The St. Louis Post-Dispatch reported yesterday on the recent national trend toward new toll roads and bridges. The local interest comes from a dispute between the Missouri and Illinois state governments over how to pay for a proposed new bridge across the Mississippi near downtown St. Louis. The Illinois legislature wants a toll-free bridge, financed by Illinois taxpayers and Missouri taxpayers. The Missouri legislature wants a toll-financed bridge, because the rest of the state isn’t keen to pay more taxes purely to benefit the St. Louis area. The Illinois counterargument is precious:

Illinois has set aside money for construction and contends that tolls would be unfair for Illinois motorists because its drivers would already have paid taxes that went toward the cost of the bridge.

Here’s a simple solution to this ethical dilemma: if Illinois will agree to tolls, it can abstain from taxing its citizens for the bridge in the first place. Then paying the tolls won’t be “unfair” to Illinois drivers. More importantly, a toll-financed bridge avoids the unfairness of taxing the many Illinois citizens who don’t live across the river from St. Louis and who may never use the bridge.

Here’s an even more radical thought: how do we know whether a new bridge is worth building? We know it only if toll collections (revealing drivers’ willingness to pay) are sufficient to cover the construction and operating costs. Without willingness-to-pay demonstrated by tolls, estimates of the size of benefits to drivers are pure speculation. If the bridge is worth building, it can be financed by tolls. And if it can be financed by tolls, there’s no reason for the state governments to mandate that the bridge be built. (I’m assuming that any spillover benefits – from relieving congestion on existing bridges – are transitory and negligible.) Private enterprise will step up to build the bridge – or two or three bridges – in order to collect the toll revenue, if the bridge is worth building. If no firm thinks that the bridge will earn the normal return on capital, than building the bridge is a waste.