My idea for Class 395s for LM / SWT

[sprinterguy]

Wouldn't be worth it rebuilding 450s as 110mph 444s, I presume.

That would be on heck of an extensive rebuild. The doors are obviously in completely different places, and the 450 carriages are three metres shorter than those of the 444s. So that's definitely a non-starter.
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Ah, so the IEPs proposed for WCML will be 110mph limited?

Given these are expensive, are 125+ mph units, isn't that a bit of a waste on the WCML? Plus as an orphan fleet alongside Pendos why bother?, why not just get more baby Pendos to do it?

The IEP proposal for the West Coast is not intended for the long distance Intercity services presently operated by Virgin, it would be to replace some of the 350s currently operated by London Midland on regional services. Pendolinos do not come into it at all.

 

[corfield]

But that still doesn't explain why you'd buy units designed for 125mph plus and use them limited to 110mph, particularly when you have perfectly good 110mph units there already.

My assumption was that the idea would be to run high speed commuter services ala HS1/395s, which would imply the logic for using IEPs would be to use the higher speed capabilities. Hence my "why not use 395s now", although it seems neither could run above 110, and hence my second "in which case, why not use baby Pendos so you can run high speed?".

 

[tbtc]

But that still doesn't explain why you'd buy units designed for 125mph plus and use them limited to 110mph, particularly when you have perfectly good 110mph units there already

I think it's more about tagging additional units onto an existing order, rather than a bespoke order (so keeping the unit costs down).

I've mixed feelings about introducing another unit type onto the southern WCML, alongside 350s and 390s, but there are plenty of trains that never reach top speed.

 

[RobShipway]

I think it's more about tagging additional units onto an existing order, rather than a bespoke order (so keeping the unit costs down).

I've mixed feelings about introducing another unit type onto the southern WCML, alongside 350s and 390s, but there are plenty of trains that never reach top speed.

I think it is more about tagging extra units on to an existing order as well, however by the time they come online it would be existing units assembled in this country rather than assembled in Italy.

 

[The Planner]

Once at that speed, running trains faster actually reduces capacity. The gap between two trains needs to be greater than the distance it takes for the train behind to stop. Braking distance is directly proportional to the square of the speed (asuming contant deccaleration in order to maintain constant G-force for passengers).

This means that increasing the services from 100mph to 140mph would lead to the distance between between trains being roughly doubled ('1.96'). Divide the distance between the trains by the speed and the frequency is reduced by a factor of '1.4' to about 70 % of what it would be at 100mph.

If the signalling system measured and controlled train speed as well as train position then trains might be able to run down a line at the same speed with a minimum distance between them. This would result in line capacity being directly proportional to the line speed (1.4 times speed means 1.4 times capacity) but a system would need to be prooved safe beyond reasonable doubt in the event of any realistic driver/system faliures.

Such a system might be in the form of:

The train behind stays within the area of speed/distance that would allow it to stop short (plus a bit) of where the train infront would stop if both were to suddenly begin to deccalerate to zero.

I am slightly confused by that as headway is defined by signal spacing and linespeed and thus is a major part of the amount of capacity. If the line was capable of 140mph then the signal spacing would be appropriate to that speed to allow a following train to stop at the red. Depending on that spacing it is pretty likely that the capacity will be very similar or improved from 125mph. It is only stopping patterns and mixed traffic that eats capacity.

 

[JamesRowden]

I am slightly confused by that as headway is defined by signal spacing and linespeed and thus is a major part of the amount of capacity. If the line was capable of 140mph then the signal spacing would be appropriate to that speed to allow a following train to stop at the red. Depending on that spacing it is pretty likely that the capacity will be very similar or improved from 125mph. It is only stopping patterns and mixed traffic that eats capacity.

Look at my later post.

 

[The Planner]

OK, but the way capacity is allocated in my world is the planning headway. Which is the time taken for the train to pass the overlap of the first signal plus the distance back to the first green signal plus the sighting distance (normally 8 seconds) plus a margin for robustness as you would never plan to a technical headway.

If the signals are spaced correctly for the line speed then a basic calculation for a 4 aspect 125mph line would be time for a 11 car Pendo to clear a 200m overlap plus, say, 1200m between signals plus 8 seconds sighting distance. So an 11 car is approx 274m, add 200m overlap, add 3600m for the signal spacing plus 448m sighting (56m/s x 8) equals 4522m. That at 56m/s is a technical headway of 81 seconds. That would normally create a 3 minute planning headway.

It then of course depends on the signal spacing required for 140mph running, make it 1400m then you get around 83 seconds technical headway. In planning terms it makes no difference. Until you get to the mythical world of driverless trains in perfect conditions it isn't really going to factor.

