Environmental Aspects

I've been putting off writing about the environmental aspects of rail versus busway. I've been putting it off because its complicated. It's complicated both in terms of the facts, and in terms of how those facts may influence our choices.

I can't offer all the answers, but can pose some questions...

Establishing the Facts

At first glance, you might assume that rail is 100% green. On reflection, you might remember that approximately 25% (pdf) of our electricity comes from fossil fuels -- so rail is "75% green".

75% of what? Does rail use more energy than buses, or less? It's widely known that steel wheels on rails have less friction than bus tires on concrete, but we also have to consider:

1. Trains are really heavy. Surely moving all that steel around impacts on energy use. Here's an example, to illustrate how heavy trains are: an English Electric "DM" unit, as used on the Johnsonville line, seats 60 and weighs 43.5 tonnes. That's about 725kg per seat. The bus I rode to work this morning seats 45 and weights 8.3 tonnes. That's about 184kg per seat.
   


2. Trains don't "scale down" well. E.g. The smallest train you can get on the Johnsonville line is a 60-seat "DM" unit pulling (or pushing) a 70-seat "D" class trailer. That's 130 seats, weighing almost 80 tonnes. (The weight is approximate, because I don't have an exact weight for the trailer.) Off-peak there might be only 8 people on the train, for example. That's 10 tonnes of vehicle per passenger. Put those same 8 people on bus, and there's only 1 tonne of vehicle per passenger.
   
   (By the way, why run near-empty trains and near-empty buses off-peak? Why not combine them, to haul more full seats and fewer empty ones.)
   


3. On the Johnsonville line, trains always have to make a return trip. There's nowhere to park trains in Johnsonville. (Contrast that with Paraparumu for instance, where there is room to "stable" trains overnight.) Trains usually have to make the return trip empty (the only common exception is reverse trips that take school students). Contrast that with buses - they can be parked overnight at the Newlands depot, so they don't have to drive back to Wellington for the night. (Are Newland's buses parked in the city during the day? I'd suggest they should be, if we're serious about fuel costs and greenhouse emissions. I know I've seen a few parked in town.)

I asked an engineer how to arrive at a definitive answer about this. He explained that you need (i) fuel consumption and ridership figures from the bus company, (ii) electricity consumption and ridership figures from the rail company, and (iii) enough time to crunch the numbers. Unfortunately, I have none of the above :-(

So, for now, I can't give a definitive analysis, but I do suggest that the greater weight of trains may undermine their "greeness" to some degree.

Choices

Let's say we did crunch the numbers, and we arrived at definitive answers about the greenhouse emissions produced by each solution. Does that result absolutely dictate our choice? Or is it just one factor, one the many which influence the overall choice between rail and busway?

For instance, we should consider not only greenhouse gases, but also "environment" in the widest sense of the word. Will building a busway encourage urban sprawl? Or is urban sprawl dictated solely by council policies? As long as the council allows new subdivisions, people will settle in them - whether there's a busway or not. At least if there is a busway, we stand a better chance of pursuading workers to leave their cars at home.