Prior to its designation as an Interstate Highway, the route was known as Illinois Route 5, and before that, IL 190. The reason for I-88's original designation and continued existence as an Interstate has to do with a technicality in the old National Maximum Speed Law. Originally passed in 1973, the NMSL was amended in 1987 to permit speed limits on rural stretches of Interstate Highways only. Even though IL 5 was fully up to Interstate Highway standards, it still had to carry a limit because of this wording in NMSL. The Illinois Department of Transportation and Illinois State Toll Highway Authority petitioned the American Association of State Highway and Transportation Officials to re-designate IL 5 as an Interstate, and in 1987, AASHTO approved the request and assigned the I-88 numbering to the highway. The NMSL would be completely repealed only eight years later in 1995, but the I-88 shields remain to this day, even though Chicago–Kansas City Expressway markers are being posted throughout the entire length of I-88, since it is now part of the Chicago to Kansas City Expressway project, bannered with special "CKC" logos.
The Ronald Reagan Memorial Tollway, originally known as the East-West Tollway, is a toll road in northern Illinois. Opened November 21, 1958, it was initially designated as U.S. Route 30 Toll, and later IL 190. The original routing extended from the I-294 interchange near Hillside to IL 47 near Sugar Grove. IL 56 was overlapped on the East-West Tollway between North Aurora and Sugar Grove in 1965. When the East-West Tollway was extended to Dixon in the 1970s, the IL 190 numbering was removed from the stretch between Aurora and Sugar Grove, making that section strictly IL 56. Once complete, the new routing of the combined tollway and freeway between I-80 near the Quad Cities and I-294 became designated as IL 5. In the late 1980s, it was renumbered I-88. Officially, the tollway portion begins in Rock Falls, starting at the intersection with US 30 at mile marker 44, although the first toll plaza does not appear until after the IL 26 interchange in Dixon, making the section between US 30 and IL 26 technically a freeway. It continues as a tollway until its terminus in Hillside, although there is a free section between exit 76 and exit 78. West of US 30 to I-80, I-88 is a freeway. The tollway portion is long. After the death of Illinois native and former President Ronald Reagan in 2004, the Illinois StateToll Highway Authority voted to rename the toll roadway "Ronald Reagan Memorial Tollway" in his memory, as it passes near his birthplace of Tampico and grazes the south outskirts of his boyhood hometown of Dixon. The tollway portion of I-88 was previously known as the "East–West Tollway" and is still displayed as such on some signs near Chicago. There is no direct off-ramp access to US 52, IL 23, IL 25, and IL 83. In addition, I-88 merges with IL 56 for a short distance. Although a federal law, 23 U.S.C. § 111, prohibits the operation of commercial rest areas constructed after January 1, 1960, on Interstate Highways, the DeKalb oasis was constructed at milepost 93 in 1975, prior to the route's designation as I-88 and remains in operation. From 2005 lasting through 2012, ISTHA reconstructed and widened much of the original portion of I-88, between York Road and IL 56. Approximately $991.6 million was budgeted for I-88 over that period. Between 2005 and 2009, I-88 was reconstructed and widened to four lanes in each direction between IL 59 and York Road, with work progressing gradually from west to east. The project included a reconstruction and reconfiguration of the Naperville Road interchange. Between IL 56 and the Aurora Toll Plaza, I-88 was reconstructed and widened to three lanes, including the reconstruction of the IL 31 interchange and new bridges over the Fox River.
