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Routing
Interstate 172, formerly Illinois 336, provides a freeway spur from Interstate 72/U.S. 36 north to the U.S. 24 interchange near Fowler via Quincy. It facilitates traffic flow through the Quincy area. Now that Interstate 72 in Illinois is complete, Interstate 172 ends at Exit 4 along Interstate 72.
History
AASHTO originally approved the numbering of Interstate 172 along what is now the Interstate 72 corridor between the Illinois 336 (current Interstate 172) east to Interstate 55 near Springfield. While AASHTO approved this routing on October 9, 1991, it was contingent upon Federal Highway Administration approval. The FHWA preferred to designate this route as Interstate 72. Due to this change, the Interstate 172 was moved to the Illinois 336 freeway around Quincy. AASHTO approved the extended Interstate 72 and new Interstate 172 on April 22, 1995.
Future Aspirations
Interstate 172 currently changes into Illinois 336 at the U.S. 24 interchange near Fowler. Illinois 336 continues as an existing at-grade expressway north toward Carthage. Illinois 336 was recently extended as an expressway northeast to Carthage, and now it is planned for extension into Macomb, where it would intersect the improved U.S. 67 corridor. From there, Illinois is planned to extend northeast on an alignment generally parallel to Illinois 9, perhaps passing through Canton. The main advocate group for this corridor is the 336 Coalition. A Phase I/Corridor study is underway as of Spring 2008 for this project; for more information, visit the official Illinois 336 Peoria to Macomb Study page prepared by the Illinois Department of Transportation. Three corridors between 57 and 61 miles in length were identified. The preferred alignment would follow U.S. 136 to Marietta, Illinois 95 to Cuba, Hickory Road to Canton, Illinois 78 north to Farmington, and Illinois 116 east. A draft environmental impact study is underway, with a public hearing scheduled in Spring 2008 and the report to follow in Spring 2009. The estimated cost is $700 million; if funds are identified to complete the work, the expressway would be constructed by 2011. To that end the federal SAFETEA-LU appropriated $7.2 million dollars for engineering and planning. The decision of whether to build Illinois 336 to expressway or freeway standards has not yet been determined. If Illinois 336 is promoted to Interstate standards from Quincy to Peoria at some point in the future, it is possible that Interstate 172 would be extended as well.1
Mileage
| State
| Mileage
| Cities
| Junctions
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| Illinois
| 19.69
| Quincy
| Interstate 72
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| Sources: October 31, 2002 Interstate Route Log and Finders List |

| Southern Terminus - Interstate 72 and U.S. 36 - Fall Creek, Illinois |
| Perspective from Interstate 172 south |
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Southbound Interstate 172, one mile outside of Interstate 72. The final two miles of Interstate 172 is part of the Great River Road system, overtaking the routing between Exit 2/Illinois 57 and Interstate 72. Photo taken by Brian Dowd (08/03/02). |
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Drawing within one-half mile of Interstate 72 on Interstate 172 southbound. There three miles of Interstate 72 west between Interstate 172 and the Mark Twain Bridge over the Mississippi River into Hannibal, Missouri. Photo taken by Brian Dowd (08/03/02). |
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An end Interstate 172 shield posted in conjunction with the entrance of the freeway from Adams into Pike County. When Interstate 172 first opened, all traffic was defaulted eastward to Hull on Interstate 72/U.S. 36 eastbound. Photo taken by Brian Dowd (08/03/02). |
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Interstate 172 ends as traffic splits between Interstate 72 east and west. Two things worth mentioning here. One, U.S. 36 overlaps Interstate 72 between Hannibal and Decatur, yet is omitted from the Interstate 172 guide signage for this exit. Two, the exit numbers 4A/B coincide with the mileage of Interstate 72 from the Missouri state line via the Mark Twain Bridge. It is not uncommon to see exit numbers of an Interstate terminus that utilize the mileage of the intersecting route. See Interstate 195 New Jersey and Interstate 630 Arkansas for more examples of this practice. Photo taken by Brian Dowd (08/03/02). |
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