[a] With the exception of a four-mile (6.4 km) expansion in 2009, from U.S. Route 34 (US 34, Ogden Avenue) to 75th Street, the highway is six lanes wide for its entire length.

[11] Officials at the Morton Arboretum, one of the nation's premier woodland research centers, promptly filed a federal lawsuit to block construction of the tollway.

In addition, they would build earthen berms along the new road, preventing salt spray from damaging arboretum plants.

In exchange, the DuPage County Forest Preserve District agreed to a 99-year lease providing 189 acres (0.76 km2) of its land to the arboretum for the development of an "urban vegetation laboratory".

Under the agreement, Morton Arboretum agreed to charge DuPage County residents lower admissions one day of the week, build a bicycle path connecting the arboretum to nearby forest preserves, and begin a joint clean-streams program to improve the water quality of DuPage County's lakes and streams.

At a public hearing a month later, arboretum executives and Woodridge officials strongly criticized the report as "fatally flawed" and a repeat of tollway-provided research, including typographical errors.

The opposition also cited outdated and inaccurate data regarding wetlands replacement, salt dispersion, and the lack of compensation to residents for lowered property values.

[15] The Corps of Engineers issued a permit for the tollway on October 8, 1986, rejecting last-minute concerns from the Sierra Club to reroute the toll road around sections of Churchill Woods Prairie, between Glen Ellyn and Lombard.

[16] The tollway authority put the total cost of 17.7 miles (28.5 km) of new pavement at $450 million (equivalent to $1.04 billion in 2023[9]).

Governor James R. Thompson and U.S. Secretary of Transportation Samuel K. Skinner dedicated the North–South Tollway on December 22, 1989.

[3] This figure has since been shown to be slightly optimistic, with maximum average daily traffic values approaching 170,200 only at the northern end of the Interstate.

[21] The old lines marking the former shoulder can still be seen in the right lane as a result of the tollway authority's attempt to grind them away.

This is primarily due to the widespread access to food and fuel throughout the western suburbs when construction began in the late 1980s.

In addition to the original alignment of I-355, the Transportation Plan of April 1962 included the concept of a route that ran from Bolingbrook south to Joliet.

[33][34] The discovery of the Hine's Emerald Dragonfly, an endangered species, and related concerns for the environmental health of the Des Plaines River wetlands in 1995, ignited a series of legal challenges that delayed construction of the I-355 extension for several years.

In January 1997, a federal judge sided with the Sierra Club, halting construction of the southern extension while the state appealed.

In 1999, the state dropped its appeal and amended the environmental impact study (EIS) to meet the Sierra Club's concerns.

[33] The state released the supplemental EIS in 2000, and in 2002 the FHWA issued a Record of Decision, allowing construction of the tollway to proceed after six years of delays.

This marked the first time that the tollway authority had required local municipalities to contribute funds for interchange construction.

[38] The towns of Homer Glen, Lemont, New Lenox, Lockport and Will County agreed in a June 2006 intergovernmental agreement to provide $20 million in both cash and in-kind contributions for the interchanges.

[40] One of "the most impressive engineering feats on the state's 274 miles [441 km] of toll roads"[36] is the Des Plaines River Valley Bridge, a bridge over the Des Plaines River, the Chicago Sanitary and Ship Canal, the Illinois and Michigan Canal, Bluff Road, New Avenue, numerous railroads, and a major Commonwealth Edison utility corridor.

Work on the bridge included the construction of 34 piers and elevation of existing high-voltage electricity lines to accommodate the highway.

[43] After noting the success of the festival, a tollway spokesman announced plans to repeat the event annually, including the closure of the entire southern extension.

[44] He later clarified the tollway's position, indicating that while the extension would probably not be closed in its entirety in the future, a possible five-mile (8.0 km) ride across the Des Plaines River Valley Bridge may be held.

This addition will link the trail to a number of businesses in New Lenox, including a shopping mall currently being constructed, Silver Cross Hospital, and medical offices.

It continues north through the rural sections of Will County, having exits that serve the towns of Homer Glen and Lockport.

Continuing north, I-355 has another multiple flyover interchange with I-88 (miles 19.5 and 23.0), officially designated the Ronald Reagan Memorial Tollway.

[53][54] All three toll plazas force traffic paying with cash to exit right into an area separate from the dedicated I-Pass lanes.

[55] I-Pass and E-ZPass equipped cars and trucks are permitted to stay on the mainline and pay tolls at highway speeds in the tollway's ORT lanes.

The tollway authority added the four-mile (6.4 km), $60.4-million project (equivalent to $85.5 million in 2023[9]) to its Congestion Relief Plan in mid-2007, and the new lanes opened on October 24, 2009.