Interstate 88 (Illinois)

Interstate 88 (I-88) is an Interstate Highway in the US state of Illinois that runs from an interchange with I-80 near Silvis and Moline to an interchange with I-290 and I-294 in Hillside, near Chicago. I-88 is 140.60 miles (226.27 km) long. This route is not contiguous with I-88 in New York. Since 2010, most of I-88 has been part of the Chicago–Kansas City Expressway. The highway also runs through the cities of Aurora, Naperville, DeKalb, and Dixon. East of Rock Falls, the route is a part of the Illinois Tollway system as the Ronald Reagan Memorial Tollway, previously the East-West Tollway.

I-88 runs concurrently with Illinois Route 110 (IL 110) and its speed limit is 70 mph (110 km/h) west of IL 47. East of this point, the speed limit is 65 mph (105 km/h) to the Aurora toll plaza, and 60 mph (97 km/h) for the rest of its route.

Starting at I-80 at a cloverleaf interchange, IL 5 ends there while IL 92 continues eastward. I-88 begins at that interchange and then traverses eastward. Immediately east of the cloverleaf, I-88, IL 92, and IL 110 meet a road at a diamond interchange. This road used to be part of IL 2 and IL 92. They then traverse eastward until IL 92 branches off east near Joslin. The freeway then meets the next two local roads, each having a diamond interchange. One of the interchanges serves Hillsdale while the other one serves Erie. The two routes then meet IL 78 near Lyndon. Near Como, they then meet US 30 at a trumpet interchange. South of Rock Falls, they then meet IL 40 at a diamond interchange. East of Yeoward Addition, they again meet U.S. Route 30 (US 30) at a diamond interchange.

After US 30, I-88/IL 110 becomes an ISTHA-maintained tollway. However, at the IL 26 interchange, there are no tolls present on each ramp. Beyond that, the tollway crosses under US 52 without direct access. Then, the tollway crosses through its first mainline toll plaza. Further east, they meet IL 251 (at a diamond interchange) and I-39/US 51 (at a cloverleaf interchange) at Rochelle. From then on, they meet another mainline toll plaza. In DeKalb, they meet Annie Glidden Road at a trumpet interchange, then cross over IL 23 without direct access, serve DeKalb Oasis, and meet Peace Road at a four-ramp parclo. South of Nottingham Woods, they meet IL 47 at a five-ramp parclo with two ramps. Further east, IL 56 enters eastward on the tollway. They then meet Orchard Road at a four-ramp parclo. Then, IL 56 leaves the freeway at the IL 31 interchange.

Across the Fox River, I-88/IL 110 meets another toll plaza. Then, the tollway meets Farnsworth Avenue at a six-ramp parclo near the Chicago Premium Outlets, Eola Road, IL 59 at a diverging diamond interchange, Winfield Road at a diamond interchange, Naperville Road at a mix of partial interchanges, and IL 53 at an incomplete parclo. Beyond that, they meet I-355 at a mix of interchanges. At Highland Avenue interchange, all but the westbound onramp are present. The other one enters I-88 westbound from Downers Drive. After that, the eastbound tollway meets another mainline toll plaza. After that, I-88 and IL 110 then meet Midwest Road at a two-ramp incomplete parclo (no westbound on/offramp), then IL 83 at a three-ramp incomplete parclo, 22nd Street at a right-in/right-out (no eastbound on/offramp), another mainline toll plaza for westbound traffic, and I-294/IL 38. Beyond I-294/IL 38, the tollway briefly becomes a free road before I-88 ends at I-290. At that point, IL 110 continues east via I-290 all the way toward the Jane Byrne Interchange near downtown Chicago.

Opened November 21, 1958, the East–West Tollway was initially designated as part of U.S. Route 30 Toll (US 30 Toll). The original routing ran from the I-294 interchange near Hillside to US 30/IL 47 near Sugar Grove. IL 56 (previously IL 55 west of Oak Brook) ran along the East-West Tollway between North Aurora and Sugar Grove. In 1966, with the removal of US 30 Toll, Illinois Route 190 was assigned to the tollway.

IL 190 was renumbered as IL 5 in 1971, as construction on the 69-mile-long tollway extension to Rock Falls began that year. Consequently, IL 190 was removed from the stretch between Aurora and Sugar Grove, making that section strictly IL 56. The extension opened in stages in 1974. The extension to DeKalb, Rochelle, and Rock Falls opened on August 15, September 29, and November 15, respectively. 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.

Beyond US 30 east of Rock Falls, further freeway extensions are not subject to tolls. The extension to US 30 near Como serves as a bypass of Rock Falls. Starting from Como, there was a plan to build two federal-aid primary (FAP) freeways connecting to the following cities: FAP 402 to Clinton, Iowa, and FAP 403 to East Moline. Ultimately, only FAP 403 was being built. By 1979, the entirety of FAP 403 opened, extending the IL 5 designation over the completed freeway and supplanting IL 2 west of Sterling.