Over at Portland Transport, EngineerScotty (also author of the Dead Horse Times) posted on improving transit speed downtown, particularly for MAX. It’s an interesting post and a lot of different ideas have come up in the comments. I was going to respond there but it got long, so I’m taking it here and breaking up my thoughts on the different suggestions that have been made.
The first of these…
One of the constraints of MAX brought up in the post is train length – Portland city blocks are about 200 feet, and a two-car consist is about 184 feet (191 feet if it’s a Type 4). All lines run through downtown, so the system is designed around that 200′ maximum length for trains. Early on in the thread, one commenter asked why we couldn’t run a train that’s twice as long (a four-car consist rather than the two-car consists run now) – even if it blocked a street while it serviced a stop, it wouldn’t be there long and this would double the capacity of service.
The exception, not the rule
Mechanically speaking and not taking anything like platforms into consideration, the cars are capable of being coupled together in consists longer than a two-car train. I haven’t really posted about how cars are coupled aside from answering questions in comments, but the trains are coupled in two ways: a mechanical couple and an electrical couple. The mechanical couple is what physically holds the cars together; the electrical couple is what lets the cars talk to each other. For example, this allows the operator to hit the door open button and have all the doors in the train open, not just the doors in the car that the operator is sitting in (this is called “trainlined” and yes, that’s where the safety communication gets its name). That works if there are two cars coupled together, or three, or four. I don’t remember if more than four cars can be electronically trainlined. This does not work for Type 4s. The coupler head located under the cabs of those is there to be used for a dead car tow or push and is capable of being mechanically coupled to any car in the fleet, but there will be no electrical communication between them.
Screen shot of Bob R’s video of the A-cab coupler head
So aside from the 4s, more than two cars could be coupled together and still function. However, there are a number of reasons why it would take so much money in construction costs to run 3-car or 4-car consists to the point where it’s just not worth it.
For one, the previously-mentioned trainline opens all the doors of the train. Assuming you have a four car consist downtown, if the operator stops to service a platform (we’ll use Pioneer Square North as an example), the rear two cars are going to be blocking SW 6th and going back up the block between 5th and 6th. When that operator opens the doors, all of the doors in the train are going to open, and remember that even on the low-floor cars, there’s a drop to the ground below when not at a platform:
Climbing into a Type 2 from the ground
So that would be opening the train doors onto the street, and even for people not using mobility devices, that’s not a comfortable way to get on or off the train. And to lengthen all of the platforms in the system to accommodate longer trains would be prohibitively expensive (just the Washington Park stop alone would be a logistical and financial nightmare)
There’s also the matter of what to do when the train gets to the end of the line.
Here at Jackson St, which is currently the end of the line for Yellow and Green trains, the first and third tracks are big enough to accommodate a two-car train, but nothing larger. The circuits in the turnaround are only big enough for one two-car train. I took this picture from the leading car looking back toward the trailing car, and the last wheel axle of the trailing car is just past the insulated joint on the eastern entrance to the turnaround. And the center track can only accommodate a single car train, such as the mall shuttle. In short (pun not really intended), there’s no room for a train longer than two cars here.
So that means no four-car consists on the Yellow-Greens, which is good because that would make things much more difficult for buses driving on the transit mall. What about on the Blue line? Cleveland has a tail track, so there actually is room at the east end of the line in Gresham. Heading out to the west side though, there’s a lack of space. Here’s a view of the platforms at Hatfield Gov Center, the western terminus of the Blue line:
As Hatfield is now, there’s no room for a train longer than two cars – to lengthen the platforms would mean shutting down Main Street which runs behind the building there.
It’s not just a lack of space and platforms big enough to accommodate them that that make it impractical to run longer consists.
Paradoxically, longer trains would actually mean slower running speeds in many sections of the alignments. At Goose Hollow (above), for example, the speed limit around that curve for eastbound trains is 10mph, and a train can’t accelerate until the entire consist is clear of the curve. You get thrown around quite a bit if you’re near the back of a trailing car going around a curve and the operator accelerates before you’re out of the curve. If the trains were twice as long as they are now, that’s waiting until another 200′ of train has gotten through a curve before the train can accelerate.
In other places, gravity would work against longer trains. For example, heading into the tunnel westbound, the speed limit is 55mph past the first cross passage. As things are now, if your train is a two car consist with a crush load of people, it’s hard to get to 55mph since you’re climbing a hill with all that weight. If you’ve got twice as many cars and people, it’ll run even slower. Longer trains might mean more capacity, but ultimately they’d mean slower running speeds.
So it’s an interesting idea to run longer trains, but it would involve so much construction to existing platforms, major modifications to city blocks in the CBD, to say nothing of the work involved in changing the circuits in the rails to accommodate longer trains that it’s not feasible to do.
More to come.