Tuesday, May 3, 2005

The Ohio Department of Transportation (ODOT) has announced plans to rebuild the interchange of Interstate 75 (I-75) and U.S. Highway 224 (US 224) in northwestern Findlay, Ohio, signed as exit 159 on I-75. Plans for the interchange, a standard diamond interchange that also carries State Highway 15 on the west and south approaches, include reversing the flow of traffic on the bridge over I-75, in what is known as a “diverging diamond interchange“.

Such an interchange does not exist in the United States; ODOT based the plan on an interchange in Versailles, France of the same design, introduced to them by a report in a trade magazine. Instead of the standard approach, widening the four-lane bridge to add turn lanes, traffic flow will be reversed between the two sets of ramps, with traffic signals controlling the flow. The only conflicts will be between the two directions of US 224; all turns to and from the ramps will be free-flowing. Traffic will be guided by barriers and islands, preventing errors in movement. As it eliminates left turns across traffic, the accident rate at the interchange is expected to be cut in half. The plan will also be cheaper than a rebuild of the bridge, and will be able to carry more traffic.

Left-hand driving is very rare in the United States, but a few freeway-to-freeway interchanges incorporate it. In those cases, rather than being traffic-light controlled, the crossings between opposite directions are separated by bridges. Another related case is the Single Point Urban Interchange, in which opposing streams of left-turning traffic pass each other on the left.

The bridge, built in 1956, currently carries about 20,000 vehicles per day. The land west of the interchange, across from downtown Findlay, is being rapidly developed, and plans for the area include a Wal-Mart.

Mayor Tony Iriti of Findlay thinks “it’s a great idea. It’s amazing to me that this has never been done before. We’ll be written up in all those magazines nobody wants to read.” Hancock County officials are similarly enthusiastic.

The decision on whether to build the interchange will not be made until late summer.