This report describes the update of New Zealand crashworthiness ratings by year of vehicle manufacture for 1964-2013 model vehicles. New Zealand crashworthiness ratings by year of manufacture were first estimated by Newstead et al (2005a) for 1964-2002 model vehicles. Crashworthiness ratings of vehicles by year of first registration in New Zealand were also examined, focusing on the fleet of used imported vehicles sold in New Zealand. Crashworthiness ratings measure the relative risk of death or serious injury (hospitalisation) to drivers of vehicles involved in crashes. The estimates are derived from analysis of data on real crashes. The estimates were subsequently updated in Newstead et al (2006) for 1964- 2004 model vehicles, in Newstead et al (2007b) for 1964-2005 model vehicles, in Newstead et al (2008b) for 1964-2006 model vehicles, in Newstead et al (2009b) for 1964-2007 model vehicles, in Newstead et al (2010b) for 1964-2008 model vehicles, in Newstead et al (2011b) for 1964-2009 model vehicles, in Newstead et al (2012b) for 1964-2010 model vehicles, in Newstead et al (2013b) for 1964-2011 model vehicles and in Newstead et al (2014b) for 1964- 2012 model vehicles as a continual monitor of the crashworthiness progress of the New Zealand vehicle fleet. The analysis in this study is based on data from Police reports on injury crashes occurring in New Zealand during 1991-2013. Crashworthiness is an estimate of the occupant protection provided by a vehicle, namely the risk of a driver of a vehicle being killed or seriously injured (admitted to hospital) when involved in a crash. It is obtained from the product of injury severity (of injured drivers) and injury risk (of drivers involved in crashes) for the drivers of vehicles of the specified year of manufacture or specified year of first registration in New Zealand. The method of analysis, first demonstrated in the study of Newstead et al (2005a), gives unbiased estimates of injury risk from injury crash data where the total number of uninjured drivers is unknown, as in the New Zealand crash data reported by Police. It was again used here. The method was used separately to obtain crashworthiness for vehicles by year of manufacture and by year of first registration in New Zealand. The injury risk estimates were based on crash data for 125,162 drivers involved in crashes between two vehicles in New Zealand during 1991-2013 where one or both drivers was injured and the vehicle was manufactured between 1964 and 2013. The injury severity estimates were based on crash data for 154,769 drivers injured in crashes in New Zealand during 1991-2013 and where the vehicle was manufactured between 1964 and 2013. The injury risk ratings were adjusted for the sex and age of the driver, the speed limit at the crash location and the year in which the crash occurred. The injury severity ratings were also adjusted for the number of vehicles involved in the crash. These factors are known to be strongly associated with injury risk and injury severity. Adjustments were made via logistic regression analysis techniques with the aim of measuring the effects of vehicle factors alone, uncontaminated by other factors available in the data that affected crash severity and injury susceptibility. The degree of accuracy of the crashworthiness ratings is represented by the confidence limits of the rating in each case. Analysis successfully estimated trends in the crashworthiness of the light passenger vehicle fleet (cars, station wagons, four wheel drives, vans and utilities) in New Zealand by both year of manufacture and year of first registration for used imports in New Zealand. Estimates of crashworthiness by year of vehicle manufacture for the New Zealand light passenger vehicle fleet as a whole along with 95% confidence limits are shown in Figure E1. Analysis of trends by year of vehicle manufacture show statistically significant improvement in the crashworthiness of New Zealand light passenger vehicles over the years of manufacture studied. The majority of the measured improvement occurred over the years of manufacture from 1983 to 2008. Over this period, the risk of death or serious injury to drivers in a crash reduced by over 79% for the fleet as a whole. During this period vehicle safety in New Zealand was affected by several competing effects: a general increase in both active and passive safety features in vehicles; increasing proportions of used imported vehicles entering the New Zealand fleet; and increases in the regulation of vehicle safety standards by the New Zealand Government. Estimates of crashworthiness trends in the vehicle fleet by year of first registration in New Zealand from 1986 to 2013 for used imported vehicle were also obtained and are shown in Figure E2 along with 95% confidence limits. They showed a numerically high crashworthiness rating (indicating poor occupant protection performance) of newly registered vehicles in the early 1990’s, the years when used imports suddenly began to penetrate the market. This was followed by statistically significant improvements in crashworthiness over the later years of that decade. Analysis shows that the new vehicles entering the fleet in any particular year are more crashworthy than the cohort of second hand imports brought into New Zealand in the same year highlighting the concern about the safety implications of the used imported vehicle program. However, the most recent analysis in Newstead et al (2014b) and the current analysis suggest this gap in crashworthiness performance may have narrowed in the last 3 to 4 years of analysis which is encouraging. The differential in apparent safety between the new and used imported vehicles continues to need further monitoring. (Author/publisher)
Samenvatting