NY 100 begins in the city of Yonkers as Central Park Avenue (almost always just called "Central Avenue") at exit 4 of the New York State Thruway (I-87). This portion of Central Avenue is maintained by Westchester County as County Route 47II (CR 47II), an unsigned reference route. Central Avenue continues south as a service road for I-87 until The Bronx, where it splits from I-87 shortly after entering the city, and becomes Jerome Avenue, a major surface road in the West Bronx. NY 100 diverges from I-87 just north of exit 5 and heads northeast, crossing over the Sprain Brook Parkway about beyond the split. Central Avenue has an interchange with Tuckahoe Road shortly after the Sprain Brook Parkway. The road continues through Yonkers in the area between the Grassy Sprain Reservoir and the Bronx River, with many shops lining both sides. At the northernmost part of the city, Central Avenue intersects Fort Hill Road, which leads to Jackson Avenue and the northbound Sprain Brook Parkway. Central Avenue continues out of the city of Yonkers into the town of Ardsley. The only noteworthy intersection in Ardsley is with Ardsley Road, and east-west road that goes straight across most of south-central Westchester. NY 100 runs through the hamlet of Hartsdale, about two miles (3 km) north of the city line, and where the bypass route NY 100A (Hartsdale Avenue) begins. Hartsdale Avenue also continues east of the intersection into the village of Hartsdale without a route designation. Central Avenue then enters the city limits of White Plains, where the road ends at NY 119 (Tarrytown Road). Within White Plains, the road is county-maintained with unsigned designations of CR 99 and CR 90.