The triplets do definitely make sense, assuming that two of them were the equivalent of 5 “normal” cars.

It also looked to me as if there were no real gangway through the articulation joint, but then, we have to take into account the year these units were built (roughly around 1930).

On the other hand, they seemed to be a little bit wider than the standard stock.

BTW, what I actually wanted to add to my previous comment, but forgot to, is that the famous North Shore Electroliners were articulated trains as well (or am I now totally off?).

“Articulated” means that there is an actual articulation joint between the carbodies. In most cases, that articultion joint is supported by a truck (but there are designs where the articulation joiint is free in the air, but a truck just nearby. Such trains are one single unit, consisting of a given number of carbodies, and cabs at their ends. The individual carbodies can not be removed under operational conditions, but only in the workshop, requiring considerable time. The examples in Paris mentioned in the discussion are articulated trains.

“Married pairs” means that an unit consists of two (or more) carbodies with their own two trucks. In very many cases, a married pair must be considered as one single unit, because one car contains electrical equipment, whereas the other car contains pneumatic equipment, which is shared by both cars. Such units can be separated only in the workshop, but one car can only be replaced by another of the same kind.

“indidvidual cars” are indeed individual cars which can be combined in specific ways. They may be configured as end cars (motorized or not) or intermediate cars (motorized or not). Depending on their configuration, sets consisting of individual cars can be separated under operational conditions.

In any cases, in order to change the total train length, only fully self-operational units (with that, I mean units which can operate on their own) can be combined (well, for commuter use anyway; adding “modules” consisting of a cab car and a number of intermediate cars to a push-pull trainset does not really make sense, because in peak times more traction units are needed anyway).

That said, combining individual cars gives most operational flexibility. However, because such individual units must be self-containing, they are rather heavy, and contain a lot of overhead. An extreme example of this approach would be the US RDCs, which could/can be combined to quite a number of cars. The typical vehicle length is 25 m in this case, and it would allow train lengths in multiples of 25 m

Married pairs are normally 50 m long, and trains can therefore be multiples of 50 m long. In some cases, a married pair could also consist of three cars, bringing the unit’s length to 75 m.

Articulated units can be of any length between 50 m and 125 m (or even 200 m). This does indeed reduce the flexibility with train lengths.

Now, why are articulated units nevertheless appealing? They offer more space for passengers (in the articulation joints). They also offer more space, because shorter carbodies mean that they can be wider and stil match the loading gauge. In addition to that, an articulated unit is much more stable in the case of derailments than individual cars and married pairs. That means that it needs much more to overturn an articulated unit than individual cars, and jackniving is way less likely.In the case a single truck derailing (as it would happen when an axle or wheelset breaks), an articulated unit would stay much better within the loading gauge than individual cars. As we are talking about subways here, which are most likely in tunnels or on viaducts, this can be crucial.

An articulated unit will also cost less, because for the same length of train, one truck can be spared. A three-unit married pair, being 75 m long has 6 trucks; an articulated unit, 75 m long consisting of four carbodies has 5 trucks.

The argument about shortening and lengthening a train during the day is valid. However, any such action requires extra staff and most likely extra storage tracks. Also, as capital cost and depreciation are a big part of the operation cost, the savings of not moving a car over keeping it in the consist are minimal, if alone existant.

Articulated units could indeed be a better choice, particularly when stops are in curves or there are tight curves throughout the network. For DC, the argument may sound silly, but it has some reasons. For New York, one could say that it was a missed opportunity.

Now, Chicago’s platform lengths are all multiples of two cars, so they could have *some* articulation — but there’s a second problem. Chicago has some *intensely* sharp turns on the Loop and a few other places. I question whether any of the standard articulated trains can make those turns.

The articulated *trams* sold in Europe, with much shorter sections between articulations, could make the turns, but the multiple unit subway stock I’ve seen seems unlikely to manage them. So it would be a custom order. Maybe when they’ve standardized the platform lengths (in, oh, 2050) they’ll do it.

New York City has less of an excuse, but their response was quite reasonable.

Washington Metro is currently piecing together trains with bits and pieces of previous orders, and would have to have a second incompatible type of trainset if they ordered artics. That’s not a bad idea, but the response amounts to NYC’s: “When we can afford to design a whole new type of car, we’ll consider it.”

Generally, I believe NYCT has found this to be operationally beneficial – that the benefits outweigh the fact that one problem takes the whole unit out of service (a significant change from NYCT experience in the 1980s, when they purposely bought single cars in order to have maximum flexibility). Significant increases in off-peak ridership have also warranted full-length trains at virtually all times too.

There is no doubt to me that there would be significant benefits to articulation in terms of passenger circulation and safety. Unlike many newer systems across the world, however, the NYC subway has many and relatively sharp curves, which are responsible for generating at least some opposition to articulation (at least in perception – I don’t know what the actual truth is).

BART was, to the best of my knowledge, the last U.S. rapid rail system to go with “individual” cars, rather than married pairs. It is, of course, largely because of BART’s experience that the later heavy rail systems went with married pairs.

Similarly, BART was the last U.S. heavy rail system with two, rather than three, doors, in a now-standard 70/75-foot heavy rail car; again, the rest of the industry learned from BART’s experience.