Hacker News Reader

Comment by realo | Hacker News Reader

30 people in 30 waymos vs 30 people in an electric bus?

No contest.

No contest when the bus is full, but the overall efficiency (/"greeness") of the system is much less clear considering: buses are rarely full, most buses are diesel, heavy buses tear up the pavement on their routes (especially near stops), and buses don't take riders directly to/from their destinations.

Most of the city buses in my UK home town are now battery electric double deckers. These carry up to 85-90 people (with 25 standing), weigh 11 tonnes, and is 10.5m long.

A typical jaguar Waymo usually carries up to 4 people (usually just one), weighs 2.1 tonnes and is 5.2m long.

So the double decker bus should be more environmentally efficient with maybe 5 passengers making independent journeys, though operational costs for paying a driver probably make the Waymo more financially efficient in that situation.

I suspect robotaxis will become very important in suburban areas with distributed jobs where buses don’t work well. In busy cities there simply isn’t the roadspace to replace buses with robotaxis (or any other form of car) for commuting.

> A typical jaguar Waymo usually carries up to 4 people (usually just one), weighs 2.1 tonnes and is 5.2m long.

A more reasonable taxi for single riders is going to weigh around 1.5 tons (e.g. the prototype Tesla Robocab).

You also incorrectly assume that the efficiency depends linearly on weight. It doesn't, it depends more on aerodynamics, speed, and the number of stops. London buses (11 tons) average around 2.2 kWh/mi, Tesla Model 3 is at 0.21 kWh/mi while weighing 1.8 tons.

Road damage scales hypercubically with axle weight, so an 11 ton 2-axle bus does ~1400 times more damage to the road than a 1.8 ton Tesla.

https://en.wikipedia.org/wiki/4th_power_law

This is the right way to think about it. Larger buses make sense when there are a lot of people going to and from the same places at the same time, but I think that is much more rare in my city after remote work became widespread.

The real question is what's the optimal size for a bus if you don't have to pay a human to drive it? Once the technology is proven, there's no reason you can't put the Waymo or other self-driving technology in a bus. A bus designed for a dozen people instead of 30, and a fleet of them that did point to point rides instead of a fixed route, just all booked via the app so you share rides with other people. I dare say that would be the best of both worlds.

> The real question is what's the optimal size for a bus if you don't have to pay a human to drive it?

It will depend on the area. Where I am in San Francisco we have articulated buses designed for 100+ people running every few minutes above BART. (We probably need more BART stations.) There’s simply not enough road space for smaller buses (let alone cars) to carry commuter traffic downtown.

(I’ve never worked downtown though so always drove to work in desolate Silicon Valley office parks.)

Even in my smaller UK home city (250k people) you need double decker 70+ capacity buses running every 15 minutes on two routes from city centre to university to handle demand because the jobs are not so distributed.

Maybe it's different where you live, but 95% of the buses I see driving around here are completely empty.

Are you near the city center, or out near the suburbs? It's common for a bus to be crowded on one part of the route and nearly empty at the end.

And this is a fundamental issue with transit. It _has_ to travel as mostly empty on avereage to be useful.

...no? In the heart of downtown, with people riding in both directions, I don't see how it follows that it has to mostly empty to be useful. If it's full you can't get on so that's not useful, but anything less than totally full should still be useful.

Its not a meaningful issue. The passenger density is higher on even a mostly empty bus than cars, and the pollution is lower as well.

Different 30 people in the US. I’d drop my car if Waymo was around and financially made sense. You’ll never catch me wasting my time on a bus though. We’ll never even be close to Europe or elsewhere wrt where public transit was even decades ago in those places.

People here only ride the bus when there’s no other option for them.

Waymo could make a bus too anyway, especially after they’ve been in an area a while and have data about where they’d have the most impact. Internet at large would probably decry it as enshittification.

Bus was just fine in Portland, Seattle, and San Francisco.

> Bus was just fine in Portland

Yes, if you live within about 1 mile of downtown and also work there. If you live downtown and your job is in Beaverton, you're likely in for a 90 minute commute. Or if you live in Beaverton and your office is downtown. Portland's mass transit is adequate for a subset of people and completely impractical for most.

Source: I've lived in and around Portland for 50 years. Worked downtown much of it, and have lots of friends and former colleagues who used public transit. You have to really want to not have a car because the time commitment is real.

Okay, but clearly there’s a difference between, “the bus makes sense if you live or work near downtown,” and, “people only ride the bus when there is no other option,” as the GP said.

