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The waiting time paradox: why is my bus always late? (2018)

(jakevdp.github.io)
219 points skadamat | 3 comments | 20 Aug 24 13:55 UTC | HN request time: 0.247s | source
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rjmunro ◴[20 Aug 24 17:11 UTC] No.41301868[source]▶
There's another thing that happens with busses that makes it worse.

The further behind the previous bus a bus is, the more people will arrive at the bus stop. The more people there are at the stop, the longer the bus has to spend picking them all up and selling them tickets etc. Therefore the delayed bus will tend to experience more delay. The bus behind them will have less people to pick up, so it will spend a shorter time at stops and tend to catch up with the first bus, so the two busses are dragged towards each other.

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mitthrowaway2 ◴[20 Aug 24 18:05 UTC] No.41302390[source]▶
That bus with more riders on board also has a higher probability of needing to stop to let people off at each location as well, slowing it down even further!
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ajuc ◴[20 Aug 24 18:45 UTC] No.41302756[source]▶
This is part of a good route design - most bus stops should be "mandatory" - which means the bus stops there no matter what. Some bus stops are "optional" - driver only stops there if there's somebody waiting or if somebody in the bus presses the "STOP" button near the doors. It's marked on the timetable which bus stop is optional.

It's not worth it to make every stop optional because then the routes become too unpredictable and scheduling is hard. Usually there's like 5-10% of optional bus stops on each route - only in the places where very few people get in/out.

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SoftTalker ◴[20 Aug 24 19:11 UTC] No.41302997[source]▶
You can do a study of the actual number of people who get on/off at each stop and then determine which ones should be optional. And at off-peak hours, almost all the stops are optional at least from what I've seen in Chicago.
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ajuc ◴[20 Aug 24 22:16 UTC] No.41304659[source]▶
> And at off-peak hours, almost all the stops are optional at least from what I've seen in Chicago.

Do you not have schedules at bus stops? If you skip almost all the bus stops you'll be like 10 minute early at the first non-empty bus stop, so you'll have to wait for these 10 minutes there (or you depart early which makes people miss their bus).

Potentially you'll be blocking the bus stop for these 10 minutes for other buses.

Why not split these 10 minutes between the empty bus stops instead?

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dotnet00 ◴[21 Aug 24 00:03 UTC] No.41305370[source]▶
From my experience in NY, where most stops are optional unless someone needs to get on/off, the schedule means very little. If the schedule says the busses come at 15 minute intervals, all you can assume is that the bus might hopefully come sometime within the next 15 minutes. There tend to be stops roughly every block, so having all stops be mandatory would make walking competitive with taking the bus.
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1. ajuc ◴[21 Aug 24 09:57 UTC] No.41308581[source]▶
I often walk from the place I live at one end of the city here in Lublin to the artificial lake at the other end of the city and I drive a bus back. It goes through the city center.

It's 12 km on foot one way and probably like 20 km in the bus the other way (it can't drive on the pedestrian/bike path along the river). I walk these 12 km in 2 hours and the bus takes 40 minutes to take me back. There's 25 bus stops on the route I take (and a few more later). There's 2 optional bus stops but they are past the point where I get off the bus.

So that's 1.5 minutes between bus stops (including the stops themselves which take around 5-15 seconds usually).

What's wrong with walking being competetive with buses BTW? The point is that it's better than driving in a car.

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2. dotnet00 ◴[21 Aug 24 12:33 UTC] No.41309641[source]▶
NYC is a big, dense city, it already takes forever to get around via public transport. If busses were about as fast as walking, people would just use cars.

There's nothing all that bad about driving a car, so public trasport has to be at least better than walking to be better than driving.

For example, looking at some of the commutes my family does (I work fully remotely), one has to spend 45 minutes to travel ~12km via subway, which would be 20 minutes via car, or 2 hours if walking. Another has to spend 2 hours to travel ~50km via subway and bus (all still within the city) or 30 minutes via car, with the equivalent walk apparently taking 7 hours.

So, in the first case, that's an extra hour and a half they're losing per day to just transport, and in the second case that's 3 hours per day being lost to transport. Now add in time spent taking kids places, and basically you end up spending most of your life outside of work just getting around instead of actually doing stuff.

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3. ajuc ◴[21 Aug 24 13:53 UTC] No.41310323[source]▶
But you have to search for a parking space and walk from the parking space to the actual destination anyway. Which is like another 10 minutes on top of everything. So buses win over cars in the city center (as long as you can plan to the exact minute so you don't waste time waiting at the bus stops).