Hello all. I am a "person of size" and was researching this topic because I absolutely need two seats to ride coach. This thread is the number one link on google regarding buying two sears, so I wanted to add my information. Just so it stands out for my fellow searchers I'm going to make it big and bold:
The official policy is you can buy two seats for one person under two specific circumstances (medical disability, obesity) -- else it is explicitly disallowed.
This is covered in the Amtrak Service Standards manual, section J4. You can find a copy of the entire 700+ page manual here:
http://www.governmentattic.org/4docs/AmtrakServiceStandardsManual_2011.pdf. It was obtained via a FOIA request, and is not publicly avaliable on Amtrak's site.
Below is the relevant section. Note that all bold/italics is present in the original document, and is not my emphasis.
4. Coach
a)
Each Coach seat reservation entitles passengers to occupy only one seat per person.
b)
An additional seat may be reserved for a Service Assistance Animal accompanying a blind, deaf or mobility-impaired person at no charge.
c)
A passenger who requires two seats due to a disability, including obesity caused by a disability, a leg in a cast, a hip operation, may book two seats and pay only one fare.
d)
A passenger who requires two seats due to size alone, not caused by a disability, may book two seats but must pay the lowest applicable fare for both seats.
e)
A passenger cannot book two seats simply because they do not want anyone sitting next to them.
If the train is full, it is very hard to explain to standing passengers why that empty seat cannot be used.
f)
A passenger cannot book a Coach seat and a Sleeping Car accommodation, just so they can move back and forth between the two spaces
That being said,
almost zero people at amtrak seem to know this is the official policy.