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.

CRASH MODIFICATION FACTORS IN PRACTICE

Quantifying Safety in the Road 

Safety Audit Process

The Quantifying Safety in the Road Safety Audit (RSA) Process guide 

describes and illustrates opportunities to incorporate the latest tools and 

techniques to quantify safety in the RSA process. The target audience 

includes RSA program managers, RSA study teams, and those 

supporting RSA study teams. The purpose of this guide is to help raise 

awareness of opportunities to apply crash modification factors (CMFs) 

in the RSA process. The objectives are to 1) identify opportunities to 

apply CMFs in the various steps of the RSA process, 2) describe the 

process of applying CMFs to quantify safety, and 3) explain potential 

challenges related to the application of CMFs and opportunities 

to overcome those challenges. Readers will better understand the 

purpose of CMFs and how they can be applied in the RSA process.

INTRODUCTION

Historically, it has been very challenging to quantify safety explicitly along 

with other factors such as design, operational, and environmental impacts

during the project development process. Instead, safety has been 

assumed to be inherent in design policies and practices. 

Tools have been available for several years to quantify the operational 

and environmental impacts of design decisions. Recently, similar 

tools have been developed to quantify the safety impacts of design 

decisions, but the tools and resources are relatively new. There is a 

need to raise awareness of the current level of road safety knowledge 

and the tools that are available to quantify safety in the project 

development process. Quantifying safety will help decision-makers 

to better understand the safety impacts of design decisions and 

allow safety impacts to be considered in conjunction with other 

factors in the project development process. It is necessary for 

professionals involved in the project development process to 

understand the importance of quantifying safety and apply 

appropriate methods or seek assistance to do so. 

Crash modification factors (CMFs) are one tool that state and local 

transportation agencies are applying to better understand the 

safety impacts of their decisions. CMFs are a measure of the 

safety effectiveness of a particular treatment or design element. 

When applied correctly, CMFs can be used to estimate the safety 

effectiveness of a given treatment or compare the relative 

safety effectiveness of multiple treatments and determine the 

potential benefit for a benefit-cost analysis. Readers can refer 

to the Introduction to Crash Modification Factors for more 

information on CMFs and how they are applied (1).

CMFs can be applied in the RSA process to quantify the 

potential safety effects of various treatments and justify 

the suggestions of the RSA team to the project owner 

and/or design team. Read more for an overview of CMFs 

in the RSA process or skip to the step-by-step process Federal Highway Administration, Office of Safety, 

1200 New Jersey Avenue SE, Washington, DC 20590
CONTENTS

1 Introduction

2 Overview of CMFs in 

the RSA Process

5 Application of CMFs in 

the RSA Process

11 Case Study

18 Overcoming Potential 

Challenges

20 References

In Idaho, the FHWA Division Office 

is supporting the use of CMFs in the 

RSA process. RSAs conducted for 

State and local agencies have 

included CMFs in the final report to 

identify the potential effectiveness of 

the RSA suggestions.

2

for applying CMFs. Examples are provided to illustrate how CMFs can be applied 

and a case study illustrates how CMFs have been applied in the RSA process. 

Finally, potential challenges are presented along with opportunities to overcome 

common application issues. While several examples and a case study are provided 

to demonstrate the basic application of CMFs, an RSA team could also contact the 

State Highway Safety Engineer or Federal Highway Administration (FHWA) Division 

Office for further guidance and assistance with the application of CMFs and 

interpretation of results.

Overview of CMFs in the RSA Process

RSAs are a valuable tool used to evaluate road safety issues and identify 

opportunities for improvement. The FHWA defines an RSA as a “formal safety 

performance evaluation of an existing or future road or intersection by an 

independent, multidisciplinary team” (2). RSAs can be used on any type of 

facility during any stage of the project development process.

RSAs result in a formal report that identifies existing and/or potential safety 

issues and mitigation opportunities. The suggested improvements can 

range from low-cost maintenance activities to high-cost, long-term 

projects that involve considerable planning and design work. It is 

emphasized that the opportunities for improvement are “suggestions” by 

the RSA team and require further consideration from the project owner/

design team before implementation.

The RSA process is an eight-step process as shown in Figure 1 and 

outlined in the FHWA Road Safety Audit Guidelines (2). Steps 1 through 4 of 

the RSA process lead up to conducting the RSA, but do not involve 

the quantification of safety. Specifically, Steps 1 through 4 involve the 

selection of a study location and RSA team as well as data sharing 

and gathering through a pre-RSA meeting and field review. Steps 5 

through 8 provide opportunities to quantify and consider the safety 

impacts of the RSA team’s suggestions. Steps 5 through 8 are 

discussed in more detail through the remainder of this section, 

noting how CMFs can be applied in each step. By applying CMFs in 

the RSA process, agencies can quantify the safety impacts and 

better understand the potential effects of the RSA team’s 

suggestions. The application of CMFs will also demonstrate that 

safety was explicitly considered using a quantitative method.

Conduct RSA Analysis and Prepare Report Findings (RSA Step 5)

The RSA team conducts an analysis to identify safety issues based 

on data from the field visit and preliminary review of documents. 

The safety issues may be prioritized by the RSA team based 

on the perceived risk. For each identified safety issue, the RSA 

team generates a list of possible measures to mitigate 

the crash potential and/or severity of a potential crash. 

The RSA team then prepares a summary of the safety

issues and related suggestions for improvement. In the past, 

RSA teams have used qualitative measures such as low, 

medium, and high to define the potential effectiveness and 

prioritize treatments. CMFs can be applied in this step 

to help the RSA team quantify the potential safety 

effectiveness of a given treatment or compare the relative 

safety effectiveness among multiple potential treatments.
Figure 1. FHWA 8-Step RSA Process

3
4

The RSA report should include a listing of the data and information used in conducting the RSA and a summary

of findings and proposed safety measures. It may also include pictures and diagrams that are useful 

to illustrate issues and countermeasures. CMFs can be included in the RSA report as additional 

information for the owner and/or design team to consider during the decision-making process.

