Quick Start Guide 

Systemic Safety Analysis

The first step in any problem-solving process is identifying and understanding the problem to solve; systemic 

safety analysis is no different. The Federal Highway Administration’s (FHWA) Systemic Safety Project Selection Tool1

describes the systemic safety analysis process beginning with Identifying Focus Crash Types and Risk Factors. This 

first step lays an important foundation for all subsequent steps in the systemic safety analysis process and involves 

three tasks: 

Systemic Safety Analysis does not require robust data or complex analysis methods to be effective. Nearly all 

transportation professionals have access to the information and data they need to pursue systemic safety 

analysis and make appropriate systemic-based decisions. The first steps of Systemic Safety Analysis primarily use 

fatal and serious injury crash data, to which many agencies have access. 

Below are tips and strategies for using resources your agency already has to perform systemic safety analysis. 

A scenario implementing each task is woven throughout to help illustrate the concepts.

systemic/fhwasa13019/sspst.pdf.

1 Identify Target Crash Types. 2 Identify Focus Facility Types. 3 Identify and Evaluate Risk (Roadway) Factors.

A target crash type represents the greatest number 

(or proportion/percentage) and type of severe 

crashes across the system being analyzed (i.e., 

has the greatest potential to reduce fatalities 

and serious injuries). Local safety data is often an 

agency’s first choice when identifying target crash 

types. Since the Systemic Safety Analysis focuses 

on preventing fatal and serious injury crashes, the 

following additional resources may be also helpful. 

TASK 1 Identify Target Crash Types. SCENARIO: TASK 1

An agency would like to make the biggest safety impact 

possible with the available (but limited) resources. From the 

State’s SHSP, the agency knows that roadway departure 

crashes account for 52 percent of all fatalities within the 

State. The agency decides to use its resources to reduce as 

many roadway departure fatalities as possible.

TARGET CRASH TYPE:

Roadway departure crashes.

Strategic Highway Safety Plan (SHSP): The SHSP promotes emphasis areas for a State or regional safety program.

Emphasis areas are typically identified through a data-driven process.

Fatality Analysis Reporting System (FARS): Agencies can use the National Highway Traffic Safety Administration’s

(NHTSA) Fatality Analysis Reporting System (FARS) database to identify common fatal crash types on a national,

State, or local level.

TASK 2 Identify Focus Facility Types.

The goal of establishing a focus facility type is to break the target crash type (e.g., roadway departure) into

smaller groupings that have similar roadway characteristics. Many agencies narrow focus groups by using crash

data to develop a “crash tree” diagram that breaks down crashes into progressively more detailed categories.

For this process, the level of data analysis can vary based on availability of reliable crash data. An agency 

may only have access to fatal crash data; if so, the staff would follow a process similar to the Task 2 Scenario.

1 Federal Highway Administration. Systemic Safety Project Selection Tool. FHWA-SA-13-019. 2013. Washington, D.C. Accessible at: https://safety.fhwa.dot.gov/
The final step is to identify and evaluate roadway 

factors. Roadway factors represent the roadway 

and traffic characteristics present at locations 

experiencing higher than expected frequencies of 

the target crash type on the focus facility type. 

IDENTIFY ROADWAY FACTORS

Identifying roadway factors can largely be based on 

engineering judgment and experience or documented 

resources. Listed are several sources agencies might use 

to identify common roadway factors associated with 

the focus crash type and focus facility type.

FHWA’s Potential Risk Factors List.2 FHWA provides a 

list of potential risk factors for curves, segments, and 

intersections. The list is classified into three categories: 

Roadway & Intersection Features, Traffic Volume, 

and Other Features.

Highway Safety Manual (HSM).3 Each chapter in 

Parts C and D of the HSM focuses on a facility type 

and organizes Crash Modification Factors (CMF) by 

roadway characteristic (e.g., lane width, shoulder 

width, roadside hazard rating). These roadway 

characteristics can be used as part of a systemic 

safety analysis.

Quick Start Guide

Systemic Safety Analysis

If more reliable crash data are available, an agency may consider 

both fatal and serious injury (F&SI) crashes as well as total crashes. 

During this analysis, the agency would calculate each facility’s 

proportion of F&SI crashes and the proportion of total crash type.

