“Coast-down” is something that carmakers rarely brag about. Not since the 1960s anyway, when Saab (remember Saab?) put a free-wheeling cog in the transmission so the engine could idle when the car was running downhill, to save gas. But Honda has dusted off a version of this idea. The company says its 2014 Acura MDX can glide for more than a mile and a half before coming to a stop from 70 mph.