Roadway Safety Data Program

NORTH CAROLINA’S STATE-SPECIFIC CMFs 

ROADWAY SAFETY DATA AND ANALYSIS

CASE STUDY

FHWA-SA-16-107

Federal Highway Administration Office of Safety

Roadway Safety Data Program

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

November 17, 2016
NORTH CAROLINA’S STATE-SPECIFIC CMFS

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Notice

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NORTH CAROLINA’S STATE-SPECIFIC CMFS

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TECHNICAL DOCUMENTATION PAGE

1. Report No.

FHWA-SA-16-107

2. Government Accession 

No.

3. Recipient's Catalog No.

4. Title and Subtitle

Roadway Safety Data and Analysis Case Study: North Carolina’s State-Specific 

CMFs

5. Report Date

Month Year 

6. Performing Organization Code

7.Author(s) 

Sarah Smith and Robert A. Scopatz

8. Performing Organization Report No.

9. Performing Organization Name and Address

Vanasse Hangen Brustlin, Inc (VHB)

8300 Boone Blvd., Suite 700

Vienna, VA 22182-2626 

10. Work Unit No.

11. Contract or Grant No.

DTFH61-10-D-00022

12. Sponsoring Agency Name and Address

Federal Highway Administration Office of Safety 

1200 New Jersey Ave., SE

Washington, DC 20590

13. Type of Report and Period

Draft Report, Month Year – Month 

Year 

14. Sponsoring Agency Code

FHWA

15. Supplementary Notes

The contract manager for this report was Esther Strawder. 

16. Abstract

North Carolina is one of a small number of States that have actively pursued developing their own crash modification 

factor (CMF) “short list” for countermeasures that are deployed throughout the State. The North Carolina Department of 

Transportation (NCDOT) wanted to develop a list of CMFs to use in benefit cost analyses across the State. To develop the 

CMF list, NCDOT reviewed studies found online and later, they reviewed the available CMFs in the CMF Clearinghouse. 

The primary benefit that NCDOT has realized from conducting evaluations of countermeasures that previously had 

subjective CMF values is that the agency does not continue to implement countermeasures that have little to no quantifiable 

crash benefit. This is especially helpful with project selection processes and makes better use of safety dollars. 

17. Key Words: 

crash data, data analysis, crash modification factor 

(CMF), crash reduction factor (CRF), benefit cost

analysis, empirical bayes analysis

18. Distribution Statement

No restrictions.

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this 

page) Unclassified

21. No. of Pages

 15

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed pages authorized
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TABLE OF CONTENTS

INTRODUCTION.........................................................................................................1

OBJECTIVE....................................................................................................................1

AUDIENCE....................................................................................................................1

DEVELOPING STATE-SPECIFIC CMFS...................................................................1

PRACTICES IN PLACE FOR USING THE CMF CLEARINGHOUSE ...................1

EVALUATION OF SPECIFIC CMFS..........................................................................3

Evaluation of “Upgrade Warning Flasher Actuated Vehicles Entering” 

Countermeasure.........................................................................................................3

Evaluation of “Widen or Improve Shoulder” Countermeasure ...........................4

RESULTS........................................................................................................................5

FUNDING ......................................................................................................................5

BENEFITS......................................................................................................................6

BARRIERS AND HOW THEY WERE OVERCOME.................................................6

LESSONS LEARNED....................................................................................................6

NEXT STEPS.................................................................................................................6

REFERENCES................................................................................................................7

CONTACT INFORMATION.......................................................................................7
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List of Figures

Figure 1. Revised CRFs for “Vehicles Entering When Flashing” Scenarios................4

Figure 2. Current subject CRFs for “Widen or Improve Shoulder” ...........................5
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ACRONYMS

AADT Annual average daily traffic

AASHTO American Association of State Highway and Transportation Officials

CMF Crash Modification Factor

CRF Crash Reduction Factor

CRFC Crash Reduction Factor Committee

DOT Department of Transportation

FDE Fundamental Data Elements

FHWA Federal Highway Administration

GIS Geographic information system

GPS Global positioning system

HPMS Highway Performance Monitoring System

HSIP Highway Safety Improvement Program

HSIS Highway Safety Information System

HSM Highway Safety Manual

KML Keyhole Markup Language

LIDAR Light detection and ranging

MIRE Model Inventory of Roadway Elements

MIS Management Information System

NCHRP National Cooperative Highway Research Program

NHS National Highway System

TMS Traffic Monitoring System

XML Extensive Markup Language
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EXECUTIVE SUMMARY

North Carolina is one of a small number of States that have actively pursued developing their 

own crash modification factor (CMF) “short list” for countermeasures that are deployed 

throughout the State. It is important that all safety units across North Carolina use the same 

CMF value for a particular countermeasure in their benefit-cost analyses so that each safety unit 

has a level playing field when competing for safety dollars.