Present RSA Findings to Owner/Design Team (RSA Step 6)

During this step of the RSA process, the RSA team presents the preliminary results of the study to the project 

owner and/or design team. The purpose of this meeting is to establish a basis for writing the RSA report 

and to ensure that the report will adequately address issues that are within the scope of the RSA 

process. This is an opportunity for the project owner and/or design team to discuss and clarify any safety 

issues and suggestions with the RSA team. The project owner and/or design team may 

ask questions to seek clarification on the RSA findings or suggest additional/alternative 

mitigation measures. The RSA team can reference the applicable CMFs in this step to justify the 

suggested improvements.

In some cases, the RSA findings may be presented in a public meeting, or the report could be 

made available to the public to help garner support for the findings and the overall RSA process. While 

public opinions can be beneficial on projects with a high degree of public involvement, such as 

pedestrian facilities, it is common for community members to pre-determine the “needed” 

treatment for a given location without fully understanding the potential safety effects. These 

preconceived notions may differ from the suggestions presented by the RSA team. CMFs can 

be highlighted from the RSA report during the presentation to quantify the relative effects of 

various potential countermeasures and support the team’s suggestions. 

Prepare Formal Response (RSA Step 7)

Once the owner and/or design team have reviewed the RSA report, they should prepare a written 

response to its findings. A letter, signed by the project owner, is a valid method of responding to 

the RSA report. The response should identify those suggestions from the RSA report that will be 

implemented and document the reasons why the other actions may not be taken 

or why they may be delayed. In effect, the project owner identifies an improvement plan. 

In some cases, the plan is incremental where some of the near-term and/or low-cost suggestions are 

implemented and monitored to determine if the targeted safety issue was addressed. In 

this way, limited resources are not wasted on more costly improvements that may not be 

necessary if the low-cost measures achieve the desired effect. CMFs, along with treatment cost and 

implementation timeframe, can be used in this step to help the project owner and/or design 

team justify or prioritize actions to be taken.

Incorporate Findings into the Project when Appropriate (RSA Step 8)

After the response to the RSA report is prepared, the project owner and/or design team should work to 

implement the agreed-upon safety measures or create an implementation plan. CMFs can be applied 

during this step to help set priorities or further evaluate the alternatives. 

With respect to the implementation of countermeasures, the main function of CMFs is to help estimate the 

benefits of proposed treatments as part of benefit-cost or cost-effectiveness analyses. Depending 

on which type of economic appraisal is conducted, benefits may be quantified in different forms. 

In a benefit-cost analysis, benefits are measured in terms of monetary values. Specifically, estimated 

crash reductions are converted to monetary values using average crash costs. In a cost-effectiveness 

analysis, benefits are quantified simply as the estimated reduction in crashes. In either case, CMFs 

indicate the potential change in crash frequency associated with proposed treatments.

RSA findings can be incorporated into an agency’s planning process. Once the suggestions have been 

implemented, an important consideration is to evaluate the RSA program and share lessons learned. In 

the near-term, an RSA “after action review” can be scheduled for the RSA team to perform a 

qualitative safety evaluation of the implemented measures. The qualitative review would help to identify 
5

any issues with the implemented suggestions, ensure that road users are responding appropriately, 

and to determine if other measures are needed. In the long-term, it is also important that the implemented 

measures be evaluated quantitatively, or at least tracked so that others may quantify the 

safety effects. This information will allow an agency to show the benefits of RSAs and possibly develop 

new CMFs or refine existing CMFs for future decision-making.

Application of CMFs in the RSA Process

As discussed in the overview, there are several opportunities for applying CMFs in the RSA process, including the 

following: 

• Conduct RSA Analysis and Prepare Report of Findings (RSA Step 5).

• Present RSA Findings to Project Owner/Design Team (RSA Step 6).

• Prepare Formal Response (RSA Step 7).

• Incorporate Findings into the Project when Appropriate (RSA Step 8).

The application and level of analysis varies among these four opportunities, ranging from a cursory review 

of potential treatment effects to a detailed benefit-cost analysis. This section presents the step-by-step process 

for applying CMFs in each of the four opportunities.

Conduct RSA Analysis and Prepare Report of Findings (RSA Step 5) 

CMFs can be used to help reduce the list of potential treatments in the RSA analysis or at least be included in 

the final report to help the project owner in further evaluating the options. The following steps define the process 

of applying CMFs to reduce the list of potential treatments, but the first step would also apply 

to situations where CMFs are simply identified and included in the RSA report. 

CMF Step 1: Identify Applicable CMFs and Standard Errors for Potential Countermeasures

CMFs are first identified for each potential countermeasure developed in Step 5 of the RSA process. As 

discussed in the Introduction to Crash Modification Factors (1), the CMF selection process involves several 

considerations including the availability of related CMFs, the applicability of available CMFs, and the quality of

applicable CMFs. The CMF Clearinghouse (3) contains more than 3,000 CMFs for various design 

and operational features and also provides detailed information for each CMF to help users identify 

applicable scenarios and the related quality of the CMF. The most applicable CMF should be 

listed for each countermeasure along with the standard error (if available) and applicable crash types and 

severities.

CMF Step 2: Apply Screening Techniques and Engineering Judgment to Reduce List

There are several potential screens to reduce the list of countermeasures. In addition to physical, financial, and 

political constraints, the following CMF screens may be applied:

1. Absolute value of the CMF: Countermeasures are eliminated if the associated CMF is greater than a given

threshold. For example, those treatments with a CMF greater than or equal to 1.0 may be eliminated as they 

are likely to result in an increase in crashes.

