Think they want to know whether to keep the tranny in Drive when idling at a stoplight, or if they should switch it to Neutral.

I've always been taught that an auto tranny was *meant* to idle in Drive, and doing so doesn't cause much wear. The process that incurs wear is the actual changing of gears within the transmission.

With that thinking, moving it into Neutral at each stoplight would cause significantly more wear and tear (two unnecessary gear shifts each time).