Bridge-building for dummies

Our hardhats are off to the 7,000 skilled union workers who turned raw American-made steel into the gleaming new Tappan Zee Bridge, which opens to traffic this weekend. The $4 billion span, pushed by Gov. Cuomo after decades of inaction, took four years to complete and came in under budget thanks to an innovative design-build approach.

Rather than separating the planning and construction phases, which stretches out timetables and inflates costs, design-build puts them together. It should be widely employed in public projects, including here in the city, where short-sighted political foes have blocked its use.

If only the pretty new Tappan Zee — it’s named after Mario Cuomo now — didn’t have to be where the old one was. Back in the 1950s, they put it in the worst possible place due not to engineering and geography, but naked politics. There’s a moral in this story for present day. Gov. Tom Dewey wanted the new Thruway to cross the Hudson between Westchester and Rockland. His engineers identified the ideal place near Dobbs Ferry, where the river was only a mile wide and the ground was solid rock — excellent for a bridge.

But even though the bridge would connect New York to New York, the site happened to fall within the jurisdiction of the bi-state Port Authority. Dewey asked the New Jersey governor if he could okay the bridge and the answer was sure, as long as Jersey got half the tolls.

Dewey said no and ordered it moved to just beyond the Port’s reach, which happened to be at just about the Hudson’s widest point, three miles. Making matters worse, the ground was very soft.

The old Tappan Zee went up, doomed to an early demise. The new Tappan Zee had to go there, too.

When crossing it, know why the ride is three times the distance it should be and why the old bridge had to come down. And know how not to build.