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28.12.2007  |  127× přečteno      vytisknout článek

Porovnání způsobů cestování v angličtině

Introduction

Modern Jet aircraft can travel at great speed, there is no doubt about that. They are only limited by the speed of sound, about 780mph or 1250km/h. This is at the limits though, 600mph or roughly 1,000km/h is a more reasonable amount for the top speed of aircraft, sufficiently below the speed of sound so that there is no risk of breaking it. However in commercial use aircraft usually travel in the region of 300mph - 500mph or 500km/h to 800km/h. The speed at which it flies is calculated based on how much fuel it will consume at the various speeds.

Trains however travel at a maximum of 186mph or 300km/h. This is considerably less than the aircraft, only about one third of the speed. So how can they still compete?

Aircraft have crucial disadvantages. Although once cruising up in the air they may reach very high speeds, it takes a long time to arrange everything.

What makes aircraft slow?

First of all Airport exist out of town. This is because they take up a large amount of room, often several square miles as with major airport. To get to the airport people face a journey, often in the region of 30 minutes. Train stations on the other hand usually exist in the centre of cities, for historical reasons. Even if there is no room for a train station, it can be built underground, so there would be no reason for a major station not to be at the heart of the city. Hence journey time to and from stations is considerably less than to airports.

Secondly there is beurocracy. Airports require people to check-in, leaving baggage behind, and provide their tickets all the time. People are usually requested by the airline to arrive early. There is no such thing in trains, you just find out the platform and walk straight onto it. With aircraft once you get to the other end you have to hang around and wait for the baggage at the reclaim facitlity. For international journeys immigration has to be done at the airport too. However immigration and passport control can be done on board trains, so not wasting time.

Thirdly there is boarding time. Trains have doors down the length of them. The eurostar with an 800 capacity has 18 doors, thats 45 passengers per door. A boeing 747 (capacity 400) has at best 3 doors. (Front, middle rear), that is 133 passenger per door. Since the rear door is often not used this goes up to 200 pessangers per door! While it is possible to board TGVs in 2 minutes (the general time spent at stations) it can take as long as 15 minutes to board an aircraft because of the few entry/exit points. (Note: Peak capacity stations have a platform both sides of the train, effectivly doubling the number of entry/exit points). Another thing is that before the aircraft can leave the terminal everyone has to be sitting with all their luggage put away (saftey reasons). However its perfectly acceptable for a train to start leaving the station while everyone is still standing up and stowing their bags.

The fourth reason is that aircraft cannot leave immediately. Once everyone is on board and ready to go the aircraft still has to spend a long time getting to the runway (taxiing). And at busy airports such as London Heathrow they then have to wait for clearence to take off, and queues of planes often 4 long build up, meaning you have to wait for 4 aircraft in front to take off. This is the same with landing, aircraft spend a long time circling around the airport and then there is the usual time taken to get to the gate. At busy airports sometimes aircraft have to wait on the tarmac until a gate becomes free.

All of this means that in fact the door to door Journey time for distances up to 400km or 250miles is faster by high speed train than it is for the aircraft. This usually means bankrupcy for any airline serving to cities connected with high speed rail.

Well, why not compete on price?

If aircraft cannot compete with trains on journey time you might think they could try price. This is very difficult. Aircraft are very expensive to build and maintain, much more than trains. The most expensive train in the world is the Eurostar at $40,000 a seat. Most aircraft by comparison are $200,000 per seat! Trains do have costs such as paying for the railway lines which are expensive, then again, so are airports, and airlines have to pay airports a lot of money. (Landing charges). Also there is energy, aircraft consume a hidious amount of fuel when compared to trains, which has to be paid for. As a result operating costs for airlines two to three times higher than for trains. Offering a cheap and cheerful service isn't possible.

Examples of Aircraft being displaced by trains.

The Paris to Lyon line is the famous example. Frances two biggest cities, about 450km (280miles) apart. This was the most obvious candidate for high speed rail, and in 1981 the first TGV services on new high speed line started. The journey time from Paris to Lyon at only 2 hours. This crippled the airlines, a 40% drop in air travel between the two cities occurred.

Above: The Thalys, top speed: 186mph (300km/h)

More recently Paris to Brussels high speed line has been completed in January 1998, a distance of 340km or 210miles. By taking a Thalys between the two cities direct, journey time is a staggering 1hour 30minutes! This is very likely to cripple air services too.

