From I-190 exit 20, NY 324 runs in a more southeasterly direction, serving as the main commercial strip on Grand Island, before it overlaps I-190 in order to cross the Niagara River. Once on the mainland, the structure of exits on I-190 allows only the westbound portion of NY 325 to use Grand Island Boulevard west of I-190's exit 15, following Grand Island Boulevard past the exit to an intersection with NY 266, then turning right to follow it to exit 17 to merge with I-190. The eastbound route of NY 324 is unable to do so; instead, it parts company with the Interstate Highway on the other side of the river at exit 15, where it turns north to parallel I-190 on Kenmore Avenue. The eastbound portion of Grand Island Boulevard on this stretch is maintained as reference route 950C. After , it veers east onto Tonawanda's portion of Grand Island Boulevard for to a junction with Sheridan Drive. The latter carries NY 325, a route that begins at NY 266 on the banks of the Niagara and passes through a commercial and industrial area of the town of Tonawanda. NY 324 takes on the Sheridan Drive name here and assumes a more due easterly course across northern Erie County. Though the street is signed as a state highway on both NY 324 and NY 325, most residents simply refer to this road by its local name.