Don't forget that electrified high-speed passenger trains
can handle grades much better than heavy diesel-powered
freight trains. Germany's high-speed line along the Rhine
River between Framkfurt/M. and Cologne has grades exceeding
4 per cernt. The line also has lots of tunnels.

(Due to the grades, there are special operating rules that
apply only to that line, such as procedures for coupling
up to a disabled train stopped on one of these grades.)

Modern tunnel boring machines make tunnel construction much
more feasible than a century ago.

-- Ernest