Boston & Maine F2 units were also Drawbar connected. Note that FTB units lacked batteries for starting, they were cabled to use the batteries in the A-units.
Commuters railroads have a tendancy to design or at least spec. out their own locomotives. That’s why they cost twice the standard models. If they think that there is a need they could order new locomotives with double cabs. As of now they use push-pull with cab cars at the non loco end.
I think it’s natural to make a lococmotive forward facing in one direction (single ended). It is more that Europe may have had space problems for turning a locomotive in many locations as space was more premium then in North America. So with smaller trains with single units on short runs and limited space at terminals very commun they opted for double ended units.
In the USA one of the few similar situations was the comuter trains on the CNJ. Also the PRR and NH but they were electric in the dense areas. But duoble ended units are a custom option. Electric locomotives cannot turn as easily as a diesel (string wires around every wye) so they are more often double ended.
Lets talk Horse Power.
With Electric Locomotives, PRR GG1, NH EP5, you start talking at 4,000 hp and go right up to 8,000 hp with modern Electrics, HHP8. Enough power to move a heavy train at speed.
The Road Diesels of the 1940s, both EMD “E” series and ALCO’s DL109 were rated at 2,000 hp per unit (and they both did it by putting two 1,000 hp diesels in each carbody). Running a pair back to back on the road or single units in commuter service worked well. The New Haven used two DL109 diesels back to back for a total of 4,000 hp. Geared for 80mph service, they pulled passenger by day and feight by night.
The first of the order of DL109 deisels arrived on property in December 1941, in time for Pearl Harbor. A total 60 units were ordered making thirty 4,000hp pairs. The first 30 units were appproved by “The War Production Board” and delivered as designed, the second 30 were built with tin covered plywood car bodies to save steel.
Modern freight electric locos were built as single ended RS style (E-33 & E-44). They often ran in multiples. Even some E-60 wide bodies were built single ended for BM&LP. The passenger electrics stuck with boxcabs or their streamline variants, and often ran singly, so remained double ended.
We run 'em bigger here! One engine may be fine on a shortline where trains tend to be short but on the big class one mainline trains we need more than one. I’ve noticed in photos and videos of the last days of steam the train sizes were increasing here to the point where one engine wasn’t sufficient. And if it took more than one gigantic articulated steam engine to power the train it definitely was going to take more than one diesel.
From an operating point regarding diesels if you have three units and one goes down you will probably still have enough power on hand to keep the train moving. If you only have one unit and it dies then your stuck and if it is in single track so is everyone else. This is the main reason the 6000 hp engine wasn’t popular. Two could pull an 8000 ton train the same as three 4000 hp engines but if one of the 6000 hp engines died then you’d probably wouldn’t make it if you had any kinds of grades whereas if one 4000 hp engine died in a three unit consist you still had 8000 hp available to pull the train.
Tim
The preference in the UK for double cab diesels may also have to do with the fact that the vast majority of diesel powered trains,both freight and passenger, operated on that rail system are powered by a single locomotive. In Australia with it’s heavier loading gauges and longer, heavier trains multiple- unit operation is more the norm…