Metro's buffet line effect: Proceed directly to dessert for best results
When a Metro car breaks down or becomes otherwise delayed on the Metrorail system, it creates a logjam of trains behind it. Even after the incident clears, it can take over an hour to return service to normal. Metro could speed up this process with strategic use of express trains.
With only two tracks on each line, it is difficult or impossible to reroute the trains that are behind an incident, and trains can't pass each other. Once the issue is resolved, the trains continue to follow each other one by one. But the first train is the slowest, already crowded with a crush load of passengers before arriving at one overcrowded platform after another. At these stations, people take longer to board and deboard. Each stop becomes a two-minute drill for just 20 or 30 people to squeeze on and off the train. In many cases the vast majority of people on the platform can't even get on and have to wait one or two or three trains to finally board. It can take a couple of hours for all the trains to move through the system and return service to normal.
This resembles a restaurant buffet line, which always moves not at the speed of the average diner, but at the speed of the slowest diner. Everyone backs up behind the one person who is carefully scrutinizing each and every offering. Relief finally comes when they move off to the dessert table and the whole line speeds up.
The simple and easy solution to the Buffet Line Effect is to express the trains after a delay. There are miles of empty track in front of the first train. If the trains that are backed up express forward to fill in the empty space, then normal service can return within minutes rather than hours.
This will, of course, inconvenience some passengers whose stations the train will skip. They either have to deboard and wait for a later train, or backtrack to their station. However, I believe that the overall savings for passengers will be much, much larger than the inconveniences. Given the capacity stresses Metro is experiencing on a regular basis, simple, no-cost solutions like these need to be part of their short-term strategy.
Assume a breakdown at Gallery Place on the Red Line to Shady Grove. A mechanical breakdown causes a 20-minute delay and a train is taken out of service. There are now 5-6 trains backed up behind, probably out past Union Station. The track is empty from Gallery Place to beyond Friendship Heights, and the platforms are filled to overflowing in the downtown area.
First train: Skips Metro Center and stops at Farragut North (which has a center platform). The dispatcher has been alert and makes sure a train going the other way arrives immediately or is waiting for this train. Riders for Metro Center can choose to wait at Gallery Place or backtrack from Farragut North. The train then expresses to Bethesda. The train operator will have to clearly and constantly communicate to his/her passengers throughout this whole process, allowing everyone to make decisions about how they are going to deal with it. A train immediately arrives or is waiting at the platform in Bethesda for passengers to backtrack.
Second train: Services Metro Center (at the same time the first train is servicing Farragut North) and then expresses to Van Ness (with a center platform). Similarly, the dispatcher makes sure there is a reverse train ready to take passengers back.
Third train: Services Judiciary Square (while the first two are servicing MC and FN). Skips Gallery Place and Metro Center and services Farragut North like the first train. The dispatcher makes an informed decision about skipping another stop to create breathing room behind or allowing the train to proceed as usual. If this train is going to create its own "buffet line effect," then it should express ahead to allow the faster trains behind to proceed normally.
Fourth train: Services Gallery Place and Metro Center and proceeds normally from there, possibly skipping Farragut North if the third train skipped Dupont and created space (and also to get the riders at Dupont, who have now watched three trains go by).
How about those riders at Dupont who watched three trains go by? In the universe we inhabit now, most of them would have had to wait for two or three jammed trains just to board. And those trains would have been progressing at "buffet line effect" speed. In the end, they probably reach their destination just as fast. The overall system is returned to close to normal service within fifteen minutes, with trains more evenly spaced along the tracks rather than bunched together behind a dysfunctional, overcrowded train. It helps to imagine looking down on the system from above. It makes absolutely no sense to have 8 miles of empty track followed by a "buffet line" bunch of six trains clunking along at half speed.
Obviously, the exact best way to deal with any delay will vary every time, based on how long the delay is, time of day and other variables. This is why it requires intelligent dispatching and on-the-spot decision making to maximize the value.
The other requirement is courage. If Metro were to put this into effect, they need to do so consistently for a solid six months or longer, to allow riders to get used to it and to realize that they are actually getting better service than the current dysfunctional way of dealing with delays. They have to have the courage to stand up for the vast multitudes who save five or seven minutes against the vocal few who might lose fifteen or twenty on a single occasion and then complain. I don't know if Metro has the courage to do that.
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