for a quick response my father is a mechanic and i too have worked on cars, and have an auto mustang. Nowadays there is no differentiation between overdrive and drive the D is overdrive and is never encircled in the O as it is arbitrarty, there is simply no need for drive, and if i am wrong about this let me know but as i am aware my stang only has a 2 and 3 there is no 1.

 

My Civic has all four gears on the shifter... I rarely use 2nd or 1st (2nd in the snow). I do a fairly decent amount of shifting between 3rd & 4th however. Over 40 my engine revs fairly high in 3rd so I push it to 4th (essentially OD in a Civic). City driving I run in 3rd.

Going down from 4th to 3rd helps breaking a lot when stopping from a high speed.