Drunk driving charges are serious business in Texas, and a conviction can lead to license suspension or license revocation, significant fines and jail time, among other penalties. A driver can be charged with an offense owing to his or her level of impairment based on objective evidence presented by a law enforcement official or charged with a per se DWI based on the driver’s blood alcohol content or blood alcohol concentration. DWI laws also apply to what is often called ‘drugged driving.” Currently, there are no breath tests available to law enforcement for the detection of drugs, but that soon may be changing.

Scientists have now reportedly developed a method to isolate and measure the amount of THC, the psychoactive ingredient of pot, in an individual’s system. It took many years after the development of a BAC test for alcohol before there was general agreement regarding the level of alcohol in a driver’s system and per se impairment, and that remains controversial to this day. Similarly, there is a lack of consensus among scientists regarding THC level and impaired driving.

It is likely that a pot breath test will be approved by the legislature sooner rather than later. However, it is important to realize that current laws regarding alcohol and breath tests distinguish between pre-arrest testing and post-arrest testing. The roadside test administered as a field sobriety test is voluntary, and the post-arrest test is mandatory as part of what is known as the implied consent law. Marijuana tests will almost certainly be the same.

The police are unlikely to inform a driver detained for DWI that the roadside breath test is voluntary, and if the driver refuses, it is probable that an arrest will follow on other grounds. However, it is important to realize that constitutional rights are at play in any DWI stop, which a criminal defense lawyer may fully explain.