14-08-2013, 04:53 PM
The contribution of alcohol to night time crash risk and other risks of night driving
contribution of alcohol.pdf (Size: 207.57 KB / Downloads: 24)
Abstract
Many studies show that driving at night is more risky in terms of crash involvements per distance travelled than driving during the day. The
reasons for this include the more prevalent use of alcohol by drivers at night, the effects of fatigue on the driving task and the risk associated
with reduced visibility. Although the consumption of alcohol prior to driving occurs most commonly at night, drink-driving is not inherently
a night time risk factor. This study decomposes the New Zealand risk of driving at night into risk associated with alcohol and risk associated
with inherently night time factors. The overall risk associated with alcohol use by drivers was shown to decrease with increasing age for the
most risky situation analysed (male drivers on weekend nights). Given the levels of drinking and driving on weekend nights, the overall effect
of alcohol was shown to contribute almost half of weekend night time risk for drivers aged under 40 on lower volume roads, but to contribute
little to overall risk on higher-volume roads, consistent with other research showing that higher-volume roads are not favoured by drinking
drivers. Risk at night relative to risk during the day (excluding risk associated with drinking and driving) was shown to decrease with age.
Roads with illumination at night are less risky at night relative to during the day than roads without illumination. The risks estimated in this
paper reflect the behaviour of the road users studied and their prevalence on the roads under the conditions analysed.
Background
There are several well-researched factors that contribute
to higher night time than daytime risks for drivers, including
impaired vision, fatigue and alcohol (Saunders, 1997). Vis-
ibility at night is limited by the range of headlights and the
fact that many important obstacles, like dark-clad pedestrians,
animals, or unmarked vehicles, present little contrast with
the environment (Leibowitz et al., 1998). Visibility is fur-
ther impaired by glare from oncoming headlights (Theeuwes
et al., 2002). Nevertheless, most drivers do not adjust their
speed sufficiently to compensate for these visual problems
(Leibowitz et al., 1998; Owens and Tyrrell, 1999), contribut-
ing to elevated risks when driving in the dark (Sullivan and
Flannagan, 2002).
Method
The study was a case-control design of driver-kilometres
(a kilometre of travel by a particular driver) by light four-
wheeled vehicles (cars, vans and utility vehicles). The driver-
kilometre was defined as a case if the driver had been involved
in a crash on that road section. A control driver-kilometre
consisted of a kilometre of road travel not involving a crash
driven by a representative sample of New Zealand drivers.
Thus, risk of crash involvement per distance travelled can be
estimated by the number of case driver-kilometres divided
by the number of control driver-kilometres. As this study is
particularly concerned with the effect of night (as discussed
above) on driving risk, the main quantity estimated is the
relative risk of driving at night compared to driving during
the day for the same driver group and driving situation. A
high value for this relative risk measure does not imply that
both day and night risks are high, just that the ratio of night
risk to day risk is high.
Conclusions
The overall impact of alcohol use on driver risk was shown
to decrease with increasing age for the most risky situation
analysed (male drivers on weekend nights). Given the levels
of drinking and driving on weekend nights, the overall effect
of alcohol was shown to contribute almost half of weekend
night time risk for drivers aged under 40 on lower volume
roads. There was estimated to be a smaller overall impact of
alcohol-related risk on higher-volume roads at night or roads
(including lower volume road types) during the day. Risk at
night relative to risk during the day (excluding risk associated
with drinking and driving) was shown to decrease with age.
Road types illuminated at night were safer than roads without
lighting, consistent with prior research, but this result may
be explained by other differences in road design as well as
by lighting.