In Harrison, NY 120 passes several mansions on both sides of the highway as it gradually turns northwestward and approaches I-287 (the Cross Westchester Expressway). The route parallels the western edge of the freeway for several blocks to Westchester Avenue, where NY 120 meets the southern end of NY 120A, an alternate route through the easternmost part of Westchester County. While NY 120A heads east toward Port Chester, NY 120 takes on the Westchester Avenue name as the two directions of the route split to follow collector/distributor roads running northwestward along both sides of I-287. The route remains on the frontage roads for about a half-mile (0.8 km) to another section of Purchase Street, where NY 120 turns to follow a slightly more northward track through another residential section of Harrison.