Making sense of carbon comparisons THE REVIEW ›› GREEN WATCH
IF YOU are working out which travel mode to choose for a UK journey, it is often difficult trying to determine the cheapest. Try factoring in the environmental cost and it gets a whole lot harder, writes Roger Gardner. Ask a rail company which is the cleanest method of transport and the answer is rail. Airlines and motoring organisations will also be able to offer reasons why their modes of transport are better. Objective observers usually side
with rail but that is not the whole story. Electric trains are better than diesel, high-speed trains worse than regular electric and it is better if the electricity comes from nuclear generation rather than fossil fuel combustion. Carbon comparison is something
of a minefield topic as answers depend upon so many variables such as the length of the journey, the alternatives available or the number of people making the journey. Just to make it still more difficult, a proper environmental comparison between rail, air and road should include the fully integrated carbon life cycle analysis of a journey – ie, it should also account for the carbon that goes into transport infrastructure. That is fiendishly difficult to do
and reliable data is hard to find. Most comparisons are therefore based just upon the headline energy consumption in grams of
CO2 per passenger kilometre. So what do you do? Let's take an example from a
while ago. The BBC reported a University of Southampton study looking at options for a journey between Southampton and Edinburgh that compared a turbo-prop aircraft, a train and two types of car. At 81g CO2/passenger km, the
plane was cleaner for a single traveller than a hybrid car (which came in at around 100 grams) but the train (a cross-country diesel) was best at 74g. For four people travelling together, however, the car becomes a much cleaner option – half the
CO2 of the train – and, hardly surprisingly, much cheaper too. Life is too short to try and line
up data so you need some basic indicators. The more people
travelling together, the better car travel looks for longer domestic journeys. But if there are only two of you travelling, the carbon differences narrow. If your rail option is electric powered it will be better than diesel so that is something to check. The air option looks increasingly
attractive for one person from the carbon perspective if the journey is long. Our example journey was 572km as the crow flies but there are not many air connections of this length in the UK. For most journeys, inter-city electric trains come out best and by quite some margin for the single traveller. Here is a further complication. If you travel on a full train or
aircraft, the CO2 is clearly going to be better per passenger km than if it is half full. So, while hard to determine, you really need to know the likely ‘load factor’ for those options too. That will be dependent upon time of day and competition on the route. Eurostar, for example, is nearly
always full so if journeys are being made to near European destinations, the train is definitely going to be far cleaner. Rail travel into Europe becomes even more carbon attractive due to the fact
"Carbon comparison is something of a minefi eld topic as answers depend upon so many variables, including the length of the journey, the options available and the number of people making the journey"
that Eurostar and the TGV mainly use electricity from nuclear power generation. For the business traveller, the
choice is further complicated by scarcity of another important commodity: time. If you are travelling the length of the country or close to it, then air travel is very attractive and will allow a return journey in the time of a single by the other modes. Despite the absence of real high-speed rail in the UK, trains still have an advantage over car but if you are embarking upon an awkward cross-country journey, the time advantage can reduce a lot or even disappear. You might well think I am no
nearer to being able to make a judgment call on the right carbon choice for a journey after reading this. Well that's partly true, and the simple fact is that choice is dependent upon so many factors that you have either to do the maths or use common sense. However, if you are at least
now savvy to some of the issues involved, aware of the potential to save carbon and better able to factor that into your cost and time equations, then your common sense judgment will be just that little bit more sensible!
44 THE BUSINESS TRAVEL MAGAZINE
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