2.2 Scope – travel on public transport

Travel on public transport poses similar questions. If a service is running anyway, is the marginal energy use (and hence CO₂ emissions) from you getting on that service close to zero? Or should you average the emissions across a typical load factor? Otherwise, we could all fly anywhere guilt-free on the assumption that the flight was not scheduled especially for us! Data on some forms of transport is quite hard to come by or surprisingly complex. For example, how can you compare emissions from a crowded electric commuter train with an almost empty diesel multiple unit on a rural branch line? And should you try to estimate the higher emissions associated with a high-speed intercity train, compared with a slower multiple unit? It is even harder as we don’t know where the train companies buy their electricity from.