London Waterloo (Main) Speed Limits

[SpacePhoenix]

When trains depart Waterloo it's 15mph till they reach the first signal gantry that crosses all the tracks, then it's either 50mph or 60mph depending on which track. What's the reason for the 15mph for the short bit? The only reason that I can think off is the amount of points in that section

 

[Sean Emmett]

When trains depart Waterloo it's 15mph till they reach the first signal gantry that crosses all the tracks, then it's either 50mph or 60mph depending on which track. What's the reason for the 15mph for the short bit? The only reason that I can think off is the amount of points in that section

If you look at the curvature the reason for the 15 mph is obvious!

Those points are short lead to fit them all in, and the turnouts onto the adjacent lines are sharp. OK some of the straight routes into certain platforms could have a higher limit, but if the divergence is more than 5 mph different from the straight line speed limit you need complicated approach control.

So they are all set at 15 mph, except the turnouts into the former International Station which are 20 mph.

 

[SpacePhoenix]

Long term could some of the points for changing between adjacent lines be moved further along the line to get rid of some of the points in the station area?

 

[The Planner]

Approach control is 10mph difference, not 5mph.

 

[MarkyT]

Long term could some of the points for changing between adjacent lines be moved further along the line to get rid of some of the points in the station area?

Problem with that is you end up with a longer junction that for some moves may take longer to negotiate and clear for other conflicting traffic. It also means the incoming home signals would have to be further out, meaning something stopped on the way in would then have further to go to reach its platform. Blanket speed restrictions like this also dramatically simplify speed signage, which in a complicated throat can become difficult to design and interpret.

 

[Sean Emmett]

Approach control is 10mph difference, not 5mph.

I thought it was only 5mph at lower speeds, happy to be corrected.

 

[swt_passenger]

Presumably with such a complex layout you always have to sign the worst case?

There must be a fairly small subset of platforms that have a relatively straight route onto their respective down lines, but trains will not always be outbound routed that way, and I expect that taken over all possible permutations of routeing then the least risk is achieved by having one figure for all routes.

Also. and at the risk of stating the obvious, the speed limit increase to line speed has to be positioned a maximum train length beyond the restriction. So there's a 240m length for a start...

 

[Bald Rick]

I thought it was only 5mph at lower speeds, happy to be corrected.

It is 10 mph

 

[Bald Rick]

Presumably with such a complex layout you always have to sign the worst case?

There must be a fairly small subset of platforms that have a relatively straight route onto their respective down lines, but trains will not always be outbound routed that way, and I expect that taken over all possible permutations of routeing then the least risk is achieved by having one figure for all routes.

Also. and at the risk of stating the obvious, the speed limit increase to line speed has to be positioned a maximum train length beyond the restriction. So there's a 240m length for a start...

Sort of. If a layout is too complex to sign, then the worst case is signed. This is unless there are just one or two lower speed routes where signing them for the lower speed is straightforward.

Re the train length point, the speed restriction changes where the infrastructure deems it. It is up to the driver to determine when the rear of her/his train clears the restriction. The exception ( as ever) is on HS1 where the coding in the track circuits is set for the maximum length of train; for example when a javelin departs St Pancras it is a long way into the London tunnels before it gets clearance to increase to linespeed.

 

[Bald Rick]

Problem with that is you end up with a longer junction that for some moves may take longer to negotiate and clear for other conflicting traffic. It also means the incoming home signals would have to be further out, meaning something stopped on the way in would then have further to go to reach its platform. Blanket speed restrictions like this also dramatically simplify speed signage, which in a complicated throat can become difficult to design and interpret.

Exactly, indeed that is what has happened for the suburban line platforms at Waterloo. Because the layout has been stretched out, it has reduced the capacity of that part of Waterloo. To retain the current level of service is why the suburban services will in future be using 1-6 rather than 1-4, which means fewer conflicting moves thus restoring capacity.

 

[Ianno87]

The blanket 15mph is also related to simplicity of signage for drivers.

 

[HarleyDavidson]

It's also done to mitigate against SPADs of which there have been many arriving at & leaving Waterloo.

A rough guide for drivers is that West Crossings is a 10/12 car clear at the back of everything. For an 8 car it's where the exit from South Sidings used to be.