Aug 14, 2014 · 3 minutes

Yesterday, Weedmaps, a marijuana dispensary locator and community site for pot enthusiasts, announced a partnership with ridesharing giant Uber. The seemingly strange bedfellows are working with a Denver-based marijuana dispensary called the Clinic to raise money for multiple sclerosis research. For every rider that uses the promotional code "clinicms," Uber will donate $5 to the National MS Society.

Companies run charity campaigns all the time, and certainly MS research is as worthy a cause as any, what with 2.3 million people suffering from the disease worldwide and no cure yet in sight. What's interesting is Uber's choice to partner with a marijuana-related startup. It may sound odd, but there are some definite synergies between ridesharing and marijuana. After all, one of the biggest arguments against legalizing marijuana is related to high-driving, and the fact that there's no foolproof way to determine if a driver is under the influence of the drug.

Unlike alcohol, where a driver's level of impairment is directly correlated with the amount of alcohol in that person's blood, there's no easy test for marijuana impairment. A metabolite of THC, the active ingredient in marijuana, can be detected in urine long after the effects of the drug have worn off. Depending on how often a user tokes up, the drug may stay in a person's system anywhere from a week to 90 days. A blood-THC test will yield fewer false positives, but even then THC can remain the the blood for hours and even up to a day after the user is no longer impaired. Still, that's a more accurate test, but unfortunately most state laws equate the discovery of THC metabolite in the urine to THC in the blood, making both illegal.

As for field sobriety tests, a 2012 study found that only 30 percent of drivers under the influence of marijuana failed the sobriety test. That's largely because experienced pot smokers are more accustomed to how the drug affects their body. The New York Times' Maggie Koerth-Baker describes it like this:

A 21-year-old on his first bender and a hardened alcoholic will both wobble on one foot. But the same is not necessarily true of a driver who just smoked his first joint and the stoner who is high five days a week.
There's no easy legal answer to how to cut down on high-driving. In fact, some experts say the best way to prevent deaths caused by impaired drivers is to focus all public resources on battling drunk driving. There's little states can do, argues UCLA public policy professor Mark A. R. Kleiman to the Times, other than, say, banning "pot bars" that encourage people to get high away from home.

That's where private enterprise can help. By marketing its service at potsmokers, like it's done here with the Weedmaps campaign, Uber increases its visibility to the people who need its service most. Not only does Uber keep stoned drivers from getting behind the wheel, it also doesn't require that a person hail a cab on the street, speak to a human operator at a car service, or determine an appropriate tip -- activities which can all pose challenges depending on a user's level of intoxication.

Sure, there's no legal way to require stoned people to take Ubers or any other cab or ridesharing service. But I'd love to see more cross-promotions like this -- Buy some weed cookies at the dispensary, get $5 off your next Uber or Lyft ride. That coupon might be incentive enough to keep a blazed driver off the road when she gets a craving for a Taco Bell. And while a lot of Uber drivers or cab drivers are rightfully annoyed when asked to go through a drive-thru, maybe the company could institute some sort of surcharge for drive-thru visits.

This may all sound a bit silly, but make no mistake -- these are the types of questions that will inevitably arise as Uber looks to replace not only cabs, but cars in general. Those who are most bullish on Uber, like Benchmark's Bill Gurley, believe that Uber's eventual market size is bigger than most think because it will be used in cases when taxis and black cars previously weren't.

Of course any promotions that help keep stoned drivers off the road will have to benefit Uber -- the fact that the company instills massive surge pricing rates on New Year's Eve proves that keeping impaired drivers off the road isn't enough of a priority to forgo profits – or "disrupt the balance of supply and demand," as the company rationalizes it. Nevertheless, in the absence of good legal ways to curb stoned driving, Uber may play an important role in achieving this goal through private enterprise. That's something any good libertarian like Travis can get behind.

[image adapted from Thinkstock]