What’s the Best Car for the Environment? Maybe Not What You Think

Kevin Dooley

The pending arrival of the Nissan Leaf got me thinking about cars and the environment again.  (BTW my previous post on the Prius vs. the Hummer is here). Considering that for many of us an automobile is a necessity, we have a new range of choices in automobile purchases to minimize the impact.

• High efficiency conventional (like Honda Fit)
• Gasoline-electric hybrids (like Toyota Prius)
• Clean Diesel (like Volkswagen TDI, which COULD run on biodiesel)
• Electric only (like the Nissan Leaf)

So which type is best?

There are different ways to consider the problem.  Some choices are to look at total cost of ownership, look at tailpipe emissions, or look at total life cycle cost.

Each of the manufacturers have their own arguments about why their technology is superior, and they are basically correct even when they disagree with each other.  That’s because it is possible to consider a select measurement of impact for any particular engine system find a way that it is best.

For example, if we look at tailpipe emissions there is no competition.  Electric vehicles win.  They make no exhaust, just heat, and less heat than other cars.

But, suppose we look at the emissions associated driving the car.  The electric cars got their power from somewhere, and that somewhere probably had emissions.  We could look at the total greenhouse gas emissions associated with driving (like GHG per mile) that includes the electricity generation.

The Institute for Life Cycle Analysis did this.  When they considered total greenhouse gas emissions, the biodiesel has the smallest total impact, the electric car the worst (still good, but worst of the 5) and the other 3 about equal in the middle.

It gets more complicated the closer you look

What is the real greenhouse gas emissions associated with an electric car?  Clearly it makes a difference if you got your power from a coal burning plant, a nuclear plant, or an hydroelectric dam.

And if that’s not complicated enough, we really need to consider the energy and pollution associated with actually making the car.  The Center for Transportation Research at Argonne National Laboratory has developed a detailed model of green house gases over the lifetime of automobiles. This includes the pollution associated with producing the car and what is created while driving (or charging).

A telling comment from one of their research papers is:

We found that the production of materials accounts for a majority of the vehicle-cycle energy use and emissions of all the vehicles examined.

As cars get more energy efficient, the production of the car is more polluting than running it!

You might think the key would be to reduce the weight of the car.  If there’s less stuff, there must have been less energy to produce the stuff.  And that would be right if we were using the same stuff.  5,000 pounds of steel is more polluting than 3,000 pounds.  And a lighter car makes the engine more efficient.

But, in order to keep the cars safe while making them lighter, designers are using advanced materials – high tech aluminum alloys, carbon/epoxy composites, etc. And these materials use more energy per pound to produce than traditional materials!

What car should you buy?

I think at this point it is fair to say that when you want a car with minimal impact, just make sure it is energy efficient, look for government incentives, and find something you like.  One’s not really better than the other right now.