety 

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safety problems to other professionals, the traveling public, and elected officials. Engineers and 

planners can apply the information gathered from the LOSS method to many types of projects, 

including resurfacing, reconstruction, realignment, widening, and in documents such as 

Environmental Assessments (EA) and Environmental Impact Statements (EIS).(3) 

Using GIS allows agencies to spatially integrate roadway data with crash data. Integration is 

necessary because developing SPFs requires homogeneous roadways (i.e., roadways with similar 

geometric features).(6) Once the LOSS method is complete, GIS is also essential for visualizing 

the data. Visualization tools greatly aid the final step of the LOSS methodology, which includes 

prioritizing safety countermeasures. GIS is particularly helpful during prioritization, which is 

consistent with the roadway safety management process; it also helps analysts observe spatial 

trends and communicate those trends to decision makers.(3) 

KEY ACCOMPLISHMENT 

The principal output of LOSS is a collection of calibrated SPFs for highway types and 

intersections configurations. By analyzing these, analysts can develop sophisticated predictive 

and diagnostic tools, which in turn informs policies or safety countermeasures to maximize 

crash reduction across a State—and within budget constraints. The key accomplishment is a 

reduction in crashes.(2) In addition to helping improve roadway safety, the information collected 

from LOSS has provided substantive conceptual and analytical inputs to Colorado’s HSM

implementation. The HSM, in turn, provides a realistic estimate of the expected crash frequency 

per unit of traffic exposure over a unit of time for various kinds of transportation facilities.(4)

Agencies can use GIS to map this information. This provides the ability to integrate data with 

visualization, which is needed to understand levels of LOSS within an area and optimize the 

steps taken to improve safety. 

TARGET AUDIENCE 

Highway safety professionals, transportation planners, and transportation engineers can use 

LOSS methodologies. 

The CDOT established and began the LOSS method when developing the methodologies in 

2002. It was developed and implemented by Safety Programs Engineer and Safety Engineer. 

Since the implementation, the agency’s analysts have applied it to all State projects.(1) 

DOTs and other transportation agencies can use the methodology presented in this paper. Staff 

members who have experience with SPF data usually implement this process. It is crucial to 
Colorado’s Implementation of Level of Service of Safety 

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note that States must calibrate this method to account for local factors, such as the prevalent 

characteristics of crash reporting, climate, driver behavior, and design practices, among 

others.(2)
Colorado’s Implementation of Level of Service of Safety 

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PROGRAM AND PROCESSES 

CDOT IMPLEMENTATION OF THE LOSS PROGRAM 

CDOT applies LOSS to all infrastructure and behavioral projects. Over the seven years of 

sustained application of these advanced methods on all infrastructure and behavioral projects, 

the CDOT achieved an unprecedented 36 percent fatal crash reduction. Figure 2 provides an 

example of a CDOT LOSS map. It includes LOSS severity levels, as well as land use, county, and 

municipal boundaries.(4) 

Figure 2: Statewide Highway Intersection Level of Service of Safety 

for Injury and Fatal Crashes where Coinciding with Recognized Crash Patterns
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CDOT uses GIS as a visualization tool. However, integrating crash and roadway data is a 

necessary step in developing the SPFs. The crash data are linked to the roadway type based on 

location—in this case using a GIS. Both datasets are based on a linear reference system. 

However, using a coordinate system can georeference some crash data.(5) 

CDOT has found LOSS to be very effective. Between 2002 and 2011, fatal crashes in Colorado 

declined by 36 percent without a reduction in travel or increase in safety expenditures (Figure 

3).(1, 4) 

Figure 3: Colorado Fatal Crash Reduction 
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SUMMARY 

BENEFITS/RESULTS

CDOT’s pioneering work on LOSS led to the creation of a sophisticated predictive and 

diagnostic tool able to maximize potential crash reduction while not stretching alreadyexhausted budgets. These efforts have proven successful, with crash reductions of up to 36 

percent. LOSS has also expedited the process of estimating the effects of different measures on 

safety because transportation agency stakeholders can develop their analyses based on a single 

authoritative document.(1, 4) 

The specific benefits and strengths of the LOSS method include the following: 

 Accounts for variance in crash data and traffic volume, thereby establishing a threshold 

for comparison. 

 Using the Empirical Bayes method corrects for the RTM bias. 

 Facilitates communication regarding the magnitude of the safety problem. 

 Provides unifying frame of reference to make decisions about which safety 

countermeasures or roadway improvements will lead to the greatest increases in 

roadway safety. 

