CRASH MODIFICATION FACTORS IN PRACTICE

Real-world Application of Crash 

Modification Factors

“The CMFs in Practice series is an excellent tool to show how 

crash modification factors help rationalize risk and build better 

projects. The series addresses important situations such as design 

exceptions, which are essential for allowing flexibility in design.”

- John E. Wright, P.E., Director, Highway Design and Technical Support

Indiana Department of Transportation

Nationwide, transportation professionals are using Crash Modification Factors 

(CMFs) to estimate how the design of a roadway element or implementation 

of a countermeasure can affect crashes. In the new Federal Highway 

Administration’s CMFs in Practice series, road safety experts explore the many 

ways in which CMFs are being used, and demonstrate the value of this 

information in making educated decisions in the project development process.

Five separate guides document the use of CMFs in the following activities:

• Roadway Safety Management

• Road Safety Audits

• Development and Analysis of Alternatives 

• Design Decisions and Exceptions

• Value Engineering

Each guide in the series includes a step-by-step demonstration of 

how CMFs can be applied in a specific activity, a case study to show 

real-world application of CMFs, discussion of potential challenges in 

applying CMFs, and opportunities to overcome those challenges.

Roadway Safety Management

When used in the roadway safety management process, CMFs can 

help teams select countermeasures and prioritize projects through 

an economic evaluation. A case study follows the Strategically 

Targeted Affordable Roadway Solutions program in Virginia, aimed 

at improving critical safety and congestion hot spots throughout 

the state. Study teams identify potential safety and operational 

issues, along with a list of potential countermeasures. CMFs are 

then applied to help justify and prioritize suggestions. Results 

are used by decision-makers to identify cost-effective strategies, 

eventually leading to more safety-focused projects.

Road Safety Audits

CMFs can be applied in the Road Safety Audit (RSA) process to 

quantify the safety effects of treatments and justify RSA team’s 

suggestions to the project owner. A case study shows how CMFs 

were applied by the Michigan Department of Transportation in 

a RSA. In their report, the RSA team provided CMFs for several of 

their suggested countermeasures, an estimate of the annual 

crash reduction based on the CMFs, an estimate of the costs 

for each countermeasure, and a benefit-cost analysis. Results 

of the analysis can be used when applying for funding.

Crash modification factors 

(CMFs) support a number 

of safety-related activities 

in the project development 

process. The CMFs in 

Practice series includes 

five separate guides that 

identify opportunities to 

consider and quantify safety 

in specific activities, including 

roadway safety management 

processes, road safety audits, 

design decisions and 

exceptions, development and 

analysis of alternatives, and 

value engineering. The purpose 

of the CMFs in Practice series is 

to illustrate the value of CMFs in 

these five activities and 

demonstrate practical 

application of CMFs.

Federal Highway Administration, Office of Safety, 

1200 New Jersey Avenue SE, Washington, DC 20590
For More Information: 

For more information about CMFs 

or the CMFs in Practice series, 

contact Karen Scurry, FHWA Office 

of Safety, karen.scurry@dot.gov, 

609-637-4207.

Visit us on the web at: 

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

tools/crf/resources/cmfs/

Design Decisions and Exceptions

CMFs can be applied to quantify the safety impacts of individual design elements 

and evaluate the overall impact of design exceptions on the safety performance 

of a facility. One case study illustrates how CMFs were applied by the California 

Department of Transportation to estimate the safety impacts of proposed 

engineering improvements after 24 collisions occurred over a three-year 

period on a section of US 199. While some of the proposed changes do not meet 

California design standard, the use of CMFs demonstrated that a substantial 

reduction in crashes could be achieved compared to the existing conditions. 

Another case study illustrates how CMFs were applied in conjunction with safety 

performance functions (SPFs) by the Missouri Department of Transportation to 

quantify the safety performance of various design elements. SPFs were used to 

predict crashes for baseline conditions and CMFs were applied to adjust the 

baseline predicted crashes to reflect the conditions of interest. Results were used 

to select values for design elements that enhance safety.

Development and Analysis of Alternatives

CMFs can be applied in the analysis of alternatives to quantify the safety 

performance of alternative designs. In the first case study, to accommodate 

growing development in the Castle Rock, Colorado, area, the Colorado 

Department of Transportation considered two intersection designs as part 

of a new interchange on I-5. CMFs were employed to estimate the longterm safety performance of the two alternatives. The estimated safety 

performance of each alternative was compared with the operational 

performance, project costs, environmental impacts and other factors to 

identify a balanced design and the most desirable alternative. Another 

case study illustrates how CMFs were used in conjunction with SPFs by the 

Arizona Department of Transportation in the development and analysis of 

alternatives. SPFs were used to predict crashes for base conditions and 

CMFs were applied to adjust the baseline predicted crashes to reflect 

the conditions of interest. The results were used to identify an optimal 

shoulder width for the corridor based on cost-effectiveness.

Value Engineering

CMFs can be applied in the Value Engineering process to explicitly 

consider and quantify safety impacts of opportunities identified by 

the study team. A case study illustrates how CMFs were applied in 

conjunction with SPFs by the Missouri Department of Transportation 

to quantify the safety impacts of opportunities related to the crosssection and roadside design. SPFs were used to predict crashes for 

baseline conditions and CMFs were applied to estimate crashes 

for the opportunities of interest. The results were used to compare 

the safety performance of the original design with alternatives that 

incorporated the value engineering team’s suggestions.

“The application of CMFs is an effective follow-up 

measure for prioritizing safety improvement 

projects for roadways that have been identified as areas 

with a high crash reduction potential by safety 

performance function models. With limited 

resources available to fund these projects, these tools 

are necessary to establish transparency 

and accountability.”

- David Swenka, P.E., Traffic Engineer

Colorado Department of Transportation

FHWA-SA-13-017