On 8 heading out of San Diego, you go from sea level to 4000 feet, down to (IIRC) 3000, and then back up to 4000 before going back down to sea level. Once over the Arizona border, you pretty quickly go from sea level up to about 2000 feet.
40 goes through Flagstaff, the elevation of which is almost 7000 feet. Albuquerque is at 5000 feet.
So, where in the world do you find HSR that transits not one, but three or four 4000 foot passes?