How is ATFM handled in the USA? In my answer to this question, I describe how calculated takeoff times (CTOT) are used as a tool in European air traffic flow management to prevent overload and maximize capacity. I expect the ATFM system used in the USA to be quite similar, but I'm sure there are technical differences. I am hoping someone can provide a similar answer, detailing ATFM procedures in the USA.



original question:

Air traffic flow management (ATFM) is a service established with the objective of contributing to a safe, orderly and expeditious flow of air traffic by ensuring that ATC capacity is utilized to the maximum extent possible and that the traffic volume is compatible with the capacities declared by the appropriate ATS authority.

In Europe, air traffic flow and capacity management (ATFCM - notice the additional C) is handled by EUROCONTROL.

Each air navigation service provider (ANSP) is responsible for declaring the capacity of their ATC sectors in terms of a maximum number of movements that can be safely handled in given time intervals.

All IFR flightplans in Europe are processed centrally by the Integrated Initial Flight Plan Processing System (IFPS). If, based on the flightplans, it is calculated that capacity within a sector will be exceeded, flights might be rerouted or level capped, or they receive ground delay (a slot time).

This system works very well, and ensures an efficient and safe flow of air traffic within Europe. However, flights originating outside of Europe cannot be processed in the same way. For example, flights departing outside of Europe will not receive any slot times, which makes the system inflexible, since these flights still have to be taken into consideration, but cannot be adjusted the same way other flights can.

This has made me wonder, why is it not possible to simply link the European system with similar systems around the world, to create a global ATFM network? Specifically, I am interested in how ATFM works in the USA. I would like to identify the main differences between the European system and the system in the USA, with the goal of understanding what prevents these systems from working together.
The problem with working together on a global scale or even trans-Atlantic is the long time and distance between. Flow control at least in the U.S. (and I'm sure elsewhere) is more short-term (1-2 hours out), mainly based around airport acceptance rates (AAR) which can change hourly or even more frequently for example because of runway configuration changes, or weather or visibility changes. There is also short-term projected sector saturation issues, and short-term sudden localized things like weather buildups that can come and go.  

That means for trans-oceanic flights you can't effectively implement departure metering (the main tool in the U.S. for flow control) or ground stops because you can't predict 5-10 hours in advance the traffic level and acceptance rate at the destination airport. It's much more effective to wait until they're back in radar coverage and closer time-wise to the destination when flow control calculations will be more accurate, and controllers can achieve miles-in-trail spacing requirements with quick radar vectoring. Over the ocean, outside of radar coverage, significantly adjusting in-trail spacing is more difficult because you really only have speed adjustments which are limited because of the narrow aircraft envelopes at high altitudes.   

For situations where there will need to be long-term flow control (such as, the only other runway is suddenly closed and will be indefinitely), we already do have a manual process to implement flow restrictions trans-oceanic, by each facility passing restrictions to adjacent facilities, on and on up the chain.  For example, Shanwick can tell Gander we need 10 minutes all aircraft all tracks landing EGLL, Gander tells Boston 12 minutes in trail, Boston coordinates with U.S. command center, etc to ensure Boston doesn't get overwhelmed with EGLL-bound aircraft. Those kinds of things happen very rarely though, so it's probably not worth connecting our different automation/flow control systems together and instead just keep handling it manually on a case by case basis.

(Source: I'm a former FAA controller and worked in flow control/Traffic Management Unit for several years).