Feature

Drinking Drivers: You and me, or social deviants?

What sort of people are causing carnage on the road?

John Bailey

The Government tells us that "If you drink then drive, you're a bloody idiot". Since nearly all of us drink, and most drive, it seems likely that a high proportion of people drink and drive to some extent. Does this make most of us bloody idiots? I think not.

I have been studying drinking drivers in New Zealand for 25 years. In that time my research has shown clearly that the problem of drinking and driving, at least as it leads to accidents, is strongly associated with a small minority group. By studying such accidents, we can learn how to focus interventions on the groups at greatest risk, and so minimise the damage they cause.

We need data to study the problem. Much of the data on drinking and driving in New Zealand is of poor quality and can be quite misleading. For example, the accident reports of the Land Transport Safety Authority (LTSA) record in most cases only whether the driver was believed to have been drinking.

The best measure is a blood or breath alcohol level, since a number of thorough studies overseas have shown that until a driver has a blood alcohol level of about the legal limit in New Zealand (80 mg/100 ml), he or she is not at heightened risk of an accident. LTSA labels drivers who probably had a blood alcohol level below the legal limit as drinking drivers, and misses other drinking drivers because the investigating policeman failed to identify alcohol -- possibly because the driver had already been taken away by ambulance. LTSA fails to report on many injury road accidents, because the police either were not notified or did not attend the accident.

I will limit my comments to drivers involved in fatal accidents, since virtually all such accidents are reported to the authorities, and blood samples are taken from about three-quarters of the fatally injured drivers. However, even in these accidents the information is incomplete -- only about 30% of surviving drivers in fatal accidents are tested for alcohol.

To maximise the information available on the fatal accidents, I combined data from ten different files:

• the accident reports of the LTSA
• the post-mortem reports from ESR
• Coroners' reports
• Court data on prior traffic convictions
• Court data on prior criminal convictions
• LTSA's quick fatal accident report
• LTSA's breath test reports
• hospital blood alcohol results of injured drivers from ESR
• the mortality file from Ministry of Health
• newspaper reports

This has provided me with the most comprehensive database on fatal road accidents in New Zealand (for the years 1991-1993) ever acquired.

I interrogate this database to study the characteristics of various groups of drivers involved in fatal accidents. This shows the contribution made to the road toll by various groups and shows how, for example, the drinking drivers differ from the non-drinking drivers.

Since the information on alcohol levels is not complete, we cannot be certain as to exactly what proportion of fatal road accidents involve alcohol in excess of the legal limit. It is probably about 35%. Approximately half of all fatal accidents involved one or more drivers who had drunk some alcohol. The available evidence is that, for the extra 15% or so of drivers not over the legal limit, alcohol was probably not a contributing factor. In some cases the driver may have been impaired by a drug such as cannabis. At present, we have very little information on cannabis in road accidents. We are currently researching this at ESR.

We can say more about the differences between various groups of road users and the characteristics of the groups.

The most important feature of the drinking drivers is that their blood alcohol levels are very high. The average level, for those over 80 mg/100 ml, is about 180 mg/100 ml. This corresponds to the consumption of at least four and a half jugs of beer -- probably much more if the drinking session lasted more than an hour or two, or if the driver had had a substantial meal. This is not light social drinking. Only a very small proportion -- unknown in New Zealand -- of drivers on the road would have a blood alcohol level in this range.

The next important difference between the drinking drivers and sober drivers who were at fault in the fatal accidents is in their prior offending records. Half of the drinking drivers had a prior criminal conviction, compared with about 20% of the sober drivers. The average number of criminal convictions for those drinking drivers who had a criminal conviction was about 10. Many of the convictions were for violence, drug-taking or burglary. A high proportion of the drinking drivers appear to be habitual criminals.

The prior traffic-offending records show major differences between the drinking and sober drivers. About 40% of the drinking drivers had a prior conviction for drinking and driving, compared with only 10% of the sober at-fault drivers. Many also had prior convictions for dangerous driving, careless driving or driving while disqualified. However, the proportions with a prior conviction for speeding were similar for the two groups. This may be because both drinking and sober at-fault drivers in fatal accidents are likely to be speeding drivers. A more interesting comparison might be with licensed drivers generally.

I compared the prior involvement of drinking and sober drivers in reported injury accidents. The drinking drivers were appreciably more likely to have had a previous accident. Often this was while sober, suggesting that drinking drivers may be poor drivers even when sober.

An appreciably higher proportion of the drinking drivers were aged 20 to 24 than were the sober at-fault drivers. About 90% of the drinking drivers were males. However, the number of female drinking drivers involved in injury accidents has been increasing in recent years, whereas the number of males has been decreasing.

I have found in a number of studies that there are differences between drinking and sober drivers as regards socioeconomic status. A high proportion of the drinking drivers were unemployed, and the unskilled group accounted for more of both drinking and sober drivers than would be expected.

Data on ethnicity is incomplete and sometimes contradictory, since it is measured differently in different sources of data. Maori appear to be seriously over-represented among the drinking drivers, but not among the sober drivers. Some of this is associated with differences in socioeconomic status, but much seems related to different drinking patterns.

So, decide for yourself whether you match the profile given for those drinking drivers involved in serious accidents. If you do, you should seek help before you kill yourself or someone else. Your GP would be a good person to direct you elsewhere. If you do not fit the profile, then carry on with your drinking and driving or otherwise, but keep your alcohol consumption prior to driving to no more than three cans of beer or its equivalent, avoid speeding, which is associated with drinking and driving, and avoid cannabis.

John Bailey is with ESR:Health in Porirua.