FHWA-SA-018-41
September 2018

• Introduction
• Crash Reduction Factors
• Using the Tables
• References

Introduction

A CMF is the proportion of crashes that are expected to remain after the countermeasure is implemented. For example, an expected 20 percent reduction in crashes would correspond to a CMF of (1.00 – 0.20) = 0.80. In some cases, the CMF is negative, i.e. the implementation of a countermeasure is expected to lead to a percentage increase in crashes.

One CMF estimate is provided for each countermeasure. Where multiple CMF estimates were available from the literature, selection criteria were used to choose which CMFs to include in the issue brief:

Crash Reduction Factors

A CRF is the percentage crash reduction that might be expected after implementing a given countermeasure. In some cases, the CRF is negative, i.e. the implementation of a countermeasure is expected to lead to a percentage increase in crashes.

One CRF estimate is provided for each countermeasure. Where multiple CRF estimates were available from the literature, selection criteria were used to choose which CRFs to include in the issue brief:

• First, CMFs from studies that took into account regression to the mean and changes in traffic volume were preferred over studies that did not.
• Second, CMFs from studies that provided additional information about the conditions under which the countermeasures was applied (e.g. road type, area type) were preferred over studies that did not.

Where these criteria could not be met, a CMF may still be provided. In these cases, it is recognized that the estimate of the CMF may not be as reliable, but is the best available at this time. The CMFs in this issue brief may be periodically updated as new information becomes available.

The Desktop Reference for Countermeasures includes most of the CMFs included in this issue brief, and adds many other CMFs available in the literature. A few CMFs found in the literature were not included in the Desktop Reference. Those excluded CMFs were considered to have smaller sample sizes or too large a standard error to be meaningful, or the original research did not provide sufficient detail for the CMF to be useful.

A CMF should be regarded as a generic estimate of the effectiveness of a countermeasure. The estimate is a useful guide, but it remains necessary to apply engineering judgment and to consider site-specific environmental, traffic volume, traffic mix, geometric, and operational conditions which will affect the safety impact of a countermeasure. Actual effectiveness will vary from site to site. The user must ensure that a countermeasure applies to the particular conditions being considered. The reader is also encouraged to obtain and review the original source documents for more detailed information, and to search databases such as the National Transportation Library (ntlsearch.bts.gov) for information that becomes available after the publication of this issue brief.

Using the Tables

The CRFs for pedestrian crashes are presented in three tables which summarize the available information. The Tables are:

• Table 1: Signalization Countermeasures
• Table 2: Geometric Countermeasures
• Table 3: Signs, Markings, Operational Countermeasures

Each table has the following columns:

• Countermeasure = the countermeasure name.
• Crash Severity = the crash severity used in the analysis. Where available, separate CMFs are provided for different crash severities. The crash severities are: all, fatal/injury, fatal, or injury. The categories depend on the approach taken by the original study. For example, some studies referred to fatal/injury (fatal and injury crashes combined). Some distinguished fatal from injury. "All" is used for CMFs from studies which did not specify
  the severity.
• CMF for Crash Type (SE) = the CMF value selected from the literature, listed under the column(s) for the appropriate crash type (All, Left-Turn, or Pedestrian). CMFs listed under the Pedestrian column refer to the reduction in crashes involving pedestrians crossing the street, unless otherwise specified. Standard error (SE) for the CMF is provided in parenthesis where available. The standard error is the standard deviation of the error in the estimate of the CMF. The true value of the CMF is unknown for a given treatment type. The standard error provides a measure of the precision of the estimate of the true
  value of the CMF. A relatively small standard error indicates that a CMF is more precisely known. A relatively large standard error indicates that a CMF is less precisely known.
• Reference Number = the reference number for the source information, as given in the reference list in this document.
• CMF ID = ID number of the CMF in the CMF Clearinghouse.
• Star Rating – an indicator of the quality or confidence of the CMF and is based on the following factors: study design, sample size, standard error, potential bias, and data source. The ratings range from 1 to 5 where 5 indicates the highest or most reliable rating.

Cells with "—" indicate that no information is reported in the source document. For additional information, visit the FHWA Office of Safety website (safety.fhwa.dot.gov).

