William J. Frith

THE INFLUENCE OF ALCOHOL, AGE AND NUMBER OF PASSENGERS ON THE NIGHT-TIME RISK OF DRIVER FATAL INJURY IN NEW ZEALAND

Breath alcohol measurements and other data collected at randomly selected roadside sites were combined with data on fatally injured drivers in crashes occurring on the same weekdays and times (Friday and Saturday nights) at locations matched by the size of the nearest town. A logistic model was fitted to these data for the years 1995-2000 to estimate the effects of alcohol, drivers age and the influence of passengers carried on the risk of driver fatal injury in New Zealand. The estimated risks increased steeply with increasing blood alcohol concentration (BAC), closely following an exponential curve at levels below about 200mg/dl (i.e. 0.2%) and increasing less than exponentially thereon. The model fitted to data for drivers under 200mg/dl showed that risks at all BAC levels were statistically significantly higher for drivers aged under 20 (over five times) and for drivers aged 20-29 (three times) than for drivers aged 30 and over. Further, controlling for age and BAC level, driving with a single passenger was associated with approximately half the night-time risk of driver fatal injury relative to driving either solo or with two or more passengers. According to a recent travel survey, the types of passengers carried at the times of night and days of week studied appear to differ significantly from the types of passengers carried generally, which may lead to different passenger effects on driver behaviour. The high relative risk of teenage drivers means that they reach high risk levels commonly regarded as unacceptable in the field of road safety even at their current legal limit of 30mg/dl, particularly when more than one passenger is carried in the car.

Older driver crash rates in relation to type and quantity of travel

It is a well-established phenomenon that, notwithstanding their overall good crash record, older drivers have a higher than average rate of involvement in injury crashes when the rate is calculated by dividing crash numbers by distance driven. It has been hypothesised that at least some of this higher crash rate is an artefact of the different nature of driving undertaken by many older drivers. For example, driving in congested urban environments provides more opportunities for collisions than driving the same distance on a motorway. However, there have been few opportunities to investigate this theory, as relevant data are difficult to acquire. High-quality data from the New Zealand Travel Survey (1997/1998) were combined with crash data to enable a statistical model to estimate the risk of driver groups under various driving conditions characterised by the type of road used, time of day, day of week, and season of year. Despite elevated crash risks per distance driven compared with middle-aged drivers for most road types, older drivers were as safe as any other age group when driving on motorways. Accounting for the fragility of older drivers and their passengers in the risk estimates for other road types, older drivers appeared to have daytime risks comparable to 25-year-olds and night-time risks as low as any other age group. The driving patterns of older drivers (in terms of when and where they drive) were estimated to minimize their risks in comparison with the driving patterns of other age groups. These results are of interest to both policy makers and transportation planners working against the background of inevitable increases in the number of older drivers as the population ages.

Association between older driver characteristics, on-road driving test performance, and crash liability.

From May 1999, a new system for licensing older drivers was introduced in New Zealand. It included a practical on-road driving test with expanded scope, to be completed every two years from the time the driver turns 80. The relationship between crashes and test performance needed to be studied to inform the debate regarding the testing system. The population studied was all drivers who entered this licensing system during its first three years of operation. They were defined as crash involved if they were involved in an injury crash during the two years following their first licensure under the new system. Logistic regression was used to describe the risk of crash involvement in terms of driving test performance and other driver characteristics. Each driving test failure was associated with a 33% increase in the odds of crash involvement (95% CI 14% to 55%), controlling for age, gender, minor traffic violations, and whether the older driver lived with another licensed driver or not. Minor traffic violations in the two years following the driving test were associated with twice the odds of crash involvement. These results suggest that the new on-road driving test does identify older driver behaviors or limitations that are related to crash liability. It is anticipated that the results presented here will provide essential information for discussing older driver licensing systems, whose impact will grow in importance as the population of drivers ages.

THE EFFECT OF INCREASING RURAL INTERSTATE SPEED LIMITS IN THE UNITED STATES

Within a year of the repeal of the National Maximum Speed Limit in the United States, 23 states had raised their rural interstate speed limits to 70 or 75 mph. The effect on rural interstate fatalities was examined by modeling fatalities between 1992 and 1999 against the size of the new speed limit (no change, 70 mph, and 75 mph), the period before and after the speed limit change (1992 to 1995 vs. 1996 to 1999), and their interaction. Fatalities in the groups of states that raised their speed limits to 75 mph and 70 mph were 38% and 35%, respectively, higher than expected based on fatalities in the states that did not change their speed limits. Furthermore, the states that raised their speed limits to 75 mph had a higher rural interstate fatality rate before the speed limit was changed than the other groups of states.