NCDOT wanted to develop a list of CMFs to use in benefit-cost analyses across the State. To 

develop the CMF list, NCDOT first reviewed studies found online. Later, they reviewed the 

available CMFs in the CMF Clearinghouse. The primary benefit that NCDOT has realized from 

conducting evaluations of countermeasures that previously had subjective CMF values is that 

the agency does not continue to implement countermeasures that have little to no quantifiable 

crash benefit. This is especially helpful with project selection processes and makes better use of 

safety dollars. 
NORTH CAROLINA’S STATE-SPECIFIC CMFS

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INTRODUCTION

North Carolina is one of a small number of States that have actively pursued developing their 

own crash modification factor (CMF) “short list” for countermeasures that are deployed 

throughout the State. It is important that all safety units across North Carolina use the same 

CMF value for a particular countermeasure in their benefit-cost analyses so that each safety unit 

has a level playing field when competing for safety dollars.

OBJECTIVE

NCDOT wanted to develop a list of CMFs to use in benefit-cost analyses across the State. To 

develop the CMF list, NCDOT first reviewed studies found online. Later, they reviewed the 

available CMFs in the CMF Clearinghouse. To summarize, update, and validate the information 

for use across the State, NCDOT created the Crash Reduction Factor Committee (CRFC) in 

2002 responsible for monitoring, updating, and evaluating the applicability of CMFs selected for 

the North Carolina Project Development Crash Reduction Factor/CMF list.

AUDIENCE

The audience for this case study includes:

 State Departments of Transportation: Safety Engineering, Design, Planning, Maintenance, 

GIS, and Asset Management Units.

 Local and Regional: City and County Public Works/Engineering/Transportation 

Departments, Metropolitan Planning Organizations, and Regional Planning Commissions.

 Local Technical Assistance Programs.

 University and Research Academia

 Consultants and private industries involved with safety.

DEVELOPING STATE-SPECIFIC CMFS

PRACTICES IN PLACE FOR USING THE CMF CLEARINGHOUSE

In North Carolina, all potential spot safety projects are required to have a benefit-cost analysis 

(B/C) submitted with a project proposal. There are four main components in a B/C calculation:

 Cost of the target crashes prevented

 Service life of the countermeasure
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 Cost of the countermeasure

 Estimated CMF of the countermeasure

In order to level the competition for safety funds between the eight different regions in North 

Carolina, NCDOT developed a list of countermeasures with a standard CMF for use across the 

State. NCDOT staff review and add new countermeasures to the list as necessary and then

redistribute the list to appropriate parties.

NCDOT established the CRFC in 2002. The committee members are a NCDOT safety 

engineer and five regional engineers. The CRFC developed the first list of 28 recommended

CMFs in their first year. Most of the CMF values came from research reports found online. The 

CRFC repeated this process approximately every six months to identify new CMFs to add to 

the list. The CRFC formally revised the list in 2007, and committee responsibilities increased as 

the list continued to grow. When the CMF Clearinghouse debuted in 2009, the CRFC

downloaded and reviewed the CMFs of countermeasures that are used in North Carolina.

Since 2009, the Committee’s update period has varied from as little as 3 months to as long as 

18 months. The timing depends on the volume of material to be reviewed and the workload of 

the committee members.

It is important to note that NCDOT uses both “CRF” and “CMF” terminology. NCDOT used 

“CRF” terminology when the CRFC was established in 2002; however, the current practice in 

the traffic safety field is for all references to countermeasure effectiveness be expressed as 

CMFs to be consistent with the Highway Safety Manual, which was published in 2010. The main 

difference between CRF and CMF is that CRF provides an estimate of the percentage reduction 

in crashes, while CMF is a multiplicative factor used to compute the expected number of 

crashes after implementing a given improvement. For example, a 0.70 CMF corresponds to a 30 

percent reduction in crashes (CRF of 30) and a 1.2 CMF corresponds to a 20 percent increase 

in crashes (CRF of -20).

Part of the purpose of the CRFC is to determine which CMF for a particular countermeasure 

from the CMF Clearinghouse should be included in the NCDOT list. Generally speaking, when 

there are multiple CMFs for a particular countermeasure, the committee selects the CMF from 

the Clearinghouse with the highest star rating and lowest standard error. There are no 

requirements for minimum star rating. When needed, the committee determines which CMF 

value to use by vote. In situations where a vote is necessary, a member of the CRFC pulls all 

potentially relevant information from the CMF Clearinghouse for reference and context. The 

CRFC divides the workload so that one member may review the information and present

recommendations for which CMFs should or should not be adopted to the full Committee. The 

CRFC then votes on the recommendations from the committee member.
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NCDOT also uses countermeasures that are not yet represented in the CMF Clearinghouse. 

