Road Safety Part 1: Alcohol, drugs, ageing & fatigue - Spring 2003


The Government's ten-year road safety strategy "Tomorrow's Roads - Safer for Everyone" outlined 3 priority areas for research into drug driving:

  • Research to identify the extent of the drug driving problem;
  • Research to identify those drugs which are a particular cause for concern for road safety; and
  • Research to improve enforcement methods.

Previous research has helped to improve our knowledge of the extent of the problem and those drugs that are primary concerns. Current research is focusing on the third of these priorities - ways to improve the enforcement techniques available to the police.

Recently completed projects

The Interaction of Cannabis and Alcohol

Overseas surveys have consistently demonstrated that cannabis users frequently drink alcohol to levels lower than the drink drive limit, whilst consuming moderate amounts of cannabis. The same pattern of consumption is less evident in this country, but consideration needs to be given to the possible impairing effects of a combination of moderate levels of each.

A group of experienced cannabis and alcohol users carried out a similar range of tests to those employed in the original cannabis research, under the influence of cannabis, alcohol and combinations thereof, as well as placebo conditions. The levels of cannabis and alcohol used in the research (low dose cannabis, THC 1.67%; <50mg/100ml BAC respectively) were, in isolation, unlikely to produce significant levels of impairment. However, this research explored the theory that in combination the two drugs have an impairing effect greater than that of either in isolation.

Key findings:

The combination of alcohol and cannabis was shown to have a more severe effect on aspects of driving performance than either cannabis or alcohol in isolation. Although the research showed some interaction effects, these were not as great as might have been expected, possibly due to the relatively low levels of each substance employed in the study.

The finding that cannabis reduces driver's self confidence was not moderated by alcohol, which has been shown to have the opposite effect.

Publication: TRL Report 543

Available free to download at the TRL website:

Next steps: Consideration is now being given to a targeted publicity campaign on the dangers of driving under the influence of drugs, or in the hours after consuming drugs, when driver fatigue becomes a problem.

Over-the-counter Medicines and the risk of driver sleepiness

This report, compiled by Loughborough Sleep Research Centre, identifies those medicines available over the counter (OTC) that have the potential to cause drowsiness, and therefore the potential to be hazardous to drivers and other road users. A total of 102 medicines for the treatment of coughs and colds, allergies, pain, nausea and gastrointestinal upsets were identified, all with the potential to cause sedation.

These medicines fall into three main groups, antihistamines, opioids and muscarinic antagonists.

From the literature it is clear that the antihistamines cause the most sedation. One subgroup, the classical H1-receptor antihistamines are particularly sedating, and are even used for the relief of temporary sleep disturbance in some instances.

The impairment caused by the recommended doses of at least two of these drugs is greater than that caused by the legal blood alcohol concentration limit for driving in this country. The elderly are particularly vulnerable to the sedative effects of these drugs. In old age, renal dysfunction develops. The excretion rate of these drugs decreases and drug accumulation occurs within the body. Recommended doses of drugs that normally do not cause impairment, will begin to cause drowsiness and affect performance in these people. Many of the medicines examined do not carry specific warnings for the elderly.

The interactions between drugs were also considered. The majority of the reviewed substances enhanced the sedating effect of ethanol.

A person impaired in this way, but still legally allowed to drive, is a potential hazard to themselves and other road users. It is highly likely that people will combine several OTC drugs for the treatment of an ailment. It is often the belief that as medicines contain different compounds they will not have an additive sedating effect; this is not the case.

The labelling on these medicines warning the consumer of potentially sedative effects was also considered. This labelling was not consistent.

Several medicines that were recommended by the British National Formulary (BNF) to have such labelling had none on the packaging. Even within classes of medicine there appears to be no labelling consistency. Several mentioned drowsiness as a side effect on the package insert, but no mention of this was made on the exterior packaging.

The report concludes that the labelling of OTC medicines liable to cause drowsiness needs to be monitored more closely.

Publications: Road Safety Report No. 24 - Over-the-counter medicines and the potential for unwanted sleepiness in drivers: a review Available free to download from DfT:

Next steps: DfT is discussing the findings with the Medicines Control Agency in order to address this issue.

