Add your information to this petition by Anna Berlanga of Transportation Alternatives. It spells out the Why pretty well.
Provide an alternate route to Cherry Walk and the pinch point on the Henry Hudson Greenway at 125th Street
Enable accessible, stair-free travel to the the tennis courts and greenway at Riverside Park.
What the petition does not say is that:
having this route would save the NYC Department of Parks and Recreation and the Riverside Park Conservancy (RPC) time and money when moving vehicles between the lower and upper parts of Riverside Park. A minor investment would need to be made in doing something with the existing desire line that runs on the west side of the 119th Street Tennis Courts. Some of these vehicles are low speed vehicles (eg Gators, GEMs) that do not belong on Riverside Drive.
If NYC Parks and RPC used this alternate route to and from the northern part of Riverside Park, then congestion and conflict would be lowered on Cherry Walk and these vehicles would no longer need to travel on Riverside Drive which would benefit other drivers and make the experience of going between parks less traumatic for park workers.
Even before the ramp was closed by NYC DOT, several of us had a proposal to Community Board 9 Manhattan to repurpose one of the two lanes to accomplish the above.