One toke over the limit

Until such time as we had a profusion of automobiles on the roads, we didn’t need many regulations governing their public operation. Once that changed, we quickly needed a whole bunch of rules.

Some people would be allowed to drive. Others wouldn’t. Then came all kinds of conditional provisions, namely physical abilities to permit basic safe operation of the vehicle. For instance, visually impaired people might not be permitted a license. Some people had to have their car fitted with special equipment. Some people could only drive during the day… As a culture, we accepted that the privilege of driving brought with it several stipulations.

As technology changed, so too did these stipulations. One of the more obvious — yet widely flouted by foolish people — is the wearing of seat belts. We get it. They’re uncomfortable. So is paralysis and lingering death.

Another is the requirement that children of certain ages or sizes be restrained in an appropriate manner. Adult seats don’t fit small children. We are legally obliged to adjust. Parents who fail in this regard should be vigorously prosecuted.

Then there’s the specter of driving while under the influence of alcohol or other impairing substances. Most states have wrangled the alcohol dimension of this problem pretty well. Through a litany of science and practical experience, a number of tests and procedures have been developed to objectively determine whether a person under a given level of influence should be legally permitted to operate a motor vehicle.

Just as seat belts and car seats required that we rethink safe operation, a new turn along the road of happy motoring has again forced us to develop new rules.

In states like Colorado and Washington, where use and possession of very small amounts of marijuana is now perfectly legal, a new question arises. As the New York Times recently posed it: How many tokes can a driver take before the ability to control a vehicle is compromised to the point of being a danger on the road?

As the NYT correctly observes, while alcohol has an undisputed — and usually quite apparent — influence on driving, there is no clear-cut consensus on the amount of marijuana that must be consumed to impair a driver’s ability.

Enter the politicians, bio-chemists and lawyers.

Colorado lawmakers recently crafted a regulatory compromise — including taxes, of course — that sets legal limits on marijuana levels in the bloodstream. Under the new law, which took effect on May 28, a driver is assumed to be impaired if a blood test shows a level of tetrahydrocannabinol, or THC, that is five or more nanograms per milliliter. A nanogram is a billionth of a gram.

This would be all well and good save for a couple of problems. In the first instance, those who use marijuana in the most narrow and medicinal sense tend to have residual amounts of THC in their bloodstream that exceeds the five nanogram threshold — so much for driving yourself to the doctor.

Then there’s the equally concerning matter of the blood tests required to determine THC concentration, which detractors have characterized as too intrusive. Readers may remember a recent U.S. Supreme Court (Missouri v. McNeely, 2012) case that changed the warrant requirement for obtaining a blood sample from persons suspected of driving while under the influence of alcohol.

As we’ve argued here dozens of times, there’s an inevitable lag between shifts in culture and shifts in law. This particular instance is merely the latest among many.