Eurostar, London to Paris and Brussels also has stolen some of the market. Since the train only runs at 100mph (160km/h) through England though, Journey time is stuck at 3 hours. The flight time is 45 minutes, although surveys find point to point time using airlines is…. 3 hours coincidentally. However when the channel tunnel rail link is built and Paris to London is down to 2 hours 30 minutes, it is expected Eurostar will get the majority of the market.

Supersonic Aircraft

 

 

The concorde, developed in the 1970s by British Aerospace and Air France as a supersonic passenger aircraft is the only type in the world. British airways have 7 of these planes, Air France has 7 too. They have a top speed of 1,448mph (2316km/h), roughly twice as fast as the speed of sound. They can do London -> New York in only 3 hours. While techincally these are marvelous machines, commercially they are a complete failure. They are not allowed to travel at supersonic speeds over land because of the sonic boom they create (they will never compete with trains!) and use so much fuel and need so much maintanence prices are very high, London to New York return is £3,000 or US $5,000. In about 10 years time when they will have to be scrapped due to old age, it is likely they will never be replaced by new supersonic aircraft.

The Enviroment

So is it a good thing the aircraft are being replaced by fast trains? From an environmental point of view it certainly is:

Energy Consumption

Trains do have air resistance, but the faster you go the more air resistance you face. As a result the faster you travel the more energy you consume between two points since energy=force x distance. Now one advantage of aircraft is they climb to where the air is thinner, so air resistance is 40% less. But because they go 300% faster than trains, its not a benefit. Also the design of aircraft makes them more prone to air resistance… they rely on air resistance to stay in the air. Aircraft use a lot of fuel to climb about 10km or 7 miles (30,000ft) into the air.

The Jet engine is always going to be inneficient too, because it relies on blasting burnt fuel out of the rear. This means that the vast majority of energy goes speeding up the air. It doesn't divide 50/50 because kinetic energy is a funtion of the square of velocity (double speed quadrouble energy). So most of the energy is used to make a huge hurricane with a little left for the actual aircraft. Another reason why it is inneficient is because it relies heat… so you get a hot hurricane! Not only that but because there are so many moving parts there is a huge amount of noise. In short, noise, heat, wind come out of the jet engine as wasted energy, meaning only about 10% left goes into making the aircraft go.

Electric trains on the other hand don't make noise greater than conversation volume even at full power, although motors get hot they don't reach thousands of degrees, and they don't produce 1,000 mph winds. As a result power efficiency is very high, in the 40%-60% of the energy goes into making the train go.

Emmisions

Electric trains by definition don't produce emmisions, although the electricity has to be generated. Even if it is through oil-powered stations as opposed to cleaner electricity generation because energy efficiency is so high. Assuming electricity is generated by oil powered stations, aircraft will produce about 5 times more carbon dioxide than trains, plus producing toxic nitrous oxides

Noise

High speed trains do produce noise, however not that much noise. A high speed train passing at full speed (300km/h 186mph) is still slightly quiter than a busy motorway. Aircraft are extremly noisy, this occurs because they have to shoot air out of the back at beyond supersonic speeds. However this is only a problem for those living around an airport. Once at altitude noise on the ground is not noticable. A high speed railway is noise all along. However air craft are flying at low altitudes for a considerable distance around the airport itself, usually over cities. A high speed railway only affects those near the railway, but more importantly 98% of the noise from a high speed line can be cut out by building a sound barrier next to the line.

Is this good for the consumer?

Well it finally means that we no longer have to rely on people's enviromental concience to choose the train instead of the aircraft/car because the high speed train will provide most of the benefits of competing forms of travel, and more. It will also mean airlines tightening up procedures to get people through airports faster and will encourage airports to have better city links (such as with the Heathrow Express train) so high speed trains will mean improved quality of service for those still travelling by air.

For longer flights, where the aircraft gets to spend longer at its full speed, the high speed train looses its edge and building a high speed railway line for exclusive distances much more than 500km (300miles) would be a mistake seeing as such a long distance would be incredibly expensive, and air could probably beat it for time, meaning profits wouldn't be that good. Having said that, if there were a major city half way down then it would be an excellent idea since services could stop in the major city and go on. Even if we do get 300mph (500km/h) trains, it will not completely mean the end of aircraft because trains cannot cross oceans obviously, although the channel tunnel does indicate trains can cross small seas. It is likely as the high speed rail grows in europe, flying around will become a way of the past.

ZDROJ:www.o-keating.com, kráceno


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