One of the things I've noticed when travelling on Southern or South West
Trains in the commuter belt is that their carriages generally don't have any
sets of three seats on one side of the aisle. By contrast the local National
Express London to Shenfield service has the old layout with one side having
three seats except for immediately adjacent to the vestibles or doors.
London Overground services have a mix with some third seats removed, and
also has some side-ways seating that creates more standing room.

A consequence on the National Express services is that the trains get
horrendously overcrowded, not least because it's hard to move down the
carriages quickly and so passengers instead crowd in the vestible areas.
Consequently these are often rampacked, with people physically forcing their
way in at Stratford, whilst not every seat is used. This has led to more
than one incident and I fear it won't be long before someone's badly hurt or
worse.

An obvious simple solution would be to remove the third seats in the
carriages, thus creating wider aisles that allow more standing room and also
make it easier to get out of the train in time. This could reduce some of
the sardine effect, and very few more passengers would have to stand as it's
rare for every seat to be taken even when there is a scrum.

How do the other commuter carriages handle this?