In Wellington, New Zealand, a large proportion of the
traffic lights in
the central city (A city of 450,000 people) is controlled by a
PDP11/34a.
This 11/34a has been in place since 1981, I believe,
and since it just
continually does its job, its yet to be replaced.
They use a VAX of some description as a backup unit.
At last count - which was maybe 3 or 4 years ago now - the unit hadn't
been power cycled since '84.
The really amazing part to all this is that they apparently haven't had
a power failure in 18 years...