I usually shift into N when stopped. Wanted to look at differences between this technique and leaving it in D. Can't get MPG data, but I did find this plot of the "Engine Load" interesting. It's pretty obvious where I shift from N to D . . . I would expect this to mean more fuel is used to idle in D than N.
2011 335d Sport Package/Cold Weather Package
2004 Ram Cummins with lots-o-mods
1990 YJ Repowered with modified Cummins B3.3T