Dr. Strangebus or: How I Learned to Stop Worrying and Love the Trolleybus

I think we ought to look at this from a military point of view. Say the NIMBYs stashed away a few hundred million in highway funding. When they regain power, they could take over!

I agree Mr. President, they might try a sneak attack so they can take down our trolley poles.”

It’d be extremely naive of us to imagine that these new developments are gonna cause any change in highway expansionist policy. I mean, we must be increasingly on the alert to prevent them from taking over other bus-only spaces, in order to induce demand more prodigiously than we do, thus knocking us out through superior numbers when we emerge!”

Mr. President, we must not allow a Trolleybus gap!

In science fiction, there’s a distinction known as “AM vs. FM,” and it’s not radio. AM refers to the world of “Actual Machines,” that is, known technology. It is anything that exists in the present day that, for lack of a better term, works. This is opposed to the world of “Fucking Magic,” also known as the cool parts of sci-fi. It’s the spaceships and FTL drives and laser guns and such. Things that are, at best, a very early prototype. More often, they’re just an idea in people’s heads.

Transit blogger Anton Dubrau coined a similar term, “gadgetbahn,” for use in public transit contexts. These are pie-in-the-sky solutions to already-solved problems. Hyperloop, maglevs and monorails are some of the most famous examples. A technology doesn’t need to be completely theoretical to fall under the gadgetbahn or FM umbrella, so long as it’s blatantly obvious that what’s promised is not what was delivered.

A great example of the contrast between AM and gadgetbahn/FM is trolleybuses and battery electric buses (BEBs). The former is a proven technology that has existed for almost 150 years; meanwhile the latter is only just starting to see widespread use, with mixed results at best.

A History of Electric-Powered Transit

Overhead electrification (OVE), which makes trolleybuses possible, has existed for 142 years, debuting at the 1881 International Exposition of Electricity in Paris. A similar technology, third rail electrification, was invented two years earlier. Both were conceived by Werner von Siemens, which is a name you might recognize. Siemens’ eponymous company still makes trains powered by overhead electrification to this day, along with many other kinds of heavy-duty electrical equipment. They often claim at trade shows that Siemens moves 70% of the world’s electrons, a claim that both seems plausible and is impossible to prove or refute.

Many of the world’s premier rolling stock and electrical equipment companies would cut their teeth in this market. General Electric’s transportation division, once the largest locomotive manufacturer in the world, first entered the market with OVE trains for the New York Central Railroad. Other big names, like Westinghouse, Alstom, Bombardier, Hitachi, and Talgo, would come and go. Some of these crossed over into the trolleybus business as well.

The trolleybus’s story starts only a year later in 1882, as another invention of Werner von Siemens. Not much more than a wagon with some wires attached, the Electromote used most of the same technology seen today. While the pickup is no longer just a wire itself, it still draws power from two overhead wires — one live and one ground. DC current flows from the live wire, through the motor, and back to the ground wire, turning its electrical potential energy into kinetic energy and heat. This simple system minimizes complexity and weight while maximizing efficiency and therefore power output.

Five gentlemen sit in a horse-drawn carriage with no horse. Instead, there's a pole in the center that has a wire on it, with the wire leading to a contraption made of pulleys attached to two overhead wires.
The Electromote. Source: Wikimedia

Locally, Minnesota had two trolleybus systems. Twin City Lines (a.k.a. the Twin City Rapid Transit Company) operated a short route in the south metro as an extension of the streetcar system. To move buses to and from the car barn, they drew power from the streetcar wire and were grounded through the rails (this is why trains only use one wire). This lasted for just over a year, from May 1922 to 1923, until the streetcar was extended to replace it. The second system was operated by the Duluth-Superior Transit Company from 1931 to 1957. These trolleybuses replaced Duluth’s streetcars, until both ridership and the Twin Ports shrank and they, too, were replaced by regular diesel buses. The Minnesota Streetcar Museum has an excellent presentation on both systems.

An Ohio Brass ad touting the popularity of trolleybuses in Duluth. Points include popularity, longevity, return on investment, hill climbing ability, and cold weather endurance.
An Ohio Brass ad touting the popularity of trolleybuses in Duluth. Source: Trolleybuses.net

Perhaps ironically, the story of the battery electric locomotive, ancestor of BEBs, started almost 45 years earlier in 1837, when it was invented by Robert Davidson. It had a galvanic cell battery and was thus named Galvani. It weighed 7 tons, had a maximum speed of 4 mph, and a range of 1.5 miles. Impressive in 1837, and while the technology has come a long way since then, making a better battery is still one of the greatest material science challenges of our time. As such, battery locomotives did not see much use outside of mining operations, where the lack of smoke and soot outweighed any downsides. Only recently have they seen mainstream use and the results have been poor. They’re quite limited in speed and/or range, and the most promising use right now is as a booster for diesel units.

