CMF / CRF Details

Convert a conventional unsignalized intersection to an unsignalized superstreet

Countermeasure ID: 4885

Description: Convert a conventional unsignalized intersection to an unsignalized superstreet (also known as a restricted crossing U-turn intersection or a J-turn intersection)

Prior Condition: conventional unsignalized intersection

Category: Intersection geometry

Study: Superstreet Benefits and Capacities, Hummer et al., 2010

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Star Quality Rating:3 Stars  [View score details]
Rating Points Total:85
Crash Modification Factor (CMF)
Value:0.25
Adjusted Standard Error:
Unadjusted Standard Error:0.08
Crash Reduction Factor (CRF)
Value:75  (This value indicates a decrease in crashes)
Adjusted Standard Error:
Unadjusted Standard Error:8
Applicability
Crash Type:Angle,Right turn
Crash Severity:All
Roadway Types:Principal Arterial Other
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:Divided by Median
Minimum Speed Limit:
Maximum Speed Limit:
Speed Unit:
Speed Limit Comment:
Area Type:Rural
Traffic Volume:
Average Traffic Volume:
Time of Day:All
If countermeasure is intersection-based
Intersection Type:Roadway/roadway (not interchange related)
Intersection Geometry:3-leg,4-leg
Traffic Control:Stop-controlled
Major Road Traffic Volume:Minimum of 5900 to Maximum of 33500 Annual Average Daily Traffic (AADT)
Minor Road Traffic Volume:Minimum of 330 to Maximum of 5000 Annual Average Daily Traffic (AADT)
Average Major Road Volume :
Average Minor Road Volume :
Development Details
Date Range of Data Used:1991 to 2010
Municipality:
State:NC
Country:U.S.A.
Type of Methodology Used:Before/after using comparison group
Other Details
Included in Highway Safety Manual?No
Date Added to Clearinghouse:Jun 04, 2012
Comments:This CMF was obtained from Table 3.13 for “rear ends” crashes from the unsignalized set (p. 83). The years of data were obtained from Table 10.2 (p. 161). The sample size for the treatment group (total) was 156 crashes. According to the executive summary, all the superstreet sites have a rural area type (p. iv). The minimum and maximum major roadway AADTs were obtained from Table 10.4 (p. 163), and the minimum and maximum minor roadway AADTs were obtained from Table 10.5 (p. 164). The number of legs of intersections was obtained from Table 10.3 (p. 162). The after periods of some of the sites were rather short (i.e., < 1 yr). See Table 10.2 (p. 161). The number of crashes in the after period were not reported in this study, however, they have been recorded as 300 to give 10 points as a beneift of doubt for one or more of the following: (1) number of miles/sites in the reference/treatment group, (2) number of crashes in the references/treatment group, (3) reporting AADTs for the aggregate dataset but not for the disaggragate dataset used for CMF development.

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