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Given the challenges with charging them with limited real estate in city centers, would it make more sense to install overhead wires, like a trolley bus, but retaining the ability to drive disconnected from the wires and constantly charge when in an area with the wires?

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Like most thing, its an "it depends" situation. The tech exists, but isn't in wide usage. There's a higher upfront infra cost to pay back, and while short distance reroutes can be accommodated, you do set the general routing in stone. This works fine for larger, denser areas with routes that are more or less fixed.

King County metro (includes Seattle) is one of the agencies that's made major investments in trolley buses.

2011 study: https://metro.kingcounty.gov/up/projects/trolleyevaluation.h... (recommended trolleys with batteries for off-wire capability)

2015 press release on arrival of new trolley wire/battery backup buses: https://kingcounty.gov/elected/executive/constantine/news/re...

Battery only bus tech is also growing. I don't think it's viable for large scale usage yet, but KC Metro has been working on and piloting it seriously for a few years. It's possible that by the time more places would look into trolley buses during fleet replacement, battery ones will be ready.

Trolley buses are necessary on many Seattle routes because of all the hills, you just can’t beat torque on a good electric (same is true for many other hilly cities like SF, Vancouver, and Lausanne).

Metro and sound transit has also invested in a lot of hybrids. The most recent fleet is pretty interesting (they also have a few battery-only electrics, but these seem more like testing).

I work for https://www.proterra.com, King County has number of our buses in service.

> The tech exists, but isn't in wide usage.

The buses in Lausanne when I lived there were on overhead electric when in the city center and switched back to diesel when they came off the wires. The same was true in a number of other Swiss cities. So I would hardly call it "not in wide use." Just not in the USA.

Ah, I think we're both right here, just on slightly different things. You're correct, trolley with diesel backup isn't new and is in fairly wide usage around the world. To the original comment:

"retaining the ability to drive disconnected from the wires and constantly charge when in an area with the wires"

Seemed to refer to trolley buses with rechargeable battery backups, which are much less common. Admittedly, I don't have non-US stats, just that there are only a handful of cities in the US that use them.

Which routes in Lausanne had that? I never noticed any dual use buses when I lived there. It isn’t surprising, Seattle used to have dual engine buses in the 80s/90s that were diesel until they went into the downtown bus tunnel. They got rid of that when they brought the train in, and I guess the buses were cleaner by then as well.

I lived there up to about eight years ago, and I recall most of the routes running through the center city were dual. I couldn't name route numbers at this remove, though.

Buses are pretty big and don't care too much about weight. Surely you can slap on a battery big enough to power the bus all day.

Since the bus is already parked somewhere during the day, couldn't you charge it then? From what I've seen there's usually a gigantic parking lot somewhere in the city where all the buses go to sleep. Would the parking lot need to be much larger to accommodate charging stations? I assume it's already got a diesel pump of some sort to feed the buses since you don't exactly see city buses at normal gas stations.

It comes down to energy density.

That setup (charging where the buses go at the end of the day) requires the buses have enough battery to go their entire day on one charge. But then, that restricts the ability to take a just-now-ending-service bus that's out on the road, and redeploy it to fill in for a bus that is running late, or a bus that has broken down.

(I have seen this happen: I have seen a VTA "Rapid" 522 bus, just about to go in-service at the start of its route, switch to "Not in Service" and leave without picking anyone up. When I called in to report the weirdness, the agent on the other end checked and told me that an Express bus nearby had broken down. That was the right call: The Raid bus was closer, and the Rapid schedule frequent enough to absorb the loss.)

So ideally, you would want charging points to be available where buses sit during the day. That is at least at one end of the route. It can be done, it just takes more infrastructure.

> I assume it's already got a diesel pump of some sort to feed the buses since you don't exactly see city buses at normal gas stations.

While I was an undergrad at Ohio State, I drove 35- and 40-foot buses for CABS (the campus bus service). We did indeed have a diesel tank and pump on-site. But occasionally it would break down. When that happened, we would indeed use a normal gas station! All of the nearby gas stations with diesel pumps were evaluated for bus access.

I wonder if you could get away with charging most of the buses by having overhead lines in heavy bus traffic areas to power and charge the buses during a portion of the route before having them return to full battery usage. This might also simplify overhead line deployment as there are some areas that are poorly suited for lines - line deployment could be focused on easy to service and deploy areas.

There are at least charging stations for buses.

For example: https://www.oppcharge.org/ https://www.heliox.nl/

What I would really like to see are small self-driving battery powered trams. (Seems like large "bi-mode" human operated ones already exists).

I thought the same too, to the point that maybe even lead acid batteries could work. Unfortunately, buses still care somewhat about weight--from a 2005 report: https://www.transit.dot.gov/sites/fta.dot.gov/files/Electric...

> Consequently, powering a full-size bus would require a battery pack that is unacceptably large and heavy, as well as too costly to make a battery-electric bus commercially competitive.

Of course, the energy density of lithium may change things!

I can't speak for the relative costs but adding a bigger battery adds cost, it also adds weight which increases the motor size you need, further increasing costs, it also increases wear and tear on the road.

Also the article mentioned $1.5million for infrastructure to charge 20 buses. Ideally you'd want that running 24/7, not lying dormant for 16 hours a day.

And lastly, you're adding a massive single point of failure. What if the power goes out overnight? Suddenly you don't have any buses the next day.

Ps I like the idea of buses going to sleep at night :)

Why would it increase the motor size significantly? Even low voltage electric motors have insane torque compared to fossil fuel engines.

Well its like the tyranny of the rocket equation. Yes the size increase isnt linear, but it isn't a free lunch either.

Don't forget, once you've added an extra tonne of batteries your suspension and chassis need upgrading (ie get heavier) to compensate, so you need to add more batteries to compensate....

