Bridges

One of the many simple ideas of economics is the principle of diminishing marginal utility. A single bridge linking two sides of the river has a very high marginal utility, boosting trade from one side to the other, opening opportunities to residents of both sides to conveniently work, shop or play on the other bank. However, any economic benefits derived from the first bridge will need to be revised downward for each additional bridge. Downtown Chicago has an enormous network of bridges over a rather small river, with the business core spilling over to the north and west from the loop. More or less every street in the central district bridges the river, since the river magically makes a 90 degree turn at wolf point, so that the loop is bounded by water on 3 sides. Although the short length of these bridges made construction less costly than longer bridges (Astoria or San Francisco), each bridge costs money to maintain, at approximately fixed levels (a low value bridge is likely just as troublesome to operate each year). I can see in the future a number of these being abandoned, and traffic routed over some of the remaining ones.

The government highway inspectors lament the sad state of the network of highway overpasses and bridges in the US, after considerable scrutiny followed the collapse of the I-35W Mississippi crossing in Minneapolis. The obvious answer is to pour more federal and state funds into repair and replacement of an aging infrastructure. Which is great, since the federal government of the US, just like that of Italy, Greece, Ireland, Iceland, Spain, Mexico and all the other countries of the world, can just print money indefinitely, and use its sterling credit rating to finance an over-sized network of roadways. Hmm...