Comment by mafuyu | Hacker News Reader

Comment by mafuyu | Hacker News Reader

It's exciting to see Waymo and self driving technology in general doing well, but the analysis on the broader implications fell flat for me. Claims about improving commutes or being more effective than mass transit need to be substantiated - there's a ton of stuff out there on traffic engineering, mass transit, and urban planning that can help perform these sorts of analyses.

Some thoughts:

* For the purposes of transit efficiency, self driving cars are very similar to Ubers. They have a low passenger density (being a regular car), and once the passengers disembark, they still take up space on the road with 0 passengers. Better experience and lower costs will basically just induce more demand over more efficient mass transit options. If you imagine everyone at a bus stop ordering an Uber, or have ever seen the flurry of Ubers after a big event, it's clear why self driving isn't really addressing the core issue.

* You can't really make direct cost comparisons to the infrastructure costs of bus lanes or subways like that. Infrastructure is ungodly expensive in the US, yes, but there are very well understood reasons to make dedicated bus lanes and subways: they don't compete with cars on the road. They're high density transit options, so having more reliable service will impact a lot more people (and reduce car congestion on the road!) A rideshare service is wholly unprepared to deal with the transit demands of a larger city, and imagining that we'd replace existing mass transit options with it is silly.

* I don't really understand the point about suburbs. You can already get that experience today by ordering an Uber to and from work. If there's more demand, it's just going to make traffic even worse while promoting more suburban sprawl.

Hello! Author here. Quick responses:

1) With superior scale, the utilization of each Waymo approaches 100%. "Empty rides" going to a new pickup spot become more and more rare because they immediately get a ride close-by.

2) I think you underestimate the case for shared rides. Any Waymo with >= 2 passengers is reducing congestion, not adding. When you consider small bus-shuttles, e.g. 6 or 12 or 18 seats, it gets even more impactful.

3) The point with suburbs is that they become more accessible when the price point comes down. If you have a 45-minute commute to drive yourself, an Uber might cost you $60, which would be prohibitive. If a seat in a carpooled Waymo costs only $5 or $10, the incentives and customer behavior change significantly.

I disagree with your three points.

> *”because they immediately get a ride close-by”

That’s is unsubstantiated utopia (from you POV). People do not have uniformly distributed locations for starting and ending routes. There are concentrations of where people work, live, go to restaurants, schools, etc. More so if you are assuming suburban homes. The direction of routes also have very strong biases.

You very strongly and, again, unsubstantially overestimate shared rides. Shared rides could already be happening at scale with a human driver and are not. There is nothing about self-driving tech that solves any urbanistic, social or economic barrier to shared rides. Also, a shared ride negates most of the benefits of self driving cabs. You are not alone in the confined space, you are sharing with others, others that will likely be more intrusive than a professional driver. The vehicle will not be as clean, as comfortable, as silent, etc.

About commute getting cheaper seems a pipe dream. There is nothing in the self driving tech remotely indicating that a currently $60 ride will cost $5 with self driving cars.

Dedicated bus lanes absolutely compete with cars on the road. You could drive a car in the bus lane, except for the words 'bus only'.

Most of the dedicated bus lanes I've seen were once open to all vehicles, but later restricted. Some were built specifically for busses, but not many.

In order for a bus to actually be an efficient mass transit option, it has to be used.

Buses on regular roads create a "shadow" that affects other vehicles behind it and reduces 2 lanes in one direction to an efficiency of much less than 2 lanes, due to stops and starts. And except for peak usage times outside of a few major US cities, I would argue it is a net congestion creator rather than congestion reducer. A bus has the same effect as 10 or 15 cars, from my observation; so if there are less than 15 people on a bus, it's worse.

Part of the reason that buses have wraps or tinted windows is so you can't see how few people are riding on it.

At least the Waymo is not moving and not on the road when not in use.

> And except for peak usage times

Peak usage times are obviously what matters for congestion

> I would argue it is a net congestion creator rather than congestion reducer

I think buses even outside of peak hours are usually net congestion removers... but if you want them to be congestion removers during peak times, you also need to offer service during other times.

Yeah, bus systems suck. People avoid buses because they have unreliable schedules, and dedicated bus lanes are intended to improve that. Putting every rider on a bus into their own dedicated rideshare car isn't really going to improve things, though...

Can you explain how a bus, which takes up only the space that 2-3 vehicles can add the equivalent of 10-15?

Even triple the space usage, is leas than what you claim to observe. What is your methodology for determining this?

The claim is that this is because buses start and stop more often. I can see how that would affect congestion. The specific numbers to seem to be an ass-pull though.

The dedidicated lne even just at the bus stops eliminates that issue.

But like I said, triple the “physical space” the bus actually takes up and that is still less than their claimed “space consumption” of a bus.

And Waymos would need to also stop to pick people up as well…

Buses are much slower to accelerate, and unlike most cars, you can't see what is ahead of the car in front of you.

When you get a chance, follow behind one during a non-congestion period and count the cars that pass you in the other lane (meaning, your lane is slower) and estimate how many additional cars it would take to have the same speed of traffic (how many cars would need to be in your lane, instead of 1 bus, for the lane to be as slow?).

That behavior inconsequential during non-congestion hours as the traffic can flow around the bus or else there'd be congestion, and helpful when traffic is near congestion. Traffic models show that it's the sudden acceleration and esp deceleration that "propagate" and cause congestion, accelerating slower and staying (at a safe distance so you don't have to hit the brakes) behind the bus are helpful.

Imo everyone driving unpredictably to "get ahead" and save (literally, do the math) 1 minute on a 30 minute commute is what causes a lot of congestion.

Imo even if a bus took up 10 car spaces, the more predicable driving and slower accel/decel might still be a net positive for traffic flow.

Traffic congestion increases nonlinearly[1]. i.e. the 10th car on a road has a smaller effect than the 100th car on the road. Accordingly, the cost of increasing a bus' size and decreasing its speed pales in comparison to the value derived by removing 5-20 cars from the road.

https://www.youtube.com/watch?v=cHSCmQnGH9Q

But there have to be 20 people inside the bus (approximately 50% utilization) for that effect to be seen. Do you see that many on the bus at non peak times?

Realistically a bus is 2-3 times the size of a car. I think you need like 5 people to justify it. And 6 before you're actively addressing traffic. Most bus capacity is around 10. Which is 4 cars saved.

Also, do you care about the state of traffic at off-peak hours? who cares if buses don't run at peak capacity when there's no traffic?

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