2. Relative value of the CMF: Countermeasures are eliminated based on the relative values of the associated

CMFs. For example, those treatments with the greatest CMFs (i.e., least effective treatments) are eliminated. 

Note that countermeasures should only be compared if the respective CMFs apply to the same crash 

conditions (i.e., crash type and severity). For example, it would be appropriate to compare multiple 

countermeasures if the associated CMFs are related to angle crashes of all severities. If the 

applicable CMFs are related to different crash types and severities, it is not appropriate to make direct 

comparisons without further analysis (e.g., benefit-cost analysis).

3. Confidence interval: Countermeasures are eliminated based on the absolute or relative confidence 

in the associated CMF. For example, treatments could be eliminated if the confidence interval for the 

associated CMF includes 1.0 as this indicates that the treatment could be ineffective or produce a negative 

effect. The confidence interval is computed as follows:
Note that the 

confidence 

interval can 

only be provided if 

the standard error 

is available.

6

Confidence Interval = CMF ± [Cumulative Probability * Standard Error]

The following table indicates the cumulative probability for common confidence 

intervals.

Confidence Interval Cumulative Probability

99% 2.576

95% 1.980

90% 1.645

This process is highly dependent on engineering judgment, but supported 

by CMFs. While it may be desirable to reduce the list of potential 

countermeasures, it is important not to eliminate treatments prematurely. 

As such, the RSA team may choose not to eliminate potential treatments 

and simply present the project owner with the complete list of suggestions 

and related CMFs. The project owner can then conduct a more formal 

economic appraisal to compare the potential effectiveness of 

countermeasures, incorporating the relative costs. 

CMF Step 3: Present CMFs in RSA Report

The RSA report documents the findings and suggestions of the RSA 

team. A typical report includes a detailed explanation of each safety 

issue identified by the RSA team and the related suggestions to 

address or mitigate the issues. The following provides an example 

template for presenting the most applicable CMF information with the 

detailed RSA results.

Identified Safety Issue Suggested Improvements

Lack of exclusive turn lanes.

There are no existing turn lanes along Main Street 

at First Street, which requires all turning movements 

to be made from the through lanes. There are heavy 

turning movements at this intersection during the AM 

and PM peak periods and the RSA team observed 

several potential conflicts between turning vehicles 

and through vehicles.

Consider installation of exclusive left-turn lanes.

• CMF: 0.53

• Standard error: 0.04

• Confidence interval: 0.45 – 0.61

• Applicable crash types: All

• Applicable crash severities: All

• Source: CMF Clearinghouse

• Reference: Harwood et al. Safety Effectiveness of 

Intersection Left- and Right-Turn Lanes. Report 

number FHWA-RD-02-089, Federal Highway 

Administration, Washington, DC, 2002.
7

The following is an example from an RSA conducted for the City of Nampa, Idaho. The RSA report included common 

elements such as a description of each issue, suggestions for mitigating the safety issue, and photos/illustrations. The report also identified 

applicable CMFs (when available), noted the relevant crash type/severity, and identified the source of the CMFs. 

2. Flashing Left-Turn Yellow Arrow Signal Indication

A steady red arrow means stop. 

Drivers turning left must stop.

 A steady yellow arrow means the signal is getting ready to turn red. 

Drivers turning left should stop if it is safe to do so.

A flashing yellow arrow means left-turns are permitted. 

Drivers may turn left but must first yield to oncoming traffic

 and pedestrians and then proceed with caution. 

A steady green arrow means left-turns are protected.

Drivers may turn left. Conflicting traffic must stop.

To decrease confusion regarding the meaning of the green ball for permissive left-turns on the existing five-section traffic signal 

head, replace all units with a four-section flashing left-turn yellow arrow (FYA) signal indication. This is the preferred display for 

permitted left-turn indications. See MUTCD Section 4D.04 and 4D.20 among others.

From NCHRP Report 705, Evaluation of Safety Strategies at Signalized Intersections (http://onlinepubs.trb.org/onlinepubs/nchrp/

nchrp_rpt_705.pdf), converting from protected-permissive to FYA: CMF=0.922 (all crashes), 0.806 (left-turn crashes), although these 

were not statistically significant.

The RSA report may also include a summary table of results, indicating the primary safety issues 

identified by the RSA team, perceived risk rating for each issue, and suggestions to address or mitigate the 

potential safety issues. The summary table could also include the most applicable CMFs for the specific 

suggestions as shown in the following example. 

Safety Issue Risk Rating Suggestions CMF Applicability

1

Lack of Left-Turn Lanes: Turning movements are made from the through 

lanes, which creates conflicts between 

turning and through vehicles.

C Consider Installation of 

Left-Turn Lanes. 0.53 Total Crashes

2

Narrow Shoulders: Narrow shoulders 

increase the potential for 

run-off-road crashes.

D Consider Installation of 

Edge Line Rumble Strips. 0.67 Fatal/Injury Crashes

Present RSA Findings to Project Owner/Design Team (RSA Step 6) 

CMFs can be used to justify the RSA team’s suggestions or to show the relative safety effectiveness of various 

countermeasure options. No further work is required for this step of the RSA process as the CMFs identified during 

the RSA analysis are simply presented with the list of suggestions. The most applicable CMF should be listed for 

each countermeasure along with the standard error (if available) and applicable crash types and severities. The 

following provides an example template for presenting CMF information with the RSA results.
8

Identified Safety Issue: 

Severe Horizontal Alignment

Potential 

Treatments Timeframe CMF Standard Error Crash Type Crash Severity

Install Chevrons Near-Term 0.961 0.09 All All

Install Advance 

Curve Warning 

Signs

Near-Term 0.902 Not Reported All Fatal/Injury

Flatten Curve Long-Term 0.333 0.32 All All

1 Srinivasan, R., Baek, J., Carter, D., Persaud, B., Lyon, C., Eccles, K., Gross, F., Lefler, N., “Safety Evaluation of Improved Curve Delineation.” 

