If a municipality sets the price of a bridge at the level where it equals the marginal cost of usage, it guarantees that the total economic surplus is maximized, regardless of the level of demand for the bridge.

When a municipality sets the price of a bridge equal to the marginal cost of using it, it means that the cost of allowing one more vehicle to cross the bridge is the same as the price charged for crossing. This approach ensures allocative efficiency, which happens when resources are distributed in a way that maximizes total benefits to society. For example, if the cost to maintain the bridge is $2 per vehicle, and the toll is set at $2, then everyone who values crossing the bridge at $2 or more will use it. This way, the total economic surplus, which is the sum of consumer and producer surplus, is maximized because all users who benefit from the bridge at that price will pay it. In contrast, if the price were set higher, fewer people might use the bridge, leading to lost benefits, while a lower price could lead to overuse and congestion.