They all have 7-speed dual clutch transmissions and are comparatively fuel efficient, but there is an important difference between VAG’s DSG/S-tronic and the Mercedes-Benz system. VAG insists on an interlock forcing you to press the brake pedal before you can move the lever from N to D and this is not only irritating, it causes another problem. The brake light switch sends a signal to the ECU that the brakes are applied and as a result the ECU cuts power. The problem is that this signal can be delayed, so you can emerge from a side road on the fuel in the combustion chamber, then, halfway across the road, power is cut and you can be stranded for a second or two before the system self corrects. With the Mercedes system the lever can be moved from N to D without pressing the brake pedal. Ford and Volvo fit Getrag Powershift Dual Clutch transmissions and, again these have no interlock between N and D.