The cars of today are far too light and fast on the acceleration.  You talk  about fuel economy, but it's 99.99% dependent on how you drive it,  I can slam mine into gear and spin the wheels wearing out my tyres any time I want, but what's the point if forty feet from the crossroads the lights are almost guaranteed to turn red?  It's all down to reading the road.  If the lights are green 100 yards from you, slow down.  Nobody does though, so they all have to brake at the last moment.  A lot of the traffic lights have built-in speed monitors which are able to determine whether anybody's speeding, and flick it across to red.  I'm quite happy about my economy.  On a run I'll get about 35 miles to the gallon.  About town, rather less.  

The other thing that gets me is how other road users dogmatically refuse to let anybody out of a side road - totally pointless.  If every fifth car let just one person out, there'd be no queue, and how long does it take: four seconds?  Or even more ignorant - if you see a man trying to turn right across you path, let him!  There will invariably be a string of cars behind him, all stuck because there's no room for them to get past.  It's not even courtesy - it's just straight common sense.