Report No. FHWA-HRT-09-045, Federal Highway Administration, Washington, D.C., (2009).

2 Montella, A., “Safety Reviews of Existing Roads: A Quantitative Safety Assessment Methodology.” Vol. TRB#05-1295, Washington, D.C., 2005 

TRB 84th Annual Meeting: Compendium of Papers CD-ROM, (2005)

3 Pitale, J.T., Shankwitz, C., Preston, H., and Barry, M.”Benefit-Cost Analysis of In-Vehicle Technologies and Infrastructure Modifications as a 

Means to Prevent Crashes Along Curves and Shoulders.” Minnesota Department of Transportation, (2009).

Prepare Formal Response (RSA Step 7)

Agencies may not have the necessary funds or staff available to implement all suggestions from the RSA 

report; however, the project owner is expected to consider each of the suggestions. If the project owner does 

not intend to implement one or more suggestions, they are expected to document the reasons. CMFs can be 

used to justify the project owner’s intended course of action. Specifically, the project owner may choose not to 

implement treatments that are relatively ineffective with respect to safety. This process is similar to the three-step 

process discussed previously under Conduct RSA Analysis and Prepare Report of Findings (RSA Step 5). 

Incorporate Findings into the Project when Appropriate (RSA Step 8)

Project owners may be able to implement near-term and low-cost suggestions using internal staff, such as 

maintenance personnel. For more costly improvements, it may be necessary to conduct a formal economic 

appraisal to prioritize treatments, particularly if the project is competing for other safety funds or 

transportation funds in general. An economic appraisal may be based on a benefit-cost or costeffectiveness analysis. The following steps outline the two approaches, which incorporate CMFs to estimate 

project benefits. The process would be repeated for each potential countermeasure identified in the RSA report.

CMF Step 1: Estimate Cost of Treatment

The treatment cost includes the installation costs and annual maintenance costs (e.g., repainting, 

replacing parts, and repairing hits). The expected service life should also be identified. 

CMF Step 2: Estimate Annual Crashes WITHOUT Treatment

The annual crashes without treatment have to be estimated before applying CMFs. The Highway Safety 

Manual (HSM) presents several methods for estimating the future safety performance of a roadway or 

intersection (4). The most simplistic method to estimate crashes without treatment is to compute the long-term 

average (i.e., 5+ years) based on observed crash frequency before treatment. In this method, it is 

assumed that the observed crash history before treatment will represent the future safety performance in 

the absence of any changes. Safety performance functions (SPFs) are another method to estimate crashes 

without treatment. SPFs provide an estimate of the predicted annual crashes for the site of interest 

based on the crash history of other similar sites. The Empirical Bayes method, described in the HSM, is a 

rigorous method for estimating the expected crashes without treatment as it combines the observed 

crash history from the site of interest with predicted crashes from a SPF. Drawbacks and opportunities 
9

Observed crashes 

are based on 

reported crashes 

for the site of 

interest. 

Predicted crashes 

are based on 

estimates from a 

safety performance 

function. 

Expected crashes are 

based on the Empirical 

Bayes method, which 

combines the observed 

and predicted crashes.

The annual crashes 

without treatment should 

be estimated for each 

year over the service life 

and also correspond with 

the specific crash type and 

severity for which the CMF 

is applicable. If the CMF 

applies to total crashes, then 

Step 2 should estimate the 

total annual crashes without 

treatment. If the CMF applies 

to a specific crash type or 

severity, the annual crashes 

should be computed for that 

crash type or severity.

to overcome potential challenges related to these methods are discussed 

in Estimating Annual Crashes without Treatment in the Overcoming Potential 

Challenges section.

CMF Step 3: Estimate Annual Crashes WITH Treatment

The CMF is multiplied by the estimated annual crashes without treatment 

from Step 2 to estimate the annual crashes with treatment for each year of the 

service life.

CMF Step 4: Estimate Annual Reduction in Crashes

The estimated annual reduction in crashes is computed as the estimated 

annual crashes without treatment minus the estimated annual crashes with

treatment for each year of the service life.

At this point, there is enough information to conduct a cost-effectiveness 

analysis. The cost-effectiveness is simply the treatment cost divided 

by the estimated reduction in crashes. The result is a cost per crash 

reduced. For a benefit-cost analysis, it is necessary to complete one more 

step (CMF Step 5).

CMF Step 5: Convert Estimated Annual Crash Reduction to Monetary Benefit

The estimated annual crash reduction is converted to a monetary benefit 

by multiplying the estimated annual crash reduction by the appropriate 

average crash cost for each year of the service life. Many agencies have 

developed or adopted their own crash costs, but national estimates 

are also available such as those provided by FHWA. The following table 

shows the comprehensive crash costs, in 2001 dollars, by severity level 

from the HSM (4), which are based on the cost from the FHWA report, 

Crash Cost Estimates by Maximum Police-Reported Injury Severity within 

Selected Crash Geometries (5). These costs should be adjusted by 

the gross domestic product (GDP) to better reflect the actual costs 

associated with the analysis period. The FHWA crash cost report also 

provides crash costs disaggregated by crash type, severity, and 

posted speed (5).

Crash Severity Estimated Cost

Fatal (K) $4,008,900

Incapacitating Injury (A) $216,000

Non-Incapacitating Injury (B) $79,000

Possible Injury (C) $44,900

Property Damage Only (O) $7,400

It is necessary to adjust the annual monetary benefits to a 

present dollar value. This can be accomplished by multiplying 

the computed monetary benefit in a given year by its present 

value factor. The present value factor is computed from the 

following equation.

