Over the summer we upgraded our petrol engine renault megane hatchback and replaced it with a diesel megane estate (the dCi-100 version). We’ve gone from 40 miles per gallon (sorry about the imperial units) to between 55 and 60 miles per gallon. (Our first full tank did 59.5 mpg.)

One of the things I like about the new1 car is the computer mpg readout … we both tend to drive with that showing, and both of us have started driving slower and more carefully so that the mpg figure will go up. What a simple innovation … knowing when you’re being a gas hog makes one do it less!

I’ve noted that driving at 55-60 mph is the optimum, and 70-ish mph results in mpg figures in the high forties …

All of this has me wondering why, as an easy and effective way of dropping the greenhouse gas emissions we in Britain don’t

  • Make the motorway speed limit 60 mph (yes, I’ll hate it too from a driving point of view, but from a conscience point of view I’ll feel better), and
  • Make diesel cheaper than petrol, to encourage more folk to move over …

As far as I understand it, here in the UK the price difference is down to taxation. The only explanation I’ve heard is that the greater price is a hangover from the days when diesel engines delivered bad particulate pollution. It would seem to me given modern engine technologies, there is a prima facie case for putting the taxation boot on the other foot, making petrol more expensive per litre (yes, we really do measure our petrol prices per litre and our performance in miles per gallon).

Are there any reasons why diesel production is more expensive economically or in greenhouse gas terms to make my argument wrong?

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Answers.Yahoo.Com to the rescue (from “Bryan’s Blog” on (on Sunday 12 November, 2006))

Once upon a time I mentioned that we now have a megane estate car. I raved about it’s fuel economy. Today I was confronted with two light bulb failures to fix: the reversing light, and the front left indicator…

  1. Strictly, it’s a newer car, since we didn’t buy it new