I have asked several times about extending LD trains and one of the most common responses was that only a few stations are able to service LD trains.
On the other hand, the through car model seems to work very well for some of the LD trains. The Lake Shore Limited has a Boston leg, the Empire Builder has a Portland leg, and there are through cars connecting the Texas Eagle and the Sunset Limited. Amtrak has discussed at least three more through car possibilities: a Pennsylvania leg of the Capitol Limited, a St. Louis leg of the Cardinal, and a Los Angeles leg of the California Zephyr.
In addition, All Aboard Ohio has suggested through cars off the LSL to serve CLE-CIN (http://freepdfhostin.../cf26514bc8.pdf) although they proposed switching the schedule which hurt or eliminate possible transfers in CHI.
I think this is a good way to add city pairs and potential one seat rides to existing LD routes without requiring transfers. In the example of the Capitol-Pennsylvanian, no new train miles are required as the two trains in question are already running. The negative is that you are holding one train back and delaying it if the other portion is delayed (ex. the Pennsylvanian must wait for the CL). I would still think the through cars is a net positive (and Amtrak agreed even though they haven't implemented the through service yet).
Some more possibilities I came up with:
Boston section of SM (Split/Merge anywhere between NYP and RVR)
Richmond section of CL
Oklahoma City section of TE (Just merge the TE and HF)
San Jose section of CZ (Split/Merge at EMY or SAC)
San Diego section of SWC
San Diego section of CS (Split/Merge at Santa Barbara or LAX)
For some of these, simply split/merge two trains similar to the proposed Capitol/Pennsylvanian through cars. Others require some more creativity. Example: Terminate 86/164 in NYP, Run 498 NYP-BOS in its place between the cities. Essentially you are splitting the 86 and 164 in NYP and passengers on those trains would have to transfer to go north of NYP (although there will still be other direct trains from Virginia to New England including the 498 for passengers in Richmond, Fredricksburg, and Alexandria). For some, you may just want to "add" the through branch as an additional frequency between the two cities (not practical for NYP-BOS because of capacity limitations).
For some of these, instead of splitting a train so one leg goes to one city and one goes to another (LSL), have a reduced consist continue to another city and leave the rest of the LD train in the regular terminal point (similar to TE/SL).
Hopefully this will expand the Amtrak LD system without drastically increasing costs.
You could also add new legs to LD trains on tracks/routes that Amtrak doesn't already use (ex. SLC-LAX) but that would require a bit more money.
Edited by Philly Amtrak Fan, 20 April 2016 - 05:45 PM.