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Driving Under the Influence

Volume 476: debated on Thursday 22 May 2008

To ask the Secretary of State for Transport (1) what comparative assessment her Department has made of the effects on driving ability of consumption of (a) cannabis and (b) alcohol; and if she will make a statement; (206624)

(2) whether her Department has a means by which to measure the extent to which driving ability may be compromised by the consumption of cannabis; and if she will make a statement.

The Department has investigated the combined effects of cannabis and low amounts of alcohol. The report ‘The influence of cannabis and alcohol on driving’ was published in 2002 by TRL Ltd (formerly the Transport Research Laboratory) and is available free on-line as report TRL 547 at:

The Department has not commissioned research specifically comparing the effects of cannabis with differing levels of alcohol.

The Department has also investigated the effect of cannabis on driving. The report ‘The influence of cannabis on driving’ was published in 2000 as TRL477 which is similarly available on-line at

In addition the Department's Road Safety Research Report No 12 ‘Cannabis and driving: a literature review and commentary’ was published in 2000 and is available on-line at: