I was wondering if anyone can shed some light on this. Considering that with a diesel locomotive hood unit, you've got 4 walkways-2 on either side of the cab on the short hood side, and 2 on either side of the cab on the long hood side.

Does anyone know the background as to why design was standardized with only 2 doors (fireman's side facing the short hood; and engineer's side, facing the long hood)?

TIA!

For a dual-control unit, both doors are on the fireman's side facing the direction of movement. (that's the same location you described)

This is to keep a solid wall in front of the engineer which will keep the rain/snow and cold wind from blowing around the door into the cab and onto the control stand (and engineer). It will blow into the fireman's side but you need a door somewhere and the engineer has to stay at the controls.

Also, no one has any reason to walk through the engineer's work space.

Phil Mulligan

Thanks, Phil!

Considering that there maybe weren't so many dual-control units out there, I would think three doors (2 on fireman's side) might have made more sense. As to a second door on the engineer's side, fair enough (even though steam locomotives often had doors in front of the engineer).

How often does someone need to walk out of the cab and have direct access to that side of the hood?

Not very often.

So one door suffices for economy and reliability.

Beyond simply requiring more construction time an additional door means increased complexity with air operated wipers, additional seals that can go bad, and of course, an additional source of drafts. That's not really worth it if there's no need to quickly access the hood there.

CN's units with the original safety/comfort cab (SD40-2W, GP38-2W, etc) have a rear door on the fireman's side. It doesn't get used very often, and later units like Dash-9's and SD70s do not have a door there. Newer units built in the last couple years have a 'escape hatch' there instead of a solid window, but this is not intended for regular use and I don't think it's hinged (I've yet to open one).

Unlike an F-unit, our EMD and GE freight cowls only have a rear passage into the engine room on the engineer's side, but there is a gap between the generator and electrical cabinet so you can walk around the engine once you're in there, not that an operating crew would ever need to, the start station, water sight glass and handbrake are all on the right/engineer's side of the unit.

CN did not buy air conditioning on new locomotives until the last order of Dash-9s in the mid-2000s, and opening the second rear door did provide a bit more airflow when trundling around yards or slow branchlines on a hot summer day.