Train Braking: Questions for the Informed

[whole diary]

[trainer]

Today I was particularly aware of the slow speed at which trains approach platforms in apparently (from the non-professionals's perspective) good conditions.  The 09:45 from Yatton to Weston-super-Mare was announced as up to 12 minutes late (it varied over ten minutes and I didn't catch the reason) and finally arrived at the Bristol end of the platform at 09:54.  It's approach appeared to me to be painfully slow and was probably doing no more than 10mph as it passed along the platform.  I was on the 09:56 to Cardiff on the opposite platform and as we left on time the engines of the Weston train revved and clearly they were moving, having gained no time.  For those who don't know, Yatton is on a dead straight piece of track - I can't be sure of the visibility of the platforms behind the road bridge abutments.

I remember being behind the driver many years ago on what would now be called a 'heritage' unit when to my surprise he slowed from nearly 40mph to a stand in the length of Small Heath (Birmingham) platform, which is/was long.  I also recall the smell of the breaks of the HSTs^▸ (High Speed Train) when first in service as they braked heavily. Certainly, compared with mainland European railways, our trains appear to be very cautious in their arrivals.

My questions:
Is there any allowance for faster approaches when late running?
Has there been a change in the rules since the 70s?
Is there an economy reason for cautious braking rather than an engineering/safety one?

[Southern Stag]

The reason the 09:45 to Weston-super-Mare would have been approaching so slow is because it was being routed in to the loop to allow a fast Cross Country service to pass it. That means it would have had a red signal at the end of the platform, and train will approach red signals slowly. If the signal was fitted with the TPWS^▸ (Train Protection and Warning System) safety system, which I believe it would be as it is on the approach to the loop, then if the train is running overspeed according to the speed set on the system when the train runs over the detection loop for the TPWS a distance prior to the signal, then the emergency brakes would be applied. The train must approach the signal at a safe speed to prevent the brakes being applied, and also generally for safety.

[John R]

This is called "approach control" and is designed to slow a train down before a divergence which is at a significantly lower speed than the main route.  Thus preventing an accident whereby the driver thinks he is going one way, fails to register the feather pointing out that he's actually going a different way, and derails at the turn out.

 

[Thatcham Crossing]

Trainer said:

I also recall the smell of the brakes of the HSTs^▸ (High Speed Train) when first in service as they braked heavily

I travel on FGW^▸ (First Great Western) HST's fairly regularly (mostly at speed between Reading and Paddinngton, or on the B&H^▸ (Berks and Hants - railway line from Reading to Taunton via Westbury)) and
smell the brakes at some point on almost every journey, although obviously most noticeable when decelerating from 125 to a stand, or near stand.

It is most noticeable if you're sat near the bogies, or in the vestibules, but it's definitely there.

[trainer]

Thanks JR and SS.  As I was not looking towards the signal I wouldn't have noticed the red aspect and then my own train obscured it.  I didn't know about the approach control at such a signal, so I have learned something.  It was the second train to be looped within 15 minutes as there was a 150 (I think) at the far end of the Down Loop when I arrived at about 09:35 and I assume it was released after the Penzance HST^▸ (High Speed Train) had scuttled through.

TC^‡(resolve), your experience is also interesting: the only time I have noticed the smell in recent years is in emergency braking.

(All abbreviations refer to posters)

[Red Squirrel]

Thanks JR and SS.  As I was not looking towards the signal I wouldn't have noticed the red aspect and then my own train obscured it.  I didn't know about the approach control at such a signal, so I have learned something.  It was the second train to be looped within 15 minutes as there was a 150 (I think) at the far end of the Down Loop when I arrived at about 09:35 and I assume it was released after the Penzance HST^▸ (High Speed Train) had scuttled through.

TC^‡(resolve), your experience is also interesting: the only time I have noticed the smell in recent years is in emergency braking.

(All abbreviations refer to posters)

Who is HST?

[trainer]

Until this moment I have always had a soft spot for red squirrels...however one can change one's mind.    Your pedantic credentials show you are a worthy member of the forum. 

[chuffed]

You have just proved by your last post trainer, that red squirrels love nuts ....

[swrural]

He's been shelling out sarcastic comments since he joined.  Very bright and bushy tailed about everything.  I wonder how many more he has hoarded away.

[John R]

Thanks JR and SS.  As I was not looking towards the signal I wouldn't have noticed the red aspect and then my own train obscured it.  I didn't know about the approach control at such a signal, so I have learned something.  It was the second train to be looped within 15 minutes as there was a 150 (I think) at the far end of the Down Loop when I arrived at about 09:35 and I assume it was released after the Penzance HST^▸ (High Speed Train) had scuttled through.

(All abbreviations refer to posters)

With all the West country services diverted from their normal route (via Castle Cary) I would expect that the Yatton loops have been busier than usual. Should be the same again Mon to Thu next week.

An interesting result of the rules around approach control of turn outs is that when the up relief line into Swindon became the normal route a few years ago the 75mph turn out presented a problem as the main line was 125mph (IIRC^▸ (if I recall/remember/read correctly)).  The speed differential would have resulted in approach control being needed, which would have affected just about every passenger train as it would result in a slower approach. This would have negated some of the benefit to be had by using the relief line (which affords a faster approach into the platforms).

So the solution was to lower the speed limit through the area to 85mph, which meant approach control was no longer needed for the divergence. With very few services not calling at Swindon, the reduction in the max speed had little adverse impact.

[bobm]

I assume that was when Platform 4 was brought into use.  Is the up relief Platform 1 or 3?

[John R]

The up relief starts about a mile west of Swindon (at Rushey Platt), and is a straight run into platform 3, whereas previously trains approaching from the west used the up main and then had a very slow switch on the approach to the platform.

I think it was done at the same time Wootton Bassett junction was relaid around 5 years ago. Platform 4 was opened around 10 years ago, so the two improvements were not related.

[bobm]

Thank you very helpful - obviously time I got a new Western TRACKmaps book!