Present Value Factor = ----------------------------------------------------------

1

(1 + Discount Rate) Year of Service Life
10

It should be noted that the discount rate is dependent on the service life and may change over time. 

Discount rates typically range between three and seven percent. The current discount rate can be 

obtained from the Office of Management and Budget (http://www.whitehouse.gov/omb/circulars

_a094/a94_appx-c) or agencies may have a standard discount rate.

At this point, the estimated annual benefit (i.e., cost savings) can be summed and divided by the treatment cost 

to estimate the benefit-cost ratio.

Example: An RSA was conducted at a midblock pedestrian crossing on an urban, four-lane, divided arterial with a posted speed of 

45 mi/h. The purpose of the RSA was to identify potential safety issues and to develop suggestions to address the specific concerns. The 

following is a benefit-cost analysis for one of the RSA team’s suggestions, a pedestrian hybrid beacon. A CMF for fatal and injury 

(FI) crashes was obtained from the CMF Clearinghouse based on a study by Fitzpatrick and Park (6). The CMF was developed from 

intersections in Arizona with a suburban or urban area type and it is assumed that the CMF is applicable to the location of interest. 

The treatment cost was estimated from another study, assuming a $100,000 installation cost, 10-year service life, and negligible annual 

maintenance costs (7). A five percent discount rate is also assumed for the computations. The mean comprehensive crash cost for FI 

crashes is assumed to be $158,177 (5).

The following table presents the estimated crashes for each year of the service life. These values were estimated using the procedures 

outlined in the HSM. The CMF is applied to each of the estimated annual crashes without treatment to estimate the annual crashes with 

treatment. The annual crash reduction is estimated as the difference between the estimated annual crashes without and with treatment, 

and the mean comprehensive crash cost ($158,177) is applied to the reduction to estimate the annual monetary benefit. Present value 

factors are then computed and applied to estimate the annual benefit in terms of present dollars. 

The present monetary benefit is estimated to be $236,427 while the monetary cost is estimated to be $100,000. Thus, 

the BCR is 2.36 indicating a favorable result of the proposed treatment.

Year

Estimated 

FI Crashes 

Without 

Treatment

CMF

Estimated 

FI Crashes 

With 

Treatment

Estimated 

Reduction 

in FI 

Crashes

Estimated 

Monetary 

Benefit

Present 

Value 

Factor

Estimated 

Present 

Benefit

1 0.96 0.849 0.82 0.14 $22,929 0.95 $21,837

2 1.00 0.849 0.85 0.15 $23,885 0.91 $21,664

3 1.05 0.849 0.89 0.16 $25,079 0.86 $21,664

4 1.12 0.849 0.95 0.17 $26,751 0.82 $22,008

5 1.20 0.849 1.02 0.18 $28,662 0.78 $22,457

6 1.30 0.849 1.10 0.20 $31,050 0.75 $23,170

7 1.41 0.849 1.20 0.21 $33,677 0.71 $23,934

8 1.55 0.849 1.32 0.23 $37,021 0.68 $25,057

9 1.72 0.849 1.46 0.26 $41,082 0.64 $26,482

10 1.92 0.849 1.63 0.29 $45,859 0.61 $28,153

Total 13.21 11.23 2.00 $315,995 $236,427
Case Study

CMFs can be applied in the RSA process to quantify the safety effects 

of various treatments and justify the RSA team suggestions to the project 

owner and/or design team. The following case study illustrates how CMFs have 

been applied in the RSA process. It also identifies noteworthy practices 

and actual challenges encountered by agencies with respect to this process. 

Project Description

The Michigan Department of Transportation (MDOT) conducted an Operational 

and Preliminary Design Stage RSA along the first horizontal curve on M-26 north 

of the village limits of South Range, in Houghton County. The RSA location is 

circled in Figure 2. This curve was chosen by MDOT on the basis of crash history.

 The objectives of the RSA were to:

• Review road safety at the curve.

• Identify physical and operational issues that may affect road safety.

• Review the proposed plan concept.

• Develop and evaluate potential countermeasures to reduce the 

frequency and severity of collisions.

An aerial image of the site is shown in Figure 3 and site photographs 

are provided in Figure 4. The RSA curve is characterized by the following 

variables. 

• Functional classification: principal arterial.

• Land use: surrounded by homes and small businesses.

• Annual average daily traffic (AADT): 5,003 vehicles per day.

• Area type: rural.

• Number of lanes: two-lane road.

• Posted speed: 45 mph.

• Horizontal curvature:

• Radius: ~637 ft.

• Length: ~609 ft.

• Vertical curvature: located on down-slope of crest curve.

• Existing countermeasures: curve warning signs, chevrons, and 

shoulder rumble strips.

11

Figure 2. Study Location
12

Practical Application of CMFs

The RSA team identified six potential safety issues at the study location 

including the following.

1. Limited curve radius.

2. Inconspicuous signing.

3. Winter weather crashes.

4. Violations of driver expectation.

5. Vertical curve obstructs sight distance.

6. Poor visibility of Academy Road Intersection.

The RSA team also developed several potential countermeasures to address the 

identified issues including the following.

• Increase curve radius.

• Flatten crest vertical curve.

• Upgrade signing.

• Install variable speed limit signs.

The RSA report is generally the final deliverable of an RSA team, including a list 

of potential safety issues and associated countermeasures. It is then 

the responsibility of the project owner/design team to consider the 

RSA team’s suggestions and determine which countermeasures will be 

implemented and the relative timeframe for implementation.

In this case, the RSA team provided additional information in the final report 

to assist the project owner/design team with their subsequent 

decision-making. The additional information included the identification 

and application of CMFs, which resulted in an estimate of 

the potential safety benefits of the identified countermeasures. The 

RSA team also estimated the construction costs for each 

countermeasure and compared these costs to the safety benefits 

in a benefit-cost analysis. The following explains the process 

involved in the identification and application of CMFs in the 

benefit-cost analysis. 

