CMF / CRF Details

Install variable speed limit signs

Countermeasure ID: 3340

Description: Install variable speed limit signs

Prior Condition: No variable speed limit sign present

Category: Speed management

Study: Evaluation of Variable Speed Limits on I-270/I-255 in St. Louis, Bham et al., 2010

 
Star Quality Rating:2 Stars  [View score details]
Rating Points Total:45
Crash Modification Factor (CMF)
Value:0.92
Adjusted Standard Error:
Unadjusted Standard Error:
Crash Reduction Factor (CRF)
Value:8  (This value indicates a decrease in crashes)
Adjusted Standard Error:
Unadjusted Standard Error:
Applicability
Crash Type:All
Crash Severity:All
Roadway Types:Principal Arterial Interstate
Street Type:
Minimum Number of Lanes:
Maximum Number of Lanes:
Number of Lanes Direction:
Number of Lanes Comment:
Crash Weather:Not specified
Road Division Type:
Minimum Speed Limit:40
Maximum Speed Limit:60
Speed Unit:mph
Speed Limit Comment:
Area Type:Urban
Traffic Volume:
Average Traffic Volume:
Time of Day:All
If countermeasure is intersection-based
Intersection Type:
Intersection Geometry:
Traffic Control:
Major Road Traffic Volume:
Minor Road Traffic Volume:
Average Major Road Volume :
Average Minor Road Volume :
Development Details
Date Range of Data Used:2007 to 2009
Municipality:St. Louis
State:MO
Country:U.S.A.
Type of Methodology Used:Before/after using empirical Bayes or full Bayes
Sample Size (crashes):1636 crashes after
Other Details
Included in Highway Safety Manual?No
Date Added to Clearinghouse:Jun 04, 2012
Comments:The crash count sum in Table S4 (p. 24) is for the 'after' period. The crash count for the 'before' period is not given. Although the crash count in the after period is substantial, the after period is only 1 year (p. 38); therefore, the crash count may give an inflated impression of the sample size. Traffic volume data is not given in this report. According to Table S2, the total length of the segments is 35.21 mi.

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