Crowthorne, Berkshire, United Kingdom:  Marijuana appears to have less adverse impact on driving ability than does alcohol, according to findings from a recent study by the UK's Transport Research Laboratory (TRL).  The results replicate earlier findings recorded in the US, Australia and elsewhere indicating that marijuana intoxication plays a relatively insignificant role in vehicular accidents.

The TRL study examined the driving performance of fifteen volunteers while under the influence of low and high doses of marijuana, and while sober.  All volunteers were tested using a sophisticated driving simulator.  Researchers found that marijuana appeared to adversely influence subjects' ability to accurately steer a car (so-called "tracking ability"), but found their reaction time and all other measures of driving performance to be unaffected by the drug.  Researchers further noted that subjects were cognizant of their impairment and "attempt[ed] to compensate for [it] by reducing the difficulty of the driving task, for example by driving more slowly."

The authors concluded:  "In terms of road safety, it cannot be concluded that driving under the influence of cannabis is not a hazard... However, in comparison with alcohol, the severe effects of alcohol on the higher cognitive processes of driving are likely to make this more of a hazard, particularly at higher levels."

Similar trials previously conducted by the TRL have shown that alcohol and sleep deprivation have a more adverse impact on driving ability than does marijuana.  Tests from other countries have yielded comparable results.  A May 1998 Australian review of 2,500 injured drivers reported that cannabis had "no significant effect" on driving culpability.  A pair of studies released by the US National Highway Traffic Safety Administration in 1992 and 1993 found the adverse effects of marijuana on driving "relatively small," and concluded that "there [was] no compelling evidence that marijuana contributes substantially to traffic accidents or fatalities."

The most recent TRL study was commissioned by the British Department of Environment, Transport and the Regions.

Copies of the TRL study, titled "The influence of cannabis on driving," are available at http://www.trl.co.uk/detr/abstracts/477.htm online.

See Also: http://www.detr.gov.uk/roads/roadsafety/cannabis/index.htm.

http://www.dtlr.gov.uk/roads/roadsafety/cannabis/ - Cannabis and Driving: A Review of the Literature and Commentary Department of the Environment, Transport and the Regions.

http://www.ukcia.org/lib/driving2.htm - Cannabis and Road Safety: An Outline of the Research Studies to Examine the Effects of Cannabis on Driving Skills and on Actual Driving Performance by Dr G.B. Chesher, Department of Pharmacology University of Sydney and National Drug and Alcohol Research Centre University of New South Wales.

http://www.ukcia.org/lib/driving3.htm - Drugs and Accident Risk in Fatally-Injured Drivers by Olaf H. Drummer, Ph.D., Victorian Institute of Forensic Pathology, Australia.

http://www.ukcia.org/lib/driving.htm - Marijuana And Actual Driving Performance Conducted by: U.S. Department of Transportation, National Highway Traffic Safety Administration (DOT HS 808 078), Final Report, November 1993 Conducted by: HWJ Robbe, Institute for Human Psychopharmacology, University of Maastricht, The Netherlands.