For these, the CRFC has a separate procedure in place for determining what CMF value to use.

In these cases, the CRFC searches online for recent research. If they find a published CMF for 

the countermeasure of interest, they use it. In cases where no information can be found, the 

CRFC uses subjective data (agreed upon by the committee members) until empirical data can 

be gathered. The subjective data comes from experience and opinions of the CRFC members 

as well as small samples of internal NCDOT simple before/after analyses. These values are 

based on NCDOT’s own effectiveness evaluations after a specific treatment has been 

implemented. In many cases, the method does not control for regression to the mean; 

however, the estimated CMF values are considered preliminary and are used only until new 

research provides a more rigorously obtained value.

As of 2016, there are approximately 166 countermeasures in the NCDOT list. About 42 

percent of the CMF values for these come from the CMF Clearinghouse. The rest are either 

based on prior published research or NCDOT’s before/after studies. The full listing is available 

here: North Carolina Project Development Crash Reduction Factor Information.

EVALUATION OF SPECIFIC CMFS

The CRFC recognizes the need to evaluate, when possible, the CMFs selected using subjective 

data to ensure that the CMF chosen is appropriate to use based on empirical data. As an 

example, NCDOT has completed an analysis for the original countermeasure called “Upgrade 

Overhead Warning Flasher – Actuated Vehicles Entering” and they are currently evaluating the 

countermeasure called “Widen or Improve Shoulder”.

Evaluation of “Upgrade Warning Flasher Actuated Vehicles Entering”

Countermeasure

The “Upgrade Warning Flasher Actuated Vehicles Entering” was evaluated by comparing crash 

frequency before and after NCDOT installed “Vehicle Entering When Flashing” systems at over 

70 sites in North Carolina. These systems alert an approaching vehicle to other vehicles 

entering the intersection from other approaches.

NCDOT began implementing this countermeasure in 1999 but there was no known CMF 

available at the time. Based on their own discussions, the CRFC assumed a 25 percent 

reduction in total crashes and set the preliminary, subjective CMF at 0.75. They also began 

collecting simple before/after data on each site where the system was installed in order to 

eventually validate the subjective CMF value chosen.

After many years of using the subjective CMF value and collecting simple before/after data, the 

CRFC conducted a basic benefit-cost analysis of 74 sites to see if the crash pattern changed 
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after implementation of the countermeasure. The empirical data showed the crash pattern was 

not changing and thus a more detailed analysis was warranted. A detailed investigation revealed 

that there were four types of “Vehicles Entering When Flashing” scenarios and each needed to 

be evaluated separately.

After doing a detailed analysis (before/after empirical Bayes) on the four types of scenarios, the 

CRFC found that scenarios one and two had a minimal effect on crash reduction and scenarios

three and four had a larger effect on crash reduction. Therefore, the results of the study 

changed the NCDOT CMF list as noted in Figure 1.

Countermeasure 

Name

Countermeasure 

Scenario

Crash 

Type CRF CMF

Countermeasure 

Name

Countermeasure 

Scenario

Crash 

Type CRF CMF

2.2 Upgrade 

Overhead Warning 

Flasher Actuated 

Vehicles Entering

N/A Total 

Crashes 25% 0.75

2.2 Actuated Vehicle 

Entering When 

Flashing

Overhead signs and 

flashers on major, 

loop on minor (2-lane 

at 2-lane 

intersections)

Total 

Crashes -5% 1.05

Overhead signs and 

flashers on minor, 

loop on major (2-lane 

at 2-lane 

intersections)

Total 

Crashes 5% 0.95

Post mounted signs 

and flashers on 

major, loop on minor 

(2-lane at 2-lane 

intersections)

Total 

Crashes 32% 0.68

Combination of signs 

and flashers on 

major/minor, loop on 

major/minor 

(combination of 

countermeasure 

scenarios above)

Total 

Crashes 25% 0.75

All potential 

countermeasure 

scenarios (4-lane at 

2-lane intersections)

Total 

Crashes

-7% 1.07

October 2010 (value from original CMF list) November 2012 (results from NCDOT study)

Figure 1. Revised CRFs and CMFs for “Vehicles Entering When Flashing” Scenarios

Evaluation of “Widen or Improve Shoulder” Countermeasure

NCDOT recently conducted a similar evaluation for the countermeasure for “Paved Shoulders”

that focused on developing new CMFs for installing one- to two-foot paved shoulders on rural 

two-lane roads. Their original CMF list used the values circled in red in Figure 2 (in terms of 

crash reductions) for rural 2-lane total fatal crashes, total non-fatal injury crashes, and total 

