Former Seattle (now Las Vegas) resident here. To make the buses run on time, the planners build in "time stops." These are locations where the bus should go through at specific times to not be too early for the rest of the schedule, and they also provide some buffer for buses to recover time lost due to bike loading, disabled passengers, and traffic congestion. If you're getting the bus after a time stop, you'll likely almost always get it on time. If your stop is before the time stop, bus arrival times will vary wildly.
It gets even more interesting when you add transport of the bus: the Seattle (King County) Metro also serves Vashon Island, so some of the buses travel on ferries with their associated delays and peculiarities.
Bus routes are a circuit, so they are more heavily impacted by traffic than other modes of transportation. Thus, heavy traffic regularly makes Seattle's commuter buses 10-20 minutes late. The bus from Mountlake Terrace can sometimes be over an hour late, and rush hour makes this a 2-hour ride on top of the wait.
With a car, you can hop off the freeway and take a side street and you're there in 30-40 minutes instead of 2+ hours.
If you want to discuss borderline-criminal mismanagement, there's the $50 billion ST3 plan. We could put one WA State resident on the moon for that price.
Where I live, buses have a few points where they 'synchronize'. That means they wait there long enough to be exactly on schedule.
This to prevent people missing a bus that goes every hour because it was 5 minutes early.
I get on a bus right before a time stop. It's only about 30 blocks after the previous time stop (Northgate TC) but has arrived as soon as 5 minutes before the posted time. That's always fun when combined with a 10 minute late bus following it.
It always stings to see the bus approach early such that I have to run for it, only to then have it wait for 5 minutes at the time stop 2 stops later.
That's good, because it means that your transit agency(ies) respect timing points.
It's difficult to always know when the bus will pass a certain place, even with Bus Rapid Transit systems that have dedicated lanes. Timing points are points on the schedule where the bus is guaranteed to leave on time or late at that point.
So I presume that in your case, if the bus is late, it doesn't wait, but if it's early it waits.
This is not true in my experience, Seattle has a pretty solid bus system and we still felt like we were having to plan around them even though they generally would stop every 15 minutes. You could not count on them 100% either. Occasionally they just don't show up.
Hah great analysis. One factor with bus' is the schedule is likely planned to minimize early arrivals at the risk of being late more often. Usually when a bus is early it has to sit and wait until its departure time. A late running bus can be more efficient, and if kept until departure time might not ever get a chance to average down the bursts of lateness.
Seattle has bus priority at multiple intersections and it does not cause problems.
At those intersections busses arrive at the curb lane to pickup/dropoff. Then a special light tells the bus driver that it is ok to proceed into the intersection, while all other cars have a red signal. The bus pulls out and leapfrogs traffic.
It's got nothing to do with traffic delays. There are plenty of buses at each leg in my route. My specific problem is that I have to ride for 20 minutes in the opposite direction to get to a transit station where I then transfer to an express bus out to UW Bothell. But the bus from UW to my office isn't synchronized with the express bus so I either wait 15 minutes or walk a mile and a half across I-405.
On the other hand it's very efficient for getting in to the city, as I can hop on a single bus and be in Green Lake or the U district in about 15 minutes, and it's another 10 to cross the canal.
It strikes me that even with a perfectly regular starting schedule, buses might clump together in time because the schedule is probably dynamically unstable. To explain, picking up passengers from a stop costs time and a long time between buses implies a high probability that passengers will be waiting at a given stop. This further adding to the delay and shortens the time to the next bus in the schedule.
I'm sure drivers try to actively manage this, but if they didn't I suspect the system would naturally evolve toward pairs of buses leapfrogging each other on long routes.
When I did a couple bus commutes while living in OC, I remember the bus actually stopping on the side of the road for a while because it had got ahead of schedule. Probably a good thing given the infrequency of buses for the buses to stick religiously to the schedule (as opposed to suburban Chicago where I live now where it's actually impossible for the buses to meet the posted schedules even if they travel at the speed limit without stopping).
Ah yeah, I've done bus boarding before (although not the Dulles thing), wasn't considering that. Still seems like you could time that boarding of the earlier vehicle to just start earlier.
In smaller cities, buses are frequently on demand service, rather than planned routes (In Michigan, there are many county transit authorities, _ATAs, that do this). It's because they don't have the ridership to support planned routes.
There must be some tension between point to point service and having each passenger walk a few minutes, where the walking ends up saving time, even if it doesn't seem like it.
If nobody signals to get off, buses sometimes will skip if they're bunched. I've seen it in at least three cities before. I have no idea if it's policy or if the drivers on those routes juts took matters into their own hands.
I see bunched buses on the stop right outside my work basically every day. Sometimes four from one route and another three from another parallel route all within a ~5 minute span.
It gets even more interesting when you add transport of the bus: the Seattle (King County) Metro also serves Vashon Island, so some of the buses travel on ferries with their associated delays and peculiarities.
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