I-172  Illinois (link)

19.69 miles [1]; north from the (temporary) end of I-72 to US 24, east of Quincy. Formerly IL 336, Interstate 172 got the upgrade when US 36 east of Springfield was renumbered as part of an extended I-72.

Illinois' first idea for I-172 is a bit of a surprise: in 1991 it proposed the number for the freeway upgrade of US 36 from I-55 to E. Hannibal, near the Mississippi River; a distance of about 93 miles. In other words, this is today's I-72 extension. This was approved by AASHTO on June 9, 1991, subject to completion of the route. [2]

It became apparent that upgraded US 36 would make more sense as an extension of I-72 itself. On April 23, 1995, AASHTO approved this, extending I-72 westward from I-55 to US 61 in Hannibal, Mo., including a Mississippi River crossing. Interstate 172 became the northward spur along IL 336, leading from I-72 to US 24. [3]

The 336 freeway has been around, in part, since the late 1970s.

The justification for the 72/172 upgrade is familiar. From the Associated Press:

"'This interstate designation puts the CIE in the big leagues and gives the economy a shot in the arm,' U.S. Rep. Richard J. Durbin, D-Springfield, said at a Capitol news conference.

"'If you go around to small towns in this district and ask them the one thing they would most like to see happen, they'd like to be connected up to the interstate highway system,' Durbin added.

"Durbin noted that western Illinois has been called 'Forgotonia,' for lack of services including good roads, and the new designation shows the area has not been forgotten."

Don't be too outraged, however. I-172's 19 miles are all "non-chargeable," meaning there was no federal responsibility for funding its construction.

See also:

• Interstate 172, Illinois (Bill Burmaster)
• Interstate Guide: I-172 (AARoads)

Sources

1. Route Log and Finder List - Interstate Highways, FHWA, Oct. 31, 2002.
2. AASHTO SCOH. Report to the Special Committee on Route Numbering to the Executive Committee. June 10, 1991.
3. AASHTO SCOH. Report to the Special Committee on Route Numbering to the Executive Committee. April 23, 1995.