Geography Reference
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Fig. 4 Comparison results of GIS estimates of arrival times and reported arrival times on
selected samples. a The differentiations between two versions of arrival times. b Rated accuracy
levels of reported arrival times
values in the figure indicate that the reported arrival times are later than the
estimated values (journey took longer than the model).
Approximately 58 % of records have a variance in arrival time that is less than
half an hour from the GIS estimates of arrival times. In addition 13 of reported
arrival times are more than half an hour early, and nearly 30 % are half an hour
later than GIS estimated arrival times. This seems to imply that the bulk of
sections had drivers who complied largely with expected norms but dallied a bit
more than expected, while only a third arrived appreciably (over 30 min) early. It
is easy to dally, and even easier to forget a small stop that slowed you down, but
harder to cut time off a solid driving performance. Clearly there is also a variance
in reporting ability as well as in perseverance in completing all the questions.
While variation of driving times is to be expected, a large differentiation
between GIS estimates of arrival times and the reported arrival times can indicate
that there might be inconsistent temporal values being recorded (misreporting of
arrival times) or there could be actual stops omitted between two reported stops.
However, to determine the data accuracy only based on the raw difference in
minutes is arbitrary. A more suitable assessment matrix for identifying likely
anomalies was developed based on the weighting of the impacts from travel time,
duration and the difference between the GIS estimates of arrival times and the
reported late times. This adjusted for the length of particular legs of the trip, since
longer travel times (or longer stays) reduce the relative significance of a particular
divergence between estimated and reported travel times. By adding the weighted
values together, the accuracy levels of arrival times were rated and summarised
into four types which are displayed in Fig. 4 b.
Figure 4 b shows that there are approximately one out of four reported arrival
times matching the GIS estimates of arrival times; 59 % recorded arrival times
which are acceptable with reference to the modeled driving times and duration
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