There is a tunnel that runs under the Turnpike on the North side of the Rancocas River just after the bridge. It was negotiated by the landowner, Granville Haines, the farm is now an industrial park. Haines owned 35 acres of pasture on the other side and wanted direct access. When he sold off the main portion of his farm he deeded the 35 acres to the state, it's now part of Rancocas State Park. The tunnel is large enough to get a Ford 9N tractor through and to my knowledge is still there.
Trivia- The Haines farm was where they took Nikita Kruschev, in order to show him a typical working family farm. His response, "when do we go to "Disneyland".