Michigan has joined California, Nevada and Florida in allowing self-driving vehicle research to take place on the state's highways.

It now means companies like Nissan, Ford and Google, among others, are able to test their autonomous vehicles on public roads, furthering research into self-driving car technology. According to The Detroit News, the Michigan state Legislature passed the bill unanimously, with just one dissenter in the House. All that remains is for Gov. Rick Snyder to sign the bills, pending final review and analysis.

That's likely to pass without much issue, given Snyder's own state address back in January called for Michigan to join California, Nevada and Florida in allowing autonomous vehicles to roam its roads. Several companies testing the technology have now covered several hundred thousand miles during their research, with technology leader Google racking up more than half a million miles of real-world testing on its fleet of converted Prius cars.

Under the bill, Michigan rules dictate that a driver must remain in the driver's seat at all times while the vehicles were on the roads, allowing them to take over should the technology fail or in case of an emergency. Cars will carry an 'M' license plate for identification, and third party "upfitters" of vehicles, such as Google, will be allowed to test just as major manufacturers will. Among the major automakers already testing self-driving cars are Ford, Nissan, Volvo, Toyota and Mercedes--all of which have shown off autonomous vehicle technology in the past few months.

State Sen. Mike Kowall, who introduced the legislation, says the bill will ensure that research and development and taxes related to self-driving vehicles are kept within the state's economy. The state already has high hopes for such technology--the University of Michigan believes that Ann Arbor could become the first U.S. city with a shared fleet of networked, driverless vehicles, as early as 2021.