 Aligns models of roadway safety the actual measures safety performance. 

 Builds consensus on the often emotionally charged issue of road safety.(4)

 

LOSS provides a sound, intuitive, and easily interpreted tool to identify and describe safety 

problems. GIS, in turn, allows officials to visualize the LOSS data and thereby increase efficiency 

for addressing safety issues. 

IMPLEMENTATION CHALLENGES 

Using LOSS depends on the availability of SPFs for segments and intersections. This work 

generally requires specialized in-house technical expertise or resources allocated to consulting 

services. Integrating the data requires personnel with database and GIS expertise. Developing 

or using SPFs and LOSS also requires knowledge of the HSM and facility with advanced 

statistics. Most safety engineers are becoming more knowledgeable in these methodologies.(2)
Colorado’s Implementation of Level of Service of Safety 

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FUNDING/COST 

Typical approximate costs for the development of State-specific knowledge base are comprised 

of*: 

1. Data-prep=$100,000 

2. Development of segment SPF/LOSS/Stratified Diagnostic Norms=$150,000 

3. Development of intersection SPF/LOSS/Stratified Diagnostic Norms=$250,000 

(*These are estimates only and will vary based on a State’s needs and level of 

resources/capability) 

It is important to note that agencies can calibrate the LOSS boundaries after they estimate the 

SPF model parameters. Developed SPFs can significantly reduce the costs related to LOSS. 

Spatially enabled data (crash and roadway) can vastly improve the efficiency of the integration 

component. Nonspatial data require georeferencing, which can add to the cost.(2) 

TIME FRAME 

Implementing the LOSS approach requires a minimum of 3 years’ crash data. Analysis also 

necessitates crash data by location and any information used to generate SPFs, which can be 

gathered for the selected time period. Time for data analysis varies, depending on required 

depth of study.(6) 

LESSONS LEARNED 

 Use LOSS methodology in combination with some kind of diagnostic technique to 

develop effective safety countermeasures. 

 GIS is an important part of leveraging LOSS information.(2)
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REFERENCES 

1. Federal Highway Administration. Level of Service of Safety and Diagnostic Analysis. HSIP 

Noteworthy Practice Series. Federal Highway Administration, Washington, DC, 2011. 

2. Kononov, J, and B. Allery. Level of Service of Safety: Conceptual Blueprint and Analytical 

Framework. In Transportation Research Record 1840, TRB, National Research Council, 

Washington, DC, 2003, pp 57–66. 

3. Data-Driven Safety Management: Analysis and Visualization of Crash Patterns and Level 

of Service of Safety In Colorado and Montana, PowerPoint presentation, AASHTO GIS 

for Transportation Symposium, 2015. 

4. Herbel, S., L, Laing, and C. McGovern. Highway Safety Improvement Program (HSIP)

Manual, Federal Highway Administration, Washington, DC, 2010. 

5. Kononov, J. Identifying Locations with Potential for Accident Reductions Use of Direct 

Diagnostics and Pattern Recognition Methodologies. In Transportation Research Record 

1784, TRB, National Research Council, Washington, DC, 2003. 

6. Kononov, J., C. Durso, C. Lyon, and B. Allery. Level of Service of Safety Revisited, In 

Print, Transportation Research Board, 2015. 
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EXPLANATION OF TERMS 

AADT – Annual Average Daily Traffic

DOT – Department of Transportation

EA – Environmental Assessment

EIS – Environmental Impact Study

FHWA – Federal Highway Administration

GIS – Geographic Information System

HSIP – Highway Safety Improvement Program

HSM – Highway Safety Manual

LOSS – Level of Service of Safety

SPF – Safety Performance Function
Colorado’s Implementation of Level of Service of Safety 

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AGENCY CONTACT INFORMATION 

Bryan Allery, P.E. and Jake Kononov, Ph. D., P.E. 

DiExSys, LLC 

jakediexsys@aol.com and Bryandiexsys@aol.com 

8608 W. Mountain Lane 

Littleton, CO 80125-9406 

Phone: 303-910-1401

William Johnson 

Colorado Department of Transportation 

4201 E. Arkansas Ave. 

Shumate Bldg. 

Denver, CO 80222 

Phone: (303) 512-4808 

Email: will.johnson@state.co.us 

Evan Kirby, GIS Professional 

Felsburg Holt & Ullevig 

6300 S. Syracuse Way, Suite 600 

Centennial, CO 80111 

Phone: 303-721-1440

Email: evan.kirby@fhueng.com