I was chatting with a guy from the mechanical department of Eastern Railway in India who is familiar with the handling of the rakes (as consists are called in India) for the fast overnight trains (Rajdhani Express) between Delhi and Calcutta, which are maintained out of Howrah and Sealdah base in Calcutta. These trains take 16 to 17 hours as per schedule for the 905 mile journey. A rake goes out on day 1 and arrives Delhi in the morning of day 2 and starts back evening of day 2 arriving back in Howrah on day 3 morning. Each rake is 19 cars (2 End on Genrator/brake, 2 ACI Sleeper, 2 Pantry, 5 AC2 Sleeper, 8 AC3 Sleeper capacity about 950 all sleeping accommodation).
If the train arrives late in Delhi making it impossible to meet the scheduled departure, it is turned around ASAP, which usually means 3 hours and sent back on its way. This includes cleaning and re-stocking for the 950 or so passengers, but usually very little mechanical work unless absolutely required. They are basically run as if they were on an 1800 mile two night journey as far as mechanical maintenance is concerned.
Theoretically this could be run using two rakes (consists). But according to this guy experience shows that the wear and tear both mechanical and to passenger amenities through the 17 hour journey is such that it is more reliable to use 3 rakes and as necessary rotate out an arriving rake and replace it with the third rake. This becomes even more critical in the winter when due to fog it is not unusual for the return to arrive 12 to 14 hours late. That at least answered my question on how they manage to run the daily service even in the face of these huge fog delays in the winter with no cancellations almost ever.
So all in all whether such a service can be run with two rakes (consists) or not depends on the operating conditions, dependability requirements, wear and tear and requisite necessary downtime for repairs and maintenance and other factors like weather etc. It does not follow that because SEPTA can turn a train around therefore Amtrak should be able to, or that because it could be done 50 years back it can be done now. One has to look at the overall operating conditions at present and plan accordingly.
Of course the example that I gave above is operated in an environment where people absolutely critically depend on those trains running for their day to day livelihood and business. Those trains are heavily used by both government and business personnel as part of their day to day business, so just canceling them is not an option. These are so called class 1 priority trains which continue running until literally hell freezes over.
Also, the equipment pool to draw from is large. Just to give you a sense they are effectively handling 6 rakes (2 trains per day each way to Delhi and back from Howrah and Sealdah the two main stations of Calcutta) of on an average 18 cars (6x18 = 108 cars + few additional standby cars making the total pool about 120 cars) of which at any time at least 4 rakes are on the road). Cars that would go into forming the third rake may be running around somewhere else (though unusual), but scheduled to be back in town should they be needed. In times of known trouble like winter, they add equipment to the pool to actually keep a third rake available since they know they will need it on most days.
OK now back to the originally scheduled program, and the usual expected few snide remarks about toilets on Indian trains