Assisting the older driver - SWOV

Effects of a driver support system on workload and driving performance
enter‐sign’, whereas only one functionally middle‐aged participant did so
after being warned by the support system.
The safety of driver decisions was not analysed for these messages, as
messages regarding higher speed limits and messages regarding the allowed
direction of traffic were considered to be more related to driver comfort and
route errors than to driver safety.
8.4. Results regarding user acceptance
Before analysing the answers to the questionnaire on user acceptance,
reliability analyses were performed to test whether the items of the
composite questions on user acceptance could be combined into the two
subscales on system appreciation described by Van der Laan, Heino and De
Waard (1997): usefulness and satisfaction (see Section 8.2.8). As can be seen in
Table 8.14, all coefficients (Cronbach’s alpha) were well above 0.80, indicating
that inter‐item consistency of the subscales was high (Walsh & Betz, 1990),
and item scores could be combined safely into one subscale score.
Before (n=105)
After (n=40)
Usefulness Satisfying Usefulness Satisfying
Right of way .88 .91 .89 .94
Safe gap .91 .93 .91 .93
View of the intersection .92 .93 .90 .89
Deviating rules or situations .92 .92 .92 .87
Table 8.14. Reliability coefficients (Cronbach’s α) for usefulness and satisfying
subscales.
Subscale scores were computed for each time of measurement and type of
message by taking the average of the scores on the items belonging to that
subscale (see Table 8.15). Item scores ranged from 2 to ‐2, positive scores
indicating that participants considered the message as useful or ‘nice to have’
(satisfying).
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