Car companies like Tesla, Faraday Future and more are working to develop autonomous cars that can drive around without a human — but too many self-driving cars on the road can clog up traffic, meandering through the streets like a horde of four-wheeled zombies searching for parking, according to Massachusetts State Senator Jason Lewis. But Lewis’s solution — a flat 2.5 cents per mile tax on all self-driving vehicles — could go too far for the fledgling market.

Lewis introduced a bill in the Massachusetts state senate would charge self-driving car owners 2.5 cents for every mile their vehicle drove, and require all autonomous cars in the state to be all-electric. The 2.5 cent tax is meant to offset state revenue from gasoline taxes, as well as limit “zombie cars,” or autonomous vehicles that drive around to avoid parking fees or because parking is unavailable.

“Since this is such whiz-bang technology already, requiring that they all be electric seems like a reasonable thing to ask,” Lewis said, according to local news outlets. The Democratic State Senator said he wants to continue to “move away from fossil-fuel vehicles and to zero-emission vehicles.”

The bill focuses on two types of autonomous cars: completely self-driving cars, and level 3 autonomous vehicles, which means a driver can take over driving if necessary. According to the bill, if human drivers want to cop out of parking fees by having their autonomous cars circle around the block a couple dozen times with no one inside, there will still be a cost.

Some car companies, like Ford, have plans to create autonomous cars for ride-sharing. In other words, when a human driver isn’t using a vehicle, it can drive itself around and pick up other passengers. But if it’s just roaming the streets without passengers, this could be an issue, with unnecessary cars causing congestion on the roads.

The 2.5 cent fee “can be increased for every mile traveled without a passenger or for daytime travel within a severe congestion zone.” The fee can also decrease for situations like traveling in places that lack public transit options, vehicles with multiple passengers and others. Still, part of the draw of an electric vehicle is the savings owners receive from getting away from the gas pump, and a flat tax on autonomous vehicles could be a major burden on their success.

To protect vehicle cybersecurity, cars should include privacy protections so hackers can’t find out where a car or a driver is traveling. The measure is also environmentally friendly, since it requires self-driving cars to be zero-emission vehicles (unless it’s a truck weighing over 8,500 pounds).

The bill also puts restrictions on testing autonomous vehicles. According to the bill, if the Registrar of Motor Vehicles allows autonomous vehicles to be tested on public streets without a passenger inside, only freight and emergency vehicles will be allowed to travel more than one mile continuously without any passengers.

Don’t worry, autonomous cars won’t cause a zombie apocalypse anytime soon, but it might lead to bad traffic.