CHAPTER 4: PREVALENCE OF DRUG DRIVING
The objectives of this chapter are to:
- outline the prevalence of drug driving in 17-39 year old drivers
- identify the characteristics of those who have driven under the influence of drugs
- identify any link between drug driving and sensation seeking, a personality characteristic frequently found to be related to risky behaviours
- explore the circumstances of drug driving
6% had ever drug driven. 3.5% had done so in the last 12 months.
Although lower, these figures were not significantly different from those in the 2000 drugs and driving survey and may be a result of under-reporting of drug use
Analysis of demographic variables showed:
- men were no more likely than women to report drug driving
- there were no clear age trends
- single people were more likely to have drug driven in the past year than those who live with a partner
- more people who do not drive often, reported drug driving than those who drive every day or every week
- drug drivers have higher sensation seeking scores than other drivers
The drug most commonly used before driving under the influence was cannabis.
Most journeys were for social reasons
The recreational drug users mostly drove while under the influence for social and personal reasons
The problem drug users said that they were almost always under the influence of drugs. Thus every time they drove, they were under the influence.
Prevalence of drug driving
Respondents who had ever used any drugs were asked if they had ever driven a vehicle within a defined period of taking each drug they reported having taken. For example, a respondent who reported having used cannabis was asked if they had ever driven within 12 hours of taking cannabis. The period varied depending on the drug. The shortest period was 30 minutes for Amyl Nitrate to 24 hours for Heroin. Times were chosen to reflect, as closely as possible, the time within which each substance was likely to have an impairment effect.
Across the sample as a whole, 6% of respondents said they had ever driven under the influence of any drug and 3.5% had done so in the last 12 months. As a proportion of those who had ever taken drugs, 16% had ever driven under the influence of drugs.
In 2000, 10% of respondents said they had ever driven under the influence of drugs and 5% of respondents said they had done so in the last 12 months. As shown in Figure 4.1, this represents a decrease in the prevalence of drug driving. It is important to note, however, that this decrease is not statistically significant, i.e. it is not large enough for us to say that it is not caused by the type of random variation that might be expected in a sample survey like this.
Figure 4.1: Drug driving ever/past twelve months
Base: All drivers 17-39 years (1,008), All drivers 17-39 years (1,031)
However, having concluded in the previous chapter that recent drug use was likely to have been under-reported, we need to consider the implication of this for our estimate of drug driving, since the two are directly related in the survey design. 8
The only reasonable assumption that can be made about the impact of under-reporting is that the relationship between 'ever' drug use and drug driving is as stable as the relationship between 'ever' drug use and recent drug use. If this were the case it would suggest that, rather than 16% of recent drug users having driven while impaired, the figure should be closer to the 29% recorded in 2000. This results in an estimate of 11% ever having driven under the influence of drugs, with 6% having done so in the previous twelve months. While this suggests a slight increase in drug driving since 2000, this is not statistically significant, i.e. it is likely to be attributable to sampling variation rather than any real change.
The important conclusion to draw from this is that drug driving among 17-39 year old drivers appears to be no more or less prevalent than it was five years ago. This is true whether we take the figures directly as they were reported by respondents or make adjustments to account for under-reporting.
The other important conclusion to draw from this is that the most likely explanation for under-reporting is that there is more stigma attached to drug use than there was in 2000, which makes people less likely to report their behaviour. This might be context sensitive, i.e. in the context of a survey about driving. It suggests that, although evaluation research questioned the effectiveness of the drug driving campaign, 9 this and more general campaigns directed at drug use, notably the "Know the Score" campaign, 10 may have impacted on perceptions of impaired driving at least to an extent that makes people less likely to want to admit to it (in spite of assurances of confidentiality). While the prevalence of drug driving has not decreased since 2000, this under-reporting might indicate increased stigma around drug use in general, and with driving while impaired by drugs.
Characteristics of drug drivers
In order to successfully target campaigns, it is crucial to identify which groups are most likely to drive while impaired by drugs. As noted in Chapter 3, drug use was associated with gender, age and marital/living status.
As Figure 4.3 shows, 8% of men said they had ever driven while impaired by drugs and 4% said they had done so in the previous 12 months. The proportions of women who said they had drug driven was 5% for the 'ever' measure and 2% 'in the previous 12 months'. Although women appear to be less likely to drive while drug impaired, the difference is not statistically significant. Also, when compared with the 2000 survey, it is clear that the proportion of women who had driven while impaired by drugs has not increased over the previous five years, despite the recent upwards trends in drug use and driving patterns among women.
