London's Heathrow Airport said today that it using technology to inform airlines when individual passengers are running late and haven't yet entered the security checkpoints.
If a traveler hasn't yet made it to a checkpoint and has less than half an hour before their flight departs, they'll be stopped by automated gates.
When the passenger scans his or her boarding pass at the automated gates to enter the security checkpoint area, screens will direct them to return to the check-in desk instead.
The airline will also be instantly informed that the passenger won't be making it, allowing it time to remove any bags from the aircraft. No bag can travel without its owner. So airlines appreciate having a few extra minutes to make sure that the AWOL passenger's bag isn't in the cargo hold.
Similarly, if the passenger is in the wrong terminal, they'll be re-directed -- and the airline alerted if the passenger will be late.
A study showed some gains
Says Heathrow:

During the first week 35,000 passengers successfully used the positive boarding technology as part of their departure journey.
Of these travellers, 700 late passengers were informed by the automatic information display to promptly make their way to the departure gate to ensure they didn't miss the flight, and 10 late-running passengers were instructed to go back to check in as they didn't have sufficient time to clear security and make their flight.
This meant the airline could unload their luggage and depart on time.
The software, currently working in terminals 1 and 3, will be rolled out to terminal 4 in September and other terminals soon after. It is compatible with all airlines’ computer systems.
"World first"
Heathrow claims this software is a "world first" among airports. British Airways, which dominates Terminal 5, has deployed a similar system for some time.
At most airports, boarding passes are currently checked by human agents before passengers enter the security area. Heathrow previously replaced these agents with the use of automated gates, and it is now adding new software at the gates to make better use of them.
The primary benefit of the new system is that the airlines are instantly informed via their computerized systems about the passenger's lateness.
Some skepticism
Heathrow officials told The Telegraph that late-running passengers cause 50,000 minutes of delays a year at Terminals 1, 3 and 4, creating a bill of £3.5 million.
The Flyer Talk message boards instantly started carping that the real causes of delayed flights are 1) overzealous security checks that snarl passengers; 2) flight information display screens that publish inaccurate information, thus reducing compliance with their messages.
NB: Image courtesy of Heathrow.