London Banter - View Single Post

Colin Rosenstiel · October 21st 03, 11:46 PM posted to uk.transport.london

In article ,
(John Rowland) wrote:

"Huge" wrote in message
...
"Peter Smyth" writes:

"Huge" wrote in message
...

What's an overrun tunnel?

When the tunnel continues past the terminus
so that if a train fails to stop
for any reason it doesn't go straight into a wall.

Ah. Thank you.

More to the point, safety rules stipulate that a train must approach a
dead end at very slow speeds. If there is an overrun tunnel, the trains
can enter the terminal station at the same speed as any other station.
This slightly improves journey times to and from the last station: more
importantly, it also increases the service frequency that can be run
with a given number of trains and drivers. It also increases the maximum
number of trains that can be run into the terminal station, and so
possibly increases the number of trains that can be run on the entire
line.

That isn't the initial reason why the Charing Cross (Jubilee) overrun
tunnels are so long. The line was planned with the expectation of imminent
extension in that direction. Highly restrictive approach speeds to dead
ends are a product of the 1975 Moorgate crash.

--
Colin Rosenstiel