Is sobriety an issue in the passenger seat?

State law is quite clear on most issues involving drunk drivers, but there are a few murky areas.

For example: What are the legal consequences when a driving instructor is drunk? Or if a parent is inebriated but is acting as a supervisor and watching his or her child drive with a learner’s permit?

Under California’s zero tolerance law, teenagers with learning permits cannot have any alcohol in their blood while driving, and they must be supervised by a licensed parent, guardian, spouse or other adult over the age of 25.

But the law is moot on the point of whether that supervising driver must be sober, much to the surprise of many experts, such as Tina Pasco, executive director of the Los Angeles chapter of Mothers Against Drunk Drivers.

“It isn’t illegal?” Pasco asked. “I am stunned. How can you supervise somebody if you are under the influence of a drug.”

Although there is no specific law against mom or dad being dead drunk with a teenage driver at the wheel, police take a pretty dim view of the practice, and say that in the case of an accident they would try to find a way to file charges against the supervising adult.

The issue is part of a much larger and even murkier issue of exactly what supervising adult drivers are supposed to do when accompanying their teenage learners.

In 2003, the state’s Department of Motor Vehicles issued 216,168 licenses to 16-year-olds who had been driving with learning permits, but the DMV and the California Highway Patrol offer little guidance to parents on their responsibilities and how they can best help their kids.

A quick look at the law would surprise a lot of people.

The theory of California’s law is that the supervising adult driver is not only available to offer guidance and suggestions to the teenage driver, but in an emergency can lean over and commandeer control of the car.

The applicable vehicle code section states that the supervising driver “has to maintain position in the vehicle compartment where they can assist the driver in controlling the vehicle as may be necessary,” said John Sampson, a California Highway Patrol spokesman.

Police say it rarely happens that adults grab the steering wheel or attempt to hit the brake while the kids are driving. That’s good, because it sounds remarkably dangerous to me.

“It happened to me when I was taking driving lessons in 1964,” said DMV spokesman Steven Haskins. “We were practicing on a football field and I was going too fast. The instructor leaned over and hit the brake.”

I’m sure Haskins no longer speeds, but the point is that authorities do regard the adult in the front seat as the higher authority who can intervene when necessary. In Sampson’s view, if a drunk adult did intervene, the police would have a basis to charge the adult with drunk driving.

Other police say they might go further and charge a drunk adult in an accident, even if the person did not attempt to intervene with the teenage driver.

The question of a drunk supervising parent was raised by a reader of this column who wondered whether one would be breaking the law by having a couple of glasses of wine during dinner and then allowing a teenager with a learner’s permit to drive.

More than likely, the two glasses of wine did not push the reader over the 0.08% blood alcohol limit that applies to adults. And in any case, being under the 0.08% level while supervising a teenager would have to be safer than driving the vehicle itself.

But Pasco takes a dim view of anybody in such a situation, and believes California needs a law that requires the supervising adult to be sober.

“It is one of those assumptions that you would be sober if you are supervising a teenager,” Pasco said. “Are you going to go into a bar while your teenager waits outside? It sends the worst possible message you could send.”

But it’s really hard to judge how much another law on drunk driving, coming after the enactment of dozens of such laws over recent decades in California, would improve public safety. At the very least, the DMV and CHP should issue a letter or instruction sheet to parents laying out their responsibilities every time they issue a permit.

Ralph Vartabedian can be reached at ralph.vartabedian @latimes.com.