Assisting the older driver - SWOV

Effects of intersection design on workload and driving performance
Workload was measured by performance on a secondary task while passing
the intersection. The secondary task consisted of a peripheral detection task
(PDT; see e.g., Van Winsum, Martens & Herland, 1999 for a description of
this task). While driving, a small red square was presented on the simulator
screen in front of the participant during one second. Subjects were required
to respond as soon as they detected the red square by pressing a microswitch
that was attached to the index finger of their left hand. Reaction time was
measured in milliseconds. If a reaction time had not been detected by the
system within 2.5 s from the onset of the stimulus, this was coded as a
missed signal. Series of signals were presented during the approach and
passing of a selected number of intersections and while driving on three
straight road sections. The 28 selected intersections were representative for
the total group of 71 intersections, at the same time preventing participants
having to perform the detection task at every intersection they passed. The
onset of a series of signals was announced with a bell tone. During the series
of signals (one series per intersection), on average every 3.5 s, with random
variation between 3 and 4 s, a stimulus was presented at a horizontal angle of
10 to 20 degrees to the left of the line between the eyes of the participant and
the centre of the screen. Stimuli were presented at a vertical angle of 3
degrees above the horizon. Average reaction time and fraction of missed
signals per intersection (number of missed signals divided by total number
of sent signals while passing the relevant intersection) were used as
workload indices for the intersections. Higher reaction times and higher
fractions of missed signals were interpreted as being the result of a higher
workload.
Baseline reaction times and fractions missed were collected at the start of the
first experimental drive. While the simulator car was parked at the beginning
of the route, and the participant was sitting in the driver seat, one series of
twenty stimuli was presented. On average every 4 s, with random variation
between 3 and 5 s, a stimulus was presented at a horizontal angle of 10 to 20
degrees to the left of the line between the eyes of the participant and the
centre of the screen. Again, participants were instructed to press the button
as soon as they saw the stimulus. A second baseline was provided by the
straight road sections at which the same series of stimuli were shown as
during the approach and passing of the selected number of intersections.
This second baseline differed from the first one in three ways: 1) participants
were driving, 2) it always took place during the same drive as in which the
relevant intersection data were gathered (no support), whereas the first
baseline also could have taken place at the start of the drive in which driver
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