Originally Posted by Daveyc
Wow, that's outrageously good! Are you driving like a mouse on the dual carriageway - i.e. staying below 70mpg and really light on the throttle?
It is a surprise to me that you think that 64mpg is such a good figure. However, it is a lifetime average and individual journey figures, after taking into account the 5% error produced by the on board computer, range from 58mpg to 74mpg.
To answer your question, on my normal 10 mile trip I drive at about 60mph on the dual carriageway. This is in ECO PRO mode and therfore light on the throttle. I also use a number of special driving techniques.
On such a short journey the time difference between 60mph and 70mph is minimal.