Surely efficiency is based on choosing any route where you can drive at the most efficient speed for fuel economy, i.e. not too fast (freeways/motorways) and not too slow (inner city traffic). Quickest will often be longer than shortest and most efficient will sit somewhere between the two.
BMW X3 (F25) xDrive20d SE . . titanium silver . . titanium front grille . . 309s . . xline . . xenons . . black leather . . alu trim . . professional multimedia package . . dynamic package . . climate package . . electric seats . . folding mirrors . . servotronic steering . . DAB radio . . business speakers . . sun protection glass . . split rear seats . .