My drive each day is 74 miles each way in heavy rush hour traffic from J29 on the M25 to J11 via the Dartford Crossing. About 10 miles to get to the M25 from home cross country, and about 6 miles from J11 into Woking. Normally being rush hour I use Drive select in Auto mode - which on the trip usually gives me an average mpg of about 33.4 mpg with odd drops into Sport mode for pulling onto roundabouts etc either end of the motorway. Today just for the hell of it I thought I'd try Efficiency mode. Drove at normal speeds, the only difference was that I gently accelerated the car to keep with traffic. And what a difference! 37.8mpg going to work, 40.1mpg on the return. And as I say, the only difference was in accelerating gently. So used properly Efficiency mode does work after all.....couldn't drive like this all the time but nice to know it can be done.