World: A Challenger to the Tram Arrives.

Bi-Articulated Trolleybuses offer True Competition to Street Railways.

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I have a reputation — deserved or not — for being tram-skeptical. I do love trams, but I think they have been used in a lot of places where other transport solutions would make more sense. Trams make a lot of sense for dense urban routes where a large, 40 metre-long vehicle can navigate tight quarters on rails, frequently stopping along the way. But, for service along mostly grade-separated routes, or on railways, or on suburban streets, or in mixed traffic, the features that are an asset to trams in dense urbanity become liabilities.

Fortunately, there is a very compelling alternative that has been growing rapidly in adoption in recent years — the bi-articulated bus.

Modern bi-articulated buses are very similar to regular articulated buses, but instead of having a single “trailer”, they have two. This kind of bus is kind of famous for operating on the true BRT systems of Latin America, but in these situations it’s easy to write them off for use in other parts of the world. For one, buses as mass transit is not financially sensible in countries where bus drivers are paid high wages: you want to build a rail system because beyond all the technical benefits of rail, it also enables massive improvements in labor productivity where a single driver (or no driver) can suddenly move ~1000 people, as opposed to maybe 200 on one of these giant buses.

A High Floor Bi-Articulated Bus in Curitiba By Mariordo by (Mario Roberto Duran Ortiz) - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=24484092

There are other issues too: these Latin American buses are high-floor, which means there is a need for specialized high boarding platforms and stop infrastructure that only really makes sense on the sort of BRT systems that I mentioned are not really viable in high-wage countries. The other issue is that these buses, despite being used for a mass transit service, are particularly bad for air quality. While it is the case that cleaner diesel with more exhaust treatment is an option in the global north, it’s also the case that mass transit sort of implicitly indicates electric.

But what we’ve seen in the last two decades, and accelerating recently, are solutions to most of these problems.

For one, there are now numerous low-floor bi-articulated bus models, from Volvo, Van-Hool, Solaris, and Swiss manufacturer Hess. These vehicles look and feel just like the regular articulated buses from these manufacturers, but with an extra articulation. Furthermore, thanks to advancements in battery technology, which also has sort of revived interest in trolleybuses, there are now both standard and in-motion charging variants of these buses available.

In-motion charging is a real game changer, because it makes trolley infrastructure a lot simpler. Traditionally you had to wire up all kinds of annoying locations, like depots and transit exchanges, because trolleys had limited battery capacity, and these complex areas often were expensive and issue-prone. With a battery range-extended trolleybus you can take an inverse approach to wiring up a route, simply installing wires that charge and power the buses in the easiest places, so that vehicles can complete a journey with a little slack. The infrastructure goes from maximal extent to minimal extent, and in many cases could be shared between several routes. Rewiring the vehicles has also been automated, and made faster and easier.

Outside of central Europe and Switzerland where bi-articulated trolleys have been popular for a while, this technology has seen limited deployment, but I think two recent projects are opening peoples eyes.

The Big Deployments

Brisbane has introduced a (poorly-named) service on their rather extensive transitways called “Metro”, which utilizes full battery bi-articulated buses from Hess. The transitways are a well-suited operating environment for what are very long buses (~24 metres), but they also have exchanges along them for rapid charging. I think there will be another boost in the awareness of this technology when the Brisbane 2032 Olympic Games happen and international reporters inevitably end up on these very nice buses.

Brisbane Metro By John Robert McPherson - Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=141330457

It does feel like a bit of a miss to not include overhead wires for in-motion charging on Brisbane’s system given it already has control of the right-of-way, but this is probably downstream of the general problems English-speaking countries have with building infrastructure, especially when it’s novel. It should be cheaper to get less expensive, lighter buses that don’t need to idle and charge, but it clearly isn’t. This is bad.

Perhaps even more exciting that the Brisbane case though is Prague’s new airport trolleybus route. It’s the sort of thing that you can instantly imagine tons of cities could do fairly easily. Basically, Prague airport does not currently have a rail link, and while one is being considered, bi-articulated electric range-extended trolleybuses are a great solution. These vehicles run from a tram, metro and railway station on the edge of the city using trolley infrastructure, along wide streets to the airport, and then run on battery through the terminals themselves (where presumably structural modifications and disruption might have made wire installation annoying). Since the vehicles are big, they allow for a comfortable ride for lots of passengers, as well as dedicated space for luggage (which can seriously reduce the capacity of traditional buses on airport routes — which leads to cities like Montreal running basically continuous lines of buses on their 747 bus). When I saw news of the service opening, with the huge buses all lined up (they bought a lot of them) and the videos of the service operating, I realized that I think this service looked serious enough to get the kind of political attention that only rail really did until this point.

One of Prague’s Airport Trolleybuses By Zubozrout - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=144773931

Trams

The whole point of this article was to contrast these vehicles against trams, so let’s do that.

