California lawmakers are moving forward with a study to explore a mileage-based tax as a potential replacement for the state’s traditional gas tax — a shift supporters say is driven by declining fuel tax revenues as more drivers switch to fuel-efficient and electric vehicles.

The research, tied to Assembly Bill 1421, would extend and support work by the state’s Road Usage Charge Technical Advisory Committee through 2035.

Under current law, California depends heavily on revenue from the gas tax to fund roads, highways, and infrastructure, but those revenues are projected to shrink as electric vehicle use grows and overall gasoline consumption drops. The mileage study would look at a “road charge” system where drivers pay based on how many miles they drive, rather than how much gas they buy.

The bill does not yet enact a new tax. Instead, it extends the study and advisory work until 2035 and would have the Legislature receive findings and recommendations, with a report due by Jan. 1, 2027.

Republicans in the California Legislature have been vocal in their opposition. Assembly Republican Leader Heath Flora criticized the proposal.

“We already pay the highest gas taxes in the nation. Now Sacramento is talking about adding a new tax for every mile people drive,” Flora said. “Piling on another tax right now shows just how out of touch politicians in Sacramento are with the reality working families face.”

The plan has drawn broader GOP criticism from leaders outside the Legislature as well. California Republican gubernatorial candidate Steve Hilton called a mileage fee “absolutely outrageous” and said, if elected, he would veto the tax, adding that tracking and charging drivers for every mile is unacceptable.

Supporters say the study is a pragmatic response to long-term funding challenges.

On the Assembly Floor on Jan. 29, Assemblymember Lori Wilson (D–Suisun City), the bill’s author, said that California’s transportation funding is “becoming less stable, less equitable, and less sustainable as more drivers switch to fuel-efficient and zero-emission vehicles.”

“Drivers using the same roads often pay different amounts for that use,” Wilson continued. “Low income and rural commuters who must drive farther and less efficient vehicles can pay more while others contribute less despite roadway impacts.”

Wilson and other supporters contend that a per-mile road charge could ensure that all drivers contribute fairly to the costs of maintaining roads, regardless of the type of vehicle they drive.