Apple claims that its CarPlay interface, released in 2014, can reduce distraction by letting drivers use their iPhone as part of the car’s infotainment system. Many drivers in California are using it, but they may want to be cautious because one study shows that the claim is not really true. In fact, using CarPlay may make drivers more distracted than if they were physically holding a phone.

The study was conducted by the U.K.’s largest road safety charity, IAM RoadSmart. It involved 40 drivers in a simulation, 20 of whom used CarPlay at certain points and 20 of whom used Android Auto. In both systems, the voice and touch controls were found to make drivers slower in reaction times: 36% and 57% slower, respectively, in the case of CarPlay. Android Auto’s voice and touch controls increased reaction times by 30% and 53%.

The increase was found to be greater than that which drivers experience when texting (35%), talking on a hands-free phone (27%) and using marijuana (21%). Even driving at the U.K.’s drink-drive limit only raises reaction times by 12%.

Of course, any amount of distraction is unacceptable. Researchers have suggested that Apple improve CarPlay in various ways. One way is to render certain features unavailable to drivers once their car is in motion.

Distractions will always be a prominent factor in motor vehicle crashes and form the basis for personal injury claims. Victims of another’s negligence can file a claim and, if successful, be compensated for legitimate losses like medical expenses, vehicle repair costs and income lost during their physical recovery. They may even seek reimbursement for non-monetary damages like pain and suffering and emotional trauma. To see how strong their case is, victims might see a lawyer for an assessment.