Assisting the older driver - SWOV

Effects of intersection design on workload and driving performance
left and right side of the intersection, participants may have completely
overlooked the stimuli that were presented at a more central location of the
screen.
Results on the safety of driver decisions showed different trends for the
difficulty of passing the various types of intersections. According to these
data, turning left or right at a T‐junction hardly ever led to unsafe decisions,
whereas passing roundabouts and crossing three‐way intersections with a
side‐street at the driver’s right‐hand side most frequently led to unsafe
decisions. Considering the reputation of roundabouts as one of the safest
types of intersections (Elvik, 2003; Elvik & Vaa, 2004; Ogden, 1996), these last
results were unexpected. Moreover, these results were unexpected given the
results on workload. Participants had shorter reaction times and lower
fractions missed while passing roundabouts than while passing several other
types of intersections.
This discrepancy between the results on workload and safety of driver
decisions may have been caused by behavioural adaptation. Participants may
have been less alert while passing ‘easy’ intersections and extra alert while
passing ‘difficult’ intersections, thus being keener on avoiding errors at the
latter. Another explanation for the unexpected results concerning safety of
drivers’ decisions lies in the collection of deceleration data (i.e., those data
that were used to determine the safety of driver decisions). In this study, it
was assumed that in case our participants failed to yield to vehicles that had
right of way, the latter vehicles would decelerate to avoid a collision.
However, with hindsight there may have been other reasons for them to
decelerate. As a matter of fact, surrounding traffic also decelerated in case
they had to take a bend. This other reason for decelerating, which was not
related to the safety of participants’ decisions, appeared to be more prevalent
at some intersections than at others. At roundabouts, for example, a part of
the surrounding traffic had route instructions that made them leave the
roundabout at the same spot as where participants were about to enter the
roundabout. As the intelligent surrounding traffic knows that it has to reduce
speed to take a bend safely, those vehicles that had to leave the roundabout
were decelerating for another reason than for the participant not yielding to
them. Similarly, at three‐way intersections with a side‐street at the driver’s
right‐hand side, all vehicles coming out of these side‐streets were confronted
with a T‐junction at which they had to turn left or right and thus had to
reduce speed. Unfortunately, it was not possible to eliminate the deceleration
data of those vehicles that were decelerating because of a bend. Therefore,
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