score:4
Hmm... Technically, I suppose all of these answers are somewhat opinion-based, but I would personally plan a bit longer than 1.5 hrs for a layover to an international flight at ATL. I usually try to plan at least that long even for domestic layovers there. While Michael is correct that, if you did miss your flight, they would put you on the next available flight to your destination since you booked a single ticket, if you'd rather avoid that possibility, I'd personally advise planning a bit longer than 1.5 hours between flights. Keep in mind that the times listed for the flights are not including the time required to deplane and board the next flight, so even if you have a 50 minute layover scheduled, your departing flight is likely already boarding by the time you step off your arriving flight, even if it's on time. It's definitely possible that you'll make the 1.5 hr connection here, but it's also possible to miss it, especially if your inbound flight is delayed for some reason.
As far as the 'plane train' is concerned (that's what they call the light rail you mentioned,) this map does seem to suggest that it connects to concourse F. Note that international flights in Atlanta can depart from either Concourse F (which is directly attached to the new international terminal) or Concourse E (which housed all of the international flights prior to the new terminal.) As far as I know, the plane train connects to both, though.
Upvote:3
Atlanta airport is huge (the biggest in the world, IIRC), but well organised. If your baggage is checked through, one and a half hours are enough for transit between a domestic flight to an international flight. The train that connects the terminals is very easy to find and use.
Of course, if your arrival is delayed you might still miss the connection, but if it's on a single ticket, the airline will put you on a later flight. For separate tickets, I'd prefer to have an extra hour safety margin.
Upvote:4
If your flight into Atlanta is domestic (originating in the US), you should be fine.
The International terminal is quite a ways away from the domestic terminal, but the light train goes there.
On the return, 1.5 hours may be cutting it close, as you'll have to go through customs during that time. But for your outbound flight, I expect no problem.