"Richard J." wrote in message ...

Even in a platform mostly used for terminating trains at very low speeds?

I had a good look at the site this afternoon (Platform 3 at Edgware Road
Circle Line, as identified by Smokeyone in another post). It was only
possible (as it was dark) to inspect the rail nearest the platform, but
that had a total of 15 missing keys. In the middle of the platform was
this sequence, where o = missing key and K = key present:

o K o K o o o K o K K o K K K K K o o o K K K o

Note that the first 12 chairs in this sequence had 7 missing keys!

The tracks are patrolled every 48 hours, the patrolman will replace
them on his next round. Patrolmen replace keys routinely, sometimes
none, sometimes 20 or 30 in one shift, usually 5-10.

One problem here may be that trains are stabled in the platform overnight.

If there's more than 5 in a row missing, we'd be very grateful if
you'd inform the station staff, because then it could become
unsafe.......

There weren't more than 3 in a row, but I thought 7 missing in 12 was
worrying, so I found the station supervisor and told him. He said he
thought that one train was stabled overnight alternately in platforms 2 and
3. It occurs to me that if the track is patrolled on the same days every
week, e.g. Tue, Thu, Sat, it could be that there is always a train on
Platform 3 at the time. (Platform 2 had only one missing key on the rail
nearest the platform.)

Smokeyone said he saw 4 in a row, but I assume he actually miscounted part
of the above sequence.

It will be interesting to see how long it takes LU/Metronet to fix it!

Yup, even in low-speed areas keys work loose (due to dynamic loading
and vibration) or break (they fatigue over time).

7 out of 12 missing is unusual, though. Looks like the patrolmen have
problems getting access when the trains are parked there.
I'm also keen to see how long it takes to get them replaced!
John