Serious injury single vehicle crashes

Monash University Accident Research Centre - Report #175 - 2000

Authors: N. Haworth and L. Bowland

Abstract:

This report describes the methods used in the study, the characteristics of serious injury single vehicle crashes and how these differ from fatal single vehicle crashes. It then compares the serious injury crash data with control data to estimate the risk factors for serious injury single vehicle crashes and then compares these with the risk factors previously identified for fatal single vehicle crashes.

The comparison of risk factors for fatal and serious injury crashes was complicated by the poorer data quality for serious injury crashes than fatal crashes for some factors. For both fatal and serious injury crashes, the most important risk factors in terms of prevalence and increase in risk were:

BAC>.05
driver aged under 25
driver aged 60 and over
learner permit or probationary licence
pre-1978 vehicle
curved road

Fatal crashes were more likely to involve impact with a tree or pole than serious injury single vehicle crashes.

Executive Summary

This report describes the characteristics of serious injury single vehicle crashes and how these differ from fatal single vehicle crashes. It then compares the serious injury crash data with control data to estimate the risk factors for serious injury single vehicle crashes and then compares these with the risk factors previously identified for fatal single vehicle crashes.

Characteristics of Single Vehicle Serious Injury Crashes

There were 960 single vehicle crashes in which 1170 persons were seriously injured in the period 1 December 1995 to 30 November 1996. The crashes had the following characteristics:

Type of crash

87% of the crashes involving hitting objects
the object hit was coded as a tree or a pole or post in 55% of all crashes (60% metropolitan, 47% rest of study area crashes)
if traffic signals, traffic signs and guide posts are classified as poles, almost 60% of all crashes involved hitting a tree or a pole or post
impacts with trees were more common outside the metropolitan area and impacts with poles or posts were more common in the metropolitan area

Temporal characteristics

The single vehicle serious injury crashes were most common

from midday to midnight
on Saturdays and Sundays
in December and January

Persons seriously injured

the driver was seriously injured in 85% of crashes
almost half the persons seriously injured were aged under 25

Drivers

66% of the drivers were male
more than 40% of the drivers were aged under 25
6% of drivers did not hold a current licence (2% had lapsed licence)

Alcohol

BAC was known for 51% of crashes. The percentages in this section are percentages of known cases.
BAC>.05 in 46%, BAC>.15 in 23% of crashes
drivers with BACs between .05 and .15 appeared to be somewhat less severely injured than those with higher or lower BAC levels - further data are needed to assess this finding
males were more likely than females to have BAC>.05 and much more likely to have BAC>.15
BAC>.05 was equally common among drivers aged under 25 and 25 to 59. It was considerably less common for drivers aged 60 and over
drivers aged 25 to 59 were more likely to have BAC>.15 than those under 25 or those aged 60 and over
proportions of crashes with BAC>.05 were somewhat greater in metropolitan than rural areas

Passengers

passenger information was reliable only for injured passengers and therefore underestimates numbers of passengers
there were passengers recorded in 41% of crashes
41% of those seriously injured were passengers
passengers were predominantly male (61%) and under 25 (65%)
young drivers were more likely to have passengers (and more passengers) than other drivers

Vehicles

about 20% of the vehicles involved in crashes were manufactured before 1978 and so were not required to comply with some of the current safety standards
age of the vehicle was not related to age of the driver

Locations of crashes

63% of crashes occurred in Melbourne metropolitan area, 37% in the remainder of the study region
40% of the crashes occurred in 60 km/h speed limit areas, while 40% occurred where the speed limit was 100 or 110 km/h
79% of rural crashes and 21% of metropolitan crashes occurred in high speed areas (100 km/h and above).
28% of crashes occurred on curves (24% of metropolitan, 35% of rest of study area)
30% of metropolitan and 9% of rest of study area crashes occurred at intersections (most commonly T intersections)
traffic controls were present at the site of 5% of crashes (6% of metropolitan, 3% of rest of study area)
the road was wet for 28% of crashes

Comparison of Characteristics of Fatal and Serious Injury Crashes

Crash characteristics

The time and location patterns of occurrence of fatal and serious injury single vehicle crashes were similar. However fatal crashes were less likely than serious injury crashes to occur on gravel or unpaved roads and were more likely to occur where a traffic control was present or on divided roads.

Fatal crashes were more likely to involve impact with a tree or pole than serious injury single vehicle crashes.

Driver characteristics

The age distributions of drivers in fatal and serious injury single vehicle crashes did not differ but drivers in fatal crashes were more likely to be male and more likely to be unlicensed.

Drivers in fatal crashes were significantly more likely to be recorded as not wearing seat belts, compared with drivers in serious injury crashes. However, some of this difference may be attributed to the greater reliability of judgement that the driver was not wearing a seat belt in fatal crashes where the judgement may be based on observation, rather than the statement of the driver.

Alcohol

Comparison of the prevalence of alcohol in drivers in fatal and serious injury single vehicle crashes is complicated by the large amount of missing data (almost 50%) for drivers in serious injury crashes. The effect of this missing data is likely to be one of increasing the proportion of positive BAC values in the known data for serious injury crashes.

Possibly as a result of this factor, among the drivers with BAC known, the proportion of drivers with BAC>=.05 was almost statistically significantly higher in serious injury than fatal crashes. However, among the drivers with BAC levels greater than zero, drivers in fatal crashes were more likely to have BACs of .150 and above than drivers in serious injury crashes.

Passengers

There was no significant difference between the proportions of fatal and serious injury crashes where there were passengers present. However, the number of passengers may have been underestimated for serious injury crashes.

Vehicles

The proportions of vehicles manufactured before 1978 did not differ significantly between fatal and serious injury crashes.

Comparison of Risk Factors for Fatal and Serious Injury Crashes

The comparison of risk factors for fatal and serious injury crashes was complicated by the poorer data quality for serious injury crashes than fatal crashes for some factors (particularly alcohol, passengers and seat belts). The prevalence of the factors in fatal and serious injury crashes, compared with controls and the relevant odds ratios are compared in Table 1. In general, the risk factors for fatal and serious injury crashes were similar and the odds ratios were of similar magnitude. Thus for both fatal and serious injury crashes, the most important risk factors in terms of prevalence and increase in risk were:

BAC>.05
driver aged under 25
driver aged 60 and over
learner permit or probationary licence
pre-1978 vehicle
curved road

While the increase in risk associated with not wearing a seat belt was smaller and not statistically significant in serious injury crashes, this difference is likely to have resulted from poorer data quality for serious injury crashes, rather than not wearing seat belts being not a risk factor for serious injury crashes.

Table 1. Summary of risk factors and their magnitude in fatal and serious injury single vehicle crashes. Odds ratios not in bold text are not statistically significant.

Table 1

Possible Improvements in Investigation Procedures

This report identified a number of additional possibilities for improvements in investigation procedures for serious injury single vehicle crashes to improve data relating to alcohol, seat belt use and uninjured passengers.

Sponsoring Organisation: Baseline Research Program - Department of Justice, Transport Accident Commission, Royal Automobile Club of Victoria (RACV) Ltd, VicRoads