CO2 emissions

Last updated: July 2015




Climate Impact of Transport


Occasionally pieces appear in the media proclaiming that “everything you think you know is wrong!” which quote some calculation about the climate impacts of various forms of transport and then announce some counter-intuitive conclusion like that it’s better to drive an SUV than get the bus. So are they right?


Figures based on DEFRA, 2014, Greenhouse Gas Conversion Factor Repository.
* This is a loose estimate as no figures are available. It is made on the basis of a suggested 35% current average occupancy rate for trains. [1]



The thing is, comparing the climate impacts of various forms of transport is not straightforward because their impact depends on how you use them. As shown on the table above, buses are much more energy efficient than cars when they’re full. But a bus with one passenger is a very inefficient way to transport a single person around – they would burn less carbon driving an SUV. The average occupancy of UK local buses is low (11%) which can make buses’ carbon profiles look rather poor.

But it’s important not to leap to conclusions from this. For one thing, occupancy levels aren’t fixed. Although there are some routes that will always be unpopular, if more people start using the bus then, clearly, occupancy levels will increase. We have shown the impacts of vehicles at different occupancy levels in the table so you can see not only the current emissions, but their potential for improvement at higher occupancies.

Additionally, while some people argue that we should only use the bus on popular routes, for most of us, that isn’t how it works – you either have a car and use it, or you rely on public transport. And if you are going to rely on public transport, you need to be able to use it for unpopular routes as well as popular ones.


Over long distances

It is in the long distance arena that buses really come into their own, as can be seen in the table. Coaches benefit from the efficiencies of scale without stopping all the time like local buses, and are the climate winner even at reasonably low occupancy levels. Trains are not a bad option either, but they can’t match coaches.

There are two main long distance coach companies – National Express scores higher than Megabus.

The climate profile of cars, as shown, greatly depends on how many people are in them. A car which contains only a driver is dreadful for the climate. But a completely full car has a comparable carbon footprint per person to an averagely occupied train. The overall effect of giving up your car is likely to be a good thing for the climate, even if certain journeys appear worse when looked at in isolation.

The rule of thumb is that mass transport is generally better than personal transport, but occupancy levels matter just as much as the choice of vehicle, and that means we need some systemic change.


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1 Pritchard et al, 2015, Making meaningful comparisons between road and rail – substituting average energy consumption data for rail with empirical analysis