Here is an excellent economics puzzle by David Kestenbaum at NPR:

You would never look at a map of the Hudson River, point to the spot where the Tappan Zee Bridge is, and say, “Put the bridge here!” The Tappan Zee crosses one of the widest points on the Hudson — the bridge is more than three miles long. And if you go just a few miles south, the river gets much narrower. As you might expect, it would have been cheaper and easier to build the bridge across the narrower spot on the river. So I wanted to answer a simple question: Why did they build the Tappan Zee where they did, rather than building it a few miles south?

MR readers will no doubt guess the correct answer in general terms, Kestenbaum had to dig hard to find the interesting specifics.

The Port Authority — the body that proposed putting the bridge further south — had a monopoly over all bridges built in a 25-mile radius around the Statue of Liberty. If the bridge had been built just a bit south of its current location — that is, if it had been built across a narrower stretch of the river — it would have been in the territory that belonged to the Port Authority. As a result, the Port Authority — not the State of New York — would have gotten the revenue from tolls on the bridge. And Dewey needed that toll revenue to fund the rest of the Thruway. So Dewey was stuck with a three-mile-long bridge.

The decision to locate the bridge at the much longer location has had continuing costs and repercussions:

Today, the Tappan Zee is in bad shape, and the State of New York is looking into fixing or replacing it. But none of the proposals would move the bridge to a narrower spot on the river. It’s too late now: Highways and towns have grown up based on the bridge’s current location. We’re stuck with a long bridge at one of the widest spots in the river. The repairs are expected to cost billions of dollars.

Hat tip: Monique van Hoek and Mark Perry at Carpe Diem.