In article , Robert Woolley
writes
a) Routes numbered in the 600 series are school routes. With the
exception of the 607, which is a limited stop version of the 207.

Routes numbered in the 500 series are Red Arrow buses. Used to be
limited stop and special fares.

Before that, 500/600 was the trolleybus series. Where a trolleybus route
replaced a tram route, the last two digits remained the same (so if tram
14 became a trolleybus, it would be 514 or 614).

--
Clive D.W. Feather, writing for himself | Home:
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