Crashes at rural thru-stop intersections arise primarily from a driver attempting to cross or enter the mainline
traffic stream after failing to recognize an unsafe gap condition.
Because the primary cause of these crashes is not failure to stop, but failure to recognize an unsafe condition, the
US DOT FHWA, MnDOT, and the University of Minnesota ITS Institute undertook the Cooperative
Intersection Collision Avoidance System – Stop Sign Assist (CICAS-SSA) program. CICAS-SSA uses roadside
radar sensors, a computer processor and algorithms to determine unsafe conditions, and an active LED icon based
sign to provide timely alerts and warnings which are designed to reduce the frequency of crashes at rural
The focus of this report is the alert and warning timing used to provide a driver with assistance in recognizing
and taking appropriate action when presented a gap which could be considered unsafe. The work presented
herein uses both macroscopic data collected by roadside sensors and data acquisition equipment in Minnesota,
Wisconsin, and North Carolina, and microscopic data collected using an instrumented vehicle and test subjects at
the Minnesota Research Intersection, located at the intersection of US Hwy 52 and Goodhue County Road 9.
Three tenets that are particularly germane to the determination of alert and warning timing for the CICAS-SSA
system are: (1) the system does not help a driver choose a safe gap; it is designed to assist a driver with unsafe
gap rejection, (2) it indicates when it is unsafe to proceed, not when it is safe to proceed, and (3) it must
complement good decision making, and address those instances where poor decision making could lead to a
Gorjestani, Alec; Menon, Arvind; Cheng, Pi-Ming; Shankwitz, Craig; Donath, Max.
Determination of the Alert and Warning Timing for the Cooperative Intersection Collision Avoidance System-Stop Sign Assist Using Macroscopic and Microscopic Data: CICAS-SSA Report #1.
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