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FHWA Home / Safety / Intersection / Low-Cost Safety Enhancements for Stop-Controlled and Signalized Intersections

Low-Cost Safety Enhancements for Stop-Controlled and Signalized Intersections

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7. Multiple Countermeasures Applied at the Same Intersection

A number of intersections will have more than one set of crash characteristics that can be impacted by more than one countermeasure. Estimates of the overall effectiveness of the combined countermeasures may be needed. There are a number of methods to estimate the combined effectiveness of multiple countermeasures. A suggested methodology follows.

The overall crash reduction factor (CRFt) at intersections with multiple countermeasures (basic plus supplemental) can be estimated by applying the following formula:

CRFt = 1 – (1- CRF1 )(1- CRF2)(1- CRF3) …

Where,

CRFt = Total CRF
CRF1 = CRF for the first countermeasure
CRF2 = CRF for the second countermeasure
CRF3 = CRF for the third countermeasure

As an example, for a stop-controlled intersection that has the basic sign and markings (CRF-40) and flashing solar powered beacons (CRF-10), the total estimated CRF is 1-(1-.40)(1-.10) = .46

An intersection that has multiple countermeasures in which one countermeasure only impacts a portion of the total crashes requires a slightly more complicated calculation. As an example, if a stop-controlled intersection has basic sign and marking countermeasures (CRF-40) and lighting (CRF-50) and 25 percent of the crashes occur at night, the total estimated CRF for crashes is .75[1- (1-.40)]+.25[1-(1-.40)(1-.50)] = .475

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Page last modified on September 4, 2014.
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