Public transport emissions in NZ

A few months ago, I looked at the greenhouse gas emissions from cars in New Zealand. As promised, here’s the follow up on public transport emissions.

Trains

Sadly, the New Zealand data on public transport emissions is pretty sparse. An OIA request to Auckland Transport only turned up information on Auckland’s train network – and given that we’re going to be completely replacing our diesel trains with electrics by 2016, this information will be out of date pretty soon. The new electric trains will use much less energy (electric motors are much more efficient than diesel engines), and emissions will plummet, especially given New Zealand’s high proportion of renewable electricity. Even the current trains, though, have much lower emissions than cars. In the last 18 months, Auckland’s trains used an average of 1.42 litres of diesel fuel for every 100 “passenger kilometres” they travelled. That means 1.42 litres used to move five people 20 km each, or ten people 10 km each.

From my previous post, New Zealand’s cars use around 10 litres of fuel for every 100 “vehicle kilometres” – that is, for each 100 km travelled by the vehicle. To compare the statistics, you’ve got to know something about the typical number of passengers in a car. Luckily, the Ministry of Transport collects information on this, and it turns out that Auckland cars carry an average of 1.5 people – so one vehicle kilometre becomes 1.5 passenger kilometres.

All up, then, Auckland cars are likely to use about 6.67 litres of fuel per 100 passenger kilometres – and, once you factor in that diesel has slightly higher emissions per litre than petrol, cars create about 4 times the greenhouse gas emissions of Auckland’s diesel trains, per passenger kilometre. Once we switch to electric trains (more energy efficient), using our mainly renewable electricity (much lower emissions per unit of energy), it’ll be a heckuva lot more than that. I haven’t seen any estimates of what the emissions from the new trains will be – surely there are some somewhere? – but it’s probably no exaggeration to say they could fall by 80% or so.

Buses

As another comparison, a report authored by MRCagney and featuring our very own Stu Donovan estimates that Christchurch buses get 0.76 passenger kilometres for each megajoule of energy. With a bit of rearranging (energy content of diesel = 36 MJ/ L, and emissions content of diesel = 2.670 kg of CO₂-equivalent/ L), I’m calculating that those Christchurch buses use 3.65 litres per 100 passenger kilometres, or 9.8 kg of CO₂-equivalent emissions. This is around 36% lower than Auckland’s cars.

Summing Up

So what am I trying to say here? Public transport is good for reducing transport emissions. I’d like to see more New Zealand evidence on this point, and HOP cards will hopefully help with that as it becomes possible to build better estimates of distances travelled. There’s plenty of international evidence, and I’ll tackle that in another post.

In New Zealand, electric trains can do an excellent job of reducing transport emissions, thanks to our wonderful renewable electricity. Buses offer much smaller savings, but, of course, they are much cheaper. There are new technologies coming along for buses, as they are for cars – gas-powered, hybrid, or even electric buses – and those could help to reduce emissions. For the time being, these things are pretty expensive, and it’s hard to know how much this will change in the future (although the costs will come down).

The other thing that makes a big difference is the loading factors. A full bus is going to be much more efficient than a nearly empty one, just like a car. With PT usage generally on the rise, and the redesign of Auckland’s network over the next couple of years, we should be running fuller services a lot of the time (although hopefully not overloaded!)

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