Interstate172 (I-172) is a spur route, the only auxiliary route of I-72. It is located entirely within the US state of Illinois and is completely concurrent with IL110. The highway runs north from its start outside of Hannibal, Missouri, to about 2.5 miles (4.0km) west of Fowler. At U.S. Route24 (US24), I-172 becomes Illinois Route 336 (IL336), which runs north and east to Macomb via Carthage. The entire portion of I-172 and I-72 from I-172 east to Springfield is also known by its former name, the Central Illinois Expressway.[2] I-172 is 19.69 miles (31.69km) long.[1]
On April 23, 1995, after a reexamination by the Federal Highway Administration (FHWA), the highway to Hannibal was redesignated I-72, with the highway north to Quincy redesignated as I-172. The highway is non-chargeable, meaning that, even though it is an Interstate (designed and constructed to Interstate Highway standards and specifications), it was not built with federal funds.[3]