Antidepressants and Driving

Antidepressants are used to relieve severe depression and are classified according to their chemical structure (for example, tricyclic antidepressants - TCAs) or their biochemical actions (for example, monoamine oxidase (MAO) inhibitors and SSRIs - selective serotonin reuptake inhibitors). Modern day antidepressants such as SSRIs are widely considered to have less impairing effects than previous treatments.

This project, undertaken by University of Leeds, collated in one volume a review of research and literature on the impairing effects of antidepressants and identified those that are most problematic in terms of their effects on driving performance.

The report concludes that there is reliable evidence that older types of antidepressant drug such as TCAs do affect psychomotor functions in a manner that can impair driving and increase accident risk.

However, whereas there is some evidence that newer drugs such as SSRIs can also affect some functions, there is less evidence that driving performance is impaired and very little research that considers the accident risk of these drugs. In addition, far less research has examined other novel antidepressants. At present, those studies that exist suggest that the effect of RIMAs on psychomotor performance is also less than for TCAs. It is too early to conclude that the newer generations of antidepressants do not have implications for driving performance or accident risk. Moreover, the validity of much of the research could be questioned, as it has focused on normal rather than clinical populations, or has been confounded by indication. The report concludes with recommendations for research to investigate further the effects of new generation antidepressants on driving performance.

Publication: Road Safety Report No. 18 -

Antidepressants and road safety - A literature review and commentary.

Available free to download from DfT:

Next steps: DfT is discussing the findings with the Medicines Control Agency in order to address this issue.

Ongoing research

Roadside Evidential Breath Testing Instruments: Practicalities And Suitability Of Available Devices

Currently, drivers who fail or refuse a roadside screening breath test are taken to a police station for a second test of the alcohol level in their body.

This test, known as an evidential breath test, is the only one admissible in court - those results taken at the roadside are not admissible. However, modern roadside breath testers are sufficiently technologically advanced to be able to provide admissible evidence. The introduction of evidential breath testing instruments (EBTIs) at the roadside could streamline the process and allow the police to test more suspects with the same level of resources.

In conjunction with the Home Office and the police, DfT are currently examining the procedural and legal implications of evidential roadside breath testing. Before introducing evidential roadside testing it is clearly necessary to research fully the practicalities associated with taking evidential breath samples at the roadside, as well as assessing the suitability of potential roadside instruments.

This research project will investigate the practicalities of evidential roadside breath testing, and will compare the performance of the various breath testing devices which are considered as potential roadside EBTIs against that of a currently approved EBTI, used at police stations.

Anticipated completion date: April 2003

Monitoring the effectiveness of drink-drive rehabilitation courses

An earlier report into the effectiveness of drinkdrive rehabilitation courses suggested a very substantial reduction in re-offending rates for convicted drink drivers who attend a course. Since then, such courses have become available nationwide, and the current project is monitoring several aspects of the courses in a larger countrywide sample.

The study consists of three main parts:

  • On going data collection and analysis: tracking re-offending rates and the take up of course places by referrals;
  • Monitoring: including an investigation of reasons why some offenders who have been referred choose not to attend;
  • Evaluation: in depth investigation of how the various bodies (course providers, Court Officials, and offenders) interact to identify best practice and assist all providers to maintain high standards.

Anticipated completion date: April 2003

Monitoring the Effectiveness of Police Field Impairment Tests

As several Police Forces across the UK have trained police officers on DRT/FIT, we are keen to monitor the effectiveness of police use of FIT to identify drug-impaired drivers.

This study, carried out by the University of Glasgow Forensic Science Department, collects data from the police forces that have trained officers in DRT/FIT techniques. Biological samples are taken from those whose driving was observed to be impaired by a police officer, who have completed a FIT test at the roadside and for whom the Forensic Medical Examiner certified that a condition that may be due to alcohol or drugs is present. Analysis of drug presence in these samples and its association with the results of the FIT test will provide a measure of the test's effectiveness in correctly detecting drug drivers. The project also presents an opportunity to collect data on both the extent and nature of drug driving cases.

A substantial amount of work has been carried out in Scotland to date, while progress in England and Wales has been slower.

