California would have become the first to require such systems for all new cars, trucks and buses sold in the state starting in 2030. The bill, aimed at reducing traffic deaths, would have mandated that vehicles beep at drivers when they exceed the speed limit by at least 10 mph (16kph).

The European Union has passed similar legislation to encourage drivers to slow down. California’s proposal would have provided exceptions for emergency vehicles, motorcycles and motorized scooters.

In explaining his veto, Newsom said federal law already dictates vehicle safety standards and adding California-specific requirements would create a patchwork of regulations.

The National Highway Traffic Safety “is also actively evaluating intelligent speed assistance systems, and imposing state-level mandates at this time risks disrupting these ongoing federal assessments,” the Democratic governor said.

Opponents, including automotive groups and the state Chamber of Commerce, said such regulations should be decided by the federal government, which earlier this year established new requirements for automatic emergency braking to curb traffic deaths. Republican lawmakers also said the proposal could make cars more expensive and distract drivers.

The legislation would have likely impacted all new car sales in the U.S., since the California market is so large that car manufacturers would likely just make all of their vehicles comply.

California often throws that weight around to influence national and even international policy. The state has set its own emission standards for cars for decades, rules that more than a dozen other states have also adopted. And when California announced it would eventually ban the sale of new gas-powered cars, major automakers soon followed with their own announcement to phase out fossil-fuel vehicles.

Democratic state Sen. Scott Wiener, who sponsored the bill, called the veto a setback for street safety.

“California should have led on this crisis as Wisconsin did in passing the first seatbelt mandate in 1961,” Wiener said in a statement. “Instead, this veto resigns Californians to a completely unnecessary risk of fatality.”

The speeding alert technology, known as intelligent speed assistance, uses GPS to compare a vehicle’s pace with a dataset of posted limits. If the car is at least 10 mph (16 kph) over, the system emits a single, brief, visual and audio alert.

The proposal would have required the state to maintain a list of posted speed limits, and it’s likely that those would not include local roads or recent changes in speed limits, resulting in conflicts.

The technology has been used in the U.S. and Europe for years. Starting in July, the European Union will require all new cars to have the technology, although drivers would be able to turn it off. At least 18 manufacturers including Ford, BMW, Mercedes-Benz and Nissan, have already offered some form of speed limiters on some models sold in America, according to the National Transportation Safety Board.

The National Highway and Traffic Safety Administration estimates that 10% of all car crashes reported to police in 2021 were related to speeding. This was especially a problem in California, where 35% of traffic fatalities were speeding-related — the second highest in the country, according to a legislative analysis of the proposal.

Last year the NTSB recommended federal regulators require all new cars to alert drivers when they speed. Their recommendation came after a crash in January 2022, when a man with a history of speeding violations ran a red light at more than 100 mph (161 kph) and struck a minivan, killing himself and eight other people.