OK, I've got it and thank you.
I know how it works with Amtrak LD trains boarding either coach or sleeper, I'm guessing the staff have a manifest that tells them if passengers are boarding or getting off their car(s) at any given station. Didn't have any idea how US commuter trains worked as the very few that we have boarded we haven't had bags so just went to the car we wanted to with an open door. Also have never ridden a NER so far.
Last Wednesday we used trains to visit a relative in Saxmundham, Suffolk, UK (very pretty ancient small town but hard to live in as it is not laid out for modern living). We would usually drive but the scenery is pretty in north Essex and Suffolk and we have become rail fans too, on top of that it was a treat for another relative who went with us. So trains from Brentwood, Essex to Saxmundham, Suffolk. It's a very fragmented journey involving 3 changes and 4 different trains each way, all commuter trains but of three types. It's a 2 hour journey, not long for so many changes. The number of cars varied from 2 up to about 12.
On all trains we could board into any car, there is only one conductor/car attendant for the whole train. The doors are opened or closed either manually by passengers with catches or electronically by passengers with a time limit controlled by the conductor. Can't say for certain if there is an electronic check if all manual doors are closed or not, but the conductor is usually at the rear of the train and sometimes walks forwards maybe to check that all doors look closed?
So I had assumed that a NER commuter train where getting on and off has to be fast as commuters are often in a hurry, and would be similar to the UK versions, but obviously not and closer to the LD train system, it's a good thing to know.
