Why so few hood units for passenger trains?

Trains magazine has an interesting piece on cowl units: locomotives that have a shell that fully encloses them, including walkways. Freight locomotives, conversely, usually are hood units; the walkways on the sides aren't enclosed, and it's easier to access their "innards" from the outside. Apparently freight locomotives usually aren't cowl locomotives because they are more expensive to maintain and are necessary really only in colder climates.

So...why are almost all passenger locomotives cowl locomotives? Metro-North has a few Brookvilles that aren't cowl locomotives, but almost all others are. If they cost more to maintain and aren't necessary except in really cold areas, why spend the money on them? Do they just look better? Or are they more aerodynamic, which would help higher-speed passenger trains? Or is there another reason?

Thanks.

Several possibilities:

1 - Weight - The monocoque-bodied P42AC scales around 275,000 lb, primarily because it does not have a heavy underframe. The approximate horsepower equivalent ES44AC hood unit runs about 430,000 lb. Since high speed passenger trains typically do not require the additional weight for adhesion, a cowl unit provides faster acceleration and better fuel economy than a hood unit with a similar horsepower rating.

2 - Aerodynamics - At typical passenger train speeds a cowl unit will have slightly reduced aero drag, thus improved fuel economy.

3 - Aesthetics - To most of the traveling public a streamlined cowl unit simply "looks better" than a road switcher leading a passenger train.

Just my guesses however.

...FB

All good reasons. Question: how important is each one relative to the others?
--Appearance. In my heart of hearts I suspect this has driven a lot of design since the 1960s. Santa Fe ordered the first "cowl" units (U30CG, FP45), and I think fundamentally this was because the Santa Fe's leadership didn't think "road switcher" carbodies were in keeping with the image they wanted their prestigious passenger trains to project.
--Aerodynamics. My guess is that this is a minor consideration. Yes, a streamlined locomotive will slightly reduce the aerodynamic drag, but… Most American passenger trains aren't really very fast. And my guess (note that word "guess" again-- I don't claim to be an expert, would love it if a real expert corrected me where I'm wrong!) is that streamlining the locomotive doesn't do much to improve the TRAIN's aerodynamics: full-width diaphragms between cars, some sort of shrouding of all the under frame machinery, would both be needed if you were seriously worried about aerodynamic drag. (For that matter: a round-end observation car would probably help with train aerodynamics: the rear end of an ordinary coach looks about as bad as it could possibly be, from that point of view!)
--Weight. This OUGHT to be important, but recent passenger locomotives (any recent commuter power) are, by the standards of the (1935-1960) streamliner era VERY heavy: heavier than most first generation 4-axle FREIGHT diesels-- suggesting to me that the people who order passenger locomotives in North America don't think very much about weight. A true monocoque design (e.g. Genesis) is lighter than a corresponding roadswitcher, but cowl units (including the FP40 and its many derivatives) isn't: structurally a cowl unit is just a hood unit with a ten-foot-wide hood, and so no lighter than a conventional hood unit.

I agree with all of the reasons given. I think there is one more.

A carbody or full-cowl body is easy to keep clean using automatic washers.

The problem with washing a hood unit is the fact that the hood sides are set in from the edge of the frame by the width of the walkways on either side.
This makes them difficult to keep clean using rotating brushes. Combined with the handrails, this keeps the brushes from directly contacting the hood.
So this type loco would need to be washed by hand, using high-pressure spray equipment.

Since the carbody units have the same, or close to the same, width and height as the passenger cars themselves, the whole train can be pulled through a brush-type car washer and clean locos and cars together.

Les

I think the weight issue is the most important. MBTA and NJT both used GP40 platforms, extended for hep. Some systems have height restrictions, where a road switcher might be too tall. This is where a special body would be needed. The dual modes are in vogue too. MN, LIRR, NJT, and AMT. All require a specialized design.

One has to wonder why some bought F59s. A GP59 adaptation could have been cheaper. These commuter carriers are all on the public funds makes price no problem.

Keep in mind that during the period when passenger service hood units were being bought, most of the purchasing railroads wanted locomotives that could be readily converted to freight service once passenger operations were eliminated. This is what happened to most of them when Amtrak took over post -1971.

Hood units have also been a popular choice for commuter railroads that needed to rapidly expand the size of their locomotive fleets but couldn't afford brand-new purpose-built commuter locomotives... so they chose to have old freight locomotives (primarily GP40s) rebuilt as passenger locomotives. For example:

CDOT GP40-2H (GP40 rebuild)

MARC GP40WH-2 (GP40 rebuild)

MARC GP39H-2 (GP40 rebuild)

MBTA GP40MC (GP40-2W rebuild)

SunRail MP32PH-Q (GP40WH-2 rebuild)

Tri-Rail GP49H-3 (GP49 rebuild)


Despite the fact that F40PH was apparently designed in such a way as to be "easily" converted into a freight locomotive in the event of the "inevitable" decline of passenger service, it would appear that the reverse scenario -- freight GPs converted into passenger GPs -- has been MUCH more prevalent.

To add to the previous list, I might also point out that Alaska Railroad uses a variety of hood units on passenger trains. SD70MAC's are the most prevalent, but there are also several variations of the GP40 too. In fact, the only cowl units on ARR passenger trains are former F40PH's, now known as CCU's, for Cab Control Units. They provide a cab and HEP on push pull trains.

Remember that the conversion from the F-3 to the F-7 and GP-7 was a sea change in locomotive purchasing.

The railroads liked hoods, and quickly stopped buying them for passenger service. They were easier for maintenance, and I suspect unit for unit, cost less.

John_Perkowski wrote:Remember that the conversion from the F-3 to the F-7 and GP-7 was a sea change in locomotive purchasing.

The railroads liked hoods, and quickly stopped buying them for passenger service. They were easier for maintenance, and I suspect unit for unit, cost less.

And those railroads also had little to no reason to buy passenger-equipped locomotives at all. After all, passenger service dwindled faster than the fleet of 1940s and 1950s passenger cab units did. For the few private operators that invested in new passenger equipment before Amtrak and the state agencies took over operations, both GE and EMD rostered and sold passenger hood units (the U28CG, the GP40 variants, and the various SDPs) in the late 1960s.