Reducing the weight of seating on trains

[AM9]

Funnily enough I was wondering this morning why trains are so heavy - AFAIK most coaches are of steel construction throughout. If a significant proportion could be made from aluminium or composites, perhaps a coach could be brought from ~40 tonnes to ~30.

Obviously this would increase the production cost significantly, but if it's possible wouldn't it more than pay for itself over the lifetime of the vehicle in energy and track access?

I doubt that you could get modern vehicles' weight down to less than 70% of their present level soley with material changes yet retain the same safety and equipment capabilities. Compare the equipment carried on modern stock with that of pressure ventilated MKII designs which were the first in the UK to depart from the strong chassis/non-structural bodywork route. In modern stock, all coaches have air conditioning, retention toilets, power operated doors and better soundproofing.
Aluminium does not have the same volumetric strength as steel and composites are as you say more expensive, much more in the volumes required for rail rolling stock. The same arguments apply for road vehicles, particularly cars, where steel is still the main material of choice except on cars whose market can support much higher prices.
To reduce weight significantly, look at the steps that Siemens and Bombardier have taken with their new bogies. The new type fitted to the 700s and the type that will be fitted to the 345s have inside frames with smaller wheels with shorter wheelbases. This allows much reduction in weight by smaller sections. Motor bogies will have lighter permanent magnet motors and the traction electronics will get lighter as device technology progresses. Expect to see lighter air conditioning with many plastic components like heat exchangers and reservoirs with reduced coolant volumes.
With all this weight reduction going on, the seats will take their turn, with single piece mouldings in composites with thinner upholstery. Contrary to much of the criticism of thinner seats, lightweight designs will produce seats with better posture than the soggy designs that some people call 'comfortable'.

 

[edwin_m]

Removing seats in some ways makes the train heavier, because more standing passengers can fit into the space so the maximum weight of the train is that much more. This affects the calculations made to support structural design and traction/brake performance.

 

[LexyBoy]

Yes, I suppose safety is a big part - the cost associated with proving a new design in new materials would add a lot to the cost, even without the cost of the more expensive materials. Is computer simulation used already to assess crashworthiness? I would think these techniques would help identify areas where weight can be lost.

The same arguments apply for road vehicles, particularly cars, where steel is still the main material of choice except on cars whose market can support much higher prices.

Not sure cars are a good comparison - rail vehicles are used far more intensively and for a much longer lifespan, so a small reduction in opex could justify a large capex increase (in theory, if procurement were done in a half-sensible fashion). Plus, purchasers of cars are more likely to purchase on the basis of "will it get me laid?" than "how will the running costs of expensive car compare with cheap car over the time I will own it".

Removing seats in some ways makes the train heavier, because more standing passengers can fit into the space so the maximum weight of the train is that much more.

But (hopefully!) trains would be specced based on the expected number of passengers - 8 coaches with more standees will be lighter than 10 coaches with everyone sitting!

 

[AM9]

Not sure cars are a good comparison - rail vehicles are used far more intensively and for a much longer lifespan, so a small reduction in opex could justify a large capex increase (in theory, if procurement were done in a half-sensible fashion). Plus, purchasers of cars are more likely to purchase on the basis of "will it get me laid?" than "how will the running costs of expensive car compare with cheap car over the time I will own it".

I was referring to the issue of safety. It's easier to accurately determine strength of steel panels and predict the performance of steel crumple zones under impact than dealing with fibre reinforced materials where there are many processes involved in manufacture. Also, steel is much quicker to fashion into required shapes than composite materials which involve curing times.
Steel panel design is a very mature technology whereas composites are still in development. Most of composite volume use to date has been in aircraft manufacture where the prinicipal design issues are absolute strength versus mass.

 

[Bletchleyite]

But (hopefully!) trains would be specced based on the expected number of passengers - 8 coaches with more standees will be lighter than 10 coaches with everyone sitting!

You're probably about the only Reading commuter taking the view that that would be in any way a good thing!

Neil

 

[racyrich]

Yes, I suppose safety is a big part - the cost associated with proving a new design in new materials would add a lot to the cost, even without the cost of the more expensive materials. Is computer simulation used already to assess crashworthiness? I would think these techniques would help identify areas where weight can be lost.



Not sure cars are a good comparison - rail vehicles are used far more intensively and for a much longer lifespan, so a small reduction in opex could justify a large capex increase (in theory, if procurement were done in a half-sensible fashion). Plus, purchasers of cars are more likely to purchase on the basis of "will it get me laid?" than "how will the running costs of expensive car compare with cheap car over the time I will own it".



But (hopefully!) trains would be specced based on the expected number of passengers - 8 coaches with more standees will be lighter than 10 coaches with everyone sitting!

But no help to the axle weight.

 

[physics34]

Just sad how the weight of seats takes more of a precedence than passenger comfort these days.

