Thread: Wimbledon branch of District line - why us?
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Old December 9th 04, 08:52 AM posted to uk.transport.london
TheOneKEA TheOneKEA is offline
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Default Wimbledon branch of District line - why us?
wrote:

Can you explain what bobbing is.

Kevin

"Bobbing" is when the signal rapidly changes from aspect to aspect
without warning or reason. For example, in the case of East Putney to
Wimbledon, three-aspect NR signals are used. If these signals started
bobbing, at one moment they might be green, then yellow, then red, then
back to green, or any frightening (to a driver) combination thereof.

Naturally this is a major problem because a signal could bob despite an
occupied track in front of the train; thus, if it goes to green and the
driver passes it in the correct way at speed, CRUNCH.

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