Laws legalizing recreational marijuana may lead to more traffic deaths, two new studies suggest, although questions remain about how they might influence driving habits.

Previous research has had mixed results and the new studies, published Monday in JAMA Internal Medicine, can’t prove that the traffic death increases they found were caused by marijuana use.

One study found an excess 75 traffic deaths per year after retail sales began in Colorado in January 2014, compared with states without similar laws. But it found no similar change in Washington state.

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