Comment by cyberax
15 hours ago
> Self-driving cars still take up space on the road
This is a false argument. Think about this: a bus every 10 minutes is effectively 500-900 meters long! It easily "takes" as much space as 100+ cars. In other words, nothing would change from the traffic perspective if instead of 1 bus every 5 minutes, you had 100 individual cars.
The "people in the shape of a bus" argument makes sense only when you're talking about the performance in a very narrow case of transporting people in a steady, uninterrupted stream of buses. Or if you need to size your traffic bottlenecks.
Moreover, a bus route necessarily is unoptimal for at least some people on a bus. They are effectively "thicker" than other people because they take up more "effective space". But wait, there's more! Buses also necessarily move slower due to stops, so the "effective length" of a bus becomes even longer because cars will clear the road faster.
But wait, there's even more! A single bus needs about 3 drivers to be effective. So with the average daily busload of around 15 people, you have almost 20% of the bus taken by the drivers on average. This makes bus trips pretty expensive. Not quite to the level of Uber/Lyft, but surprisingly close.
And these problems are fundamental. That's why urbanists like NJB don't like to talk about that.
Nothing about this addresses NJB's argument that self-driving cars take up more space than regular cars, because there will now be cars with 0 people in them.
Ultimately the thing you want to transport is not cars, it's people. Walking fits the most people in a limited amount of space, then bikes, buses and other forms of public transport, then cars with 4 people in them, then cars with 3 people in them, then cars with 2 people in them, then cars with only 1 person in them, and finally empty cars. More cars will never reduce congestion.
But to address your point: A bus in a dedicated lane takes up more space than a bus that's stuck in car traffic, you are right about that. On the other hand, when congestion is so bad that cars simply don't move, no matter how many lanes they have, getting people out of cars into more efficient forms of transport, will also help cars. And a bus that actually goes, can do that. If you look in cities with good public transport, more people go by public transport than by car. In cities with good bicycle infrastructure, more people go by bike than by car. That means even cars are less likely to get stuck in traffic in those cities. Even if you take away a car lane.
I don't know where you got the idea that a bus needs 3 drivers.
> a bus every 10 minutes is effectively 500-900 meters long!
uhhhhhh what. What does every 10 minutes have to do with this at all
> It easily "takes" as much space as 100+ cars.
are you ok??? have you seen a bus before??
> A single bus needs about 3 drivers to be effective
I have never ever seen a bus with 3 drivers in it. If you're talking about 3 drivers over the course of 24h, those drivers are not in the bus at the same time, and therefore don't make up 20% of the passengers on the bus. If you're saying the average bus route serves 15 people per day, you are certainly mistaken.
> If you're saying the average bus route serves 15 people per day, you are certainly mistaken.
Definitely mistaken for London - currently (according to DFT's numbers) about 18 people per bus average (not per day, though.)
> uhhhhhh what. What does every 10 minutes have to do with this at all
See the word "effective". Think about the road space that a bus requires but doesn't use if it is just once per 10 minutes.
> I have never ever seen a bus with 3 drivers in it. If you're talking about 3 drivers over the course of 24h, those drivers are not in the bus at the same time, and therefore don't make up 20% of the passengers on the bus.
Yes, I'm talking about the drivers that are needed for a reasonable 16-hour bus service. And the typical ratio is actually a bit more than 3 drivers per 1 bus.
> If you're saying the average bus route serves 15 people per day, you are certainly mistaken.
No. I'm saying that on _average_ there are 15 people in a bus. More during the rush hour, fewer during the off-hours.
So where is the 20% of passengers are drivers thing even coming from?
> See the word "effective". Think about the road space that a bus requires but doesn't use if it is just once per 10 minutes.
Excepting the case of a dedicated bus lane, the amount of road space a bus is preventing other cars from taking up at a given time is equal to the size of the bus. Technically, it's less than that in the case of bus stops littered amongst parking. In the case of a dedicated lane, it reduces the maximum throughput of the thoroughfare, but it's not a simple thing to model as there are other effects that the bus can have to reduce the number of cars when the rate limit of thoroughfare would be pertinent (i.e. usually rush hour). Just saying "think about it" when saying a bus takes up the space of 100+ cars doesn't really substantiate such a bold claim.
> Yes, I'm talking about the drivers that are needed for a reasonable 16-hour bus service. And the typical ratio is actually a bit more than 3 drivers per 1 bus.
> No. I'm saying that on _average_ there are 15 people in a bus. More during the rush hour, fewer during the off-hours.
If there is an average of 15 passengers on the bus during the operations of the bus and there is an average of 1 driver on the bus during the operations of the bus, then it is 1/16th occupied by driver(s). For it to be taken 20% by driver occupancy, then it would require there to be an average of 4 passengers on the bus during operations.