The R40 cars are unique in appearance on the New York Subway system. They feature slanted fronts on all the cars. Since the cars are in 'married pairs,' two slanting ends face each other at every other car end. The slanted ends make for excellent riding between cars, and for great views out of full length front windows, but they reduce passenger space, as the MTA discovered shortly after introducing them in the late 60s. A second order in the R40 series, the R40Ms, did not have the slanted ends.

The R40s were the second to last order of 65 foot cars on the system. At this points they are rather old and clunky, and in failing shape. They will be among the first to go when the R143s arrive.