Concurrency (road) - Concurrency Extremes

Concurrency Extremes

Some concurrencies have extreme examples such as triple, and even quadruple concurrencies. A triple Interstate concurrency is found north of Madison, WI, with I-39, I-90, and I-94. Also in Madison, there is a quadruple concurrency with four US Highways: US 12, US 14, US 18, and US 151 along the Beltline south of the city. St. Louis has an example of a quadruple Interstate concurrency, with I-44, I-55, I-64, and I-70, plus US 40 running concurrently for a brief run downtown. I-25 is concurrent with US 87 for 400 miles (640 km), running from Raton, New Mexico through the entire state of Colorado and all the way to I-25's northern terminus at I-90 in Buffalo, Wyoming, although US 87 is unsigned for most of this distance. The longest Interstate highway concurrency is I-80 and I-90 for 265 miles (426 km) across Indiana and Ohio. One of the shorter examples is the M-35 concurrency with CR 492 in Marquette County, Michigan. The two roads overlap for 153 feet (47 m) to cross a rail line, with M-35 yielding to CR 492 traffic in the process. Another short duplex is between US 49 and US 64 near Fair Oaks, Arkansas, a concurrency of 150 feet across a railroad.

I-465 around Indianapolis currently has the most concurrent routes. Portions of the 53-mile (85 km) highway overlap with I-74, US 31, US 36, US 40, US 52, US 421, SR 37 and SR 67 -- a total of eight other routes. Seven of the eight other designations overlap between exits 46 and 47 to create an eight-way concurrency.