Amtrak practices vary by region and station. Here on Amtrak Cascades, Seattle and Portland both do "airplane style" entry with ticket checks and sometimes seat

Amtrak practices vary by region and station. Here on Amtrak Cascades, Seattle and Portland both do "airplane style" entry with ticket checks and sometimes seat assignment in the station, but at more minor stops (eg Longview, Bellingham) you hop aboard one of the open cars and get checked by the conductor.