Assisting the older driver - SWOV

Effects of intersection design on workload and driving performance
To measure workload, a secondary task was introduced. This secondary task
consisted of a peripheral detection task (PDT; see e.g., Van Winsum, Martens
& Herland, 1999); a task that is based on the idea that the functional visual
field decreases with increasing workload. Performance on this task was
inferred from the reaction time of the driver and the fraction of signals that
they missed. Increases in the difficulty of the primary task (i.e., passing an
intersection) were expected to result in higher reaction times and fractions
missed.
Primary task performance was inferred from crashes, route‐errors, and safety
of the participant’s decisions. The latter was measured by the extent to which
traffic that had right of way had to decelerate when the participant was
passing an intersection. Deceleration of these ‘other vehicles’ was considered
to be the precursor of a crash. If the drivers of those vehicles would not have
reacted, a crash would have taken place. As such, the deceleration of other
vehicles is the ‘compensatory action by others’ that is mentioned in Fuller’s
model (2001) as the factor that can prevent crashes from happening in case
capabilities of a driver are lower than the driving task demands in that
particular situation.
A second aim of this study was to identify those intersection characteristics
that discriminate between the performance of older and younger drivers.
Therefore, both older (70 years and older) and younger persons (30‐50 years
old) were invited to participate in the experiment. The age boundaries of the
first group were chosen as a compromise between the preferred group of
people aged 75 and above – the group of older adults that has a fatality rate
which is higher than average (OECD, 2001; SWOV, 2005) – and the
availability of participants of a certain age. The group of people aged 30‐50
was chosen as the comparison group. People of this age group were expected
to have considerable driving experience and not yet to be confronted with
functional limitations. Realizing that ageing is a process that does not start at
the same age for every person nor continues at the same rate, with the result
that drivers having the same age – as in years since birth – can differ in the
number and severity of their functional limitations, age was both considered
chronologically and functionally (for a discussion on the prediction of
functional age see Birren & Renner, 1977, p. 15‐17). Functional age was based
on scores on three tests of cognitive functioning, relating to reaction time,
selective attention, and visual‐motor coordination. Persons scoring well on
the average of all tests were considered to be functionally younger, whereas
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