Figure 3. Site Aerial
13

Figure 4. Site Photos

Northbound M-26 approach (south of curve POB)

Northbound M-26 (at curve POB)

Southbound M-26 (at curve POE)

Southbound M-26 approach (north of curve POE)
The Empirical Bayes method 

is an alternative method 

for estimating the annual 

crashes without treatment. 

The Empirical Bayes method 

helps to account for the 

natural fluctuation in crashes 

by combining the observed 

crash history with the predicted 

crashes obtained from a safety 

performance function.

14

CMF Step 1: Identify CMFs

CMFs were obtained from the CMF Clearinghouse. The applicable CMFs are shown 

in Table 1.

Table 1. Applicable CMFs

Countermeasure CMF Applicability

Increase Curve Radius 0.331 All Crashes

Flatten Crest Curve 0.502 All Crashes

Upgrade Signing 0.703 All Crashes

Install Variable Speed Limits 0.544 All Crashes

Source:

1 Pitale, J.T., Shankwitz, C., Preston, H., and Barry, M.”Benefit-Cost Analysis of In-Vehicle Technologies and Infrastructure Modifications as a 

Means to Prevent Crashes Along Curves and Shoulders.” Minnesota Department of Transportation, (2009). 2 Agent, K. R., Stamatiadis, N., and Jones, S., “Development of Accident Reduction Factors.” KTC-96-13, Kentucky Transportation Cabinet, 

(1996). 3 Montella, A. “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). 4 Elvik, R. and Vaa, T., “Handbook of Road Safety Measures.” Oxford, United Kingdom, Elsevier, (2004).

CMF Step 2 – Estimate Crashes WITHOUT Treatment

The crashes without treatment were estimated from historical crash data. 

Specifically, the average annual crashes were computed by severity 

based on five years of observed crash data. The total and average 

observed crashes by severity are shown in Table 2. 

 Table 2. Estimated Crashes without Treatment

Crash Severity Total Crashes

(5 Years)

Estimated 

Crashes 

(Crashes/

Year)

Fatal (K) 1 0.2

Incapacitating Injury (A) 1 0.2

Non-Incapacitating Injury (B) 0 0

Possible Injury (C) 3 0.6

Property Damage Only (O) 6 1.2

CMF Step 3 – Estimate Crash Costs

Crash costs were obtained from the National Safety Council, 

which provides updated average comprehensive costs for motor 

vehicle crashes. The costs are shown in Table 3.

 Table 3. Crash Costs by Severity

Crash Severity Estimated Cost

Fatal (K) $1,300,000

Incapacitating Injury (A) $67,800

Non-Incapacitating Injury (B) $21,900

Possible Injury (C) $12,400

Property Damage Only (O) $8,200

Source: “Estimating the Costs of Unintentional Injuries, 2009” from the 

National Safety Council website www.nsc.org.
15

CMF Step 4 – Compute Value of Safety Benefit 

The value of the annual safety benefit (i.e., crash cost savings) was computed by 

Equation 1.

EAB = (1 - CMF) * (CK * EK + CA * EA + CB * EB + CC * EC + CO * EO) (1)

Where:EAB = estimated annual benefit ($).

CMF = applicable crash modification factor.

Ci = average cost for crash severity (i).

Ei = estimated annual crashes for crash severity (i).

Taking the countermeasure “increase curve radius” as an example, the 

following shows the computations using Equation 1.

EAB = (1 - 0.33) * ($1,300,000 * 0.2 + $67,800 * 0.2 + $21,900 * 0 + $12,400 *

0.6 + $8,200 * 1.2)

EAB = $194,863 

CMF Step 5 – Estimate Countermeasure Costs 

The total construction costs are shown in Table 4. For the purpose of the 

economic evaluation, the net annual operating costs, maintenance costs, 

and salvage values were assumed to be negligible. A discount 

rate of three percent was assumed to compute the annualized cost.

Table 4. Estimated Construction Costs

Countermeasure Service 

Life (Years)

Total 

Cost

Annual

Cost

Increase Curve Radius 15 $650,000 $54,450.50

Flatten Crest Curve 15 $350,000 $29,319.50

Upgrade Signing 3 $10,000 $3,535.30

Install Variable SpeedLimits 7 $250,000 $40,127.50

Source: Cost and service life data were obtained from the RSA report, “M-26 (north 

of South Range) Houghton County Road Safety Audit, Michigan Department of 

Transportation, July, 2011.”

CMF Step 6 – Compute Benefit-Cost Ratio

The benefit-cost ratio is computed as the average annual benefit 

divided by the annual cost. The results of the analysis are 

presented in Table 5.

Table 5. Benefit-Cost Ratios

Countermeasure B/C Ratio

Increase Curve Radius 3.6

Flatten Crest Curve 4.8

Upgrade Signing 24.7

Install Variable Speed Limits 3.3

The computation of 

EAB could have been 

performed in two 

steps by estimating 

the change in crashes 

and then converting 

the change in crashes 

to a monetary value 

using the average crash 

costs. It is necessary to 

apply a two-step process 

if the CMF is different for 

different severities. 
16

Sample Materials

A spreadsheet was developed to assist with the computations presented 

in the case study. This spreadsheet shows the numbers from the case study 

as sample inputs along with the results of the calculations. The user inputs 

crash costs, total crashes, number of years, name of improvements, 

applicable CMFs, service life for each treatment, estimated project cost, 

and recovery factor. The remaining values, including the B/C ratio, are 

calculated automatically using the equations shown in the spreadsheet on the 

following page. 

