LOGO Imperfect in- vehicle collision avoidance warning systems can aid distracted drivers Masha Maltz, David Shinar Transportation Research Part F 10 (2007) 345– 357

Company Logo Introduction  Automated systems designed to aid drivers are increasingly popular among car manufacturers, and exist in a myriad of forms, from the drawing board to instrumented vehicles.  It may introduce two types of problems: (1) failure by the driver to take appropriate action on the rare occasion when the system malfunctions and the driver has relaxed his/her vigilance, and (2) false alarms, when the driver responds to an erroneous signal.

Company Logo  The purpose of this study was to examine the potential pitfalls of two critical aspects of automation: information acquisition and information analysis.  An effective IVCAWS that reliably monitors headway and warns an inattentive driver when his or her vehicle approaches a lead vehicle too closely.

Company Logo Study Goals  In this study, we addressed the issue of driver mental workload.  The addition of a secondary task to the driving environment can be a realistic approximation of driving on the real road where the driver is often distracted by other tasks.

Company Logo Method-participants  Forty-three undergraduate students participated in the experiment as part of an Ergonomics course requirement.  The participants, 20 males and 23 females, ages 22–43 (average age 26) were all licensed drivers with 2–27 years’ experience.

Company Logo  The experiment was conducted on a STISIM DriveTM simulator, a fixed- base driving simulator developed by Systems Technology, Inc.  The simulator continually sent digital output, consisting of temporal headway measurement, to a second computer via coaxial cable. Method-physical setup

Company Logo  A second computer generated the auditory alarms, based on the input from the simulator and on internal calculations of warning system reliability.  The alarms were medium pitch tones emitted by a sound blaster through speakers at a sound level of 84 dBA for the regular alarms and 82 dBA for the graded alarms.

Company Logo  All performed the loading visual task that consisted of responding to changes in two peripheral targets.  The loading task (DA) appeared at random intervals of between 5 and 10 seconds.  The driver’s task was to respond to the arrow by activating the turn signal, signaling ‘left’ for a left or down arrow, and signaling ‘right’ for a right or up arrow.

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Company Logo  If at the time an error was to be generated the headway was too short (less than one second), the system would fail to sound the alarm for a 2 s period. If at the time an error was to be generated the headway was one second or more, the system would sound a false alarm for 1 s.

Company Logo  The three experimental groups had high, medium, and low reliability, with 1, 4, and 8 errors per minute, respectively.

Company Logo  Before the start of the experimental trials, the drivers were told that the visual loading task was of primary importance.  They were also told to maintain 1 s (i.e., safe) headway and to try and reach the destination as quickly as possible, while keeping a safe distance. Experimental procedure

Company Logo  The first lead vehicle appeared once the driver had traveled 100 feet. If the driver approached the lead vehicle to within.5 s, the lead vehicle sped ahead and disappeared.  During the course of the trial, nine additional vehicles entered the driver’s lane in order to ensure that a lead vehicle would always be present.

Company Logo  Participants were told that the IVCAWS system was designed to help them keep the proper headway, but that it was imperfect.  Each participant received two 4.5 mile trials that took about seven minutes to complete, one with a single alarm and one with a graded alarm.  During each trial, 85 visual loading task events occurred at variable intervals.

Company Logo Results an discussion  If TH increased by at least 3% within two seconds from the event, it was recorded as a deceleration response since lead cars were programmed to travel at fixed speeds.  TH was consolidated into five levels for the analysis: 2.0 s.

Company Logo  No significant effect or difference in the headways maintained by drivers in the experimental and the control groups was found (F(4,164) =.25; p =.91).  While the participants actually increased their short headways – from 13.6% in the pretrial segment to 35.2% in the experimental trials – the experimental groups retained the percentage of time in short headways – averaging 11.8% in the pretrial and 10.1% in the experimental trials, respectively.

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Company Logo Loading task  They responded correctly to between 73% and 100% of the events, and missed between 0% and 18% of the events.  They also incorrectly responded to some events, which, apparently, was the result of some directional confusion.  We found that the performance of the loading task remained stable across all groups.

Company Logo  The control group and the experimental groups as a whole both missed an average of 3% of the visual motor task events, and the high, medium, and low system reliability groups missed an average of 3%, 2%, and 4% of the events.

Company Logo Responses to alarms  There were no significant differences among the experimental groups in the percentage of the time that the drivers responded (slowed down in response) to graded alarms (F(2,26) =.52; p <.5983).  With the low system reliability group decelerating the over 80% of the time compared to the other groups who decelerated an average of 50%of the time.

Company Logo  Therefore, they were probably most likely to notice that they were in the danger zone independently of the IVCAWS alarms.  A 2-way ANOVA [system reliability group (3) X alarm state (sounded or not sounded)] was computed on the fraction of the time in the danger zone that the drivers slowed down, with alarm treated as a repeated measure.

Company Logo  Drivers slowed down 28% of the time in response to false alarms compared to 21% of the time when there were no alarms while in the safe zone.

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Company Logo Subjective measures  73 percent of the participants rated the single alarm system as helpful or very helpful and 60% of the participants rated the graded alarm system as helpful or very helpful.  The source of the difference between the system types was the high system reliability group: 90% of the participants in this group found the IVCAWS helpful with a single alarm, but only 50% of them considered the graded alarm helpful.

Company Logo  Post hoc comparison showed a marginally significant difference between the control group and the medium system reliability group.  The control group found the task more difficult than the medium system reliability.

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Company Logo Summary and conclusions  The general findings of this study are consistent with our previous findings that show that IVCAWS can be effective in helping drivers recognize and maintain optimum headways.  We consider that distracted drivers will maintain longer headways with an IVCAWS of this type.

Company Logo  We found that higher system reliability actually had a negative effect on performance. Surprisingly, the IVCAWS appeared to be most effective when it was least reliable.  This finding is consistent with the demonstrated phenomenon of ’complacency’ that automation introduces (Desmond et al., 1998).

Company Logo  The drivers in this study who were given the least reliable system learned from the error-prone system to discern one-second headway more slowly.  The drivers with the high-reliability system, on the other hand, were led astray when the system erred.

Company Logo  Given a demanding loading task, the drivers without an IVCAWS (the control condition) suffered the expected drop in driving performance, as measured by their headways.  The drivers with the IVCAWS maintained their driving performance at a reasonable level.

Company Logo  At higher reliabilities, the IVCAWS led to over reliance and complacency which ultimately led to more mistakes than with the less reliable system.