Electro-magnetic Exhibition, under the patronage of the Royal Scottish Society of Arts. Mr. Robert Davidson's exhibition of electro-magnetism, as a moving power, is now open! Egyptian Hall, Piccadilly. The models and apparatus comprise the following: A locomotive engine, carrying passengers as a circular railway. A printing machine and turning lathe, a sawmill. A machine for communicating the electro-magnetic shock. An electro-magnet! The largest ever made. It weighs upwards of 200 pounds and will suspend many tons. A galvanic telegraph. The Combustion of metals, [indecipherable] Model of the flying machine. Model of an aerial carriage, by Sir George Cayley . Open from 12 till 6, and from 7 till 9. Admission, one shilling. Children under 12 Years of Age, sixpence. Printed by Electro-magnetism.
A flyer showcasing the Galvani. Source: Reddit.

For BEBs, the story doesn’t really start until around 2010, when Chinese cities began adopting them en masse (we’ll get back to this later). The Chinese company BYD is now the leading manufacturer in this market, while New Flyer and Gillig are the main North American manufacturers. Initial offerings had a top speed around 50 mph and a maximum range of about 100 miles. Modern offerings are capable of full highway speeds and up to a 258-mile range. A respectable distance for any vehicle, so why do I remain skeptical?

You Cannot Change the Laws of Physics

Or as I like to say, “The physics always wins.” Batteries have pretty poor energy density — the amount of energy that a certain substance has in it per unit volume — compared to other energy sources. Sometimes specific energy (energy per unit mass) is also used. Since buses are fairly large creatures, battery size isn’t as much of a consideration as mass is, since adding mass will directly affect performance. (Good old Force = Mass x Acceleration, a classic!) Hence, for this comparison, I’m using specific energy. To the right is a table comparing the specific energy of some common rechargeable batteries to that of what I’m calling “fuel-based solutions.”

So while electric motors have two to four times the efficiency of gasoline and diesel engines, BEBs still lack the performance and range of diesel buses due to the relatively small amount of energy they can store. Even hydrogen and compressed natural gas (CNG) are not that great when compared by volume. Both are extremely light and require high pressure containment systems, which often weigh more than their contents. In this way, a mass comparison falls apart, but even by volume they’re both well above batteries (roughly 2,500 Wh/L).

Energy StorageSpecific Energy (Wh/kg)
Lithium nickel cobalt aluminum oxides220
Lithium nickel manganese cobalt oxide205
Lithium cobalt oxide195
Lithium iron phosphate90-160
Lithium titanate60-110
Fuel-based solutions
Hydrogen33,313.9- 39,405.6
Gasoline (pure)12,888.9
Gasoline (E10)12,094.5
“Gasoline” (E85)9,194.5
Natural gas 14,888.9
Sources: Comparison of commercial battery types, Energy density (both Wikipedia).

This is why we’re having so much trouble moving away from fossil fuels. Sure, they’re bad, but at the same time they’re too good! They allow us to store vast amounts of energy in a fairly lightweight and compact space, and they make transferring that energy quick and easy.

The Nitty Gritty

The optimization problem becomes thus: How do we get the most energy using the least amount of on-board mass? Simple: Get rid of the onboard energy storage and deliver it by some other means like, say, a pair of overhead wires. This allows maximum power output with less mass than battery-powered or even diesel buses.

Trolleybuses are mechanically and electrically much simpler than both, as well, requiring just the pickups, a motor, controller, and transaxle to operate (although these days they do still have a small battery for short off-wire moves). BEBs are a bit more complex, as they require more robust battery management systems, and the higher number of battery cells means more points of failure. While diesels seem more reliable on paper, they still have more ways to break. Every valve, piston, gear, chain link, injector, crank, cam, and connecting rod is a potential point of failure. Not to mention that they have entire systems that are absent on BEBs, like the transmission or various cooling systems. Unfathomable amounts of R&D money has been poured into internal combustion technology to make it as reliable as it is, and I suspect BEBs will turn out the same way.

With trolleybuses, all of the auxiliary systems, like climate control or other energy management (i.e. keeping batteries at their operating temperature) are also drawn from the wire and therefore do not impact the vehicle’s range, which is theoretically infinite anyway. These savings in weight and complexity usually translate into a lower price tag per unit as well, although factoring in the rest of the infrastructure does raise the cost significantly. That said, overhead wires can last more than 100 years once installed.

