Until the mid-1990s, I-72 ran from Springfield at Interstate 55 to Champaign at Interstate 57. On June 9, 1991, the American Association of State Highway and Transportation Officials approved the establishment of Interstate 172 from the western terminus of I-72 at Springfield to Fall Creek, east of Hannibal, Missouri, though it was contingent on Federal Highway Administration approval. The FHWA preferred to designate the route I-72. After discussions regarding extending an Interstate-standard highway through the state of Missouri, on April 22, 1995, AASHTO approved another renumbering. I-172 was renumbered in its entirety as I-72. The U.S. 36 extension west of Fall Creek was also given the I-72 designation. The Illinois Route 336 expressway was renumbered to I-172 from Fall Creek to Fowler. Prior to September 2000, Mark Twain Avenue was composed of the current Mark Twain Avenue and the portion of I-72 and US 36 west of Exit 157 to the Hannibal city limits. Route 79 terminated at the foot of the old Mark Twain Memorial Bridge at the corner of Third Street and Mark Twain Avenue. Signs along the four-lane expressway portion of Mark Twain Avenue marked the route as "Future I-72", while signs along what is now Route 79 had I-72 trailblazers to direct drivers to the temporary terminus at Fall Creek, Illinois. When the new Mark Twain Memorial Bridge was completed in September 2000, I-72 was routed over the new bridge, along with US 36. Route 79 was extended along Mark Twain Avenue to terminate at Exit 157. The portion of I-72 and US 36 west of Exit 157 is now referred to as the V.F.W. Memorial Highway. Originally, I-72 opened with a posted speed limit of. However, when it first opened, some drivers were confused and were driving it at, the old posted speed limit on Mark Twain Avenue. Later, Hannibal convinced MoDOT to lower the speed limit along I-72 and US 36 within the Hannibal city limits to.
Chicago-Kansas City expressway
The concept of I-72 across Missouri was to create the Chicago–Kansas City Expressway, a rural four-lane highway across northern Missouri and west central Illinois from Cameron, Missouri at I-35 to Springfield, Illinois at I-55. This would provide a series of rural 4-lane highways connecting Chicago to the North American Free Trade Agreement Corridor. This would reduce the amount of through traffic, primarily truck traffic, in the St. Louis, Des Moines, and Quad Citiesmetropolitan areas by serving as an alternate route for I-70 and I-80. The Missouri portion of this route is designated as part of High Priority Corridor 61. Based on the marker at Route 79, when US 36 is upgraded to Interstate standards across Missouri, the future western terminus of I-72 would be at Cameron, Missouri at the intersection with I-35. Currently, the west end of I-72 route is west of US 61 and flows concurrent with US 36 into Illinois. In 2004, US 36 was upgraded to a 4-lane expressway between US 61 and US 24 at the Rocket Junction. There are three exits along this expressway: Veterans Road, Shinn Lane, and US 24 East at the Rocket Junction. This expressway is up to interstate standards. Also, an interchange with Route 15 was installed in Shelbina. At Clarence, US 36 resumes 4-lane expressway status. Due to funding priorities, upgrading US 36 between Macon and Hannibal was a low-priority project and was officially tabled by MoDOT. MoDOT committed to constructing the four-lane highway as a non-interstate expressway only if the five counties served by US 36 east of Macon would contribute half of the $100 million cost.
Four-lane construction
The first proposition of the expressway construction, Proposition 36, was passed by a majority of the voters in Macon, Marion, Monroe, and Shelby counties. However, residents of Ralls County rejected the proposition, citing lack of economic benefit for the county. US 36 cuts through the very northwest corner of Ralls County from Monroe City to the BNSF viaduct, a distance of. Since the proposition failed in Ralls County, the entire proposition failed. Businesses and voters in the other four counties still strongly supported the four-lane expressway project. At the next election, on August 3, 2005, voters of all five counties approved Proposition 36B, which excludes Ralls County from the Transportation Development District and allows for the construction of a 4-lane US 36 to be constructed without Ralls County's participation. The Proposition passed 66 percent to 34 percent and passed by a majority in all 5 counties. In March 2008, the revised total cost of the project was estimated at $89 million. Additionally:
A fifteen-year, -cent sales tax was levied in Macon, Marion, Monroe, and Shelby counties for their portion of the construction costs for the project.
The Ralls County portion was covered by a $7 million earmark for US 36 from Congressman Kenny Hulshof.
The remainder of the project costs, including construction, engineering, right of way acquisition, survey, etc. were funded by MoDOT.
Road construction to complete the between Hannibal and Macon began in 2007. According to MoDOT, the estimated completion date of four lanes from Hannibal to Monroe City,, was September 2008, from Monroe City to Shelbina,, was December 2009, and from Shelbina to Macon,, was December 2010. In August 2010, the 4-lane expressway was completed from Macon to Hannibal, completing Missouri's portion of the Chicago-Kansas City Expressway.
Interstate 72 Business is a Business Loop of I-72 in Jacksonville. It runs from the U.S. 36/I-72/U.S. 67 interchange southwest of Jacksonville north along the U.S. 67 bypass of Jacksonville to the former alignment of U.S. 36. On Morton Avenue, BL 72 runs east through downtown Jacksonville until it reaches I-72 at exit 68. This is a distance of.
