Doubt if it could account for that much of the 25% over 5 years
I think it can. If you examine the mpg figures of cars built in the past 5 years compared to what it was like from 2007 and back, they are surprisingly more fuel efficient. I'm not suggesting that it accounts for all of the 25%, but from the figures provided with new cars these days, I think it accounts for a fair chunk of it.