In message , Richard J.
writes

Paul Terry wrote:
With the current timetable, the four-track section is used to allow
the fasts to overtake Hounslow loop stopping-services in the up
direction.

Not in the afternoon when the OP would be travelling, unless you can
give an example.

Fast trains leaving Richmond at 15 and 45 minutes past the hour pass
non-stop through Barnes 4-5 minutes later, overtaking the Hounslow loop
services that leave Barnes at 19 and 49 minutes past the hour - usually
passing in the station or soon after.
--
Paul Terry