Trains often averaged 40-50 mph over long distances, figuring slow-downs and stops. Of course, autos had to slow down as well and were lucky to average 40. The Interstates sped up the cars, and given the width and placement of rail right-of-ways, elevated bypasses could have been placed in key areas. Why should North Dakota pay for overpasses in Detroit? The same reason we all pay for ports and Interstates, especially in key manufacturing areas like Detroit (in the fifties). From what I saw on passenger rail schedules, they were healthy in 1950 and didn't not look at scaling back until after 1955-58 when cars and planes factored in. Also, labor unions kept up staffing that could have been reduced after diesel conversion, making the profit difference for freight more substantial.