For more information about the case study, please contact:

Tracie Leix

Michigan Department of Transportation (MDOT)

517-373-8950

LeixT@michigan.gov

or 

Jeff Bagdade

Opus International

248-539-2222

jeffrey.bagdade@opusinternational.com

Summary of Key Findings

The RSA process is typically a qualitative evaluation of the safety 

performance of a given facility. The RSA report is generally the final 

deliverable of an RSA team, including a list of potential safety 

issues and associated countermeasures. It is then the responsibility 

of the project owner/design team to consider the suggestions 

identified by the RSA team and determine which countermeasures 

will be implemented and the relative timeframe for implementation. 

The application of CMFs not only helps an agency to compare 

the relative effectiveness of suggested countermeasures, but it 

also provides information to be used in a benefit-cost analysis. A 

benefit-cost analysis can be used to prioritize suggested 

improvements and may be required when applying for funding.

In this case, the RSA team provided additional information 

in the final report to assist the project owner/design team with 

their subsequent decision-making process. The additional 

information included the identification and application of CMFs, 

which resulted in an estimate of the potential safety benefits 

of the identified countermeasures. The RSA team also estimated 

the construction costs for each countermeasure and compared 

these costs to the safety benefits in a benefit-cost analysis. 
17

A B C D

1 Crash Severity Level Crash Cost Total Crashes Estimated Annual

Crashes

2 Fatal (K) 1,300,000 1 0.2 [=C2/B8]

3 Incapacitating Injury (A) 67,800 1 0.2 [=C3/B8]

4 Non-Incapacitating Injury (B) 21,900 0 0.0 [=C4/B8]

5 Possible Injury (C) 12,400 3 0.6 [=C5/B8]

6 Property Damage Only (O) 8,200 6 1.2 [=C6/B8]

7

8 Number of Years 5

9

10 Improvement CMF Service Life

11 Increase Curve Radius 0.33 15

12 Flatten Crest Vertical Curve 0.50 15

13 Upgrade Signing 0.70 3

14 Variable Speed Limit Signs 0.54 7

15

16 Improvement Estimated Annual Benefit

17 Increase Curve Radius $194,863 [=(1-B11)*(B2*D2+ B3*D3+ B4*D4+ B5*D5+ B6*D6)]

18 Flatten Crest Vertical Curve $145,420 [=(1-B12)*(B2*D2+ B3*D3+ B4*D4+ B5*D5+ B6*D6)]

19 Upgrade Signing $87,252 [=(1-B13)*(B2*D2+ B3*D3+ B4*D4+ B5*D5+ B6*D6)]

20 Variable Speed Limit Signs $133,786 [=(1-B14)*(B2*D2+ B3*D3+ B4*D4+ B5*D5+ B6*D6)]

21

22 Improvement Construction 

Cost

Recovery 

Factor Annualized Cost

23 Increase Curve Radius $650,000 0.08377 $54,451 [=B23*C23]

24 Flatten Crest Vertical Curve $350,000 0.08377 $29,320 [=B24*C24]

25 Upgrade Signing $10,000 0.35353 $3,535 [=B25*C25]

26 Variable Speed Limit Signs $250,000 0.16051 $40,128 [=B26*C26]

27

28 Improvement B/C Ratio

29 Increase Curve Radius 3.6 [=B17/D23]

30 Flatten Crest Vertical Curve 4.8 [=B18/D24]

31 Upgrade Signing 24.7 [=B19/D25]

32 Variable Speed Limit Signs 3.3 [=B20/D26]

33

34 Shaded Cells = User Input
Lance Johnson (FHWA, 

Idaho Division Office) 

noted that CMFs are 

not always available for 

the recommendations 

identified in the RSA 

report. This limitation is 

related to the current 

state of research. 

Jeff Bagdade (Opus 

International, consultant 

to MDOT) indicated that 

CMFs are available for 

approximately two-thirds of 

the suggestions included in 

the RSA report.

Jeff Bagdade (Opus 

International, consultant to 

MDOT) indicated that it is 

necessary to use engineering 

judgment during the selection 

of an appropriate CMF. 

Considerations include the 

general driver population, road 

conditions, and crash reporting 

thresholds.

18

Overcoming Potential Challenges

Potential challenges may arise when applying CMFs in the RSA process. 

Many are directly related to limitations in the progress of CMF research, while 

others apply to the lack of understanding of CMFs. Despite decades of 

advancement in CMF research, there are still knowledge gaps that 

present obstacles for practitioners seeking to apply CMFs in the RSA process. The 

Introduction to Crash Modification Factors (1) provides general guidance 

related to the application of CMFs. The following were identified as 

specific challenges, lessons learned, and opportunities to overcome challenges 

based on discussions with transportation agencies.

Availability of CMFs

A notable potential challenge is the availability of CMFs for specific 

countermeasures. The CMF Clearinghouse (3) contains over 3,000 CMFs 

for a wide range of safety countermeasures under a variety of conditions. 

However, CMFs are still lacking for a large number of treatments, especially 

combination treatments and those that are innovative and experimental in 

nature. Furthermore, CMFs may not be available for certain crash types and 

severities.

As a starting point, the CMF Clearinghouse (3) provides a “Most Wanted List” 

for CMFs. Users can access the website and add to the list by submitting 

ideas for future CMF research or current needs. While the research would 

need to be completed, this link provides users with the opportunity to 

share their CMF needs.

Applicability of CMFs

CMFs are developed based on a sample of sites with specific 

conditions. While a CMF may be available for a given treatment, 

it may not be appropriate for the given scenario. For example, 

there may be significant differences between the characteristics 

of a proposed treatment site and the sites used to develop 

the CMF (e.g., different area type, number of lanes, or traffic 

volume). The CMF Clearinghouse (3) and HSM (4) provide information 

to help users identify the applicability of CMFs.

