CMF / CRF Details

CMF ID: 8733

Install Variable Speed Limits

Description: The VSL system generally displayed information on dynamic speed limits, lane closures, merge arrows and other warning information through the overhead gantries. Speed adjustments in the system are automated based on real-time traffic conditions.

Prior Condition: Roadway without variable speed limits

Category: Advanced technology and ITS

Study: Evaluating Safety Effects of Variable Speed Limit System using Empirical Bayesian Before-After Analysis, Pu et al., 2017

Star Quality Rating: 2 Stars   [View score details]
Crash Modification Factor (CMF)
Value: 0.81
Adjusted Standard Error:
Unadjusted Standard Error: 0.24
Crash Reduction Factor (CRF)
Value: 19   (This value indicates a decrease in crashes)
Adjusted Standard Error:
Unadjusted Standard Error: 24
Crash Type: All
Crash Severity:
Roadway Types: Principal Arterial Interstate
Number of Lanes: 8
Road Division Type: Divided by Median
Speed Limit: >40
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 2012
Municipality: Seattle
State: WA
Country: USA
Type of Methodology Used: Before/after using empirical Bayes or full Bayes
Sample Size (crashes): 48 crashes before, 26 crashes after
Sample Size (miles): 7.23 miles before, 7.23 miles after
Sample Size (miles): 43.38 mile-years before, 43.38 mile-years after
Other Details
Included in Highway Safety Manual? No
Date Added to Clearinghouse: Nov-17-2017
Comments: CMF of severe injury crashes, including fatal, evident injury, and serious injury crashes.