Sunday, July 08, 2007

More on Speeding

More on speeding.... On the left is a graph that shows how fuel efficiency decreases after 60mph. It's an American gragh, so the mpg are miles per American gallon rather than Imperial, but the trend will of course be the same - you use up more petrol if you drive too fast.

Essentially doing 75mph (120kmph) instead of 55mph (90kmph) increases the fuel you consume by about 20%. Given how expensive petrol is at the moment, you'd think it was a no-brainer that people cut their speed. Yet drivers rarely do this - and these same drivers then complain about fuel prices and speeding tickets.

Why do they behave this way? I think it is to do with problems with deferred gratification. The same way some people are unable to wait till the sales to buy an item, or to save for it for six months instead of putting it now on the credit card, some people can't wait an extra half hour to get to their destination (or can't be bothered to get up half an hour early to give themselves enough time to drive there at 60mph). If we could just get people to try it out, they'd not only save themselves a lot of money, the volume of petrol consumed would fall, as would the CO2 emmissions. Plus they'd stay within the law and avoid speeding tickets.

I'd say to people, just try it once - perhaps on a weekend trip to see the inlaws. You probably know already how much fuel the journey takes, and you can therefore easily compare how you do with a journey at a steady 60mph. Obviously it will hurt the self-image of some to be driving at that speed in the slow lane with the lorries. But the financial gain is substantial - I'd say, just try it out once. Then decide whether a macho self-image is worth the extra cost (hint: it doesn't matter what other drivers think of you as they don't know you from adam).

1 comment:

Anonymous said...

Sorry, but not quite true... it's true that above a certain speed, fuel efficiency drops, but the speed at which that happens depends on a whole range of factors, most notably engine size. The speeds on your graph will not be universally applicable to all cars or all engine sizes. Some engines run at their most efficient at around 70mph.