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“
There was a reduction of average speed on simulated motorway driving when
participants had the high or low doses of cannabis. This strongly suggests that the
participants as drivers are aware of their impairment, but attempt to compensate for
their impairment by driving more cautiously.
Also in the simulator trials, participants reacted more slowly to a pulling-out event
when they had taken the low dose of cannabis, suggesting a similar compensatory
action for the effects of cannabis impairment. However, when taking the high dose
this effect was not significant. When considering the simulator tracking tasks,
participants tended to drive less accurately on the left and right loops of the ‘figure of
eight’ when they had been on the high cannabis dose. This suggests that they were
unable to control their steering as well when under the influence of the high cannabis
dose. This again confirms previous observations that cannabis adversely affects
drivers tracking ability.
There is a variability in the results when considering the impairing effects of
cannabis that has been observed by other researchers. The variability of drug effects
on individuals is well recognised and this seems to be even more in evidence with
cannabis than other with drugs. The failure to produce significant results on various
driving performance measurements when compared to alcohol may be explained by
the more variable effects of cannabis on participants.
The results of the driving related laboratory tests conducted in general did not
produce statistically significant results. Although reaction times were found to
increase with dose level, there was too much variability in the data for statistical
significance. This suggests that there may be an effect on the reaction time of
participants responding to hazards, but it is quite a small effect which would require
a much larger sample to determine whether or not it was statistically significant. This
again confirms earlier observations of the effects of cannabis on the various aspects
of driver performance; the effect on reaction time being somewhat difficult to
predict.
...
Overall, it is possible to conclude that cannabis has a measurable effect on psychomotor
performance, particularly tracking ability. Its effect on higher cognitive
functions, for example divided attention tasks associated with driving, appear not to
be as critical. Drivers under the influence of cannabis seem to compensate to some
extent for the impairment, that they recognise, by reducing the difficulty of the
driving task; e.g. by driving more slowly. In terms of road safety, it cannot be
concluded that driving under the influence is not a hazard, as the effects on various
aspects of driver performance are unpredictable. In comparison with alcohol
however, the severe effects of alcohol on the higher cognitive processes of driving are
likely to make this more of a hazard, particularly at higher blood alcohol levels.
— The influence of cannabis on driving [11]
”
INSERM (Institut national de la santé et de la recherche médicale) som är Frankrikes motsvarighet till
FHI uttalar sig om cannabis i en omfattande utredning från 2000:
“
To study the effects of cannabis consumption on driving, researchers subject
volunteer drivers (non-users or occasional users) to various batteries of tests
(sensory, psychomotor, or simulator tests) or observe them in an actual driving
situation. Despite various methodological problems—defining the assay procedure,
administration of the substance, or experimental design—the results show a clear
deterioration overall in certain abilities under the influence of cannabis: slowed
reaction time, reduced ability to control a path, poor appreciation of time and space,
impaired or inappropriate response in an emergency. However, different authors still
judge the extent of the impairment very differently, in particular in the actual
situation. Some studies conclude that drivers under the influence of cannabis would
"compensate" for the reduction in their abilities by modifying their behaviour. This
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