Assisting the older driver - SWOV

Assisting the older driver
However, intersections were expected to be exchangeable as long as they
were identical according to the intersection characteristic being studied.
Between‐subjects analysis of variance showed that functional age did not
affect the average deceleration of relevant vehicles (i.e., those having right of
way) at the moment participants started passing an intersection (Acc_Pre).
The proportion of unsafe decisions per intersection type (Acc_Crit) was not
affected by functional age either (see Table 6.6). Separate mixed betweenwithin
analyses of variance for the various intersection characteristics led to
the same conclusion: age did not affect the safety of driver decisions.
However, the various intersection characteristics did influence the degree of
deceleration and the proportion of unsafe decisions (see Table 6.6). The only
exception was sight distance. This intersection characteristic did not affect the
average deceleration of relevant vehicles at the moment the participant drove
off with the intention to pass the intersection, although it did affect the
proportion of unsafe decisions (η 2 = 0.260). All other intersection
characteristics had partial eta’s squared ranging from 0.329 to 0.452 for
deceleration values and ranging from 0.538 to 0.623 for proportion of unsafe
decisions. The combination of intersection characteristics and necessary
manoeuvres (IM) had the largest influence on variation in both proportion of
unsafe decisions and deceleration of relevant vehicles. Post hoc Bonferroni
tests showed that almost all types of intersections had significantly different
proportions of unsafe decisions. Only IM2, IM6 and IM8 had similar
proportions of unsafe decisions, and IM3 and IM5. The trends were,
however, different from the ones expected beforehand. Three intersection
types that were expected to be of medium difficulty (IM3 to IM5) turned out
to be the ones that most often led to unsafe decisions. The intersections that
were expected to be the most difficult (IM6 to IM8) only seldom led to unsafe
decisions (see Figure 6.5).
This lack of correspondence between expected difficulty and safety of driver
decisions could have been the result of an intersection classification that does
not reflect the actual difficulty of passing the respective types of
intersections. After all, analyses of workload data already showed that the
results of post hoc Bonferroni tests for the combined intersection and
manoeuvre characteristics did not correspond with the expected order of
easy and difficult intersections (see Section 6.3.2). However, when comparing
the proportions of unsafe decisions for intersections classified according to
an intersection characteristic that turned out to be a better predictor of task
difficulty (i.e., intersection layout) the same pattern emerged (see Figure 6.6).
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