According to the CBP officer at IAH yes..."for now" though again he mentioned it should be coming online and be mandatory for foreigners (no idea if that includes greencard holders or Canadians as they sometimes have different rules at CBP stations). Some of the previously linked articles stated optional for US citizens also but not every article has said that.

The way US airports are set up, with no exit control measures in large numbers, I find it hard to believe this will come to fruition nationwide and for every flight as currently handled by CBP; they just do not have enough officers. Maybe they will want the airlines to run it in the future if it becomes reality. Multiple gates at large hub airports would have to be set up or they would need to be scores more mobile units. Logistics are tough with this system at the big hubs.

There is US exit border controls. You just don’t see it happening (eg APIS, facial recognition etc).

Nobody is stopping people from leaving. That is monitoring, not control -- particularly on land borders where I suppose the US may have a deal t:o get exit data from Canada & Mexico.

Process for stopping people from leaving is there as well. They do it in the background. If you have a warrant out for a serious crime, CBP will be waiting for you at the jet bridge. APIS submissions are run against criminal databases for both incoming and outgoing flights.

At northern land border they just wait for CBSA to deny entry and U turn you back (unless you are Canadian citizen).

examples:
https://www.cbp.gov/newsroom/local-media-release/dulles-cbp-arrests-two-wanted-men-one-week-felony-child-molestation

https://www.cbp.gov/newsroom/local-media-release/boston-cbp-officers-arrest-fugitives-attempting-flee-us

I have been at the gates and on jetbridges where US federal agencies literally stop some people from leaving the country on the flights -- some of the people stopped are even Americans. So it goes beyond just monitoring, as the monitoring at times does get followed by a very real control aspect in play at airports for flights headed out of the country.

About land exits from the US, there are times when the US monitoring leads to controlling people so as to stop them from leaving the US.

Has happened to me (as a USC); those [redacted by moderator] don't encourage patriotism.

What was the situation and end result? I imagine similar situations have to do with people with similar names suspected of crime and trying to flee the country, large quantities of cash in bags reported by customs/security, things like that.

I have seen two folks stopped including one denied boarding for a flight in the last month.

At Laredo, where exit controls are much more stringent than years past and most vehicles are questioned now, a person in the vehicle in front of me was turned around. And on my IAH-FRA flight in mid-Jan a person was pulled from the flight after questioning and search on the jet-bridge (cash search) and they did not make the flight. I do not know if they were allowed to travel on the later flight.

Point is, it happens, though is not normally as visible and formal as in the EU, for example.

How are they checking cars leaving the US for Mexico in Laredo? Or is the Mexican authorities refusing entry and turning the cars around?

They have checkpoints set up on the southbound lanes on the US side. They have been doing it for years, though before it was spotty- asking about guns, bullets, cash, reason for travel. Now it seems a more permanent, or at least more thorough from my experience. If you ever watch the National Geographic shows on CBP on the bridges and smugglers and such, they actually show some of those interactions and some of the set-ups FWIW.

I’ve seen it on Northern border during the summer. CBP funnel three lanes of traffic into a check point and ask about cash.

How close was the nearest Canadian casino? Seen such thing too on the northern border.

Exit tracking car license plates may hit more than even getting the cash ask.

ALPR is likely why you no longer have to have your car inspected for SENTRI.

Not sure but there are casinos since it is the Champlain crossing in NY/QC.

two more examples of exit control checking in action:

2 Men Wanted For Sex Offenses Stopped By Customs At Dulles Airport (msn.com)