These days people are driving less and they're using more fuel-efficient cars, meaning gas usage has gone down. While that may be good for the environment — and your wallet — it's actually hurting many states and the federal government, both of which depend on gas taxes to repair and maintain roads.

While the federal government works on a solution to this growing issue, some states are already testing out mileage tracking devices, which may someday be used to institute a pay-per-mile taxing system. 

Think of it like a black box for cars.

While this new taxing method may help fill the gaps left by dwindling gas tax revenues, some people are worried that the devices could be used to track more than just miles driven per year. 

The company True Mileage in Long Beach is working on developing this technology for wider use by addressing some of these privacy issues. True Mileage CEO Ryan Morrison joins the show with more.