More heat than light

[Martin Cassini]

Unerringly, the "debate" on Today about Spain reducing its national speed limit from 75 to 68mph "to conserve fuel" missed the point. George Monbiot claimed, spuriously, that "going faster means more noise", and Tiff Needell complained, reasonably, about loss of choice. Surely the real point is about the vanity of one-size-fits-all "solutions". It’s not speed that counts, it’s revs. If at 60mph, one engine is turning at 3000rpm and another at 2000rpm, which is using more fuel and emitting more CO2?

[timpent]

Yes, but the 2000rpm engine is using less fuel at 68mph than 75mph, as is the 3000rpm engine. Then you get on to scrapping less efficient cars, but scrapping a perfectly good car that happens to use a bit more fuel makes no sense at all once you take the energy cost of producing a new car into account.