The first cloverleaf interchange to be built in the United States, at the junction of NJ Rt. 25 (now U.S. Rt. 1) and NJ Rt. 4 (now NJ Rt. 35) in Woodbridge, New Jersey, is featured on the cover of this week's issue of the Engineering News-Record. (By contrast, a piece on the under-construction Hoover Dam was relegated to the journal's back pages.)
With their four circular ramps, cloverleaf interchanges were designed to let motorists merge from one road to another without braking. They worked well enough—and became so ubiquitous as a result—that writer Lewis Mumford once declared that "our national flower is the concrete cloverleaf." But many of the older cloverleaves were not built to handle the volume and speed of traffic they now receive, and many have been demolished and rebuilt.
Many people associate cloverleaf interchanges first of all with Southern California, which is famous for its loops and tangles of freeways. But it was an engineer from Maryland, Arthur Hall, who patented the cloverleaf in 1916, and it was an engineer from New Jersey, Edward Delano, who—inspired by a picture he saw in a magazine of a cloverleaf in Argentina—built the U.S.'s first one in Woodbridge. The intersection was a tricky one, since both highways were so heavily traveled: Rt. 25 carried Philadelphia traffic from Camden to Jersey City and Rt. 4 ran from New York City all the way down the Jersey Shore. About 60,000 cars used the interchange each day. Turning from one busy road onto the other was usually difficult and frequently disastrous. The cloverleaf solved this problem: Drivers could merge by looping to the right under an overpass, joining the traffic stream without stopping or making a left-hand turn into oncoming traffic.
These circular ramps move cars from one road to the other fairly efficiently, as long as the roads aren't too busy—but once traffic speed and volume increases, cloverleaves can be just as dangerous as the intersections they replaced. The Woodbridge interchange, for instance, had no merge lanes, so it forced motorists to stop without warning or to plunge directly into highway traffic. Many thousands of fender-benders were the result. It was "the Model T of cloverleafs," said a spokesman for the New Jersey Department of Transportation (NJDOT). "It worked well at one time, but it's beginning to reach the end of its usefulness." As a result, it's getting a facelift: the NJDOT plans to replace the sprawling cloverleaf with a more compact, diamond-style interchange that will eliminate both the dangerous merges and the associated gridlock.