@CR2721 A very nice job with the map there! But just to answer your question on the current route:
Yes, The new Raritan River Bridge would have to be built to take Plate F cars with a gross weight of 286,000 pounds. However, the new bridge would only fix part of the problem.
As it currently stands, there are serveral bridges over the NJCL in Perth Amboy. None are high enough for Plate F. In order for the current route to be completely brought up to standard, those bridges would have to be raised or replaced with new bridges that are high enough. NJ Transit does not care for freight at all and would rather have Conrail not come down whatsoever.
In addition, the current route has limitations on the gross weight of cars between South Amboy and Red Bank as well as strict limitations on what types of cars can come down. (No intermodal, refrigerated boxcars, certain flat cars and tank cars) There's a restriction on what type of freight can come down as well. (No steel coil cars or scrap gondolas between South Amboy and Red Bank)
However, nearly all areas of track south of Sayerville can support Plate F cars. This includes the old Freehold to Farmingdale route and nearly all of the Southern Secondary. Only the Tinton Ave bridge in Eatontown is low enough to not support Plate F.
It is possible to bring Conrails lines in Central NJ up to standard while also getting freight off of the NJCL. I will explain how.
It costs a million dollars to build one mile of railroad track. The abandoned Freehold to Farmingdale route is about 5 miles so 5 million dollars to fix that plus the cost of a wye in farmingdale and repairs to the railroad crossings. (Would likely bring the total cost up near 7 to 10 million)
Bringing the NJCL between South Amboy and Red Bank would mean replacing or strengthening railroad bridges, raising or replacing bridges that go over the NJCL, and raising ALL of the catenary wires to support Plate F clearance. The North Jersey Transportation Planning Authority estimates this could cost anywhere from 16 to 139 million dollars.
Then there's the current route of OI16 over the Raritan River Bridge which would have to be upgraded. The NJTPA says this could cost 6.9 to 64.9 million to upgrade this stretch.
There's a back way into Sayerville via a connection with the NEC at Monmouth Junction. The Entire NEC between Monmouth Junction and Oak Island supports Plate F cars, but there's a few bridges in New Brunswick that can't support cars weighing 286,000 pounds. The NJTPA Estimates that the bridges can be fixed for as little as 400,000 dollars.
So in short, it would be MUCH cheaper to upgrade the NEC and rebuild Farmingdale to Freehold than to rebuild the current Coast Line route. In addition, Amtrak has much less strenuous freight restrictions. They allow cars and freight that transit has a ban on. This is not only good for Conrail, but good for NJ Seashore Lines in Lakehurst should they decide to expand.
I too feel that the ability to bring down Plate F to the distribution centers in Dayton and Heightstown would be a tremendous idea.
As for Conrail having the money to pull this off: They have the money. They just don't want to spend it. The manager of Conrails North Jersey area is an old guy with the ideology of "Get rid of anything that doesn't make enormous amounts of money" and Sayerville has practically fallen apart with this guy in control. He's too cheap to spend money on almost any sort of improvement.
It may also interest you to know that he was Penn Centrals head of track maintenance...
Freight rail in Central NJ can be so much more and so much better than what it is now, but only if you have someone who cares about doing right.
That's my two cents on it at least.