As more Californians partake in medical marijuana, the challenge for law enforcement becomes how high is too high to be operating a motor vehicle? Police across the country have become increasingly confused by what constitutes stoned driving and what the limits are, much like limits for blood alcohol.

Recently a Michigan man was pulled over for speeding and the deputy detected a strange odor emanating from the vehicle. A later blood test revealed the driver had traces of THC (tetrahydrocannabinol), marijuana's active ingredient. Michigan has a zero-tolerance policy for drugged driving, but the driver was issued the medical marijuana for treatment of a hernia and rheumatoid arthritis. If he is convicted, his license may be suspended and due to a DUI conviction years ago, could face one year in jail.

The challenge for law enforcement has become: what constitutes too high to drive?

From 2009 to 2011, the number of Colorado drivers testing positive for THC, doubled. In a California survey conducted on two weekend nights over the summer, nearly 7 percent of drivers had positive THC tests.

In order to test for THC, a driver must submit to a blood test; there is no "Breathalyzer" for marijuana. In California, there is a "Drug Recognition Exam" also referred to as a DRE. This is a more complicated version of the Field Sobriety Tests such as the walk the line test that are used to determine if you are under the influence of alcohol. Special complications arise when an officer not trained in the use of the DRE attempt to determine the level of impairment a person has for drugs.

If you receive a DUI ticket for drugged driving in California, you need a traffic ticket expert to help you fight it.