Ben Wear has a nice entry on his Statesmen pseudo-blog about the myth that gas taxes fully pay for highway construction (or would fully pay for it if TXDOT got 100% of gas tax revenue instead of 24% being wasted on schools). His main point is that in the past, the legislature directly contributed to highway construction from the general fund. He indicates that is no longer the case, but didn't we just pass a five billion dollar general obligation bond for TXDOT? Isn't that money going to come out of the general fund and result in increased taxes or reduced funds for other programs? Also, not all gas is used driving on highways. People burn gas driving on city and county streets - streets paid for by city and county taxes, not the gas tax. TXDOT takes its big cut of gas tax revenues from gas burnt on regular streets and uses it to subsidize highways.

Highways don't pay for themselves, even if you only compare gas tax revenues to construction and maintenance costs. TXDOT calculates the increased gas usage associated with any new highway (the more a new highway will increase gas usage, the more likely it is to get built). Gas taxes generally pay for less than half of the construction and maintenance costs of any new highway. If you take costs associated with congestion, sprawl and global warming into account, highways look like an even bigger waste.