Characteristics of fatal single vehicle crashes

Monash University Accident Research Centre - Report #120 - 1997

Authors: N. Haworth, P. Vulcan, L. Bowland & N. Pronk

Abstract:

This report describes the characteristics of a set of 127 fatal single-vehicle crashes which occurred within 200 km of Melbourne during the period from 1 December 1995 to 30 November 1996. The crashes comprised the cases for the Case-control study of fatal single-vehicle crashes.

The main identifiable factor contributing to the occurrence of fatal single vehicle crashes in this study was BAC>.05 (and particularly BAC>.15) and the main identifiable factors contributing to the degree of severity of the crashes appeared to be impacts with trees and poles and some older vehicles which are unlikely to comply with most of the current safety standards.

A number of possible improvements to procedures for the investigation of serious injury crashes are recommended.

Executive Summary

This report describes the characteristics of a set of 127 fatal single-vehicle crashes which occurred within 200 km of Melbourne during the period from 1 December 1995 to 30 November 1996.

The crashes comprised the cases for the Case-control study of fatal single-vehicle crashes. The cases have location, driver/rider and vehicle characteristics. The controls are (non-crash) trips which also have location, driver/rider and vehicle characteristics. The comparisons of cases and controls to derive relative risk estimates are presented in the companion report entitled Estimation of risk factors for fatal single-vehicle crashes. A summary of the overall study has also been produced (Single vehicle crash study: Summary report).

The aims of the Case-control study of fatal single-vehicle crashes study were to:

investigate single vehicle crashes to determine the circumstances and factors contributing to them
estimate the over-involvement (relative risk) of these factors
identify improvements in procedures for the investigation of road deaths and life threatening injuries
provide information from which countermeasures can be developed to the agencies responsible for road safety in Victoria

This report addresses aims 1 and 3.

CHARACTERISTICS OF THE CRASHES

There were 127 single vehicle crashes in which 133 persons were killed. The crashes had the following characteristics:

Type of crash

almost 75% of crashes involved an impact with a tree or pole or both (71% of metropolitan, 78% of rest of study area crashes)
tree crashes were more common outside the metropolitan area
53% of trees and 36% of poles impacted were in the median or on the right-hand side of the road
31% of crashes involved impact with a tree or pole located within the desirable clear zone outlined in VicRoads policy

Temporal characteristics

crashes were most common from midnight to 6 am and midday to 6 pm
crashes were most common on Saturdays and Sundays
there were no clear seasonal effects

Persons killed

five crashes were multiple fatalities
the driver was killed in 81% of crashes
almost half the persons killed were aged under 25

Drivers and riders

80% were male
more than 40% were aged under 25
natural disease (particularly heart disease) was the cause of death for at least 60% of the drivers aged 60 and over
13% had been severely depressed in the previous six months
13% did not hold a current licence (6% never held a licence, 2% licence lapsed, 6% licence disqualified)

Alcohol and other drugs

BAC was known for 95% of crashes and cannabis known for 83% of crashes. The percentages in this section are percentages of known cases. All of the cases of cannabis being present were in deceased drivers where it was detected as the metabolite, carboxy-THC. This substance may be detected some weeks after cannabis use and therefore its detection does not prove that the driver was under the influence of cannabis at the time of the crash.

BAC>.05 in 36%, BAC>.15 in 27% of crashes
cannabis was most commonly found in conjunction with alcohol:
for BAC>.05, cannabis was present in 49%
for BAC>.15, cannabis was present in 52%
but for BAC<.05, cannabis was present in only 6%
males were twice as likely as females to have BAC>.05 but the proportions of these with BAC>.15 were similar for males and females
no alcohol or cannabis was present in drivers aged 60 and over
drivers aged 25 to 59 were more likely to have BAC>.15 than those under 25
higher levels of education were related to fewer drivers with BAC>.05 or cannabis for 25 to 59 year olds but not for under 25s
proportions of crashes with BAC>.05 or cannabis were similar in metropolitan and rural areas
BAC>.05 was found more often on major roads than freeways, highways or minor roads
cannabis was detected for 23% of male drivers and 11% of female drivers
cannabis was detected in 21% of those under 25 and 25% of those aged 25 to 59
cannabis-involved crashes were less common on highways than freeways, major roads or minor roads
information about consumption of prescription and non-prescription drugs was available for 78% and 73% of drivers, respectively
17% of drivers had taken prescription drugs in the 12 hours prior to the crash (14% of under 25s, 18% of 25 to 59s and 27% of those aged 60 and over)
3 drivers or riders had taken non-prescription drugs in the 12 hours prior to the crash

