Jay Bird, the first thing you need to understand is that NONE of this, not Subways, not the St. Mary's Railroad, First Coast Railroad, CSX or Amtrak, is light rail. It's not you fault for not knowing this, today's media is so ignorant of rail operations they scarcely know a coach from a crossing. Light rail is often used as-if it were "conventional rail done light," but it's nothing like conventional rail. To further muddy the water, one of the benefits of light rail is that the physical plant actually CAN BE rail done light. Rail is measured in pounds per yard, and traditionally the rails used in these projects have been in the 80 - 130 pound range. Modern freight rail usually runs from 120 - 156 pounds per yard.
Rail breaks down like this:
Streetcar (old and new), slightly smaller, vehicles, typically along or in road right-of-ways, usually electric powered
Sacramento, CA.. Light Rail, larger vehicles which might on first glance be confused as "big streetcars," much faster and generally grade separated from other traffic, usually electric powered.
Conventional Rail, Regional Rail, Commuter Rail, are all variations of a typical Amtrak or commuter train. Usually diesel powered except in congested urban areas where electric locomotives take charge.
BART in the San Francisco Bay Area. Heavy Rail, Subways and EL's which require mountains of cash to build and have unbelievable capacity, typically electric powered.
Monorail, Single on solo beam vehicles or suspended from beam, electrically powered and usually dedicated purpose such as airport or theme park or downtown applications. BTW, monorails ARE NOT, the trains of the future, in fact there is evidence that they are as old as conventional rail. Had monorails held economic promise, we would have laid the golden beam rather then the golden spike.
In a perfect world it is not very likely that commuter rail would reach all the way into Kings Bay or St. Mary's. There is a remote possibility that at least a few daily runs could end in Kingsland, likewise Fernandina Beach could be a terminus for a couple of daily trains each way. Yulee is the most likely as it will have a station right off of the interstate, US 17 and SR200 easy to get to from Fernandina Beach, Kingsland or Callahan.
The trains would likely be self powered (diesel) conventional rail cars such as rebuilt Budd RDC's or the new DMU types.
The route has no connectivity to either Amtrak or the Florida East Coast's "All Aboard Florida" trains until they reach the old Jacksonville Terminal (The Prime Osborn to the unwashed masses) in downtown Jacksonville. There could be no "through" service on the Yulee/Kings Bay/Fernandina Beach lines as they are all dead end branchlines.
Lastly there is also a remote possibility that Southeast High Speed Rail would use the former Seaboard Air Line Railroad's abandoned right-of-way between Savannah and Kingsland, and upgrade the remaining line from Kingsland to downtown Jacksonville as it is considerably shorter then the current Amtrak/CSX route through Jesup.