One issue that the article highlighted was that if you do that you might need a significant grid upgrade to handle a large number of buses charging simultaneously. If the charging stations are spread out over the city the grid probably doesn't need to be upgraded.

There's a good description of converting a central London bus depot to electric buses here.

https://www.ianvisits.co.uk/blog/2018/06/26/do-londoners-dre...

Seattle actually does this. You have some hybrid routes as well where buses will operate off of diesel for part of their route, then hook up to the overhead wires before going through tunnels downtown. Some routes outside the underground downtown core also run wires.

OTOH, a few charging spots might be cheaper/more flexible if you've got a wide variety of routes.

Seattle has not had those buses for over a decade.

The new trolley buses have the ability to run off-wire for 3 miles.

https://en.wikipedia.org/wiki/Trolleybuses_in_Seattle#Recomm...

Trolley bus wiring is infrastructure that has an ongoing maintenance cost that many places probably don't want to pay for. (In addition to the initial CapEx.)

I think that series hybrid buses would be better: battery runs e-motor, and have a range extender (generator) that kicks in when needed.

* https://en.wikipedia.org/wiki/Hybrid_vehicle_drivetrain#Seri...

In some cases, but not in general. The problem with wires is you have to put them up. While this seems obvious, it needs to be thought about carefully. You need to plan your route and be right about the path it takes (even a minor change is at great cost). It is possible to create a route from Point A to Point B and have nobody ride it. It is possible that the route that is popular today will go out of style.

With a self powered bus (any technology) running on standard streets you can have it go anywhere. If the route you choose is wrong most of the costs were the bus so you can start a different route in a different area until you get people riding. If there is a popular event one weekend you can shift buses to serve that event for just that weekend. If the needs change you shift routes to match instead of sticking with routes that no longer make sense.

Don't get me wrong, advantages of fixed wires and rails (note the and!) make it worthwhile to put in a trolley system on your busiest routes. However the advantage of a bus that can go anywhere means that in general no you can't/shouldn't.

If you just put up the wires for part of the route, can't the bus charge up while it is under the wires for the rest of the route?

No, you bring back all the disadvantages I list - perhaps on a smaller scale but they still exist. You are still forcing all your buses to put part of their time on a pre-defined route. Maybe you can say we will always use this central station and put wires for a few blocks around it - but after that your buses should be spreading out in different directions. This isn't enough to get a significant charge.

It is an idea that seems sound, but fails because of reality.

This is exactly what they do in Shanghai and it works. The rails are not for the whole route just long stretches with lots of lights.

As far as I can tell they have a mixed fleet. Electric for ones that are downtown enough to charge and natural gas for busses that are mainly outside the city.

Things change rapidly so this may no longer be true.

Well they actually do this in Seattle and it seems to work out. A fixed route is also not a bad thing (see bus rapid transit) and can encourage private development.

See the last paragraph in my original. Fixed routes to have advantages, but only when/where you are sure they are very busy and will be for a long time. Most routes are not that sure in the modern world, so the flexibility advantages of non-fixed routes is important.

Of course part of the advantage of flexible routes is we assume car infrastructure is in place. While that isn't entirely desirable, it is reality: anyone fighting it directly is ignoring reality. Better to fight it indirectly which means making public transit better and better until people decide on their own to get rid of their car - only when few people use a car regularly can getting rid of roads be realistic.

Build it and they will come doesn't always work.

You can't ever really get rid of the roads, you can only downsize them. Even if everyone uses public transit, you need some way of transporting goods and cargo, and the only way currently of doing that within a municipality or to most final destinations is by truck. Whether you're moving a shipping container full of stuff to a retail store from the train terminal, or you're packing up someone's home and moving their furniture to a new apartment, it always goes by truck, and trucks need roads.

But if we could get rid of cars, we could make the roads a lot narrower.

No. that idea is as obsolete as diesel is.

buses have fixed routes, known depots, and in many cases, share larger stations as destinations for transit to other buses or other forms of transpiration. all are suitable for charging buses.

China has over 400,000 electric buses in operation. Can’t we simply follow their lead?

By building new cities and exerting political will over eminent domain? Probably not.

Since when do you need eminent domain to buy a bus?

Did you read the article? One of the big issues that some cities are facing is finding real-estate for installing charging stations of sufficient capacity. It specifically cites Philadelphia as having run into this problem.

This doesn't stop them from copying what China does.

China has the same problem in Shanghai. The solution they use is overhead wires to charge busses while they are driving for parts of downtown that busses can connect to and disconnect from at will.

San Francisco has electric trolley buses.

https://www.sfmta.com/getting-around/muni/munis-electric-tro...

Some places in outer Boston has this. They also have hybrid busses and you can hear the engine shut off when it's been sitting in traffic for a while.

Or just swap the batteries out somehow.

Yes, this seems like the ideal solution. A bus is big enough to where you can easily engineer a quick attach/detach "cartridge". Since it's all operated by the city (or private entity), you also don't have the issue you would with consumers where you need to worry about users turning in damaged batteries for good ones.

The battery will still be ridiculously heavy and very large, well outside the limits of human ability to move it. So you need some sort of machinery to do it, as well as a human operator.

Also, keep in mind you don't just need very robust electrical quick-connects, you also need fluid quick-connects for the heating/cooling. As well as a system to bleed air from the loops inside the bus.

Some back of the envelope math:

Let's say the bus needs 50 miles of range, and it runs at 2 kWH per mile, so it needs a 100 kWH battery. Assuming 200Wh/kg density, the battery will be at minimum 500kg.

Lots of EV cars have batteries that big.

Yes, and it’s a structural member of the car that can’t be easily swapped out.

Vancouver has used buses that can get overhead power for a long time.

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