As of July 1, in Idaho, the gas tax went up 7 cents per gallon, and it costs $21 more per year to register your car.
There was no comparable bump in the cost of operating a bicycle.
That's a dangerous thing to bring up among the general public, because it invariably results in some motorists whining about the free ride that bike riders get, and how they should be paying a registration fee, road tax, etc. It's an argument they wouldn't be able to win if facts are injected... because a significant percentage of the road budget comes from property taxes which "ding" us all... and most adult cyclists also own and operate - and register - one or many motor vehicles. I ride a bike, and last week I paid $157 for a years' registration on 2 motorcycles and my wife's car. You can't convince me I'm not paying a fair share. (I re-registered 'em last week to save $50 by getting the pre-July rates. Next time I'll pay more.)