Early research has provided a mix of results. Comprehensive reviews incorporating meta-analysis by Elvik (1996) and Koornstra et al. (1979) have systematised these results. Elvik showed that studies of DRL in vehicle fleets provided larger and more consistent effects than studies of traffic systems, and that outcomes are sensitive to the type of measures used. Koornstra et al. carried this analysis a step further by statistically excluding factors such as number of vehicles already using DRL at the start of a trial to estimate the intrinsic effects of DRL, ie the effects which would occur when use rate is increased from zero to 100% of vehicles. The effect of this re-analysis was to make many studies which were previously non-significant significant, and show that by far the majority of studies found a reduction in multiple-party daytime crashes associated with DRL. Koornstra et al. proposed a set of relationships relating the extent of crash reductions with DRL to latitude, based on the longer hours of twilight in the higher latitudes. It should be noted that many later studies do not fit this model well.
Studies that have been conducted since the reports of Elvik (1996) and Koorsntra et al. (1997) have generally confirmed the reduction in crash rates associated with DRL, although the size of the reduction varies. Tofflemire and Whitehead (1997) compared crash rates in the same year for Canadian cars with and without DRL, eliminating factors such as weather, economic climate, and enforcement as a possible source of differences. They found an overall reduction of 5.3%, principally due to a reduction in crashes involving vehicles travelling in opposite directions.
A North America study by the National Highway Traffic Safety Administration (NHTSA, 2000) reinforced the sensitivity of outcomes to analysis methods, but showed an estimated effect of DRL was a reduction of 7% in multiple-party daytime crashes, which was statistically significant. Bergkvist (2001) reports upon a study conducted for General Motors Corporation by an independent consulting firm. The study involved a comparison of the crash rates of specific GM, Volvo, Saab and Volkswagen vehicles before and immediately after DRL became standard equipment on these models. The results suggest a reduction in the incidence of target vehicle-vehicle crashes in excess of 5% and a reduction in vehicle-pedestrian collisions of approximately 9%. Farmer and Williams (2002) compared makes and models which included DRL as a standard feature with the same makes and models purchased before this was the case. The reduction in daytime crashes was 3.2%, which was highly significant. When considered separately, all states but one showed a reduction in crashes for the DRL vehicles. However, only in Texas was the reduction large enough to be statistically significant. Lassarre (2002) reports a trial involving a campaign to encourage voluntary use of headlights during the day. Crash rates in the area where the campaign was run were compared with crash rates in neighbouring areas over the same period, and showed a reduction of 58.7% for fatal crashes and for serious injury crashes on major roads, but no reductions in less serious crashes and no effects on crashes on minor roads.
A study by Poole (1999) is of particular interest as it is the only fleet study carried out in Australia. DRL were fitted to 80 fleet vehicles based in metropolitan Western Australia. The crash records of the DRL equipped vehicles over a ten month period were compared with the crash records of a matched sample of vehicles not fitted with DRL. Results based on a time-to-crash analysis found that DRL fitted vehicles took more than five times longer than non-DRL fitted vehicles to be involved in a vehicle-vehicle daytime crash.
Studies that have been conducted since the reports of Elvik (1996) and Koorsntra et al. (1997) have generally confirmed the reduction in crash rates associated with DRL, although the size of the reduction varies. Tofflemire and Whitehead (1997) compared crash rates in the same year for Canadian cars with and without DRL, eliminating factors such as weather, economic climate, and enforcement as a possible source of differences. They found an overall reduction of 5.3%, principally due to a reduction in crashes involving vehicles travelling in opposite directions.
A North America study by the National Highway Traffic Safety Administration (NHTSA, 2000) reinforced the sensitivity of outcomes to analysis methods, but showed an estimated effect of DRL was a reduction of 7% in multiple-party daytime crashes, which was statistically significant. Bergkvist (2001) reports upon a study conducted for General Motors Corporation by an independent consulting firm. The study involved a comparison of the crash rates of specific GM, Volvo, Saab and Volkswagen vehicles before and immediately after DRL became standard equipment on these models. The results suggest a reduction in the incidence of target vehicle-vehicle crashes in excess of 5% and a reduction in vehicle-pedestrian collisions of approximately 9%. Farmer and Williams (2002) compared makes and models which included DRL as a standard feature with the same makes and models purchased before this was the case. The reduction in daytime crashes was 3.2%, which was highly significant. When considered separately, all states but one showed a reduction in crashes for the DRL vehicles. However, only in Texas was the reduction large enough to be statistically significant. Lassarre (2002) reports a trial involving a campaign to encourage voluntary use of headlights during the day. Crash rates in the area where the campaign was run were compared with crash rates in neighbouring areas over the same period, and showed a reduction of 58.7% for fatal crashes and for serious injury crashes on major roads, but no reductions in less serious crashes and no effects on crashes on minor roads.
A study by Poole (1999) is of particular interest as it is the only fleet study carried out in Australia. DRL were fitted to 80 fleet vehicles based in metropolitan Western Australia. The crash records of the DRL equipped vehicles over a ten month period were compared with the crash records of a matched sample of vehicles not fitted with DRL. Results based on a time-to-crash analysis found that DRL fitted vehicles took more than five times longer than non-DRL fitted vehicles to be involved in a vehicle-vehicle daytime crash.
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