STOP SIGN VIOLATION WARNING (SSVW)

9.5 STOP SIGN VIOLATION WARNING (SSVW)

The pilot testing of Pierowicz et al. (2000) indicated that drivers brake at stop-sign-controlled intersections at a mean rate of 0.19 g. They observed that the level of braking required to avoid entering the intersection is diagnostic of whether the driver intends to stop. After testing alert-criteria thresholds between 0.25 and 0.45 g, they determined that the lower values in the range resulted in an excessive number of nuisance alerts and that the higher values in the range resulted in alerts that appeared to be too late. The middle value value of 0.35 g, however, appeared to provide a reasonable balance of early warning and driver acceptance. Pierowicz et al. also observed that there were a large number of nuisance alerts at low speeds and small distances from the intersection. They argued that this was due to the fact that vehicles can stop almost instantaneously at low speeds. In the implementation that they tested, they disabled the warning system at speeds of less than 5 mph.

For the driver vehicle interface, Pierowicz recommended using the combination of a HUD that displays a stop-sign symbol, a pulsed tone of approximately 2000 Hz, and a haptic brake pulse. In their testing, the stop-sign symbol was subjectively rated as being far more effective than the other alternatives. On a five-point scale that indicated the level of meaningfulness, where 5 corresponded to “extremely meaningful”, the stop-sign symbol was rated with a mean of 4.94 and a standard error of 0.06. The SSVW could easily be implemented in the safety warning countermeasures display area, as illustrated in Figure 9.12.

To determine the distance between the host vehicle and the intersection, the system can use a GPS signal in combination with a digital map-matching system. Unfortunately, Pierowicz et al. (2000) discovered that the current digital maps that are available do not provide sufficient accuracy to support this system. In addition, the digital maps did not indicate the type of traffic control system used at each intersection. To remedy this problem, Pierowicz et al. augmented the map datafile for their testing area to provide higher precision and inclusion of the type of traffic control.