If we take greg's point-of-view to the extreme, we should require drivers to pay for their road usage by tolls on all roads, and the toll amount based on the cost of building the roadway and the weight of the vehicle. Without toll booths, gas taxes are the closest approximation to achieve this.
Another point of view is that of a transportation system, where roads, bridges, ferries, buses, trains, etc. are all lumped together as a transportation system and we all share the cost.