Going Head-to-Head

In early 2022, Metro Transit conducted a study to determine which “zero-emission” technology to choose when transitioning away from diesel buses. This is called the Zero-Emission Bus Transition Plan and there’s a variety of documents on their website, with the final report linked here. In it they go over the three existing ZEB technologies — the third being fuel cells — and do a pro/con analysis of each, studying existing installations around the country as well as how they might fit into Metro Transit’s fleet. Given what I’ve said previously, I’ve got some problems with their analysis. Many of the points they raise fall between “technically true but misses the point” and straight-up false.

Metro Transit’s stated limitations of trolleybusesMy response
“Trolleybuses require overhead catenary wires to be installed throughout the corridors and in garages where trolleybuses are assigned to, which requires extensive initial capital investments for new systems”Mostly true, but not required in garages or on the entire corridor.
“Garages need overhead clearance and need to be retrofitted with overhead wires to accommodate trolleybuses for storage and maintenance needs”False, modern trolleybuses have 15-20 miles of off-wire range. If power is necessary for maintenance or troubleshooting purposes, it’s possible to jump them like any other vehicle.
“Trolleybuses have limited flexibility for off-wire operation”Mostly true, but I think I have an idea on how to get around this that I’ll mention later.
“Trolleybuses may not be suitable for high-speed operations as faster speeds increase the likelihood that a trolleybus will detach and come uncoupled from the overhead wires particularly around curves and corners”False. Overhead wire is the preferred power delivery method for high speed rail. Even old interurban trains that used trolley poles could reach 110 mph. I have no reason to suspect buses will do much worse.
“In multi-lane operations, it is difficult for a trolleybus to overtake a preceding trolleybus without coordinated crossover points”With modern trolleybuses having some off-wire capability, this isn’t as big of an issue. Poles can be reset at layover points after an overtake or guides/switches can be installed at the busiest crossovers.
“Overhead catenary wires may have visual impacts on surroundings which may make implementation in neighborhoods protected by historic preservation laws difficult.”True, but these laws have historically been used to oppose all kinds of transit expansion, as well as other forms of development, not just trolleybuses.
“Placement of catenary poles can impact accessibility of sidewalk, underground utilities, and/or underground vaults”True.
“Increased electricity usage during peak (more expensive) periods”Overall lower energy use due to better regenerative braking and smaller transmission losses.
Source for left column: Metro Transit’s Zero-Emission Bus Transition Plan.

With all this in mind, there are a few additional downsides to BEBs that are not mentioned in the document.

  • Decreased garage capacity due to space taken by charging infrastructure.
  • Worse performance characteristics due to poor power-to-weight ratio.
  • Increased maintenance costs and shorter vehicle lifespan due to battery chemistry limitations. They’ve already had multiple cell failures after two years of limited service.
  • Unique charging infrastructure. (Trolleybuses can use LRT infrastructure to an extent.)
  • Not actually zero-emission.

Yes, that’s right, Metro’s current fleet of BEBs have diesel heaters in them. I couldn’t find a hard number on fuel usage, as New Flyer has since switched to heat pumps, but similar technology used on Moscow’s battery buses burns about 3-4 liters an hour. The average block size — how Metro Transit assigns buses to a series of routes — is 133 miles. At 6 mpg, the average diesel bus uses around 84 liters of diesel a day. Assuming eight hours of use, our battery electric buses use 24 to 32 liters of diesel a day in the winter, or about 30% to 40% of what a diesel bus uses. Not great for a vehicle with no internal combustion engine!

Then there are the admitted problems like worse equipment utilization due to charging times, worse reliability — particularly in cold climates like ours — and the fact that all this costs about twice as much as a diesel bus upfront and has higher operating costs. Throughout the ZEB final report, I see lines about managing expectations and setting clear, contractually bound goals. This line in particular has stuck with me:

It is good to be an early adopter but not the first adopter; avoid low serial-number equipment.

Metro Transit ZEB Transition Plan

So if Metro Transit wants to avoid low serial number equipment, then I have a 142-year-old technology to sell them. While not common in the U.S., four transit agencies currently operate trolleybuses: RTA (Dayton), Metro (Seattle), Muni (San Francisco), and SEPTA (Philadelphia). These are all legacy systems that opened in the 1920s to 1940s and have received upgrades over the years. There are 273 other systems in the world, with most of them operating in the former Soviet bloc. This is all to say that there’s been plenty of testing already. The kinks were worked out a century ago, so all we need to do is put up some wires and start running buses.

