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Impact of the graduated driver licensing program in Nova
Scotia
Report from the Traffic Injury Research Foundation
Results: Impact of the Program on All Novice Drivers
Both the pre-post comparisons and the time series analysis demonstrated
that the graduated licensing program in Nova Scotia was associated with
a significant reduction in collisions among 16- and 17-year-old drivers.
However, it is still possible that the observed reductions were at least
partially accounted for by a decrease in the number of novice drivers, since
the collision rates were based on population figures not licensing data.
As well, because the analyses were limited to 16 and 17 year olds, the impact
of the program on older novice drivers remains unknown. These two issues
were explored using pre-post comparisons based on groups of novice drivers
that encompass all ages.
To examine the effect of the program while controlling for changes in licensing
required collision data on all novice drivers in periods before and after
implementation of the graduated licensing program. Such data were obtained
from the Nova Scotia driver record file. Two groups were available for the
comparison: 11,777 drivers who were issued a learners permit in 1993 (pre-GDL
Group) and 8,600 drivers issued a learners permit in 1995 (post-GDL Group).
It is important to keep in mind that these two groups contained novice drivers
of all ages.
The fact that the post-GDL group had 27% fewer learners than the pre-GDL
group suggests that the introduction of the graduated licensing program
had an impact on licensing rates. Indeed, as mentioned previously, there
is evidence from other studies that graduated licensing discourages novices
from becoming licensed and, importantly, it has been suggested that this
decrease is what accounts for the reduction in collisions (Hagge and Marsh
1988; Langley et al. 1996).
An alternative explanation is that many "soon-to-be licensed" individuals
applied for a license just before the program came into effect so as to
avoid the restrictions. The latter explanation is supported by data on the
monthly number of learner licenses issued from January 1993 to December
1996, which are shown in Figure
8. As can be seen, there was a dramatic increase in the number of learner
licenses issued just prior to the implementation of the graduated licensing
program. This suggests that eligible candidates opted to qualify for licensing
earlier in order to avoid the new requirements. If the new program had not
been implemented, these individuals would likely have waited until 1995
or perhaps even 1996 to acquire a license. This initial "rush" to become
licensed had, however, dissipated by 1996, since the monthly number of learner
licenses issued in that year had almost returned to 1993 levels.
Nonetheless, the implementation of graduated licensing had a short-term
effect on the licensing patterns of novice drivers – 27% fewer learner permits
were acquired in 1995 than in 1993. At issue is the extent to which this
decline in the number of learners accounts at least partially for the reductions
in the collisions of novice drivers over this period.
To examine this hypothesis, the collision records of the 1993 pre-GDL learners
and the 1995 post-GDL learners were tracked over a 24-month period. The
results are shown in Table
5.
As can be seen, although the number of learners decreased by 27%, collisions
declined even more dramatically, by 41.2%. As a consequence, the collision
rate dropped by 19.4%, from a rate of 1,418.9 per 10,000 learners in 1993
to 1,143.0 in 1995. The significant decrease in the collision rates from
1993 to 1995 demonstrates that there was a positive impact, independent
of the drop in the number of learners.
Similar comparisons of changes in the "casualty" collision rates revealed
a 7% decrease over the 24-month tracking period. However, this difference
did not achieve statistical significance.
The significant change in the collision rate of novice drivers cannot necessarily
be taken as evidence that the program had an impact on older novice drivers
because 16 year olds comprise the largest proportion of novice drivers and
their results may be determining the overall findings.
That 16-year-old drivers represent the majority of new drivers is confirmed
by the data in Table
6, which shows that 16 year olds accounted for 71.5% of all learners
in 1993 and 81% in 1995. The data also show that the age distribution of
learners did change after the graduated licensing program was introduced.
A similar shift in the age composition of novice drivers was also observed
in Ontario following implementation of their graduated licensing program
in 1994 (Boase and Tasca, 1998). In Ontario, 49% of the novice driver population
in 1993 was aged 16 to 19 compared to 59% in 1995.
Although not directly related to the focus of this study, the findings from
Ontario, and to a somewhat lesser extent from Nova Scotia, also show that
novice drivers are not all young. This finding is consistent with an issue
the current authors identified as emerging almost a decade ago. Mayhew and
Simpson (1990) reported that the composition of the new driver population
was changing over time with a greater percentage being accounted for by
older newly-licensed drivers.
Interestingly, the introduction of graduated licensing may have a moderating
effect on this licensing change, with some novices now opting to become
licensed at an earlier age. Albeit speculative, the extended mandatory holding
period for the graduated licensing program – two and a half years in Nova
Scotia and two years in Ontario – may actually encourage licensing at an
earlier age. Because candidates for the program are required to stay in
it for two or more years, it makes sense to enter the program as early as
possible.
The central point is that the differential age composition among learners,
before and after the program was implemented, introduces a bias in the analysis.
However, it actually works against finding a program effect. Research has
shown that the youngest drivers have the greater crash rates, so the fact
that the post-program group has a higher proportion of young drivers should
suppress, or even obscure, any positive impact of the program on the collisions
of novice drivers. However, as shown in the previous section, the collision
rates of novice drivers actually declined significantly, even though the
1995 group had a higher proportion of young novices.
Table
7 shows the collision rates for 1993 and 1995 novices who received their
learner license at different ages. Similar to the previous analysis, the
collision records of the two groups were tracked over a 24-month period.
As can be seen, there were significant decreases in collision rates for
all age groups not just those age 16. The greatest improvement was actually
observed for novice drivers aged 25 and over. Their collision rate dropped
by 42.7%, from 875 in 1993 to 501.8 in 1995. The reduction for 16-year-old
novices was very comparable to that among novices age 17 to 24 – decreases
of 21.7% and 21.0%, respectively.
Thus, the safety benefits of the graduated licensing program were not restricted
to novices age 16; even older novice drivers showed significant improvements
in their collision rates.
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