By comparing the facility’s proportion of F&SI crashes to the 

proportion of total crashes, the agency can identify overrepresented 

facility types. This step allows the agency to select a facility type that 

is experiencing higher than expected F&SI crashes.

 SCENARIO: TASK 2

The agency does not have reliable total crash data, 

so it uses State roadway departure fatality data 

to identify a focus facility. The crash tree diagram 

below outlines the process, with the blue-shaded 

boxes showing the iterative focus facility type. 

The agency finds that two-lane, undivided, rural 

roadways with speed limits above 55 mph exhibit 

the largest proportion of crashes. The agency further 

compares crashes occurring on horizontal curves 

to those occurring on segments and finds that, per 

centerline mile, a much greater number of crashes 

occur on horizontal curves.

Note: Percentages in parentheses represent the proportion of total 

roadway departure fatalities on the State System (Total: 221 Fatalities).

FOCUS FACILITY TYPE:

Two-lane rural curves with posted speeds 

>55 mph, and with an Average Daily Traffic

(ADT) of 2,000 or greater.

TASK 3 Identify and Evaluate Roadway Factors.

2

 Federal Highway Administration (FHWA). Potential Risk Factors. Washington, D.C. Accessible at: https://safety.fhwa.dot.gov/systemic/pdf/FHWA_SystemicApproach_PotentialRiskFactors.pdf.

3

 American Association of State Highway and Transportation Officials (AASHTO). Highway Safety Manual. 2010.

Proportion of F&SI Crashes

 Number of F&SI Crashes on Facility 

 Number of F&SI Crashes on System =

Proportion of Total Crashes

 Number of Total Crashes on Facility

=

 Number of Total Crashes on System
Field Visits to Several Sites. Visiting several 

locations within the focus facility type 

will help identify common roadway 

characteristics that may be present at 

other locations within the same facility type. 

Transportation Personnel. Talking 

with pavement and maintenance 

staff can identify otherwise unknown 

roadway factors. EMS providers and law 

enforcement may also have an opinion of 

roadway factors that contribute to crashes 

on the focus facility type.

Note: Roadway factors do not need to 

be directly addressable. Most agencies 

select countermeasures that help mitigate

the potential for future crashes rather 

than eliminate them. For example, if a 

horizontal curve has narrow lanes, a small 

radius, and no shoulders or clear zone, 

then an appropriate countermeasure 

may be enhanced roadside delineation. 

Directly addressing a roadway factor (e.g.

widening the road or straightening out a 

curve) is probably not cost effective.

, 

COLLECTING DATA FOR SYSTEMIC 

SAFETY ANALYSIS

Some agencies have very robust data collection 

procedures while others rely on estimates. An 

agency does not necessarily need a robust dataset 

to identify locations that can benefit from a safety 

improvement. Below are several methods agencies 

use to collect data for roadway factor evaluation.

Roadway and intersection inventories can provide 

most of the data needed to identify roadway factors 

and prioritize locations based on the number and 

severity of roadway factors present. 

Online aerial imagery (e.g., Google Earth, Bing maps)

allows practitioners to view many roadway data 

attributes from their desk and estimate the number 

of roadway factors present at a given location. For 

example:

` Lane width and shoulder width can be estimated

using Google Earth’s Ruler tool.

` Clear zone width and presence of obstacles can

be detected using the Street View feature.

` Side slope can be estimated using a combination

of Google Earth’s Ruler tool and Elevation tool.

Similar to Google Earth, photo logs captured and 

retained by many agencies can be used to estimate 

many roadway data attributes including lane width, 

shoulder width, segment length, roadside hazard 

rating, and curve density.

Crash data can indicate areas where fatality and 

serious injury crashes continue to occur. An agency 

can investigate these locations and identify roadway 

factors present. The agency uses these roadway 

factors to identify other locations with similar 

characteristics, indicating a similar potential for future 

fatality and serious injury crashes.

Quick Start Guide

Systemic Safety Analysis

 SCENARIO: TASK 3

The agency does not have access to a roadway inventory system, nor 

the staff available to collect data for every location in the facility type 

category. As such, the agency selected roadway factors the staff could 

identify using Google Earth. It also selected roadway factors it believed it 

could address. 

Once agency staff had assembled the list of roadway factors, they used 

the HSM and the CMF Clearinghouse to develop threshold selection 

criteria for each. Each selection criteria is predicted by these resources to 

increase crashes by 10 percent or more over the ideal base condition. 

