Timepoints

Related to the recent post about getting left behind by a train, I wanted to bring up another part of scheduling: the timepoint.

Even though you can get arrival times for each stop, the schedules for bus and rail are not written to match every stop. Instead, a handful of stops on each route are selected as timepoints, and the schedules are written to those specific locations. Timepoints will be the ends of the lines, transit centers, major intersections for buses and interlockings for trains, other heavily serviced transfer points, and a few places in between. If a stop isn’t a timepoint, the “scheduled time” listed for it isn’t a guaranteed arrival time, but instead is an approximation based on how long it should take a bus or train to reach that stop from its last scheduled timepoint.

Visual depiction (borrowed from here) of a bus’s timepoint

On-time performance for a bus or train is determined by its departure time from the timepoints. You may have been on a bus before that pulled over and waited for a minute or two without anyone boarding or exiting the bus. When this happens, many bus drivers will announce to their passengers that they’re running early and so they need to wait briefly before continuing. Buses are more likely to be running early than a train, since an unusually light passenger load or less than the typical amount of traffic can put a bus ahead of schedule, but a train’s schedule is generally more fixed. Still, it’s possible for a train to be slightly early between timepoints, especially outside of normal commute hours. At night, for example, platform dwell time is likely to be low at several platforms if no one boards or exits the train. Also, in areas like the alignment west of Beaverton TC where your leader is a good 15-20 minutes ahead of you, you’ll get all green ABS signals instead of bumping reds on the intermediate signals waiting for your leader to clear that ABS block. These factors can make a train arrive at a timepoint early and be ahead of what is listed as scheduled times for non-timepoint stops.

Each bus and rail operator carries a schedule (called a paddle) for their run. Among other things, the paddle shows the scheduled departure times for each timepoint on that particular run, but it does not show the approximate departure times for non-timepoint stops. Here’s an excerpt from a rail paddle:

Weekday Night Blue Line Paddle

At TriMet, buses are timed to the minute; trains are timed to the half-minute. The + sign on the paddle after the times indicates 30 seconds, so this train has scheduled departure times from Hatfield at 8:40:30pm, Fair Complex at 8:48:30pm, Willow Creek at 8:57:30pm, Elmonica at 9:00:00pm, etc. I chose this paddle in particular as an example because of a recent complaint on Twitter where someone was upset that the 9:05pm eastbound Blue Line from Millikan Way was leaving at 9:02pm*. You’ll notice that Millikan Way is not listed in the paddle, and that’s because it’s not a timepoint. If Beaverton Creek and Millikan Way are quiet – and at that hour, they generally are – a train is not likely to dwell at those platforms for long if no one is boarding or exiting, and so they may run slightly early. They won’t leave Beaverton TC until the time on the paddle, but they may arrive at BTC a minute or so before then and wait there until it’s time to leave.

*This seems unlikely, by the way… There’s no way you can get from Merlo to Millikan in 30 seconds. With short dwell times I could see pulling out of Millikan around 9:04pm, maybe a little before, but not 9:02.

NE 60th Ave – like most stations, it’s not a timepoint, so scheduled departure times are an approximation. They will generally be accurate though.

So as always (and I know it’s not what people want to hear), if you want to be on a particular train, be at the platform ready to board before it gets there, and allow a little extra time if you’re at a stop that isn’t a timepoint. And by “ready to board” I mean have your fare paid and everything – if you wait until the train is approaching the platform before starting to buy a ticket from the ticket vending machine, you’re not going to make it. I’ve never timed exactly how long it takes to buy a ticket (if anyone thinks of it the next time they get one, please let me know how long it took) but I’ve seen plenty of people left behind because they start the process as the train is pulling in.

Also, check out TriMet’s tips about what you can do to help keep buses and trains running on time.

About these ads

3 responses to “Timepoints

  1. I got news for ya MR Max Faqs, trains DO leave time-points early!
    And that should be a deadly sin when approaching the end of the service day, like the last 3 trips!

  2. Nice post. I agree with your solution in the last paragraph and I try to do that. But I do have a question….After reading this I wonder, why not just have the trains spend time at a station like normal and not leave “early” if no one is getting on or off? Wouldn’t that eliminate some complaints? Just wondering…

    • Well, for a couple of reasons. As a whole, the schedules outside of commute hours take lighter passenger loads into consideration, which you can tell just by looking at the scheduled times (trips from end-to-end of the lines during rush hour can be minutes longer than trips in off-peak hours). So the “normal” amount of time to stop at a platform varies throughout the day, and it’s shorter at night, and the schedules overall are a little bit faster then as well.

      Operators do allow time at each platform to make sure there isn’t anyone trying to get off the train (e.g. someone who was sitting on the upper deck of the train and therefore has to walk back to the doors). But if there is clearly no one else boarding or exiting, there’s no reason to arbitrarily hang around (at a non-timepoint stop) since the timing of the schedule assumes lighter loads. So that can make a train leave a platform like Millikan earlier than the time that the TriMet website says a train will be there.

      And there’s not really an “early” if a stop isn’t a timepoint. If that 8:40pm Blue Line out of Hatfield was my train, I can’t tell by looking at the paddle what time the website says I’m supposed to be at Millikan – if it’s 9:04, 9:05, 9:06, etc.. All I can really tell is that if I made sure everyone who wanted to get off the train could and everyone who was on the platforms got on, if I didn’t have any speed trips, and if I didn’t pull into BTC 4-5 minutes hot, I’ll assume that I wasn’t running too early!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s