A grey trolleybus with a green stripe in Dayton, Ohio operates in what could be mistaken for the Warehouse District or Lowertown.
A brand-new trolleybus operating in the futuristic utopia of Dayton, Ohio. Source: Urban Transport Magazine.

Well, How Did We Get Here?

I am honestly a little confused as to why BEBs have taken off the way they have. They still have their advantages, don’t get me wrong. They still offer greater flexibility than trolleybuses as they can run literally anywhere so long as they have a charge, and the lower upfront cost is a huge advantage when dealing with cash-strapped transit agencies. With little to no direct emissions and no noise pollution, they’re better for the environment and the communities they serve, and some people may prefer the aesthetics of no wires. Personally, I think the wires look cool, but I’ll be the first to admit I’m weird.

Which brings me back to China. I’m guessing the reason for their quick adoption of BEBs is the aforementioned operational advantages, combined with a difference in management philosophies. The Chinese government has spent nearly two decades throwing unimaginable sums of money at not only BEBs but high-speed rail, airports, subways, highways, maglevs, and any other form of transit you can think of. As such, they may not be interested in squeezing every last bit of performance and productivity out of their equipment and employees. Cheaper labor probably plays a role as well, along with the more … top heavy structure of their government. This makes them susceptible to going all-in on bonehead technologies — like using balloons for everything — simply because one guy thinks it’s a good idea. This is all conjecture, of course; there are significant language and security barriers preventing me from learning the actual reasons.

Similar things happened in Moscow, I suspect. In a move that’s baffled transit experts, they’ve almost completely replaced their trolleybuses with BEBs. These replacements have very limited range, break down constantly in the cold, have diesel heaters, and are the most expensive buses in the country at $421,000. I suspect this one was a classic case of pork barrel politics but again, it’s hard for me to prove that.

The Best of Both Worlds?

Like I said, batteries still have some advantages, which is why modern trolleybuses still make use of them. The New Flyer XT60 has up to 22 miles of off-wire range, and some European trolleybuses have over 30 miles. Using our XT60 example and fudging some of the math from this article, the average Metro Transit but would need to spend about 11% of its time under wire in order to remain charged.

Other estimates say that about 20% of a route would need wires in order to satisfy its energy needs (see graph below, which backs up my assertion that we don’t need much wire to electrify the system). Of course, this varies wildly between systems with different infrastructure, voltages, buses, weather and geography. With proper spacing, some routes can get away with less. More likely, some that exceed this threshold still won’t be viable due to gaps larger than their range.

All that said, assuming 20% is correct, putting up wires over most current and near-term BRT lines, both downtown zones, and some other strategic spots — like 7th Street from Randolph Avenue to Arcade Street or Hennepin and First Avenues NE over to 8th Street SE – should get us 80% to 90% of the way there.

Graph showing two lines, x axis is average speed and y axis "covering rate". Two lines are on it, one for 250 kW OVE systems and one for 12 kW. The former goes from (5,11) to (20,20) and the later from (5,18) to (30,37).
Speed range is roughly 3 to 12 miles per hour.

Side note: I’m aware that half the BRT network has already been built and it’s too late for the Gold, B and E lines as well, but the Purple, F, G and H lines could still use trolleybuses. At the pace that planning and construction goes in this country, once those projects are done the A Line will need new buses and we can start the retrofit process.

Those two additions alone would allow the 2, 4 11, 17, 54, 61 and 74 bus routes to make the switch. Further small improvements will have a similar knock-on effect. Combined, these changes will also electrify certain legs of the 14, 22, and 23, whatever will remain of the 3, 6, 10, 21 and 62/68, the 7, 33, 64, 67, 71, 75, 80, 94, 250, 252, 515, 540, 824, several routes that are still suspended due to COVID-19 cuts, and probably others. It should be possible to cover all but a few of the far-flung suburban routes with this hybrid system.

BEBs still have a purpose in our transition away from fossil fuels, even if we begin mass adoption of trolleybuses. After all, BEBs already support overhead stationary charging. It’s a bit backwards, with the contacts coming down from the charger to the bus, but with a slight redesign they could easily support overhead charging by way of, say, two poles reaching to overhead wires. Perhaps these modified BEBs can fill the remaining gaps.

Battery electric buses will play a part of our transition away from fossil fuels, but they cannot be the only part. Shortfalls such as poor reliability, short range, short vehicle lifespan, and worse equipment utilization are inexcusable when we’ve had technology that never had these issues for more than 100 years. Instead, batteries should be used to enhance overhead lines, resulting in vehicles that can not only replace our current diesel buses, but even outperform them.