Two states tax some drivers by the mile. Many more want to give it a try.

States are leading the way, with Oregon and Utah launching the first programs and several others running pilots to test technology and build public support. The approach has bipartisan support in Washington, and Transportation Secretary Pete Buttigieg has signaled his openness.

But existing programs operate on a small scale, and a national system would mean tracking millions of vehicles. Supporters are pushing for the quick adoption of proposals to maintain funding of the nation’s crumbling infrastructure, while opponents, including environmental advocates, argue the shift is premature at a time when electric vehicles are a fraction of cars on the road. New fees also would slow their adoption, they say.