Below is a link to this most excellent article by James Hamilton at Econbrowser.Air resistance increases the faster you travel, which might lead you to think that higher speeds always require more fuel. However, your car's engine is designed for maximal efficiency in converting fuel into motion when you drive at higher speeds. As a result, the typical car gets much better gas mileage if you drive it at 45 mph instead of 15. However, at speeds above 60 mph, the wind resistance becomes a dominant factor, and miles per gallon for most cars starts to decline significantly if you drive faster than 60....
Driving more slowly should also reduce your carbon footprint and any other pollutants by the same amount indicated in the second column above, and should lessen the likelihood and severity of collisions. And most urban highways prohibit speeds over 65, so you're exposing yourself to risk of fines and higher insurance rates if you drive at higher speeds. Even without these added considerations, however, I would think that many people, if they knew that the immediate financial rewards were on the order of the numbers given above, might choose to drive more slowly. In which case, it is perhaps a public service to help call such numbers to people's attention.
Which, in case you were wondering, is why I wrote this post.
http://www.econbrowser.com/archives/200 ... e_mon.html