Anticipated completion date: September 2003

Analysis of Borderline Blood Samples

One of the options being considered for improving the current enforcement of drink driving laws is to repeal the statutory provision for a driver to have a breath sample replaced by a blood or urine sample where the breath sample is between 40__g BrAC and 50__g BrAC (Breath Alcohol Concentration).

Before considering a repeal of this section it will be necessary to determine how many drivers exercise this option and, of those who do, how many are above and below the prescribed limit. In particular, it will be important to know more about those drivers below the limit and the reasons why they are below.

Enquiries with the Forensic Science Service (FSS) indicate that they receive about 10 - 11,000 blood option samples per annum from the 43 forces in England & Wales. This is 55% of the total blood samples submitted by police to FSS for alcohol analysis. From the 11000 statutory options submitted for analysis in England & Wales, 75% (8250) are over the prescribed limit (80mg) and 25% (2750) are below. This project will analyse in detail the data stored by the police relating to the 25% of blood option cases that are below the limit, to understand the reasons for this and to provide policy recommendations based on this analysis.

Anticipated completion date: April 2003

Impaired Motorists: Methods of Roadside Testing and Assessment for Licensing (IMMORTAL)

This is a European-Commission funded research project, carried out by researchers from 7 countries (10 institutions). The UK partners are the University of Leeds and DfT provides matched funding for the TRL part of this study.

The TRL study examines the prevalence of illegal drugs both in road traffic accident casualties (hospital sample), and in accident-free drivers travelling at the same times and on the same roads as the RTA casualties (roadside sample). The University of Glasgow Forensic Science Department provides the analysis of body fluid samples collected from both samples.

To date, a successful pilot study at the roadside has been completed with help from Strathclyde Police, with data collection at the roadside and in hospital expected to begin shortly.

Anticipated completion date: December 2004

Labelling of over-the-counter medicines

During previous research, it became evident that the information regarding the ability of medicines sold without prescription to cause fatigue or sleepiness is inconsistently expressed. The labelling on the external package is sometimes inconsistent with the information in the insert found inside. If drowsiness or tiredness as a side effect is stated on a package insert for a medicine, it is assumed that the same statement should be seen on the exterior packaging,

This project examines the package labels and the inserts for several medications to identify inconsistencies. It also examines the way in which warning labels are presented on packaging.

Anticipated completion date: Summer 2003

Further Road Audits on sleepiness

Several road audits were conducted on 3 motorways to highlight areas of the motorway that have a higher than average incidence of sleep related vehicle accidents. The results of these first audits are being disseminated to police forces, road safety officers and local authorities in the vicinity of each motorway, with a view to raising public awareness of the problem and devising effective countermeasures.

This project extends the road audits to other areas suspected of having a Sleep Related Vehicle Accident problem. The project will deliver 6 further road audits on different types of road, and also covering both high and low traffic flows.

Anticipated completion date: May 2003

The interaction between sleepiness and moderate alcohol intake

The extent to which BAC levels below the legal limit compromise road safety is less well established than that for higher levels. There is evidence to suggest that even at levels as low as 20mg/100ml BAC there is some impairment of ability. Another widely recognised road safety problem is fatigue.

Researchers estimate that fatigue is a main contributory factor in 10% of all accidents and 20% of motorway accidents. It is clear that driving in a fatigued state is highly dangerous. Similarly, the effect of alcohol on road safety is well established. What is less well known is the effect that low levels of alcohol may have on drivers who are already in a fatigued state. This project will provide valuable data on the effects of levels of alcohol below the legal limit (80mg/100ml BAC) on driving performance via a series of experiments under laboratory controlled conditions.

Anticipated completion date: March 2004

Forthcoming research

Maintenance of alcohol database III

The existing alcohol database provides information on the blood alcohol concentrations (BACs) of road traffic accident fatalities. These data are supplied by Coroners (England and Wales) and Procurators Fiscal (Scotland) and are linked to the national STATS19 road accidents database. In order for us to be able to detect any change in trends and monitor the drink/drive situation over time, we need the continuous collection and analysis of this information.

This project will enable us to monitor alcohol levels in all types of road traffic casualties for an additional period of three years.

Anticipated start date: April 2003

Further evaluation of the Field Impairment Test

The Field Impairment Test is a roadside test used by police officers to assess impairment due to the consumption of drugs. Previous research evaluating the effectiveness of this test raised two questions. First, are normal, unimpaired drivers able to perform the test with a negative outcome?

