The A-levels or service levels are the deepest parts of the Amtrak Federation's underground facilities. Federation divisional bases run down from the interface at Level Ten-10 through some 100 floors to Level One-1, the 'ground floor' of the base. The A-levels are below that, with Level A-1 located immediately below Level One-1. The A-levels run in ten-floor blocks from A-1 down to A-10 followed by B-1 down to B-10 etc.
How far down the A-levels go is classified, but according to rumour the deep geothermal power stations are located at Level J-10, more than 3,000 feet beneath the surface.
The service levels contain the heavy machinery and equipment needed to keep the bases running. Aside from those who work down there, most soldier-citizens never see the A-levels outside of the Trans-Am train shuttle stations, which are typically located at Level A-4/5.
Working in the A-levels is back-breaking hard labour and is usually the lot of those tempermentally unsuited to working in more important fields or those found guilty of a minor infraction and sent down to the A-levels for period of several years before they are judged ready to serve in a more useful capacity.