braindump

If you’ve spoken to me in person over the past 6 months or so, you may have heard me mention that I’m considering buying a Toyota Prius to replace my six-year-old Honda Jazz (known as the Fit in Japan and the Americas). Actually, you probably think I’ve been going on about it ad nauseam, so I’ve decided it’s time to share my enthusiasm for the car with the wider internet community (or at least the seven people who follow this blog). So, here’s part one of my thinking on why I might consider buying a Prius; I’m starting with the environmental issues.

2nd gen Toyota Prius

If you don’t already know much about the Prius, I suggest you have a quick skim through the Wikipedia article linked above, or have a look at some of Toyota’s promotional material. I won’t repeat the many explanations of what a hybrid car is or how it works, but instead will concentrate on what it is about the Prius that influences my decision on whether to buy one or not.

Everyone knows that the Prius is supposed to be a “green” car – whatever that means. Rather than dealing with marketing terms, I prefer to consider things that can be measured, and that are known to have adverse effects on the environment. (The figures I quote come from Wikipedia, unless otherwise noted, and may relate to the second generation model, or the just-released third generation model.) Let’s start with carbon dioxide emissions.

First of all, carbon dioxide (CO2) emissions are bad because they cause global climate change. If that’s not a statement you agree with, I suggest you go and read Greg Craven’s “What’s The Worst That Could Happen? A rational response to the climate change debate” or watch The Most Terrifying Video You Will Ever See. I won’t discuss whether climate change is a problem in this post.

The 2nd gen Prius releases on average 104 grams of CO2 per km, while the 3rd gen releases 89 g/km. For comparison, a similarly-sized Toyota Camry releases about 210 g/km, which is the basis of the claim that the Prius has only 50% of the CO2 emissions of similar sized cars. (I can’t find CO2 figures for my Jazz with 1.5 litre engine, but I think it would be around 140-150 g/km.) However, the comparison that is commonly made at the moment is with the MINI Cooper D, which also claims 104 g/km CO2 emissions. But the MINI is a small car, without the same passenger or luggage capacity as the Prius, so it’s hardly a comparison of like-for-like.  Also, the “D” stands for diesel, and that has other implications we’ll come to in a minute.

When it comes to fuel consumption, it only makes sense to compare litres per 100 km (l/100km) figures if they’re using the same fuel.  Comparing petrol to diesel makes no sense, because the fuels have different amounts of stored chemical energy per litre, and they usually cost different amounts.  If you’re interested in climate change, then compare CO2 emissions (above).  If you’re interested in the impact on your wallet, then look at $/100km for the particular fuel.  Since fuel prices are so volatile, I won’t make that cost comparison here; the comparison which is most important to me is the CO2 emissions.

Some people only consider CO2 when they think of emissions; however, there’s a lot more nasty stuff that comes out of the tailpipe than just CO2, and it’s this stuff that contributes to pollution as it’s historically been considered. One group of those pollutants are the nitrous oxides (NOx), which are components in the formation of smog. Unfortunately I can’t find any recent evidence to support Toyota’s older claim that the Prius had only 20% the NOx emissions of similar vehicles; their recent claims are only of 50% of comparable cars, or about 0.01 g/km NOx. For comparison, the MINI Cooper D has 14 times as much NOx emissions, 0.14 g/km. There are other pollutants to consider as well – particulates, carbon monoxide and hydrocarbons – that I won’t go into details about. As far as I’m aware, the Prius meets or exceeds other comparable cars in all of these measures.

The final point of argument is lifetime environmental impact. There was a study that compared a Hummer H3 with the Prius, concluding that the Hummer was better for the environment if the manufacturing impact was included and apportioned to the actual driving environmental impact on a per-km basis over the expected driving lifetime of the vehicle. (Note that the study “does not include issues of gigajuelles”, whatever those are.) That study has been debunked numerous times; in fact, the conclusion from the Pacific Institute is “A quick re-analysis with peer-reviewed data leads to completely opposite conclusions: the life-cycle energy requirements of hybrids and smaller cars are far lower than Hummers and other large SUVs.”

So, that’s the environmental overview of the Prius; it’s more environmentally friendly than my current car, and than all other currently available similar-sized cars. But that’s not the only consideration when deciding on a car – stay tuned for part 2 soon.