Quick Start Guide 

to Using CMFs

A Crash Modification Factor (CMF) estimates a safety countermeasure’s ability to reduce crashes and crash 

severity. Transportation professionals frequently use CMF values to identify countermeasures with the greatest safety 

benefit for a particular crash type or location. Practitioners can use the following process to identify a CMF for each 

prospective countermeasure and to inform countermeasure selection. The scenario below illustrates this process. 

Develop a List of Prospective Countermeasures.

Ensure these countermeasures address the types of 

crashes occurring at the identified problem location. 

Identify All Relevant CMFs for Each Prospective 

Countermeasure. 

First, contact your State agency to see if there 

is a State-approved list of CMFs. If not, the CMF 

Clearinghouse1 is an extensive, easily accessible, 

FREE online resource that includes all available CMFs, 

including those from the Highway Safety Manual 

(HSM) and some State-specific CMF lists2. The CMF 

Clearinghouse User Guide3 provides an overview on 

how to navigate the website and use CMFs. 

Develop a list of all CMFs that relate to each 

prospective countermeasure. Note differences in 

effectiveness for different crash and injury types, as 

these factors may be important considerations when 

choosing applicable CMFs. 

Confirm CMF Applicability. 

Prioritize the list of CMFs based on their relevance to 

the project site. The most applicable CMFs are those 

which match the project site characteristics such as 

area type, number of lanes, and traffic volume. This 

may result in a list of several potential CMFs to use for 

each countermeasure.

Select a Single CMF for Each Countermeasure. 

Once you have narrowed the list of potential CMFs 

based on site characteristics, select the CMF with the 

highest star rating. If two studies have the same star 

rating but different CMF values, read each study to 

learn about potential differences in study locations 

or crash type characteristics. For more information 

about CMF star quality ratings, visit: http://www.

cmfclearinghouse.org/sqr.cfm. 

SCENARIO: STEP 1

A rural two-lane horizontal curve is experiencing an average 

of 10 run-off-road (ROR) crashes per year. The curve has 

centerlines but no edge lines. Upon taking a closer look, the 

owner agency found that an average of 4 crashes occur 

during wet conditions while the remaining occur during dry 

conditions. Due to the high proportion of wet crashes, the 

agency is considering applying edge lines, chevrons, or a 

high friction surface treatment (HFST). The agency wants to 

choose the most cost-effective solution.

1 To access the CMF Clearinghouse, visit: http://www.cmfclearinghouse.org/

index.cfm.

2 To find State Specific CMFs on the CMF Clearinghouse, visit: http://www.

cmfclearinghouse.org/stateselectedlist.cfm.

3 Federal Highway Administration, CMF Clearinghouse User Guide. Washington, 

D.C. Accessible at: http://www.cmfclearinghouse.org/userguide.cfm.

4 A.R. Tsyganov, N.M. Warrenchuk, and R. B. Machemehl, “Driver Performance 

and Safety Effects of Edge Lines on Rural Two-Lane Highways,” TRB 88th 

Annual Meeting Compendium of Papers CD-ROM. Washington, D.C., (2009).

5 Federal Highway Administration Safety Evaluation of Improved Curve 

Delineation, FHWA-HRT-09-045, (Washington, D.C.: 2009).

6 A. Montella, “Safety Evaluation of Curve Delineation Improvements An 

Empirical Bayes Observational Before-After Study.” TRB 88th Annual Meeting 

Compendium of Papers CD-ROM. Washington, D.C., (2009).

7 Federal Highway Administration, Evaluation of Pavement Safety Performance, 

FHWA-HRT-14-065 (Washington, DC: February 2015).

STEP 1

STEP 2

STEP 3

STEP 4

SCENARIO: STEP 2

The agency identified all relevant CMFs for each countermeasure. 

The CMFs range in value because each was developed for a 

specific crash and injury type.

CMF Range

Crash Type 

Addressed

Injury Type 

Addressed

Edge Lines4 0.67-0.96 All, ROR, Speed All

Chevrons5, 6 0.41-0.96 All, ROR, Wet All, Fatal & Injury

HFST7 0.13-0.65 All, Wet All, Fatal & Injury
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

Quick Start Guide to Using CMFs

FHWA-SA-17-007

Apply the CMF.

After identifying a single CMF for each 

countermeasure, use the CMF to predict 

the expected number of crashes after 

the countermeasure is implemented. 

To do this using the most simplistic 

method, multiply the CMF value by the 

average yearly number of crashes at 

the project site over the past three to 

five years. The final value represents the 

number of crashes expected to occur 

after the countermeasure has been 

implemented. FHWA’s CMFs in Practice8

series provides more guidance and 

information on how to apply CMFs using 

more advanced methods.

STEP 6 Select Countermeasure. 

Compare the crash reductions 

calculated in Step 5 for all 

countermeasures identified in Step 1. 

Use this comparison to select a 

countermeasure for the location. 

Final Note. It is important to remember 

that a CMF is only an estimated value 

of the crash reduction potential of a 

treatment. Actual crash reductions 

may vary. The standard error for a CMF 

can be used to estimate the range of 

effectiveness one might expect from 

implementing the countermeasure. 

For more information on using CMFs, visit 

the CMF Clearinghouse at http://www.

cmfclearinghouse.org.

 SCENARIO: STEP 3 & 4

Using chevrons as an example, the agency selected the CMFs most like 

their project location. Since the majority of crashes are a combination 

of wet and dry ROR crashes, and nighttime crashes are not a major 

contributor, the agency narrowed its list to two CMFs. The agency made its 

final selection based on the study’s Star Rating, even though this CMF had a 

higher value (indicating lower effectiveness). 

CMF Site Characteristics Crash Type Star Rating

Chevrons

0.78

CMF ID: 2440 Two-lane, rural

Nighttime

ROR 

Chevrons

0.94

CMF ID: 2437 Two-lane, rural ROR 

Chevrons

0.41

CMF ID: 1899 Two lane, all Wet 

The agency performed the same analysis process to choose CMFs for edge 

lines and HFST.

 SCENARIO: STEP 5

The CMFs the agency identified for each countermeasure are applicable 

to all severity levels. To calculate the expected number of crashes after 

implementation, the agency multiplied the CMF values for edge lines and 

chevrons by the total number of ROR crashes. Since the HFST CMF was 

developed for wet crashes, the agency multiplied this CMF value by the 

total number of wet crashes. It then added this value to the remaining dry 

ROR crashes to produce an estimate of the expected number of crashes 

after HFST implementation. 

Countermeasure CMF Crash Type

Total # of Crash Expected 

after Countermeasure 

Implementation

Edge Lines

0.87

CMF ID: 1948 ROR 10 x 0.87 = 9 crashes

Chevrons

0.94

CMF ID: 2437 ROR 10 x 0.94 = 9 crashes

HFST

0.41

CMF ID: 7901 Wet Road

4 x 0.48 = 2 wet crashes

2 wet + 6 dry = 8 crashes

 SCENARIO: STEP 6

If strictly considering crash reductions, the agency may choose HFST, as 

it has the lowest CMF value (highest effectiveness). However, agencies 

frequently compare the initial and life cycle costs associated with the 

treatments before making a final selection. While HFST has the greatest 

safety benefit and is ideal for treating wet crashes, it is significantly more 

expensive than the other two options. In a real-world situation, an agency 

may choose to use an incremental approach, starting with edge lines, then 

8 CMFs in Practice. Federal Highway Administration. applying chevrons. If wet crashes persist, then HFST may be worth the cost.

Washington, D.C. (2014). Accessible at: http://safety.

fhwa.dot.gov/tools/crf/resources/cmfs/.

STEP 5