On GM I40 is 90 miles less, and a hour or two faster, than I80. But with 20+/- hours of driving time, 1 hr isn't much. Distances are accurate, times are fuzzier, quality of the drive even more so.
I can force it to give me something short - using CA120 across the sierras, US6 across Nevada, US50 across Colorado, but that, of course, is impossible while 120 is closed by snow.