Pedestrian exposure and the risk of child pedestrian injury

The authors used data from the New Zealand Household Travel Survey to examine the extent to which childrens pedestrian exposure varies with age, sex and household income. Pedestrian injury morbidity data were combined with pedestrian exposure data to examine age‐specific pedestrian injury risk. The annual number of road crossings for girls was greater than that for boys. Pedestrian exposure increased with increasing age. Children aged 5‐9 years in the lowest household income bracket crossed approximately 50% more roads than those in the middle and upper income brackets. However, for children aged 10‐14 years there was little variation with household income. Sex differences in pedestrian injury rates cannot be explained by differences in exposure although increased exposure may partly explain the increased injury rates for children in lower socio‐economic groups. Prevention strategies might aim to reduce pedestrian exposure or alternatively to reduce pedestrian injury risk per unit of exposure by making safer urban living environments.

Characteristics and Risks of Drivers with Low Annual Distance Driven

Objectives. It has been noted by several authors that risk (defined only in terms of total expected numbers of crash involvements per total distance driven) paints a misleading picture of crash liability, particularly for the young and the old, as their high risk is associated with risky driving patterns typical of people who drive low annual kms. This article sets out to analyze these driving patterns of low-km drivers and to evaluate the risk of these patterns. As licensing programs tend to focus on young and old drivers, who tend to drive lower annual distances, income and employment data are also analyzed for low-km drivers. This is to provide a better picture for policy makers of the sort of people and the sorts of transportation requirements that their policies may affect. Methods. Crash data and travel data were disaggregated by driver characteristics and by driving conditions (road type, day and night, weekend and weekday) and combined to form estimates of risk for typical driving patterns of driver groups. Characteristics of driving patterns and of the drivers themselves were derived for groups defined by age and by the amount of annual driving undertaken. Results. Older drivers who drive less tend to have higher risk per km mainly due to their predominantly urban trips. Nevertheless, because older drivers on average manage to reduce their risk per distance driven by choosing driving patterns that are safer than the driving patterns of other age groups, the risk of older drivers as a group is not overestimated. Conclusion. Despite being quite different from one another, the low- and high-km driving patterns of younger drivers were found to impose identical risks.

The New Zealand open road speed limit

This paper examines changes in vehicle speeds and safety since a 50 mph open road speed limit was imposed in New Zealand in December 1973 as a fuel saving measure. It is concluded that the reduction in road injuries in the year following the change was consistent with contemporary claims that changes to the rural speed distribution were major causative factors. These changes included a sharp drop in rural mean speeds and a sharp contraction in the spread of these speeds. Although mean speeds have since climbed to nearly their 1973 levels, the spread of speeds, manifested particularly by the number travelling at very high speeds, remains smaller than in 1973. It would appear probable that this factor is still favourably influencing road injury levels. It is also suggested the lack of a discernible link between rural speed limit violations and speeds since 1974 should raise questions as to the effectiveness of speed law enforcement in New Zealand.

The safety implications of some control changes at urban intersections

Injury accident data for a sample of New Zealand urban intersections were analysed, looking for an increase or decrease which coincided with a change in control. Increases or decreases were also looked for in certain types of accidents and in accident severity. The control changes considered were from give way signs, stop signs and no control to signals and small roundabouts and also from no control to give way and stop signs.

DEREGULATION OF HEAVY FREIGHT TRANSPORT IN NEW ZEALAND AND ITS EFFECTS ON ROAD SAFETY.

In October 1983 the deregulation of the road freight industry in New Zealand began with the removal of a 150 km restriction on road carriage in competition with rail and the replacement of a quantitative road transport licensing system with a qualitative system. The effects of this change on freight movements and road safety are analysed. Although rail instituted measures aimed at increasing efficiency while reducing its freight rates and increasing its responsiveness to customers’ needs, the road freight activity increased after deregulation. The study concludes that after the deregulation the trucks’ share of accidents has increased except in the case of urban fatal accidents where it shows an opposite trend.

Adoption of right turn on red—Effects on injury accidents at signalized intersections: A comment on Zador, Moshman and Marcus

Zador, Moshman and Marcus estimated an increase in right-turn accidents of 21% following the adoption of right turn on red. However, their study contained property damage only accidents, as well as injury accidents, and the change in injury accidents was not reported. An insignificant decrease (-0.7%) in accidents involving incapacitating injury was reported, however. It is suggested that Zador et al. report on the change in injury accidents in their sample.