Assuming that the nominal coefficient of friction may be the same for either rail profile, the greater contact surface for a T-rail (I profile) permits one to take greater advantage of microscopic surface roughness (i.e., tribology), which is the source of the frictional force. Differences in the rail materials could also be a factor, however. And, the dynamic coefficient of friction is always markedly lower than static coefficient for two given contact surfaces.
Generally, I have always preferred traditional tubular rail, however, for its vintage prewar tinplate aesthetics.
T-top rail was used by Gilbert AF as a postwar selling point for their 2-rail track system over you-know-who's.
Enjoyed the video, Bruce. Have fun.
Bob
