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I think the important thing is coasting to a stop, stop being the crucial factor.
If you have to stop then coasting in gear is better if you can slow down at the proper rate of deceleration to stop in time.
That assumes you have placed yourself in a position to have to stop in the first place, at a rate of deceleration that would require engine braking.
My Altima gets 60 MPG (indicated) coasting at 16 MPH with the engine warm (idling) and no accessories running.
It IS more efficient to use DFCO if you have to stop completely. It is much more efficient to anticipate the traffic signal and coast for several tenths of a mile waiting for the light to change so you do not have to stop completely.
While DFCO gets me infinite mileage, coasting at 64 MPH with the engine running gets me 240 MPG during the coast, and that would last a whole lot longer in neutral than in gear using DFCO.
20 miles down the Interstate today from a dead cold engine got me 41.3 MPG indicated, which is actually about 39, in a car with a rating of 31. I can coast down the downslopes of the overpasses and lose only 5 MPH. Those overpasses are about the steepest grades around here unless you head west into the Piedmont region of eastern Virginia. That is in heavy traffic with a PSL of 65 MPH.
It does require significant forward distance anticipation to use coasting instead of engine engaged DFCO, but both are tools that can make a big difference in mileage.
regards
Mech
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