wrote on 29 April 2009 19:01:49 ...
"Richard J." wrote in message
om...

Whenever the (timetabled) service interval is more than 4 minutes. They
can optionally drive manually if the intervals are between 2 and 4
minutes, but my impression is that few do so.

But there is no set time when they are required to manually operate their
trains to stay in practice, as is reportedly the case in Vienna?

As I said earlier, it's when the trains are timetabled to run more than
4 minutes apart, which in practice means in the evenings, and perhaps at
other times in summer when the service is less frequent. [Info from
Brian Hardy's Paris Metro Handbook, 3rd edition]

--
Richard J.
(to email me, swap 'uk' and 'yon' in address)