It really depends. The free market is only efficient when transaction costs are low. For many forms of travel, the cost of monitoring such travel makes trackin

It really depends. The free market is only efficient when transaction costs are low. For many forms of travel, the cost of monitoring such travel makes tracking far too expensive. Even just understanding a toll scheme has its own cost; you don't want to be too worried about misestimating the cost of every drive down to the grocery store. For long-distance interstate travel, however, toll roads make a lot of sense. This is particularly the case where trucks are involved. You charge proportionally to axle weight, so the companies doing the shipping pay for the damage they are doing to the roads. In other congested areas, tolls can serve as an effective form of rationing, particularly over bridges or through tunnels. This encourages more efficient resource usage, e.g. by making carpooling more worthwhile. This also makes more sense for city centers with congestion-charge fees. The alternative rationing scheme here, "sitting in traffic", is a very bad way to pay for things and imposes its own very high transaction costs.