Figure 4.3 Differences in drug driving between men and women
Base: Drivers 17-39 years (1,031), Male drivers 17-39 years (502), Female drivers 17-39 years (529)
Drug driving is also associated with age. Previous research has suggested that younger drivers may be more likely than older drivers to drive while impaired by drugs. In 2000, more drivers in the 20-24 year old age group (13%) had taken drugs and driven in the past 12 months. This figure decreased across the age groups with only 1% of 35-39 year olds drug driving in the previous 12 months.
In the 2005 survey, the age demographic does not follow such a clear pattern, as displayed in Figure 4.4 below. Consistent with the findings for drug use, those most likely to have drug driven in the last 12 months were in the 20-24 year or 30-34 year age bands. A very small number of 17-19 year olds reported drug driving.
Figure 4.4 Differences in drug driving by age group
Base: Drivers (1,031), 17-19 year old drivers (62), 20-24 year old drivers (177), 25-29 year old drivers (209), 30-34 year old drivers (271), 35-39 year old drivers (312)
Figure 4.5 shows variation in drug driving by living/marital status. Similar proportions of respondents who lived on their own ( i.e. not with a partner) and those who lived with a partner said they had ever driven while impaired. However, more respondents who lived on their own reported having drug driven in the previous 12 months (6% of respondents who lived on their own compared with 1% of respondents who lived with a partner).
4.5 Variation in drug driving by Marital/living status
Base: All drivers 17-39 years (1,031), On own (484), With partner (547)
Drug driving was also examined by frequency of driving and this is shown in Figure 4.6. For both the 'ever' measure and the previous 12 months, those who reported that they did not drive often were more likely to have driven under the influence of drugs.
Figure 4.6 Variation in drug driving by frequency of driving
Base: All drivers (1,031), Drivers who drive every day (828), Drivers who drive weekly (160), Drivers who do not drive often (43)
Drug driving and sensation seeking
Respondents also completed a sensation seeking scale. The concept of sensation seeking was developed by Zuckerman and is defined as "the need for varied, novel, and complex sensations and experiences, and the willingness to take physical and social risks for the sake of such experiences." 11 The scale used in the survey was devised by Arnett and has been used in previous studies of driving behaviour. 12 Across the 20 items in the scale, respondents could score between 20 and 80 depending on the extent to which they thought each 'sensation seeking' item applied to them. A higher score indicates a higher propensity for sensation seeking.
Figure 4.7 shows the mean sensation seeking scores for drivers who had ever taken any drugs but not driven while impaired, those who had ever driven while impaired but not in the previous 12 months, and those who had driven while impaired in the previous 12 months. Recent drug drivers had the highest sensation seeking scores while those who had drug driven ever had higher scores than those who had used drugs but not driven while impaired. Non-drug using drivers had the lowest scores. Significance testing found that the two drug driving groups did not differ between themselves on sensation seeking but scored significantly higher than those who had used drugs ever and the rest of the population. Those who had used drugs in the last 12 months had significantly higher scores than those who had used drugs ever.
Figure 4.7 Mean sensation seeking scores
The implication of this is that the sensation seeking scale distinguishes people with personality characteristics associated with drug driving. This is discussed further in subsequent chapters.
Circumstances of drug driving
Respondents in the 2005 survey who had driven while impaired by drugs were asked to think about the last time they had driven a vehicle after taking drugs. Table 4.1 shows which drugs they had taken. The most commonly reported drug was cannabis. However, over one in ten had driven under the influence of stimulants (13%), opiates (12%) or suppressants (15%). Six percent said they had also had something alcoholic to drink in addition to the drugs but 10% said they could not remember. This suggests that the 6% may be an under-estimate of whether alcohol was also involved.
Table 4.1 Categories of drugs ever driven under the influence of/driven under the influence of in the last twelve months
Last time drug driven
Base: All drug drivers (36)
These respondents were also asked where they were going to/from the last time they had drug driven. Many were going to or from a friend's or relative's house (49%). Almost one in five (17%) said they couldn't remember. The majority of respondents (67%) said they were driving on their own but 17% were driving with a passenger. Again, a high percentage said they didn't know or couldn't remember (16%).
Further details on the purposes of journeys when people were under the influence of drugs were gained from the depth interviews. For the recreational drug users, drug driving occurred mainly at weekends and involved driving relatively short distances to visit friends or to drive to clubs and pubs for nights out, mirroring the results from the survey.
The problem drug users said they were almost constantly under the influence of drugs and, therefore, under the influence every time they drove. Most drove to such an extent that drug driving was considered to be ' just a normal routine, just everyday life'. Although some of the interviewees used the car for relatively short journeys, others were spending a lot of time on the road and travelling long distances. A small number were even driving as part of their employment.