 

[JamesRowden]

OK, but the way capacity is allocated in my world is the planning headway. Which is the time taken for the train to pass the overlap of the first signal plus the distance back to the first green signal plus the sighting distance (normally 8 seconds) plus a margin for robustness as you would never plan to a technical headway.

If the signals are spaced correctly for the line speed then a basic calculation for a 4 aspect 125mph line would be time for a 11 car Pendo to clear a 200m overlap plus, say, 1200m between signals plus 8 seconds sighting distance. So an 11 car is approx 274m, add 200m overlap, add 3600m for the signal spacing plus 448m sighting (56m/s x 8) equals 4522m. That at 56m/s is a technical headway of 81 seconds. That would normally create a 3 minute planning headway.

It then of course depends on the signal spacing required for 140mph running, make it 1400m then you get around 83 seconds technical headway. In planning terms it makes no difference. Until you get to the mythical world of driverless trains in perfect conditions it isn't really going to factor.

Using 4 aspect signals I would have thought that it would be a good idea to have the distance between the signals equal to half of the comfortable braking distance from full speed. An additional time headway of x minutes could be added to make sure the timetable is reliable. Since the x minutes headway would be independent of speed it does not need to be considered when comparing capacity to the speed of the trains.

I think that 'a = 1 m/s (~ 2.25 mph/s)' is a sensible decceleration rate.

Deccaleration distance is:
s = v^2 / (2 X a)

At 56 m/s (125 mph) the braking distance is: 1568 m
At 45 m/s (100 mph) the braking distance is: 1012 m

As a result of the signalling the distance between the trains will be 3/2 of this plus the length of the train plus the distance produced by the timing headway.

Using the 274 m legth of an 11 car pendolino, the time gap (minus the timetable robustness headway) is:

140 mph: 50.9 seconds
125 mph: 46.9 seconds
100 mph: 39.8 seconds
67.5 mph: 31.6 seconds
45 mph: 28.7 seconds
22.5 mph: 34.9 seconds
15 mph: 46 seconds

(capacities shown at very slow speeds ignore the potential difficulty of placing signals at a very high frequency)

This indicates that with 4 aspect signalling, so long as the trains running along the route operate at the speed that the line's signalling was designed for (assuming signalling had been designed to maximise capacity) and the trains were running above 45 mph, extra line speed will very slightly reduce capacity (not increase it) so long as it is the track rather than the platforms, crossover junctions or stopping patterns that are limiting the capacity.

 

[Surreyman]

If you couldn't use 395s on the London end of WCML, what difference is there for IEP ? neither tilt, which I must admit, was informing my idea on that one, only that 395s would be available sooner.

On the SWML, I agree that twin tracking south of Basingstoke would be a possible constraint - but how busy is it?, would 25% faster services, slotted in accordingly, really change anything? How difficult/costly would quadtracking be...


The 8 car / 2 unpowered trailer option was because if they aren't expected to do 140mph (as per HS1), would the extra weight affect their 125 performance?

Anyway, it's just an idea. I'd heard SWT is short 444s and using some 450s in longer distance roles. Other than a boring "buy more 444s or equivalent", this seemed a more interesting idea, offering HS servies to the Central South West, which with Woking-Bstoke-Sthampton has to be a bigger market for HS commuters (and wealthier ones) than SE HS network?

As I said, I suspect the lines would need to be up to Woking at least to make it remotely worthwhile.

I can't see us being short EMUs in the future !

A cheap and sensible solution (and there is a real chance that it could happen) is to build some new more suitable stock for the Gatwick Express and move the class 442 (12 x 5 car) back to SWT so that all the Weymouth/Southampton & Portsmouth mainline trains are 442 or 444, then cascade some class 450 to 'beef up' the outer suburban services.
The NR/CP5 plans include longer trains on SWT.
(The new owners of Gatwick are already campaigning for more suitable trains).

 

[D365]

A cheap and sensible solution (and there is a real chance that it could happen) is to build some new more suitable stock for the Gatwick Express and move the class 442 (12 x 5 car) back to SWT so that all the Weymouth/Southampton & Portsmouth mainline trains are 442 or 444, then cascade some class 450 to 'beef up' the outer suburban services.
The NR/CP5 plans include longer trains on SWT.
(The new owners of Gatwick are already campaigning for more suitable trains).

I reckon that 4 or 6 car 377/7s would be suitable for Gatwick/BML expresses. However, there are actually 24 Class 442s, but they are not AC compatible, which would cause difficulty with the Basingstoke-Bournemouth electrification conversion.