CMF / CRF Details

CMF ID: 3922

Change the inverse of the ramp spacing from X to Y (1/feet)

Description: Change the inverse of the distance between the gore of one ramp and the gore of the other ramp from X to Y (1/feet)

Prior Condition:  directional freeway segment containing two entrance ramps where the spacing between the merging tips is 1/X feet

Category: Interchange design

Study: NCHRP Report 169: Determining Guidelines for Ramp and Interchange Spacing, Ray et al., 2010

 
Star Quality Rating:3 Stars  [View score details]
Rating Points Total:75
Crash Modification Factor (CMF)
Value:Equation
Adjusted Standard Error:
Unadjusted Standard Error:
Crash Reduction Factor (CRF)
Value:Equation
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:
Maximum Speed Limit:
Speed Unit:
Speed Limit Comment:
Area Type:Not specified
Traffic Volume:
Average Traffic Volume:
Time of Day:All
If countermeasure is intersection-based
Intersection Type:Roadway/roadway (interchange ramp terminal)
Intersection Geometry:
Traffic Control:
Major Road Traffic Volume:Minimum of 3459 to Maximum of 99030 Average Daily Traffic (ADT)
Minor Road Traffic Volume:Minimum of 208 to Maximum of 27570 Average Daily Traffic (ADT)
Average Major Road Volume :42254 Average Daily Traffic (ADT)
Average Minor Road Volume :7564 Average Daily Traffic (ADT)
Development Details
Date Range of Data Used:2005 to 2007
Municipality:
State:WA
Country:U.S.A.
Type of Methodology Used:Regression cross-section
Sample Size (crashes):864 crashes
Other Details
Included in Highway Safety Manual?No
Date Added to Clearinghouse:Jun 04, 2012
Comments:This CMF was obtained from Exhibit 3-36 for the variable S^-1 for total crashes. The analysis is based on one direction of travel. The sample size was computed from Exhibit 3-34 as 28.8 crashes per segment * 30 segments = 864 crashes. The sites are comprised of multiple roadway types, primarily of interstates and freeways but also of routes with lower functional classifications (p. 3-45). Interchange-related is not available so intersection-related was selected. The traffic volumes were obtained from Exhibit 3-31. The minimum minor traffic volume was the lesser of the entrance and exit minimum ADTs. Similarly, the maximum minor traffic volumes was the greater of the entrance and exit maximum ADTs. The average minor traffic volume was computed as the average of the averages.