| Summary: | Collision warning systems encounter a fundamental trade-off between providing
the driver more time in which to respond and alerting the driver unnecessarily. The
probability that a driver successfully avoids a hazard increases as the driver is provided
more time and distance in which to identify the hazard and execute the most effective
response. However, alerting the driver at earlier, more conservative thresholds
increases the probability that the alerts are unnecessary, either because sensor error has
falsely identified a hazard or because the environment has changed such that a hazard
is no longer a threat. Frequent unnecessary alerts degrade alert effectiveness by
reducing trust in the system. The human-factors issues pertaining to a forward collision
warning system (FCWS) were analyzed using an Integrated Human-Centered Systems
approach, from which two design features were proposed: multi-stage alerting, which
alerts the driver at a conservative early threshold, in addition to a more serious late
threshold; and directional alerting, which provides the driver information regarding the
location of the hazard that prompted the alert activation. Alerting the driver earlier
increases the probability of a successful response by conditioning the driver to respond
more effectively if and when evasive action is necessary. Directional alerting decreases
the amount of time required to identify the hazard, while promoting trust in the system
by informing the driver of the cause of the alert activation. The proposed design
features were incorporated into three FCWS configurations, and an experiment was
conducted in which drivers were equipped with the systems and placed in situations in
which a collision would occur if they did not respond. Drivers who were equipped
with multi-stage and directional alerting were more effective at avoiding hazardous
situations than drivers who were not provided early alerting. Drivers with early
alerting tended to respond earlier and more consistently, which promoted more
successful responses. Subjective feedback indicates that drivers experienced high levels
of acceptance, confidence, and trust in multi-stage and directional alerting.
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