Are you specifically asking if a customer was served by his shipments using the whoe wye, or just pasrt of it, such as coming out of Tunnel #1 and using the south (railroad East) leg to head towards old Mission Bay Yard? I photographed an SP SW1500 using that part of the wye to brings 30 rock cars to and from an Kaiser aggregate plant across Third Street in 1993. At that time the north (RR West) leg was out of service. At that time I believe there were no other active shippers on that side of Tunnel #1 so the need for the wye was not there.

That said, I agree that it might have been useful to keep the wye intact for those infrequent times a need existed. I heard that the Kaiser plant shut down not long after I viewed the operation.