"High-speed rail travel is not a green option"

[Ameecher]

I think we also need more dedicated priority to bus routes. I was fuming today as I was waiting for a bus to move 100m to my stop, and it took 10 minutes. This was caused by lots of cars diverting round the High Street and cutting in the queue ahead of the bus they were previously behind. A bus can hold 80 people, and such should gain priority over 80 cars. It's a shame it doesn't happen..

Hit the emergency door release and get off then. That's the london school kids way of doing it.

[JamieLei]

Hit the emergency door release and get off then. That's the london school kids way of doing it.

Sorry, I phrased it badly. The frustrating thing was that I was waiting to get on the bus, rather than off it! Otherwise I would have politely asked the driver if I could get off!

[Ameecher]

Sorry, I phrased it badly. The frustrating thing was that I was waiting to get on the bus, rather than off it! Otherwise I would have politely asked the driver if I could get off!

Same applies.

Edit: except obviously you get on not off.

[Dave]

"i say old chap, you couldn't possibly pull the emergency handle to allow me to sneak in the back, could you?"

Gavin you're an idiot.

[Ameecher]

"i say old chap, you couldn't possibly pull the emergency handle to allow me to sneak in the back, could you?"

Gavin you're an idiot.

Not saying I do it, just some people do. The best drivers just sit there closing the doors in people's faces again.

[JamieLei]

Same applies.

Edit: except obviously you get on not off.

So instead of standing at the stop, waiting for the bus to creep forward, I can stand on the bus while it creeps forward. Where's the advantage...?
And I've never ever seen anyone in Birmingham use the emergency door controls. Mabye we're A LOT more civilised (or even sivilised in the Silverjet sense) than Norwich-ers or Londerners

[JamieLei]

Apologies for the double post.

Back on topic, trains are getting more fuel efficient as we advance. For example, it was only a while back that every intercity train was loco-hauled - today they are mainly multiple units. I haven't read the specification of the ICE project (it's on my to-do pile) but I wouldn't be surprised if it would end up as multiple unit.

What's everyone's thoughts as to what extent trains will get more efficient?

[pe13]

Obviously, a train running at 200mph is going to use more energy than a train running at 100mph, just as a car running at 100mph uses more than a car running at 50mph.

Thats right but it takes longer for a train running at 50mph to reach its destination than it takes for a train running 200mph. So the difference is not so big in the end.

[hertogjan]

Obviously, a train running at 200mph is going to use more energy than a train running at 100mph, just as a car running at 100mph uses more than a car running at 50mph.

Thats right but it takes longer for a train running at 50mph to reach its destination than it takes for a train running 200mph. So the difference is not so big in the end.

Last time I checked my physics book, energy was force times distance. The speed does not influence the amount of distance one has to cover, so that the only parameter that has an effect on the amount of energy needed is the force needed to keep the train running. And at 200 mph the amount of drag by air friction is significantly higher than at 50 mph, since air drag forces are approximately quadratic in speed. So based on air drag force alone a train running at 200 mph uses 16 times more energy than the same train running at 50 mph. There are other factors involved as well, but the difference will be more or less of that order. I cannot call 16 times a small difference.

[athanasios]

There are other factors to consider. For example the waste of time.

[paullb]

Obviously, a train running at 200mph is going to use more energy than a train running at 100mph, just as a car running at 100mph uses more than a car running at 50mph.

Thats right but it takes longer for a train running at 50mph to reach its destination than it takes for a train running 200mph. So the difference is not so big in the end.

Last time I checked my physics book, energy was force times distance. The speed does not influence the amount of distance one has to cover, so that the only parameter that has an effect on the amount of energy needed is the force needed to keep the train running. And at 200 mph the amount of drag by air friction is significantly higher than at 50 mph, since air drag forces are approximately quadratic in speed. So based on air drag force alone a train running at 200 mph uses 16 times more energy than the same train running at 50 mph. There are other factors involved as well, but the difference will be more or less of that order. I cannot call 16 times a small difference.

Yes, air friction might be 16x higher when comparing 200mph vs 50mph. But what percentage of the energy consumed by a train is in the air friction. There are also energy savings from faster trains. Just off the top of my head : You need 1/4 the train carriages because the trains go 4x faster (HUGE savings there), lower air-conditioning, lighting, heating etc because the trip is 1/4 as long.

In practical terms, here in Japan, the bullet trains have a much higher capacity than the regular trains, the longer ones are almost 400m in length.

The calculations are no where near as simple as you state above.

For instance, a car uses less energy per distance travelling at 80kph (50mph) than it does at 40kph (25mph).

[michael blunck]

[...] what percentage of the energy consumed by a train is in the air friction.

Being quadratically dependant on speed, air friction is decisive for vehicle resistance and hence energy to accelerate a vehicle.

Here´s a resistance diagram of a french TGV: it should be obvious how large resistance due to air friction would become at higher speeds.

TGV resistance.png (23.7 KiB) Viewed 2188 times

"Roll- und Lagerwiderstand" = resistance due to rolling friction and friction of bearings
"Laufunruhewiderstand" = resistance due to "rough running"
"Luftwiderstand" = resistance due to air friction

regards
Michael

[hertogjan]

(...) Just off the top of my head : You need 1/4 the train carriages because the trains go 4x faster (HUGE savings there), lower air-conditioning, lighting, heating etc because the trip is 1/4 as long.

If a train goes 200 mph then it can carry four times more passengers than it would if it went 50 mph? Does it grow larger when it goes fast?
I really fail to understand the logic here...

