3 May 2002
Marijuana, driving and police testing
Researchers at Swinburne University of Technology have proved that marijuana significantly affects driving performance.
The research, by the Centre for Neuropsychopharmacology, also showed roadside sobriety tests used by police to detect drivers impaired by marijuana are effective, despite the tests relative crudity.
The research, supported by VicRoads, used volunteers who were given marijuana cigarettes to smoke. The volunteers then completed the standard field sobriety tests used by the police on drivers they believe are drug impaired.
Although the sobriety tests are relatively simple, such as standing on one leg for thirty seconds or walking in a line and turning around, the research showed the tests can indicate a driver is drug impaired.
A driving simulator was also used to see if performance in sobriety tests correlated to driving ability.
Katherine Tzambazis the Co-ordiantor of Swinburne's Drugs and Driving Research Unit said, "our research shows that marijuana affects driving in different ways to alcohol. For example lane weaving rather than slower reaction time seemed to be the main impairment for volunteers, particularly those who were not heavy users prior to the tests."
Some of the volunteers were regular heavy users and said they, "usually took much larger doses than the 'weak' cigarettes given in the tests."Volunteers who no longer smoked or were occasional users had significantly reduced reaction times as well as lane weaving problems.
The marijuana cigarettes were provided by the American National Institute on Drug Abuse (NIDA) to enable Swinburne to conduct the research.
The Federal Government has given a $400,000 grant for Swinburne to continue the research. A larger study group will be used and the team at Swinburne will be looking at how combinations of alcohol and marijuana affect driving.
_______________________________________________________________________________________Contacts: Mark Heaney or Heather Crosling, Media Liaison Tel (03) 9214 5123 Mobile 0416 174 962
Email: Mheaney@swin.edu.au
Katherine Tzambazis - (03) 92145002 mobile 0403 209 802 email ktzambazis@swin.edu.au
Backgrounder -· Unlike alcohol marijuana produces a complex range of chemicals in the body which makes detection extremely difficult. Drivers suspected of being impaired by marijuana, having failed the sobriety test, are asked for blood samples.
· There are no set limits for permitted levels of marijuana in the blood of drivers. Successful prosecutions have been against drivers who have been severely impaired during sobriety tests and whose blood tests show the presence of THC (the active ingredient in marijuana).
· Swinburne had to apply to the Federal Australian Government for a permit to hold marijuana. It has to be stored in a safe with additional security and log books kept to record how it is used.
· Once Swinburne received the Australian permit it applied to the National Institute on Drug Abuse (NIDA) in the U.S.A. who donated marijuana cigarettes containing measured doses of the drug.
· The research involved 40 volunteers who were selected using strict ethical guidelines laid down by the University. All those in the sample group had taken marijuana at some stage prior to the research and were given medical examinations before the trial started.
· Katherine Tzambazis is a Post Doctoral Fellow and is the Coordinator, Drugs and Driving Research Unit. She has recently returned from a visit to the Los Angeles Police Department(LAPD). Researchers associated with the LAPD are interested in how the tests indicated marijuana users had different physical impairment to alcohol users. California does not randomly test drivers. Police there need to form an opinion on which class of drug they suspect a driver of taking before demanding a blood test.
· Katherine was trained by a member of the Victoria Police to carry out the sobriety tests in the same way a police officer would on the general public.
· Volunteers completed three sets of tests. Each session started with a controlled smoke of a marijuana cigarette, which was either high or low in dosage or was a placebo. Participants then performed sobriety tests and a driving simulator test. Blood samples were taken throughout each session (seven per session - 21 in total).
· Performance on sobriety tests and driving simulator tasks were correlated with the presence of THC (the active ingredient in marijuana) in blood and frequency of cannabis use in their private life.
· Volunteers had to be taught to smoke in a standard way to ensure consistency of dosage.
· The volunteers completed five sobriety tests. The Standard Field Sobriety Tests (SFSTs) used by the police contains three tests: 1. Horizontal Gaze Nystagmus (HGN) - the participant has to follow, with their eyes, an object moving horizontally and then vertically 12-15 inches in front of their face. 2. Walk and Turn (WAT) - the participant walks a straight line marked out on the ground, taking nine steps up the line, turning around and taking another nine steps back up the line, while counting each step out aloud. 3. One Leg Stand (OLS) - the participant stands on one leg, with the other stretched out in front of them, while counting out aloud for 30 seconds starting at 1000. The two additional tests were: 1. Romberg Balance (RB) - the participant stands with their feet together, arms by their side, head tilted back slightly and eyes closed for 30 seconds (estimated by participant). 2. Finger to Nose (FTN)) - the participant extends their arms at shoulder height, tilts their head back, close their eyes and then brings the index finger of the specified arm to touch the tip of their nose.
· Sobriety tests, specifically the three used by the police, predicted impaired driving ability, caused by both low and high levels of cannabis, considerably better than chance (76.3%). The best test of impairment associated with the consumption of marijuana was the One Leg Stand.
· The research also identified a possible new element to the tests, 'head movements/jerks' (HMJ) where participants are unable to keep their head still while following a moving stimulus. The research indicted that including HMJ in the SFST increased the likelihood of drug impaired drivers being identified.
· Questionnaires indicated that the cannabis cigarettes used in the study were subjectively similar to cannabis cigarettes usually smoked by regular cannabis users ('street cannabis').
· Results from the driving simulator task indicated that driving is impaired approximately 80 minutes after smoking low and high dose cannabis.
