"The Zoo Interchange is a perfect storm of design deficiencies, based on what we know now," said Kenneth R. Yunker, executive director of the Southeastern Wisconsin Regional Planning Commission. "The left hand on- and off-ramps, the move from one side of the freeway to the other, the service interchanges located just too close to the major freeway interchange."A not insubstantial amount of money has gone into rebuilding interchanges to have all slow speed exits and merges into the right lanes, preferably in a configuration with more space for merging and more room for deceleration and acceleration than the archaic cloverleaf interchange.
It probably handles more traffic than it otherwise would because other expressways were never built. It's probably been beaten to pieces by overloaded trucks, running at weights, lengths, and speeds not envisioned by the designers.
Joseph Looper was part of a team of consulting engineers on the project. He worked for Howard, Needles, Tammen & Bergendoff, now known as HNTB.
Looper, retired and living in Colorado, said the Zoo Interchange ignited a "difference of opinion among engineers." Some wanted the cars to enter and leave the freeway system on the right. Others, like Looper, favored what was known as a directional interchange, meaning that cars and trucks could exit on either the left or right.
The directional interchange won out.
"It was an interchange of roadways that were all free flowing," he said. "The whole idea of the interchange was to design and build it in such a way that traffic could use it without conflict."
Looper, now 84, and others also favored the use of concrete box girders in some parts of the Zoo Interchange. These hollow girders integrated the bridge deck to the supporting structure. While they were more attractive, corrosion from water and salt deteriorated the steel rebar used to reinforce the concrete.
"We didn't anticipate the heavy traffic volumes and the wear and tear, the actual salt on concrete in the wintertime caused a great deal of difficulty for the freeways," he said.
The freeways aged. So did the Zoo Interchange.
What the story doesn't tell readers about the summer of 1963 was that the Chicago and North Western's Twin Cities 400 and Minnesota 400, which operated the rudiments of a passenger train network connecting the Twin Cities and Rochester with Madison, Milwaukee, and Chicago, made their last runs in June of that year. The subsequent completion of Interstate 94 across Wisconsin in 1969 sealed the fate of the Afternoon Hiawatha. That history is germane to today's transportation policy debate, in which restoration of those early diesel-era train timings takes a lot of money, but an upgrade -- if not an expansion -- of the expressways takes even more.