A related challenge may be that multiple CMFs exist for the 

same treatment and conditions. This is particularly challenging 

when multiple studies have estimated CMFs for the same 

countermeasure and combination of crash type and 

severity level, but yielded dissimilar results. If the CMFs also 

apply to the same roadway characteristics, then the selection 

can become even more difficult. A star quality rating—which 

appraises the overall perceived reliability of a CMF using a 

range of one to five stars—is provided by the CMF 

Clearinghouse and may be helpful in these circumstances 

to identify the most suitable CMF. However, the ratings of 

the different CMFs may be similar as well. If the various 

CMFs have a fairly small range of values, then this situation 

may not be of great concern. Yet, it is possible for the 

CMFs to vary significantly and even indicate contradictory 

outcomes (i.e., some CMFs greater than 1.0 and others less 

than 1.0). In such cases, this potential situation would be 

highly challenging to overcome. Additional guidance on 
19

how to select the most applicable CMF is posted on the CMF Clearinghouse (3)

under FAQs.

Insufficient Expertise

A specific challenge for the RSA team could be that there is insufficient 

expertise within the team to apply CMFs. While CMFs are not a new tool, 

they have only recently gained popularity among safety professionals 

and their use has been mostly limited to applications within the 

roadway safety management process. There are a number of opportunities 

to apply CMFs in other aspects of transportation engineering (e.g., RSA 

process), but it may be necessary to solicit input or assistance from those 

who are more familiar with the selection and application of CMFs. If the RSA 

team does not have the expertise to apply CMFs, then they may decide to 

simply identify and report the applicable CMFs in the RSA report. They can also 

solicit outside expertise from the State Highway Safety Engineer, FHWA Division 

Office, or consultants. The National Highway Institute also offers several 

courses related to the quantification of safety using CMFs, including the 

Application of CMFs (#380093) and Science of CMFs (#380094). 

Scheduling and Coordination

RSAs are typically completed within one week to one month. If the RSA 

team does not have the expertise to apply CMFs and quantify safety 

impacts, then it may be difficult to coordinate with others to provide this support without some planning. To help overcome this potential issue, it may be 

useful to include an experienced CMF user as a member of the RSA team or 

coordinate with an experienced CMF user in advance.

Estimating Annual Crashes without Treatment

To quantify the potential safety impact of a given alternative, it is 

necessary to estimate the annual crashes without treatment. The 

applicable CMFs are then applied to the annual crashes without

treatment to estimate the annual crashes with treatment. The 

annual crashes without treatment can be estimated using several 

methods, with each bringing certain strengths and weaknesses. 

The most basic approach is to use the observed crash history of 

the site of interest (i.e., short-term or long-term average) to 

estimate annual crashes without treatment. This method is relatively 

simple but is highly susceptible to regression-to-the-mean bias 

(i.e., random fluctuation in crashes over time) and could 

overestimate or underestimate the annual crashes without 

treatment. Another option to estimate annual crashes without 

treatment is to employ SPFs, which provide the predicted

number of crashes. SPFs help to account for the random nature of 

crashes at a single site by incorporating data from other 

similar sites. The drawback to using SPFs is that, unless they are 

developed using local data, they may not accurately reflect 

local conditions and again could overestimate or 

underestimate the annual crashes without treatment. The 

HSM (4) presents the Empirical Bayes method as yet 

another option, which combines both the observed crash 

history of a site and the predicted crashes from the SPF to 

compute the expected crashes. 

Michigan DOT 

establishes contracts 

with consultants to 

help conduct RSAs. 

The consultants are 

knowledgeable in

the selection and 

application of CMFs 

and include a detailed 

analysis of the potential 

impacts of suggested 

strategies in the RSA report.
The prior discussion assumes that the crash history is available and applicable 

for a given site. In some cases, the crash history may not be available 

(e.g., new construction); in others, the crash history may not be applicable 

(e.g., significant changes in the alignment). For both scenarios, it may be 

necessary to rely on SPF predictions, but it is suggested that the SPFs be 

calibrated to local conditions before applying them, whenever possible. The 

Introduction to Safety Performance Functions (8) provides general guidance 

related to the selection, calibration, and application of SPFs.

References

1. Introduction to Crash Modification Factors. Federal Highway Administration. 

Available online at: http://safety.fhwa.dot.gov/tools/crf/resources/cmfs/.

2. Federal Highway Administration, FHWA Road Safety Audit Guidelines, 

Publication FHWA-SA-06-06, Washington, DC, 2006. Available online at: http://

safety.fhwa.dot.gov/rsa/guidelines/.

3. Crash Modification Factors (CMF) Clearinghouse. Federal Highway 

Administration. Available online at: www.cmfclearinghouse.org.

4. American Association of State Highway and Transportation Officials 

(AASHTO). Highway Safety Manual, 1st Edition, Washington, DC, 2010.

5. Council, F., Zaloshnja, E., Miller, T., and Persaud, B. Crash Cost 

Estimates by Maximum Police-Reported Injury Severity within 

Selected Crash Geometries. Publication FHWA-HRT-05-051, Federal 

Highway Administration, McLean, VA, 2005. Available online at: 

http://www.fhwa.dot.gov/publications/research/safety/05051/.

6. Fitzpatrick, K. and Park, E.S. Safety Effectiveness of the HAWK 

Pedestrian Crossing Treatment. Publication FHWA-HRT-10-042, Federal 

Highway Administration, Washington, DC, 2010. Available online at: 

http://www.fhwa.dot.gov/publications/research/safety/10042/.

7. Page, J. “HAWKs may soon protect S.L. pedestrians.” Deseret News, 

November 5, 2008. Accessed October 27, 2011, from http://

www.deseretnews.com/article/705260644/HAWKs-may-soonprotect-SL-pedestrians.html.

8. Introduction to Safety Performance Functions. Federal Highway 

Administration. Available online at: http://safety.fhwa.dot.gov/

tools/crf/resources/cmfs/.

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/

FHWA-SA-13-011