[paullb]

(...) Just off the top of my head : You need 1/4 the train carriages because the trains go 4x faster (HUGE savings there), lower air-conditioning, lighting, heating etc because the trip is 1/4 as long.

If a train goes 200 mph then it can carry four times more passengers than it would if it went 50 mph? Does it grow larger when it goes fast?
I really fail to understand the logic here...

No, as I said above, if the train goes 4 times as fast it can do 4 times as many trips in a given time (minus a little overhead) and thus you only need 1/4 the carriages.

[hertogjan]

You are right if you say that you would need 1/4 of the trains to maintain a certain service. But then every train travels a distance that is 4 times longer. So the number of train-kilometers (or train-miles) is the same. Now tell me where you save energy.

[JamieLei]

You are right if you say that you would need 1/4 of the trains to maintain a certain service. But then every train travels a distance that is 4 times longer. So the number of train-kilometers (or train-miles) is the same. Now tell me where you save energy.

Very true. If journey times doubled, we'd need half the amount of trains to run the service at the same frequency. However, as Michael Blunk's graph excellently shows, the increase from 150 kph to 300 kph uses just over 3x as much energy, thus there is a net gain in energy consumption.

However, as paullb also said, hotel power (the power used other than moving, eg: lighting, air-con/heating and cooking in the kitchen) also consume a large amount of energy. I remember reading somewhere that hotel power can be up to 20-30% of overall energy consumption on a Eurostar (do correct me if you have sources that know better). If hotel power was added onto Michael's graph, we'd find that the extra energy consumed may indeed be nullified by the savings from reduced hotel power.

[hertogjan]

That reasoning would be correct if the "hotel power" was comparable to the traction power. As can be deduced from Michael's graph, the traction power is in the order of MW (megawatts)*. I doubt that a train would consume 20% to 30% of that amount as hotel power, which would be in the order of 1 MW, which seems rather high. My own estimate would be at least 5 to 10 times lower. I don't expect that this effect will be significantly enough to effectively change the energy consumption.

But suppose the hotel power were 1 MW, let us make a computational example. Suppose a 80 m/s (288 km/h) train takes an hour to get from A to B. Then a 40 m/s would take 2 hours, and a 20 m/s train takes 4 hours. Now take the traction force from Michael's graph and we assume that hotel power is 1 MW (a pretty high estimate). Let us compute the energy needed for one journey.**

Code: Select all

         -----------Power-----------
Speed    Traction  "Hotel"   Total     Time   Total energy
80 m/s   5.2 MW    1.0 MW    6.2 MW    1 h    6.2 MWh
40 m/s   0.9 MW    1.0 MW    1.9 MW    2 h    3.8 MWh
20 m/s   0.2 MW    1.0 MW    1.2 MW    4 h    4.8 MWh

You see that even then the energy consumption at 40 m/s is significantly lower than at 80 m/s, and if one would assume a lower hotel power then at 20 m/s it would be even more efficient.


*At 270 km/h = 75 m/s, the graph shows a force of 60 kN, resulting in 60 kN * 75 m/s = 4.5 MW of power.
**This is an idealised computation as there are many other factors. However, the qualitative idea remains the same.

[michael blunck]

Interesting discussion!

I remember reading somewhere that hotel power can be up to 20-30% of overall energy consumption on a Eurostar

The german DB once released a number for "hotel power" of 19%, on average for all its services (local, long-distance, freight). Although this number should be contained in the DB´s "sustainability report", due to its bias (shinyness vs. lack of numbers), I don´t seem to be able to find it.
http://www.db.de/site/nachhaltigkeitsbe ... rview.html

Anyway. Power != consumption.

I.e., on an ecological background, the most important aspect for travel is capacity utilisation. And this may be largely different for medium and fast or long and short trains. E.g., the swiss SBB (I´m not willing to use the "fake" numbers of the DB here) released a capacity utilisation of 28% for long-distant services and 17% for local services in 2004. That´s not much. Indeed it shows that going by car isn´t that bad in contrast than going by train.


regards
Michael

[paullb]

You are right if you say that you would need 1/4 of the trains to maintain a certain service. But then every train travels a distance that is 4 times longer. So the number of train-kilometers (or train-miles) is the same. Now tell me where you save energy.

Because you make fewer trains!!!!

It takes energy to make trains. (16-carriage 700 series bullet trains do not grow on trees )

[doktorhonig]

I.e., on an ecological background, the most important aspect for travel is capacity utilisation. And this may be largely different for medium and fast or long and short trains. E.g., the swiss SBB (I´m not willing to use the "fake" numbers of the DB here) released a capacity utilisation of 28% for long-distant services and 17% for local services in 2004. That´s not much. Indeed it shows that going by car isn´t that bad in contrast than going by train.

Especially if you take some friends with you.
I went to Zagreb last week, and the trains are rather full between Vienna and Graz, but not between Graz and Zagreb (actually there were lots of croatian football fans on my journey back, but that's an exception). So this train's not very efficient, even though there are only two direct trains per direction between Wien and Zagreb.

The reason for this is, that the ride through Slovenia and Croatia takes ages. Bad coordination with local train traffic causes stops of 15 minutes and more, different electrical systems require changing the loco, and we still have an EU-Border between Slovenia and Croatia. Especially Slovenians have to check each passenger carefully, otherwise they are the EU's scapegoat if bad guys cross the border (which happens anyway).

So what does this tell us? If the train becomes too slow, it won't be used. I used it because I love going by train, and I can plug my notebook in. But if people can save time when going by car, they'll probably do it. So trains have to be fast enough, to be used and therefore be "green".