Halfway through the borough it begins to closely parallel the Harlem Line of Metro-North Railroad, a pairing which continues to the road's northern terminus.

In Westchester County, the road continues to have the same character until the Sprain Brook Parkway splits off at Bronxville, allowing most through traffic to bypass White Plains.

Immediately to the north is the cloverleaf interchange at the Bruckner Expressway (Interstate 278 or I-278), where most traffic enters the parkway, which begins as a six-lane freeway.

[3] Basketball courts and baseball fields flank the highway in the strip of parkland as the road leads to the north, slightly northwestward.

North of Watson Avenue, within a half-mile (1 km) of the southern terminus, an on-ramp carries northbound traffic from Metcalf.

The single ramp of exit 5 allows southbound traffic to follow East 177th Street to NY 895 (Sheridan Boulevard) and the Triborough Bridge.

Past the exit the large wooded area on the west is the New York Botanical Garden,[7] a National Historic Landmark (NHL).

[10] At the next exit, Gun Hill Road, the Williamsbridge station serving that neighborhood on Metro-North Railroad's Harlem Line, which closely parallels the parkway from this point on, is located immediately west of the highway.

[11] The railroad tracks join the river and the parkland in paralleling the road north as it continues straight along the east edge of Woodlawn Cemetery,[12] another NHL.

[13] Almost a mile and a half (2.4 km) to the north, the Woodlawn station is located at the northeast corner of the cemetery next to the East 233rd Street exit.

[14] The highway bends left and then right again, crossing the river and the railroad, near the split along the tracks between the Harlem and New Haven lines immediately north of the station.

[19] A half-mile north of that junction, the parkland and the roadway narrow as Bronxville becomes the community on the opposite side of the Bronx River.

Exit 2, West Pondfield Road, also northbound-only, is a thousand feet (300 m) to the north as the highway curves around downtown Bronxville to the east.

A thousand feet to the north, Scarsdale Road is the first at-grade interchange, and the parkway turns sharply to the east, then back to the northeast more gradually.

Exit 8, Thompson Street, serves the nearby Crestwood station as the Harlem Line's tracks begin to parallel the road again.

Another three-quarter mile north, after the road has resumed its northeast course, comes the next at-grade exit, Leewood Drive, on the northbound side.

The roadways remain apart through a wooded section as they curve westward for the next three-quarter mile, returning to the highway's northeastern heading as it leaves Yonkers and briefly enters Greenburgh south of the southbound Ardsley Road exit east of downtown Scarsdale.

The parkway begins heading even more to the northeast, the tracks immediately adjacent, past northbound exits for River and Claremont roads.

It bends north and then northwest to the first of several at-grade intersections with traffic lights, also signed and numbered as exits, with Central Avenue (NY 100), at the Westchester County Center.

The two roadways once again diverge, becoming almost 400 feet (120 m) apart in the half-mile (1 km) before they converge again as they reach the Old Tarrytown Road intersection just north of the expressway.

Another thousand feet from that intersection, the highway turns to the northeast again as the roadways diverge and cross the Harlem Line and the Bronx River for the last time.

A seven-mile (11 km) section of the Bronx River Parkway in Westchester County south of White Plains is closed to motorist traffic from 10 AM to 2 PM select Sundays in May, June, September and October (with the exception of Memorial and Labor Day weekends), allowing bicyclists to venture along the scenic road.

[31] In April 1931 steam shovels finally broke ground at Shrub Oak for the section built in Putnam County.

[32] Eight months later the two rivals were at the north portal of the triple-hinged steel suspension bridge built over the reservoir, at 750 feet (230 m) the longest of that type in the world at the time,[citation needed] for the ribbon cutting ceremony.

The road’s northern terminus was truncated to NY 22 in 1941, with the existing portion replaced by an extension of the Taconic State Parkway.

During this reconstruction period, a new overpass was built to serve the Cross County Parkway, with the ramps rebuilt into a partial cloverleaf interchange.

[38] In 1955, reconstruction and widening to six lanes began at the half mile stretch of the Parkway between the Woodland Viaduct and Scarsdale line.

[46] The southernmost portion of the parkway in Westchester, south of the Sprain, is internally designated as NY 907G, an unsigned reference route,[47] in apparent violation of the numbering standard.

Drawings and photographs from the documentation project were made available through the Westchester County Archives, winning an award of excellence from the Lower Hudson Conference.