Yeah theres a couple spots that it’s fine for people that have never experienced what’s actually possible.

That 90 minute commute by bus isn't one where you're driving though. A strict time comparison ignore the fact that the bus or train ride merely requires you to get out when you reach your destination. You don't have to sit in stop and go traffic driving. Sitting in traffic driving sucks unless you have comma.ai or equivalent. Mentally it's just exhausting by the time you get home/to work. If you have to drive and can shitpost HN for those 90 minutes, vs trying to do that while driving (don't do that), then who cares if it takes a bit longer? There's obviously too much longer, but still.

Bus is fine in select areas at current fares, but would be less popular if people realize each drive costs more like $16 in total instead of the $2 fare they pay.

> Waymo could make a bus too anyway

Oh hell no. Cars are bad enough from the damage they can cause by kinetic energy, but a bus? Especially a bus where people don't wear seatbelts or, worse, are standing?

It would probably be safer than most bus drivers currently, so I don't see the issue. The discomfort around damage being caused by statistical anomalies vs individual error is not a rational one if the former is, in the aggregate, smaller than the latter. Individuals have stories, but societies operate more closely in line with the laws of physics: probabilistic at the small scale, deterministic more broadly. From that view, we are just replacing one statistical possibility with another, one which will result in less people dying; or, more importantly, less likelihood you or your loved ones will die because of a bus accident.

> don't wear seatbelts

I just want to point out that the safety record of public transit drivers is typically impeccable. There is no safer vehicle out on the roads except buses and trains. I have been a rider of public transit for 50 years, minus about a decade when I owned a car, and in 3 different major cities, and literally I've never been aboard a bus that hit another vehicle, hit any obstacle, or had a reportable accident. Literally never happened. (I was aboard a light rail train that collided with an SUV, but that's a whole other ballgame.)

I've never felt unsafe without a seat belt on board a bus. Seat belts in cars may be a bit of a panacea, but I challenge you to find any metropolitan area where the buses have accidents, much less injury accidents, on a weekly basis.

Well, you'd need to crash for that too be an issue. We have to wait for the data to prove it out, but I much prefer a Waymo driver than a human one, especially if I'm walking home right after the bars close.

An average bus load in the US is around 18 people. So if you just compute the raw bus emissions, then an electric bus is maybe about 2x more efficient than personal EVs.

But wait, there's so much more!

A single bus/subway ride costs about $20, which is a surprisingly consistent figure for various US cities. In NYC it's $17, for example. I'm talking about the _true_ cost, as in: "yearly operational budget divided by the number of trips". And most of this cost comes from 3-4 drivers that every bus needs, not from the hardware itself.

Price is a pretty reliable proxy for CO2 emissions for general market goods and services. And with these kinds of numbers, personal cars are competitive. Even if we factor in subsidized road maintenance cost ( https://taxfoundation.org/data/all/state/state-infrastructur... ).

If we now add mild carpooling, so that a single robotaxi drives 2-3 people, then classic transit just dies. It's like comparing horse-drawn carriages with steam trains.

Most of the cost comes from paying the drivers, but also cost is a proxy for emmissions?

Yes? Why is this strange?

Drivers emit a lot of CO2, just like every person in the US. A driverless car allows these emissions to be reallocated to other more productive areas.

You're counting emissions from a person's breathing as part of the vehicle's emissions?

People take their salaries and buy food, clothes, heating and air conditioning, cars and fuel, and plane tickets, and furniture. All of those things generate emissions in their production and/or transportation. This is why dollars is such a good proxy for co2 emissions.

Surely a person driving 18 people will emit less than each person driving themselves? I can see how dollars can be a proxy for macroeconomic stuff, for example by comparing countries, but it doesn't make much sense for comparing individual units of transport.

I don't understand why we have to do napkin maths to guess what's more polluting. There is countless research showing buses emit less than individual cars per passenger per km, self-driving or not.

And there's no reason buses can't be self-driving as well, if anything, them driving slower, on dedicated lanes and on fixed routes would make it much easier.

> Surely a person driving 18 people will emit less than each person driving themselves?

No. A person driving themselves does not create any _incremental_ CO2 emissions. They don't need a dedicated full-time position to do the driving.

> There is countless research showing buses emit less than individual cars per passenger per km, self-driving or not.

Care to share it? I actually read through most of highly cited articles in this area, and it's not at all so clear-cut. For example: https://ourworldindata.org/travel-carbon-footprint

A single bus journey is $20? That's insanely expensive.

Reply on news.ycombinator.com