The Broken Algorithm That Poisoned American Transportation

"In November 2011, the Louisville-Southern Indiana Ohio River Bridges Project published a 595-page document that was supposed to finally end a decades-long battle over a highway. The project was a controversial one, to say the least.

At a time when many cities around the country were re-evaluating whether urban highways had a place in their downtowns, Louisville was doubling down. It not only wanted to keep the infamous “Spaghetti junction” where Interstates 64, 65, and 71 meet in a tangled interchange, but it wanted to build more on top of it. In addition, the political alliance behind the project aimed to expand the I-64 crossing to double the lane capacity, as well as build a whole new bridge just down the river—doubling the number of lanes that crossed the river from six to 12—all for a tidy $2.5 billion.

But in order to get approval to use federal funds for this expensive proposition, the project backers had to provide evidence that Louisville actually needed this expansion. Using a legally-mandated industry practice called Travel Demand Modeling (TDM), the project backers hired an engineering firm to predict what traffic will look like 20 years in the future, in this case, by 2030. They concluded that the number of cross-river trips would increase by 29 percent. The implication was obvious: if they did nothing, traffic would get worse. As a result, the project got federal approval and moved ahead.

Two subsequent studies, however, also funded by the Louisville-Southern Indiana Ohio River Bridges Project, came to a very different conclusion."