Passengers

74 passengers of whom 30 were killed
were more likely to be of the same sex as the driver than to be of the opposite sex or at least one of each sex
young drivers were more likely to have passengers than other drivers
most passengers were in the same age group as the driver of the vehicle (particularly for under 25s)
in four of the 24 crashes for which BAC of both driver and (killed) passenger were known, the BAC of the driver was greater than that of the passenger

Vehicles

10 crashes involved motorcycles, 7 involved light commercial vehicles and 3 involved trucks
six of the 10 motorcycles had an engine capacity of greater than 500 cc but none of the motorcycles with an engine capacity greater than 260 cc was ridden by a learner or probationary rider
almost 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

60% of crashes occurred in Melbourne metropolitan area, 40% in the remainder of the study region
most crashes occurred on highways (42%)
a larger proportion of crashes occurred on highways and a smaller proportion on minor roads in the metropolitan area compared to the rest of the study area
two-thirds of the crashes occurred on undivided roads (58% of metropolitan, 77% of rest of study area)
half of the crashes occurred where the speed limit was 100 km/h or 110 km/h (23% of metropolitan, 82% of rest of study area)
about one-third of the crashes occurred on curves (27% of metropolitan, 36% of rest of study area)
20% of metropolitan and 8% of rest of study area crashes occurred at intersections (most commonly T intersections)
traffic controls were present at the site of 13% of crashes (18% of metropolitan, 6% of rural)
mud, oil or loose material was present on the road surface for 10% of crashes in the rest of the study area
the road had a shoulder for 62% of metropolitan crashes and 96% of rural crashes. In the metropolitan area, 49% of shoulders were sealed compared with 20% of rural shoulders

POSSIBLE IMPROVEMENTS IN INVESTIGATION PROCEDURES

In order to improve the availability of information about severe crashes, it was recommended that:

The availability of toxicological information for drivers who may be charged be investigated and, if necessary, a procedure be developed to incorporate the BAC data into the State Traffic Accident Record at an appropriate time (perhaps after completion of criminal procedures).
Given the lack of information on drugs in nonfatal crashes, perhaps testing of all (or a given proportion) of blood samples for drugs should be undertaken for a specified period to increase our knowledge in this area.
Blood samples of all drivers in fatal crashes (whether or not injured) be taken and analysed for both alcohol and other drugs. An alternative would be to have blood samples taken and analysed whenever the breath shows alcohol (building on the strong relationship between alcohol and cannabis).
The family's right to object to autopsy be maintained but that the authorities have the right to take and analyse a blood sample from the deceased.
Testing for the active ingredient, rather than the metabolite, of cannabis be undertaken, at least for fatal crashes in the short term. Improvements in technology may reduce costs etc and allow this to be extended to nonfatal crashes in the future.
Vehicle Identification Numbers (VINs) be recorded to allow better identification of makes and models of vehicles and judgements of the presence of safety features. Currently, VINs could be added to the State Traffic Accident Record routinely by interrogating the registration data, using the vehicle registration number. In the future, automatic capture of VINs at the crash site may replace this method.
In addition, for the next couple of years, it would be desirable if deployment of airbags could be recorded.
It is probably preferable for items regarding the state of the vehicle immediately prior to the crash (e.g. heating and ventilation) to be collected in special studies, rather than to burden the Police with additional workload for every reported crash.
While resource limitations are an important issue which needs to be considered, it may be useful from the point of view of training Accident Investigation Section staff and developing a high quality knowledge base for prevention, to have a special focus on particular crash types (or perhaps even locations) for a particular period.

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