Why are cab units preferred for passenger service?

[steinjr]

You are partially correct that the Cab Units are for appearance in a passenger train and to a lesser degree for Aerodynamics.

I think that it is more of a weight issue.

Cab Units are lighter because they are built with an open lattice or Monocoque frame.

Ah, that makes sense - passenger trains are not quite as hard as freight trains to get moving (train length is determined more by length of station facilities than by moving max tonnage for the engines), but it is strongly desirable that they move at a good clip - so less weight (and different gearing, but that's not related to the cab vs hood issue) is strongly desirable.

Also, there is a lot more room for steam or other head end power [HEP] for heating the passenger train and providing electricity for lights etc...

Also a good point. And Triplex and BR60103 also makes good points about high short hoods on early passenger hood units and car washers.

This is one of the reasons why I love these forums - you learn something new (and interesting) every day.

Smile,
Stein