On Apr 22, 9:49 pm, "Recliner" wrote:
I wonder why Hammersmith has this unusual system? As you say, it's less
useful (if pedantically more accurate) than the usual listings of the
next three trains. Was it an experiment that failed, and so wasn't
repeated?

Hammersmith is an older signalling site that uses programme machines
to operate the signals and junctions at the station. As a result,
there is no unified information network available like the one between
Earl's Court and Arnos Grove to transmit train timing info - the
displays have to rely on the programme machines to know what the next
train's destination is.