Triangulación metodológica

3.1 Background

Chapter 2, Study Design Overview, described the procedures and tasks used in the CAMP DWM Project during test track testing at Ford Motor Company’s Michigan Proving Ground in Romeo, Michigan. Details of the materials, equipment, and procedures used are provided in appendices to this report.

This chapter presents the results of the test track work. Included are the task effects on object and event detection, driver eyeglance behavior, and lateral and longitudinal vehicle control. Summary statistics for all measures reported in this chapter are provided in the appendices.

3.2 Test Track Participants

An independent marketing firm recruited 64 licensed drivers from the Detroit metropolitan area for participation in the test track phase of the study. The participants spanned six age ranges: 21 to 29, 30 to 39, 40 to 49, 50 to 59, 60 to 69, and 70 to 79 years old.

The prospective candidates were screened for good health and a good driving record before being admitted into the study. Thirty-three of the participants were female and 31 were male. Table 3-1 presents the distribution of the age and gender of the participants. The participants were paid $400 for their two-day time commitment to the study. Additional details about the sample of subjects and the screening process are provided in the appendices.

Table 3-1. Age and Gender of Test Track Participants

20's 30's 40's 50's 60's 70's All

Male 6 4 5 6 5 5 31

Female 5 7 7 5 6 3 33

All 11 11 12 11 11 8 64

Age Category

3.3 Test Track Task Effects on Object-and-Event Detection

As part of test-track and on-road driving, the participants were presented with three types of object-and-event detection (OED) roadway events.

The first type of OED stimulus was the Center High-Mounted Stoplight event. The CHMSL of the lead vehicle would illuminate for a duration equal to the time headway between the subject vehicle and the lead vehicle. The lead vehicle, however, did not decelerate during the CHMSL event in order to roughly simulate “riding the brakes.” The participants responded if they detected the CHMSL event. The reaction time to detect the CHMSL event was recorded and the percentage of missed detections was calculated.

The second type of OED stimulus was the Lead Vehicle Deceleration (LVD) event. From time to time during test trials, the lead vehicle would begin to slow. However, the brake lights of the lead vehicle would not illuminate so as to simulate a “coast down” maneuver. If the participants detected this, they were to gently tap the brake pedal as soon as they could. The lead vehicle resumed its speed to 55 mph and the trial continued. The participants were instructed to accelerate, if necessary, at the conclusion of a trial to close the gap between the subject vehicle and the lead vehicle after this event was completed. The reaction time to detect the LVD event was recorded and the percentage of missed detections was calculated.

Chapter 3 Test Track Results

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The third type of OED stimulus was the Follow Vehicle Turn Signal (FVTS) event. Periodically, the follow vehicle would illuminate its driver-side front (left-front) turn signal for 2.5 seconds to simulate a follow vehicle’s indication to overtake. FVTS events were primarily seen in the left outside mirror and, occasionally, in the inside rearview mirror. The participants were asked to detect the FVTS event and respond if the signal was detected. The reaction time to detect the FVTS event was recorded and the percentage of missed detections was calculated.

Response time (RT) was calculated from the stimulus onset time to the participant’s response. There was a 200-mseconds lockout after stimulus onset to prevent anticipation responses, and the participant then had two seconds to respond. The participant was asked to respond to the OED stimulus during the duration of the subsidiary task. If the participant responded to the OED event after the task was completed, that response was not recorded and the trial was recorded as a missed detection. CHMSL and FVTS stimulus onsets began when a computer signal from the data acquisition system reached the follow or lead vehicle, as appropriate. LVD stimulus onset was from receipt of a signal to the lead vehicle to disable the cruise control and begin the coast down if driving conditions permitted it.

Participants were scheduled to perform each DWM task with each of the three OED events (e.g., CHMSL, FVTS, or LVD). Each test participant was scheduled to perform a task twice with a given OED stimulus on the track. Each OED presented was scored either “detected” or “not detected” based on the operational definitions used in the study. Detections were coded as one (1). Missed Detections were coded as zero (0). The binary (0, (1) detection data from the two trials for a participant were then averaged. This was done for each OED stimulus for each task. If there were no detections, the resulting participant score was 0.0. If only one trial was completed and a detection occurred, the participant score was 1.0 and 0.0 otherwise. If two trials were completed, the participant detection score was 0.5 if there was a detection on one trial and a missed detection on the other trial. If there were detections on both trials, the participant detection score was 1.0. The average of these per-participant detection scores, averaged across all participants, was taken as the proportion of “Detections.” The Proportion of Detections was multiplied by 100 to create “Percent Detections.” The "Percent Missed Detections" variable was defined as 100 percent minus the Percent Detections. This approach was motivated by the fact that the arithmetic mean (average) of a sample of binary (1, 0) scores is the proportion of scores coded as 1.

3.3.1 Center High-Mount Stoplight (CHMSL) Results

The results from the test-track CHMSL events are given in Figure 3-1. Overall, Percent Missed Detections were between 10 percent and 35 percent. Visual-manual tasks generally had higher missed detection rates (between 25% and 35%) than the auditory-vocal and Just Drive tasks (between 15% and 25%, approximately). Some auditory-vocal and mixed-mode tasks (Route Instructions, Sports Broadcast, and Delta Flight Information (Delta Flightline), respectively) had even slightly lower miss rates than Just Drive alone. Higher CHMSL miss rates for visual-manual tasks were likely due to the need to look away from the road scene while completing the task. Participants looked down or otherwise away from the road scene to execute the visual-manual tasks. Thus, foveal vision to the roadway would momentarily be removed and leave only peripheral vision to detect CHMSL onset. Task duration also appeared to play a role in object and event detection. Shorter visual-manual and auditory-vocal tasks (e.g., Book-on-Tape Summarize) showed poorer detection performance than the longer auditory-vocal, Just Drive, and mixed- mode (e.g., Delta Flight Information) tasks. Furthermore, detection was not perfect in any task condition, not even Just Drive. In fact, some auditory-vocal tasks actually had lower CHMSL miss rates than Just Drive. This suggests that driver distraction of the “lost in thought” variety may have been reduced by the presence of an in-vehicle activity.

Chapter 3 Test Track Results

Task Effect on Track Percent CHMSL Miss Rate (%)

0 20 40 60 80 100 Sports Delta RouteInstruct JustDrive BookOnTapeListen TravelComp CDTrack7 RouteOrient ReadHard BookOnTapeSum BiographicQA VoiceDial Coins Cassette DestEntry ReadEasy ManualDial MapHard RouteTracing RadioEasy MapEasy RadioHard HVAC Tas k

Percent CHMSL Miss Rate (%)

Figure 3-1. Track Percent CHMSL not Detected (Missed)

3.3.2 Lead Vehicle Deceleration (LVD) Results

The results from track testing for the LVD event showed a similar pattern to that of the CHMSL event (see Figure 3-2). Visual-manual tasks generally showed a higher missed detection rate than most auditory-vocal tasks. However, two visual-manual tasks (Read (Hard) and CD/Track (7) had LVD miss rates that were interspersed among the auditory-vocal and Just Drive tasks. The Just Drive task had nearly the lowest percentage of missed detections, although three auditory-vocal tasks (the same as those found with CHMSL detection) had slightly lower missed detections than Just Drive.

It should be noted that a portion of the LVD events were not detectable within the task length of short visual-manual tasks. One possible explanation for this may be that in short duration tasks the stimulus is below the optical looming threshold for detection. This issue is discussed further in Chapter 8, Discussion and Summary.

Chapter 3 Test Track Results

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