In the UK, I know that many of their services using EMU or DMU equipment will link and separate mid-route. Why can't this be done here? Admittedly, most of the EMU routes we have run full trains end to end, and most of the DMU routes (all 1 of them?) are too short with no branches. But from an FRA and brake test, and inspection, etc. standards, why can't that be done here? Or at least what makes the process long enough and onerous enough for it to not be worth it here?
Besides the rail corridors being owned and operated by freight railroad companies with little concerns about passenger rail in America, the distances involved are so much larger here than in Great Britian.
For example, England's proposed HSR2: the distance between London and Birmingham is approximately 120 miles, the distance between Birmingham and Liverpool is approximately 100 miles, and the distance between Birmingham and Manchester is approximately 90 miles.
Amtrak splits 3 long distance trains; the Lake Shore Limited, the Empire Builder, and the Sunset Limited with a name change on one split to the Texas Eagle. Here's their distances as America's examples:
Lake Shore > Chicago to Albany 820 miles, Albany to New York City is 150 miles, Albany to Boston is 170 miles.
Empire Builder > Chicago to Spokane is 1780 miles, Spokane to Seattle is 280 miles, Spokane to Portland is 350 miles.
Sunset > Los Angeles to San Antonio is 1350 miles, San Antonio to Chicago is 1240 miles, San Antonio to New Orleans is 540 miles.
Note the shortest distance leg for Amtrak's split trains is longer than the longest distance leg xfor England's HSR 2 proposal. The distances America's trains travel are much longer than England's trains. Longer distances means less reliability for the trains to arrive on time.