On 14 Jun, 21:58, (Mark Brader) wrote:

On the Toronto subway system, it happens fairly regularly that the crew on
one train will swap places with the crew on a train going the other way.

It's fairly common on a number of systems; I've seen 'stock and crew'
changes (as the practice is known in London) happen in Stockholm on a
number of occasions.

It tends to be used as a way of getting defective trains back to
depots early, as well as sorting crews out after service
interruptions.