I refer to your article in DN2 of 6 March, 2013 titled “Driving on Neutral, it makes no sense”.
Please clarify if driving downhill on Drive (D), with revs reading 3000RPM does not consume fuel with my foot off the accelerator. My vehicle is a Nissan X-Trail, 2000cc. Also note that on Neutral (N), the car gains much more speed than on D due to engine driveshaft resistance. On N, the revs while going downhill are 1000RPM.
In D, with the throttle closed and the vehicle going downhill, the engine is not under load at all, so the injectors do not deliver any fuel. In N, with the throttle closed, some fuel is being used for idling (it is very little fuel, I will grant you that).
The gaining of speed in N is the same as that of a bicycle with the brakes off: It is caused by a phenomenon that Isaac Newton decided to call the force of gravity. While that speed gain is largely controllable in passenger vehicles by a dab on the foot brakes, it has caused many a sweaty armpit for drivers of heavy commercial vehicles.
Smooth, steady driving is the best kind of driving. Constant changes in speed are the cause of increased fuel consumption and also wear and tear. Try to maintain a constant speed for a more enjoyable drive rather than subjecting yourself to the mercies of physics and nature. One day you might not win.