There was a diesel-powered express passenger line [0] that ran at an average 69 mph between Chicago and Denver... back in 1936. The Florida one in the OP also a

There was a diesel-powered express passenger line [0] that ran at an average 69 mph between Chicago and Denver... back in 1936. The Florida one in the OP also averages 69 mph [1]. [0] https://en.wikipedia.org/wiki/Denver_Zephyr https://en.wikipedia.org/wiki/Denver_Zephyr [1] https://en.wikipedia.org/wiki/Brightline https://en.wikipedia.org/wiki/Brightline - "The first Zephyr service to Denver began May 31, 1936, with the trainsets of the Pioneer Zephyr and the Mark Twain Zephyr, trains 9900 and 9903. This new service was known as the Advance Denver Zephyr and operated on a 16-hour schedule." (1,109 miles / 16 hours = 69 mph (112 kph))