I can't let my namesake railroad have yet another dicussion fade into the RR.net archives, like many past ones have...
I spent a good chunk of yesterday walking along the West Trenton ROW hunting down the site of the Frog War in Hopewell. I parked at the VFW Post along Van Dyke Road in Hopewell, and walked east along the present ROW for a few hundred feet before venturing into the woods. The original Delaware & Bound Brook (Reading New York Line, CSX Trenton Line) ROW actually continued curving south past its current alignment, having done so to avoid confrontation with the M&S for as long as possible. The original D&BB ROW was tough to discern at first, but working backwards from a bunch of rocks that were once part of a bridge abutment across a small stream, I was able to find it and, from there, find the approximate crossing with the M&S. When winter rolls around I hope to return to the site (it's a little overgrown now), Google maps in hand, to nail down the location for sure. It was my first trip to the Frog War site, and it was quite interesting. Plus, I got to see a little CSX action (if only the foul-smelling garbage train!)
In addition to the site from yesterday's adventure, there are many remnants of the ROW remaining, although development is fast erasing them, especially in Montgomery. Jacob's Creek Road, running from the D&R Canal to Washington Crossing-Pennington Road is laid atop the M&S ROW, on a twisting section known as "The Corkscrew" when the M&S first opened (at least according to "Frog War!"). From there, the ROW is traceable on maps.google.com until the Pennington-Titusville Road/Route 31 intersection in Pennington. The Pennington station does indeed still exist in the southwest quadrant. The station is currently aligned to be parallel to Pennington-Titusville Road; however, it originally lined up with the ROW (roughly 45 degrees askew from its present orientation). The ROW is tough to trace from Pennington to Marshall's Corner, but is easy to trace from Marshall's Corner to Hopewell, where it crosses the CSX Trenton Line just east of Vandyke Road. The trail is cold through parts of Hopewell, but Model Ave/Railroad Pl/Somerset St. appear to be where the ROW ran. From the end of Somerset St., the ROW is again tough to trace until the Montgomery border at Province Line Road. From there, the ROW is relatively easily traced on Google all the way until it crosses Willow Road in Hillsborough.
I've hiked more or less the entirety of the ROW in Montgomery--there are numerous large chunks of ROW remaining. Starting at Province Line Road, the ROW can be seen on the southern edge of the Province Line Swim Club just south of the CSX line. There's nothing of much interest from Province Line Road to Spring Hill Road. Between Spring Hill Road and Hollow Road, there are two stone embankments that allow a stream to pass through the ROW. Unfortunately, this is buried on a private hunting reserve, surrounded by electrified fencing, at the end of a target range, so I can't recommend looking for it (climbing through the electrified fence onto the gun range just to get a better picture of the stone culvert probably wasn't the best idea I ever had!) From Hollow to Route 601, the ROW is essentially intact, and will likely remain that way since a lot of the land surrounding it has been bought by the town for the new high school. The ROW along that section has a number of interesting artifacts, including a stone embankment and a an arched culvert (both featured in "Frog War!"). Potentially the most exciting part of the ROW is near the crossing of Route 206 in Harlingen, where there is a long contiguous section of the ROW. Just west of the crossing of 206 is where the Harlingen Station and turntable used to be. There is a large, circular area with much less vegetation than the surrounding area, which I assume is the site of the turntable. Most of the land containing the ROW between Kildee and 206, including the part with the turntable, was preserved last year by the township, which is good news for M&S fans!
That topographic map in the above post does accurately trace the ROW through Montgomery.
The Start of the "Corkscrew" (follow Jacob's Creek Road)
Approximate Location of Pennington Station
Approximate Location of the Frog War
Approximate Location of Harlingen Station & Turntable