Example

Using the first countermeasure from Table 1 as an example, the following information can be gained from the table:

1. The countermeasure name is "Exclusive Pedestrian Phase."
2. The crash severity is "All," meaning that the original study calculated the CMF for all crash severities combined or did not specify a crash severity.
3. A CMF of 0.49 is listed under the "Pedestrian" column, meaning that a (1.00 - 0.49) = 51% reduction in pedestrian crashes is expected for this countermeasure.
4. The "—" in the "All" and "Left-Turn" columns indicates that CMFs for these crash types were not provided in the original study.
5. The standard error for this CMF is 0.16.
6. The reference number is 2, which refers to the 2012 study by Chen, Chen, Ewing, McKnight, Srinivasan, and Roe in the references list.
7. The CMF ID is 4117 in the CMF Clearinghouse.
8. This study has a 2 star rating.

Other Useful Resources

• www.cmfclearinghouse.org
• www.walkinginfo.org
• www.walkinginfo.org/pedsafe/
• safety.fhwa.dot.gov/provencountermeasures

TABLE 1. SIGNALIZED COUNTERMEASURES

TABLE 2. GEOMETRIC COUNTERMEASURES

TABLE 3. SIGNS, MARKINGS, AND OPERATIONAL COUNTERMEASURES

References

1. Bahar, G., Parkhill, M., Hauer, E., Council, F., Persaud, B., Zegeer, C., Elvik, R., Smiley, A., and Scott, B. "Prepare Parts I and II of a Highway Safety Manual: Knowledge Base for Part II". Unpublished material from NCHRP Project 17-27, (May 2007).
2. Chen, L., C. Chen, R. Ewing, C. McKnight, R. Srinivasan, and M. Roe. Safety Countermeasures and Crash Reduction in New York City--Experience and Lessons Learned. Accident Analysis and Prevention. In print, 2012. Retrieved July 23, 2012.
3. De Brabander, B. and Vereeck, L., "Safety Effects of Roundabouts in Flanders: Signal type, speed limits and vulnerable road users." AAP-1407, Elsevier Science, (2006).
4. Fayish, A.C. and F. Gross, "Safety Effectiveness of Leading Pedestrian Intervals Evaluated by a Before—After Study with Comparison Groups." Transportation Research Record: Journal of the Transportation Research Board, No. 2198, Transportation Research Board of the National Academies, Washington, D.C., 2010, pp. 15-22. DOI: 10.3141/2198-03
5. Feldman, M., J. Manzi, and M. Mitman. "An Empirical Bayesian Evaluation of the Safety Effects of High-Visibility School (Yellow) Crosswalks in San Francisco, California." Transportation Research Record: Journal of the Transportation Research Board, No. 2198, Transportation Research Board, Washington, D.C., 2010, pp. 8-14.
6. Gan, A., Shen, J., and Rodriguez, A., "Update of Florida Crash Reduction Factors and Countermeasures to improve the Development of District Safety Improvement Projects." Florida Department of Transportation, (2005).
7. Harkey, D. et al., "Crash Reduction Factors for Traffic Engineering and ITS Improvements," NCHRP Report No. 617, (2008).
8. Institute of Transportation Engineers, "Toolbox of Countermeasures and Their Potential Effectiveness to Make Intersections Safer." Briefing Sheet 8, ITE, FHWA, (2004).
9. Markowitz, F., Sciortino, S., Fleck, J. L., and Yee, B. M., "Pedestrian Countdown Signals: Experience with an Extensive Pilot Installation." Institute of Transportation Engineers Journal, Vol. January 2006, ITE, (1-1-2006) pp. 43-48. Updated by Memorandum, Olea, R., "Collision changes 2002-2004 and countdown signals," (February 7th, 2006).
10. McMahon, P., Zegeer, C., Duncan, C., Knoblauch, R., Stewart, R., and Khattak, A., "An Analysis of Factors Contributing to ‘Walking Along Roadway’ Crashes: Research Study and Guidelines for Sidewalks and Walkways," FHWA-RD-01-101, (March 2002)

Page last modified on October 16, 2018