SAN FRANCISCO (KGO) -- A Bay Area company says it has successfully measured marijuana impairment in drivers. The test could provide law enforcement with a much-needed tool to identify people driving while stoned.At sobriety checkpoints, police are looking for drivers who may be impaired.Marijuana has become just as strong if not stronger of a problem driving as alcohol," said San Francisco Police Sargent John Bragagnolo.San Francisco police estimate one in four drivers they stop for driving under the influence are stoned. Identifying them takes a field sobriety test.Oakland-based Hound Labs wants to make that easier. It has been working on a breathalyzer for pot that measures the amount of THC in a person's breath.The company gave us video of its first field driving tests on a closed course at the old Alameda naval air station. They got people stoned, and then put them through an obstacle course of common roadside hazards."The whole point of this test was to show what happens when you get impaired," said Hound Labs founder, Mike Lynn, M.D.Lynn is an emergency room doctor and reserve police officer.Drivers navigated the course sober and then smoked marijuana 30 minutes prior to driving the same course again at speeds up to 65 mph."When they were stoned-- even when their levels of THC were very low in their breath, meaning that they didn't actually smoke very much-- some of them smoked a lot. Some of them smoked very little - they all made major errors that that would have likely resulted in a fatality," said Lynn.Hound Labs is currently conducting clinical trials and plans more driving tests soon. They expect to have their marijuana breathalyzer available by the end of the year, just in time for state's new recreational pot laws.