Assisting the older driver - SWOV

Effects of a driver support system on workload and driving performance
messages regarding safe gaps to join traffic were only given if participants
were within a distance of 10 m from the intersection (see Section 8.2.6), a
different waiting distance appears to be a plausible explanation for
functionally old participants receiving fewer messages.
Fewer messages regarding the approach of a major road may be the result of
compensatory behaviour at the tactical level. Functionally old participants
may have started reducing their speed sooner (i.e., at a larger distance to the
intersection) to compensate for their increased perception‐reaction time.
However, there is no guarantee that older participants restricted this
compensatory behaviour to intersections at which they were approaching a
major road. In other words, if older drivers approached intersections with a
major road at lower approach speeds, this does not necessarily mean that
they were aware of the fact that they had to yield to all traffic on the
intersecting road. Unfortunately, data sampling did not enable us to
determine whether participants reduced speeds at the same distance to the
intersection regardless of the type of intersection they approached.
Nevertheless, the above results are convincing enough to stress the fact that
system settings should be adjustable to the owner’s general driving
behaviour. Otherwise, drivers will not be able to trust system performance.
Similar conclusions can be drawn from the participants’ opinions about the
timing of messages. Whereas 70% of the functionally young participants
considered the timing of messages to be correct or found messages came too
soon, 60% of the functionally old participants considered them to come too
late. As Oxley (1996) concluded in his evaluation of the collision warning
system that was tested in the EDDIT‐project: uniform settings would be at
best unhelpful, at worst dangerous.
The support system that we evaluated was designed to reduce workload and
improve driving performance. Whereas the latter improvement was
established, a reduced workload was not shown. This could be the result of
the new task that was added to the driving task. After all, the driver has to
listen to and process the information that is offered by the assistance system.
This extra task may increase workload, thereby counteracting the effects of
the support system. However, the increased workload as a result of the extra
task is expected to be only temporary. Therefore, longer evaluation periods
are needed to establish the net effect of the system on driver workload. Such
an evaluation will also provide insight in the influence that behavioural
adaptation may have on effects on driving performance.
187