Assisting the older driver - SWOV

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Effects of intersection design on workload and driving performance missed per combination of intersection characteristics and necessary manoeuvres (see Figure 6.4) did not show the gradually increasing lines which were established for reaction times and fractions missed per type of intersection layout (Figure 6.3). 2 Fraction missed; Reaction time (s) 1,8 1,6 1,4 1,2 1 0,8 0,6 0,4 0,2 0 IM1 IM2 IM3 IM4 IM5 IM6 IM7 IM8 RT_old RT_middle RT_young FM_old FM_middle FM_young Figure 6.4. Reaction time and fraction missed per age group and intersection layout. 6.3.3. Safety of driver decisions Having calculated the Acc_Pre and Acc_Crit per intersection (see Datasampling), both measures were averaged over intersections that were expected to be the same based either on (a) their priority regulation, (b) the driver’s manoeuvre, (c) intersection layout, or (d) sight distance. In addition, both measures were averaged over those intersections having the same combination of intersection characteristics and necessary manoeuvres (IM). Averaging Acc_Crit over several intersections resulted in values that varied between 0 and 1. The closer the value was to 1, the more often the participant had made an unsafe decision at that type of intersection. Average Acc_Pre had a wider range of values, with negative values indicating unsafe behaviour of the participant at that type of intersection, and positive values indicating safer behaviour. Note that the deceleration measures Acc_Crit and Acc_Pre were only calculated for intersections at which participants had to yield to other vehicles. At the same time, collection of data was not longer restricted to those intersections at which participants were confronted with a secondary task (i.e., PDT). As a result, the actual intersections used to measure workload and safety of driver decisions were not always the same. 123
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). 124
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3.2.3. Conclusions regarding future
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Assisting the older driver Appendix
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Samenvatting Samenvatting Dit proef
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Samenvatting Verkeersveiligheidsmaa
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Samenvatting jongere automobilisten
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Samenvatting voordeel dat ze de rij
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Curriculum Vitae Curriculum Vitae R
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Assisting the older driver Nottingh
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Assisting the older driver - SWOV

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