just to add a little more information and background: Even in the 80's, CSX used 90 pound air for road freight and 80 pound for yard jobs. Just personal opinion and experience, but brake pipe gradient is probably not as much issue as in times past. It still is a consideration, but freight car control valves have gotten better, train lines are better, and train line leakage (overall) is better. I get a lot of trains where rear car pressure is within 2-3 pounds of the locomotive pressure. I don't remember exactly when, but they went to 90 pound for all freight sometime in the early 90's .