CMF / CRF Details

CMF ID: 3898

Provide an auxiliary lane between an entrance ramp and exit ramp

Description: Provide an auxiliary lane between an entrance ramp and exit ramp

Prior Condition:  directional freeway segment containing a combination of an entrance ramp and an exit ramp without an auxiliary lane between the entrance ramp and exit ramp

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:105
Crash Modification Factor (CMF)
Adjusted Standard Error:
Unadjusted Standard Error:
Crash Reduction Factor (CRF)
Value:20  (This value indicates a decrease in crashes)
Adjusted Standard Error:
Unadjusted Standard Error:
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 15928 to Maximum of 104079 Average Daily Traffic (ADT)
Minor Road Traffic Volume:Minimum of 84 to Maximum of 31495 Average Daily Traffic (ADT)
Average Major Road Volume :41644 Average Daily Traffic (ADT)
Average Minor Road Volume :5763 Average Daily Traffic (ADT)
Development Details
Date Range of Data Used:2005 to 2007
Type of Methodology Used:Regression cross-section
Sample Size (crashes):5177 crashes
Other Details
Included in Highway Safety Manual?No
Date Added to Clearinghouse:Jun 04, 2012
Comments:This CMF was obtained from Exhibit 3-35 for the variable AuxLn for total crashes: e^(-.2283)=0.8 Note that this analysis was based on one direction of travel. The sample size was computed from Exhibit 3-33 as 33.4 crashes per segment * 155 segments = 5,177 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.