Downgrading physically impossible track speeds?

[Egg Centric]

It is my crude understanding that the faster the speed limit on some part of track, the greater the maintenance regime requirement.

Is there any systematic evaluation of these limits for speed limits that are physically impossible (mostly due to insufficient acceleration space) for the traction that uses them? Does/would this serve any useful purpose in terms of lessening maintenance?

 

[edwin_m]

I was involved in a project a few years ago to reduce journey times, where we looked at the acceleration curve of the traction and only upgraded the permitted speeds on sections where the train could get above the previous maximum speed when accelerating from a station where all trains stopped. I think this was more about minimising the cost of making changes to the track (re-canting etc, and possibly other costs needed at certain places), rather than maintenance category.

Although downgrading permitted speed to match attainable speed might change the maintenance category of that bit of track, I doubt it would save maintenance cost in the real world. All the track monitoring would take place anyway, as its frequency would be determined by the bit of track further down the line whose speed was not reduced. And maintenance interventions such as tamping are done based on track condition, and if the trains are going slower already there will be less wear and tear than where higher speed is both permitted and attainable. Changing the number on the speed board won't affect that. Other activities are purely time-based anyway.

 

[Harpo]

If line speeds matched acceleration and braking curves, you’d get a load more PSR changes for drivers to learn and loads more signage, probably without changing the track maintenance category in most cases.

 

[HSTEd]

I imagine that if there was a significant saving to make like this, it probably would have been done at some point by BR.

 

[The Planner]

Only worth looking at if you can be certain that a speed profile will never need to change due to a timetable alteration or driven by a change elsewhere.

 

[Harpo]

Only worth looking at if you can be certain that a speed profile will never need to change due to a timetable alteration or driven by a change elsewhere.

It’s also a Network Change which opens up its own bureaucratic processes and potential for challenge from all users including those who want to argue about future aspiration, capacity effects, charter train operation etc..

 

[The Planner]

It’s also a Network Change which opens up its own bureaucratic processes and potential for challenge from all users including those who want to argue about future aspiration, capacity effects, charter train operation etc..

I was quietly ignoring the fact you would never get the NC agreed!

 

[Bald Rick]

It can be done, and has been - I’ve done some myself! Rare though, as there arent many examples where every train that uses the line can‘t achieve the speed.

 

[Grecian 1998]

I may be wrong but I believe the Brighton Main Line previously had some short 100mph sections. If this is right, it's also my understanding these were removed as they were very short and due to the congested nature of the line, particularly given the number of services which stop frequently, it was rare for this speed to be achieved. The extra maintenance cost required in maintaining the line for a higher speed therefore simply wasn't worthwhile.

Doubtless there are better informed posters here who can say if this is correct.

 

[hexagon789]

I may be wrong but I believe the Brighton Main Line previously had some short 100mph sections. If this is right, it's also my understanding these were removed as they were very short and due to the congested nature of the line, particularly given the number of services which stop frequently, it was rare for this speed to be achieved. The extra maintenance cost required in maintaining the line for a higher speed therefore simply wasn't worthwhile.

Doubtless there are better informed posters here who can say if this is correct.

There was one section authorised for 319s used on the Connex Brighton Express. It was touch and go whether they'd actually reach the 100mph limit at times and I understand the time saved was sub half-a-minute.

 

[DM352]

Just remembered the BML 100 being talked about here.

3rd Rail 100 mph stretches

I was wondering as many 3rd rail EMUs have a max speed of 100mph, is there any stretches of line were the max speed is 100 mph for these units to obtain?

www.railforums.co.uk

A small decrease I noticed a few years back was the slow New Malden to at least Surbiton where it was increased to 90 but reduced to 80. Made little difference then as 455's limited stop tapped out at 75, and before New Malden was 60 on the slow.

 

[Halish Railway]

I imagine that if there was a significant saving to make like this, it probably would have been done at some point by BR.

Wolverhampton to Shrewsbury is an example of this, going from 90mph to 70mph in the 80s I believe.