Mosholu Parkway where it enters Van Cortlandt Park at Gun Hill Road to connect with the Henry Hudson Parkway in the northern part of the park. Later, in the 1950s, Moses also ran the Major Deegan Expressway through the park, so now the the park is effectively cut up into six pieces with very little access from one piece to the other. See map.

References:

1. NYC Parks Dept press release of December 28, 1936: “It is proposed to build an entirely new parkway spur from the Henry Hudson Parkway in Van Cortlandt Park to the Grand Boulevard and Concourse, and by way of the reconstructed Mosholu Parkway to a junction with the Bronx River Parkway in Bronx Park.”
2. NYC Parks Dept press release of October 21, 1941: “Department of Parks announces the completion of work in connection with the construction of a traffic relief road connecting Mosholu Avenue and the Henry Hudson Parkway and the restoration of the park and golf course in the north central section of Van Cortlandt Park, The Bronx.”
3. New Deal Assistance in NYC Parks Department Projects, 1934-43.