Turner-Fairbank Highway Research Center

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Intersection Conflict Warning System Human Factors: Final Report

Product Type

Research Report


Vaughan W Inman and Steven Jackson




Intersection conflict warning systems (ICWSs) are used to warn drivers on the through road of the presence of traffic at stop-controlled cross streets and to warn drivers at stop-controlled approaches of the presence of traffic on the through lanes. ICWSs have been shown to reduce crashes at rural two-way stop-controlled intersections; however, there is no standard wording for ICWS messages and no standard for the placement of these signs on the stop-controlled approaches. This study was performed to provide empirical evidence to support standardization of ICWS messaging and sign placement. Data were obtained from 189 licensed drivers in a 4-part laboratory study. In part 1, participants were shown video animations of approaches with ICWS signs, and comprehension of the signs was assessed. In part 2, participants indicated their level of agreement with 21 statements concerning various aspects of ICWS messages. These ratings were used to assess participants’ mental model of ICWS messaging. Three dimensions of this model were identified. From most influential to least influential, these dimensions were comprehension, safety, and affinity or likeability. In part 3, participants rated the wording of ICWS messaging alternatives. The preferred wording included the words “CROSS TRAFFIC.” On the major road, “CROSS TRAFFIC AHEAD” was preferred. For the stop-controlled minor road, “CROSS TRAFFIC” or “EXPECT CROSS TRAFFIC” options were preferred, depending on whether the “WHEN FLASHING” placard accompanied the sign. Part 4 explored how comprehension varied between when the ICWS beacons were active and inactive, when the “WHEN FLASHING” placard was present or absent, and whether blank-out signs improved comprehension over static signs. A worrisome 28 percent of participants agreed that inactive ICWS beacons meant that it was not necessary to watch for cross traffic. Blank-out signs did not improve comprehension, and blank-out signs were often misinterpreted when blank. The “WHEN FLASHING” placard did not greatly affect comprehension.

Link To Research Report

Intersection Conflict Warning System Human Factors: Final Report


Intersection conflict warning system
sign comprehension
sign placement
driver preferences

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