Roadway Factors Baseline Selection Criteria

Lane width 12 ft 10 ft or less

Shoulder width 6 ft 4 ft or less

Roadside hazard rating Rating of 3 Rating of 1 or 1.5

Side-slope 1V:7H 1V:4H slope or greater

Advisory speed 55 mph Less than 35 mph

The agency found that:

` 100 percent of curves had three or more roadway factors.

` 54 percent of curves had four or more roadway factors.

` 7 percent of curves had five roadway factors.

Next, the agency followed the remaining steps outlined in the Systemic 

Safety Project Selection Tool, prioritized candidate locations based on 

number of roadway factors and potential for improvement, and selected 

countermeasures.
Jerry Roche

FHWA Office of Safety

515.233.7323

Jerry.Roche@dot.gov

John McFadden

FHWA Resource Center

410.962.0982

John.McFadden@dot.gov

Every Day Counts (EDC), a State-based initiative of FHWA’s Center for Accelerating 

Innovation, works with State, local and private sector partners to encourage the adoption 

of proven technologies and innovations aimed at shortening and enhancing project delivery.

www.fhwa.dot.gov/everydaycounts

For additional 

information, 

please contact:

DEVELOPING THRESHOLD SELECTION CRITERIA

For each roadway factor, practitioners can select 

a threshold value at which the factor contributes to 

significantly higher than expected frequencies of 

the target crash type. Thresholds can be selected in 

several different ways.

HSM and CMF Clearinghouse. Practitioners can use 

the HSM and the CMF Clearinghouse4 to estimate the 

degree to which each roadway factor contributes to 

increases in target crash frequencies within the facility 

type. For example, the base condition for lane width 

in the HSM is 12 ft. Incremental decreases in lane 

width below 12 ft. causes incremental increases in 

predicted crashes. An agency can either:

1. Use the CMF values in the HSM and CMF

Clearinghouse to individually predict the

increased number of crashes over the base

condition for each site. Sites are prioritized based

on predicted number of crashes.

2. Set a threshold value (e.g., lane widths of 10 ft. or

less) for which every site that meets or exceeds

this threshold is flagged. Sites are prioritized

based on those exhibiting the greatest number of

flagged roadway factors.

Qualitative Assessment. Based on experience and 

engineering judgment, an agency may choose to 

quantify levels of roadway factors as Low, Medium, 

or High, especially where exact data may be missing. 

Using the same example, a lane having a width of 11 ft. 

to 11.5 ft. may be classified as Low, 10.5 ft. to 11 ft. as 

Medium, and below 10 ft. as having High potential for 

future crashes.

Crash Data. An agency can use crash data to 

determine the threshold values for roadway factors. 

For example, an agency may compare fatality and 

serious injury crashes on roads with 9.5 ft., 10 ft., 10.5 

ft., and 11 ft. lane widths and find that a significant 

decrease in safety occurs on roads with lane widths 

of 10 ft. or less. The agency would then use lane 

widths of 10 ft. or less as the threshold value for their 

lane width roadway factor.

NEXT STEPS...

Once a focus crash type, a facility type, and 

roadway factors are identified, the next steps are to: 

` Screen and prioritize candidate locations.

` Select countermeasures.

` Prioritize projects.

Detailed guidance on each of these steps is provided 

in FHWA’s Systemic Safety Project Selection Tool.

5

 For 

more information on training and technical assistance 

on the systemic approach to safety, visit https://

safety.fhwa.dot.gov/systemic/. 

Quick Start Guide

Systemic Safety Analysis

4

 Federal Highway Administration (FHWA). CMF Clearinghouse User Guide. Washington, D.C. Accessible at: http://www.cmfclearinghouse.org/userguide.cfm.

5

 Federal Highway Administration (FHWA). Systemic Safety Project Selection Tool. FHWA-SA-13-019. 2013. Washington, D.C. Accessible at: https://safety.fhwa.dot.gov/systemic/fhwasa13019/sspst.pdf.

FHWA -SA-17-009

Jerry Roche

FHWA Office of Safety

515.233.7323

Jerry.Roche@dot.gov

John McFadden

FHWA Resource Center

410.962.0982

Jerry.Roche@dot.gov