Second, what is the cause of the reported 67% disagreement between the results of the FIT test carried out at the roadside by a police officer and the opinion of the police surgeon? This project aims to provide the answers to these questions.

Anticipated start date: Summer 2003

An investigation of the usefulness, the acceptability and impact on lifestyle of Alcohol Ignition Interlocks in drink drive offenders

Over the past 20 years the anti-drink driving public information broadcasts have proved extremely effective at changing attitudes towards drink driving. With this change in attitude has come a gradual shift in behaviour, to the current position whereby the majority of drivers in this country are anti-drink driving. However, there are still too many road traffic accidents involving alcohol, and one group of drivers in particular - repeat drink drive offenders - appear to be particularly resistant to the messages contained in public information broadcasts. In order to reduce further the number of accidents involving drunk drivers it is necessary to consider alternative approaches. One such alternative is the alcohol ignition interlock.

An alcohol ignition interlock (AII) is a device installed in a vehicle, which requires the driver to provide a breath sample every time an attempt is made to start the vehicle. If the driver has a breath alcohol concentration (BRAC) above a specified value, the ignition is locked and the vehicle cannot be started. Consequently, this prevents the drink driver from driving. In addition, the driver of a car fitted with an alcohol ignition interlock is required to provide further breath samples at random intervals.

The system is capable of recording electronically the alcohol breath test results and the attempts to circumvent the system. This data can then be transmitted to a central source and analysed to provide valuable information about the driving behaviour of the individual.

The introduction of alcohol ignition interlocks is a potentially effective measure to reduce the number of drink driving accidents. Alcohol ignition interlocks have been introduced in a number of states in the USA, in Australia, and in Canada, where courts generally prescribe them to drivers who have been convicted for a drink driving violation. In Europe, several pilot projects have already been carried out and there are plans for a demonstration project. In the United Kingdom it has been decided that before considering their introduction, we need to carry out research that examines the practicalities and social aspects of alcohol ignition interlocks use. This project aims to thoroughly examine these issues and to investigate the acceptability of the interlock device to the user and the impact on the lifestyle of the user and the other household members derived from having the interlock device fitted to the family car.

Anticipated start date: Autumn 2003

Effectiveness of motorway service areas in reducing fatigue related accidents

Most people know that it is not safe to drive when they are tired, but too often they carry on instead of taking a break. The full effect on casualties is only now becoming clear. For car drivers, fatigue may be the principal factor in as many as 10% of all accidents. Road audits conducted in conjunction with police forces report that sleepiness is a major cause of serious accidents on monotonous roads in the UK, especially on motorways, where 20% of accidents are thought to be sleep-related.

Short naps and/or caffeine are the only effective countermeasures to sleepiness. The new Highway Code advises drivers who realise they are becoming overtired to take a break, a nap and two cups of strong coffee. The location of Motorway Service Areas (MSA) is therefore potentially crucial in combating driver sleepiness on motorways.

This study will identify what evidence there is regarding MSAs' effectiveness in reducing sleeprelated accidents. It will also examine how their location affects the distribution of sleep-related accidents and will assess the effectiveness of "Tiredness Kills, Take a Break" signs.

Anticipated start date: March 2003

Monitoring the effectiveness of drink-drive rehabilitation programme II

The Road Traffic Act 1991 allows the courts to offer drink-drive offenders the opportunity to attend a rehabilitation course in exchange for a reduction in the period of disqualification. An initial study showed that, overall, those who attended a rehabilitation course were nearly 2.5 times less likely to re-offend compared to those who did not attend a course. Since this study was undertaken, the number of rehabilitation courses has greatly increased. Monitoring re-offending rates, examining the reasons why some offenders offered the course decline, and examining the effectiveness of alternative courses (e.g. probation service courses) is therefore important.

This project will allow for the long-term examination of these issues in a larger group of offenders who attend the rehabilitation courses across the country.

Anticipated start date: April 2003

For more information about any of these projects please contact:

Dr Liliana Read
Research Manager Road Safety Division,
Department for Transport
2/09 Great Minster House
76 Marsham Street
London SW1P 4DR

Tel: 020 7944 2054

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