PDO crashes (48-percent, 8-percent, and 23-percent reduction in crashes, respectively). These 

values came from an older national study (FHWA 1982 Highway Safety Evaluation System) that 

was available when the original CMF list was created in 2002. 
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The recent NCDOT study evaluated 35 safety projects where shoulders were paved on both 

sides of the roadway. Again they used the empirical Bayes before/after methodology and found 

that total crashes were reduced by 16 percent (CMF of 0.84) and lane departure crashes were 

reduced by only 7 percent (CMF of 0.93). As a result, the values circled in red in Figure 2 will 

be adjusted to a CMF of 0.93 for lane departure crashes.

Results of the analysis indicate crash reductions are not as great as the older national CMF 

value indicates. These types of projects are very expensive and if NCDOT is not getting the 

expected reduction in crashes for these projects, there is a potential that the projects may not 

rank as high on funding lists compared to other projects that have a better B/C ratio.

Values circled referenced 

from FHWA 1982 Highway 

Safety Evaluation System 

Figure 2. Excerpt from Original CRF List for “Widen or Improve Shoulder”

RESULTS

FUNDING

There are no specific funds set aside to staff the CRFC and maintain the CMF list or conduct 

safety evaluations for validating CMFs. In 1999, NCDOT formed the Safety Evaluation Group 

(SEG) in order to assess whether or not the countermeasures installed by NCDOT are 

working as intended. The CRFC is comprised of regional engineers and are not a part of the 

SEG. The SEG, which is a section within the Traffic Safety Unit of NCDOT, is responsible for 

maintaining the CMF list and validating new CMFs. They also evaluate all safety projects from 

NCDOT’s Spot Safety and Hazard Safety Programs with simple before and after evaluations. 

With these evaluations, they try to answer some simple questions: 

 Did the pattern of crashes change from the before to the after period?; and 
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 Did the countermeasure improve the situation? If not, these evaluations give the field 

engineers a second chance to mitigate the situation or problem.

BENEFITS

The primary benefit that NCDOT has realized from conducting evaluations of countermeasures 

that previously had subjective CMF values is that the agency does not continue to implement 

countermeasures that have little to no quantifiable crash benefit. This is especially helpful with 

project selection processes and makes better use of safety dollars. The goal is to gradually 

eliminate the subjective CMFs by developing estimated crash reductions based on actual data.

BARRIERS AND HOW THEY WERE OVERCOME

Perhaps the biggest barrier for the State to overcome is the selection of the correct CMF to 

use from the CMF Clearinghouse and ensuring that NCDOT staff use the CMF list 

appropriately. Another barrier to overcome is making sure the decisions of the CRFC get 

shared with and are understood by all CMF list users 

LESSONS LEARNED

NCDOT believes it is imperative to have a single CMF list for a State’s project development 

team to use. Prior to having their own list, NCDOT staff could use any CMF value that was 

available. Now the Safety Evaluation Group makes sure that everyone in the Department uses 

the same CMF across the State. This work is especially important now that the CMF 

Clearinghouse is accessible. NCDOT promotes use of selected countermeasures and 

committee-selected CMF values and discourages engineers from simply picking their most 

favored values from what is available in the CMF Clearinghouse. This levels the approach among 

districts and supports uniformity in B/C calculations.

NEXT STEPS

NCDOT and the CRFC and SEG will continue to monitor and update the North Carolina 

Project Development CMF list. They will also continue to study installations of 

countermeasures to ensure the CMF values assigned to these countermeasures are 

appropriate.
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REFERENCES

1) NCDOT. North Carolina Project Development Crash Reduction Factor Information, Revised 

April 1, 2015. Available online at 

https://connect.ncdot.gov/resources/safety/TrafficSafetyResources/NCDOT%20CRF%20

Update%20with%20References.pdf

2) Phone call with Shawn Troy, NCDOT. April 21, 2016

3) AASHTO. Introduction to the Highway Safety Manual. 2010. Accessible at 

http://www.highwaysafetymanual.org/Documents/HSMP-1.pdf. 

4) Federal Highway Administration. About CMFs. Accessible at 

http://www.cmfclearinghouse.org/about.cfm. 

5) Federal Highway Administration. Crash Reduction Factors. Accessible at 

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

CONTACT INFORMATION

Shawn Troy

Safety Evaluation Engineer

North Carolina Department of Transportation

919.814.4958

stroy@ncdot.gov