From Wikipedia:

"During 2008 the [highway trust] fund required support of $8 billion from general revenue funds to cover a shortage in the fund. This shortage was due to lower gas consumption as a result of the recession and higher gas prices. Further transfers of $7 billion and $19.5 billion were made in 2009 and 2010 respectively."

The highways are not self supporting. You have the direction of transfer with the general fund reversed. You are not alone in this misperception.

Cars more or less pay their way. Trucking is subsidized. This is not unusual as transportation is subsidized the world over. We chose highways, water transport, air and, to a lesser extent, rail.

We are now in the difficult situation of needing to spend money to rebuild our infrastructure (of all kinds) and being unable to even adjust our taxes for inflation because of politics. It is going to take a disaster somewhere with great loss of life before we wake up.

Soon twenty years will have passed since the federal gas tax was adjusted for inflation.