Why are cab units preferred for passenger service?

[michael_balcos]

I'm just curious: why are cab units preferred for passenger service when it comes to diesels? Is it just because of the appearance fits nicely in a passenger train? Aerodynamics? Why not a hood unit?

[steinjr]

I'm just curious: why are cab units preferred for passenger service when it comes to diesels? Is it just because of the appearance fits nicely in a passenger train? Aerodynamics?

Aerodynamics and looks. And not that much need for good visibility towards the rear - passenger trains rarely do much switching along the way.

Why not a hood unit?

Hood units are also used. The most important thing about a passenger train is that the train runs. Passengers get grumpy when the train doesn't run.

If the available engine is a hood unit, then you use a hood unit to pull your passenger cars.

Smile,
Stein

[TinGoat]

Hi Mike,

Let me answer your question with another question...

Why are hood units preferred for freight service when it comes to diesels?

Because of better visability front and rear.

The Cab Units were developed for main line freight. The "F" in F-Unit is for freight. But the bad rear view made switching difficult. Some F-Units were equiped with a rear window, but it didn't help very much.

EMD tried to fix the problem with the BL-2

EMD switched to Hood Units for freight, but continued to build Cab Units for Passenger Service and some long-haul freight service.

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. 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...

However, there are plenty of examples of Hood-Units in Passenger Service. HEP is in the short hood.

Here's a good webpage on Cab-Units Exotic Diesel Locomotives = <!-- m --><a class="postlink" href="http://exotic.railfan.net/">http://exotic.railfan.net/</a><!-- m -->

[Triplex]

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.

Never thought of that.

However, there are plenty of examples of Hood-Units in Passenger Service. HEP is in the short hood.

Many early passenger hoods had the steam generator in the short hood (requiring it to be high), but most later S-G and HEP installations are in the rear of the long hood.

Passenger hood units I can think of offhand:
"torpedo tube" GP9s (SG in nose)
some Trainmasters (SG in nose)
"hammerhead" RS-3s (SG in high short hood; RS-3s were long hood forward by default)
"Tempo" RS-18s (HEP in high nose)
I know a number of other first-generation types came with SGs, but I often don't know which because it didn't change the model number.
GP30Bs (SG in short hood)
some Mexican GP38-2s and GP40-2s (SG in high short hood)
GP40P, GP40P-2 (SG in rear of long hood)
GP40TC (HEP in rear of long hood)
several types of GP40/-2 rebuilds on commuter lines and Alaska RR (HEP in rear of long hood usually)
SDP35, SDP40, SDP45 (SG in rear of long hood)
some Alaska RR SD70MACs (HEP in rear of long hood)
P32-8BWH (HEP in long hood?)
U28CG, U36CG, some Mexican C30-7s (SG behind cab)
U34CH (HEP in long hood?)
Long Island C420s (SG in high nose)
some Mexican C628s (SG behind cab?)

[BR60103]

One point for cab units is that they can go through the same car washer as the passenger cars. The current set of cab units are a development of the hood units with the hood widened all the way out. Compare them to CN's 2100 series with boxy hoods.

[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

[Puddlejumper]

RS-3s only had a high short hood (hammerhead) if they had Dynamic Brakes and Steam Generator. The SG fit in the low short hood if no DB were present.

Dave

[TinGoat]

One more thing comes to mind...

Actually two...

First, many of the later [More modern] Cab Units are actually Cowl Units. They have the same structure as Hood Units with heavy frames, but with full width hoods.

This leads to the second thought...

Crew Movements.

Modern Freight Trains have an Engineer and a Brakeman who generally stay in the Cab while the train is in motion.

Passenger Trains have an Engineer, Brakeman, Fireman and Conductor and more... They need to move freely from one end of the train to the other and with some protection from the elements, under the Cowl while the train is moving...

[Triplex]

RS-3s only had a high short hood (hammerhead) if they had Dynamic Brakes and Steam Generator. The SG fit in the low short hood if no DB were present.

Good point. I'd wondered why the hammerheads existed, since I remember seeing normal RS-3s with steam generator exhausts on the short hood.

I seem to remember that even some RSD-5s had SGs - for passenger trains on lightly laid branches?

[Russ Bellinis]

I think I read somewhere as well that the railroads originally bought units like the MD E's, or Alco Pa's for passenger service because of the esthetics of "streamlining." Later on they discovered that the passenger didn't notice and didn't care what was pulling the train or what it looked like as long as it did the job of getting them from point A to point B on time. As a result in the case of the Santa Fe, they had a huge fleet of F-units they used for passenger service, but in the 1950's they bought a bunch of Gp7's and 9's equipped with steam generators to use in dual service. Later on when they replace the F-units in passenger service, they bought cowl units probably for the reasons of crew safety in moving from the locomotive to the other end of the train.

[Puddlejumper]

RS-3s only had a high short hood (hammerhead) if they had Dynamic Brakes and Steam Generator. The SG fit in the low short hood if no DB were present.

Good point. I'd wondered why the hammerheads existed, since I remember seeing normal RS-3s with steam generator exhausts on the short hood.

I seem to remember that even some RSD-5s had SGs - for passenger trains on lightly laid branches?

Yes, and I believe CNW had some Hammerhead RSD-5s as well.

[jbaakko]

You're all forgetting that Alaska RR has HEP equipped SD70MAC's. Surely a hood unit there...

[Triplex]

See my first post...