 

[AM9]

Just sad how the weight of seats takes more of a precedence than passenger comfort these days.

It's not the weight of seats that takes precedence, it's the weight of trains. Seats are just a small part of the problem but modern lightweight seats are probably better for posture than the old MKI style soggy benches. They also keep passengers from spreading across two or more seat positions.
For those who have particular problems with standard modern train seats, there is always the first class option.

 

[M7R]

I work in road vehicle safety and Homologation for my day job, and I have done a fair number of seat test for cars and buses.

On busses weight is the enemy, if you can make the bus lighter you can get more people on, seats are heavy things so saving say 1kg out of a seat on a bus could allow an extra person standing.

The problem come with crash safety, lighter seats don't tend to be as strong unless they are made from more expensive higher grades of steel or composite. That means higher costs and the extra revenue earned from 1 extra person standing is not worth the added cost for all the seats to be made out of the lighter material normally.

If you want to save weight look at the glass! Glass is heavy! And trains tend to be double glazed now, if you could get away with a thinner laminated glass you could easily save a few kg per window, however if a MU is say 40t, saving 100kg on glass and 250kg on seats is not really worth the cost.

(Do trains have a max weight like vehicles? As I know for busses when it says 50 people seated and 10 standing that is worked out on 68kg per person, and that's the max you can fit on before the weight of the bus, plus driver, plus passengers put you over the max axle masses for use on the UKs roads - and yes any full bus will be over weight as most people are more than 68kg, esp with shopping etc)

 

[Nym]

What about the fact that saving even a tonne of seating will amount to nothing with 10 ton of passengers on board? (per carriage)

 

[edwin_m]

I work in road vehicle safety and Homologation for my day job, and I have done a fair number of seat test for cars and buses.

On busses weight is the enemy, if you can make the bus lighter you can get more people on, seats are heavy things so saving say 1kg out of a seat on a bus could allow an extra person standing.

The problem come with crash safety, lighter seats don't tend to be as strong unless they are made from more expensive higher grades of steel or composite. That means higher costs and the extra revenue earned from 1 extra person standing is not worth the added cost for all the seats to be made out of the lighter material normally.

If you want to save weight look at the glass! Glass is heavy! And trains tend to be double glazed now, if you could get away with a thinner laminated glass you could easily save a few kg per window, however if a MU is say 40t, saving 100kg on glass and 250kg on seats is not really worth the cost.

(Do trains have a max weight like vehicles? As I know for busses when it says 50 people seated and 10 standing that is worked out on 68kg per person, and that's the max you can fit on before the weight of the bus, plus driver, plus passengers put you over the max axle masses for use on the UKs roads - and yes any full bus will be over weight as most people are more than 68kg, esp with shopping etc)

Buses stop and start a lot more than trains, using more fuel every time if they are heavier, and I guess the extra weight on the tyres probably means more rolling resistance or even needs more wheels to comply with axle load limits. I remember a few years ago being on a London bus when the DLR was shut down, passengers packed right up to the front windscreen and the vehicle underside scraping on speed cushions.

Trains are much less weight sensitive. Some routes are limited in axle weight but this is mainly an issue for freight with any passenger train well within any route limit. The extra charge Network Rail makes for heavier trains is pretty small. The rolling resistance is almost independent of weight and while more energy is needed to accelerate a heavier train some trains have regenerative braking which recovers some of this when slowing down.

Hence train builders or specifiers will tend to go for a cheaper seat even if it is heavier. Using aerospace or even bus industry techniques the weight of a train could be reduced drastically but aerospace technology would probably cost a lot more and either would fall short of the standards for structural strength, which are far higher than anything seen on the roads. Train seats are also subject to crash safety standards but research has shown that fitting seat belts on trains would be counterproductive, so they don't need to accommodate the mounting points or their crash loads.

The glazing in a train is also an important safety feature, as it needs to survive well enough to prevent passengers from being thrown out of the train in an accident if at all possible. Latest thinking is to make windows as strong as possible and get rid of the emergency window hammers that used to be be provided, because it is usually safer to remain on the train in an accident and emergency services have no difficulty getting entry to the toughest sort of window if they need to.

 

[northwichcat]

What about the fact that saving even a tonne of seating will amount to nothing with 10 ton of passengers on board? (per carriage)

As I already said the seats are always there even for ECS and training, the passengers aren't.

 

[cjmillsnun]

What about the fact that saving even a tonne of seating will amount to nothing with 10 ton of passengers on board? (per carriage)

I disagree, every tonne saved will save energy.

 

[edwin_m]

I disagree, every tonne saved will save energy.

It will, but as I posted above there are other factors to be taken into account. Even taking a purely environmental perspective, a lighter but more exotic material is quite likely to consume more energy in manufacture and be less recyclable than traditional materials.