For one, capacity figures aren’t all that different. Most “light rail” systems out there have vehicles that are longer than 24 metres, but many trams are also about 24 metres long and have a similar ~200 person capacity to these buses. At the same time, most light rail systems in the US in particular do not use their capacity: they will run a big train at relatively low frequencies, but they probably could be running one of these bi-articulated trolleys at twice the frequency, offering the same nameplate capacity, but a more attractive service that would quite possibly be less expensive to operate and maintain, but also would be more likely to spur ridership growth — thanks to the improved frequency.

There’s also the huge benefit that these are buses. While they are sure to cost a lot more than a regular 12-metre diesel bus, they are also going to cost a lot less than a tram, and have simpler, or at least more familiar maintenance. For a city that is thinking about building a single tram line as its transit backbone, it could instead created a bi-articulated trolley line and avoid a lot of the costs and extra personnel required to “step up” to trams. This means that at least at the low end of tram capacities, these vehicles probably make more sense.

There’s an extra boost because buses just run on roads. Many places around the world are very effective at quickly and cost-effectively building roadways, something which is less the case for trams.

The battery element is also really important. With a system like Prague’s airport line you, get the sleek buses and overhead wires that to regular people looks basically like a tram system, but with way lower capital costs because you don’t need to build that much wire. I also would say that while there are increasingly battery and super-capacitor tram options, doing away with overhead wires feels like less of a magical win when you still need to install rails, and a different roadway, and possibly other infrastructure. With these electric buses, you get a lot of the benefit of a tram with waaaaaay less infrastructure and investment. You can see that manufacturers like Solaris are starting to catch on to how cool this is, as they have a new sort of design package called “Metrolike”.

All of these benefits can be combined with the fact that modern buses, especially in Europe and Asia, already have a lot of features that in some places (North America mostly) are limited to trams: Lots of big screens telling you where the bus is stopping, how long from now that will happen, and the services you can connect to; high-quality, perhaps even textured grab bars and hanging straps; comfortable seats; and probably most importantly, a very comfortable quiet ride.

And of course, there’s the obvious operational benefits of buses over trams. They are more flexible (weaving around traffic but also around disruptions), which improves reliability and resilience, as well as allowing for more intense service. And they also don’t need tracks, and with batteries overhead wires — simplifying corridor construction when a decade down the road you want to do a resurfacing.

North America

The natural place for this technology is North America. We are bad at building trams, the US is bad at operating them, and we have huge roads which makes operating giant buses a kind of obvious thing.

You do see more bi-articulated buses in central Europe where roads are often generous, or on major arterials or busways, but they are hardly restricted to that type of environment — they are operated in some pretty tight spots in Switzerland for example. I think a lot of the beliefs around appropriate operating environment is more driven by perception than anything — buses with added trailers are not as hard to operate as you might guess.

The infrastructure-lite nature of this solution also fits us well, since we do usually seem capable of building really easy infrastructure at more moderate prices (the complex stuff seems to be disproportionate in its driving of costs).

I’m a big proponent of “BRT-lite” systems for medium to large cities, and these systems would be a perfect place to deploy this technology. These are often suburban corridors where we haven’t already built rail, connecting existing transit exchanges and running along wide roadways — you could easily imagine wiring up those roadways (on the specific segments where it’s easiest) and having the buses run on battery otherwise.

You could also imagine a bi-articulated trolleybus service would be perfect as the backbone “higher-order transit” line for university towns, creating a similar charismatic infrastructure effect as the ION light rail in Waterloo Region in Canada, but without the need to get planning and engineering ducks in a row the way that region did (a subsequent extension of the system is estimated to cost four times the initial system cost). You can imagine building these lines, marketing them really well, providing great service, and getting a huge transit network uplift, and a drive for denser urban development.

And then there are the sort of “airport shuttle” services like Prague. Right away I think such systems could make sense in a bunch of places in Canada, like Edmonton, Calgary, Quebec City, and Winnipeg, and I’m sure there are many similar small- to medium-sized cities in the US with major airports that would benefit.

A friend of mine often discusses a counterfactual where Ottawa built a downtown bus tunnel (probably similar to Seattle’s) and then expanded its bus system and electrified it through downtown. I have to admit that this is a pretty compelling idea, especially with bi-articulated trolleys.

The obvious thing is that the first places you’d want to build these systems are in cities that already have trolleybus know how — Vancouver, the Bay Area, Seattle, Philadelphia, etc. it’s remarkable how perfect these cities are as examples of in-house capacity. I remember Translink was able to wire detour routes for trolleys during Broadway subway construction quickly and for what appeared to be very little money, and you could imagine how the agency could turn that ability into something very powerful by wiring other parts of the region (subscribe for an article on that soon).

There is also the hitch of getting bi-articulated buses proven here. This shouldn’t be insurmountable, but like with many things (elevators for example) we have a weird regulatory environment that sort of operates separate from the rest of the world. Clearly some city and transit system will need to go out of its way to get these certified for Canada-US roads, and we will all owe them a debt of gratitude, like Edmonton introducing German Stadtbahns to the continent.