But only about 30 percent of the Illinois Tollway's 286-mile network will get the higher speed limit, according to a map released by IDOT. And in the Chicago area, the 70-mph limit will be posted only on five fairly short stretches of interstate. Those are sections of I-80 and I-55 in Will County, a stretch of I-57 in far southern Cook County and all of Will County, a portion of the I-88 toll road in far western Kane County and part of the I-94 tollway in northern Lake County.