You Won’t Believe The Incredible Engineering That Allows Articulated Buses To Bend

Every day, countless people around the world board a bus to travel to a destination. These buses come in all shapes and sizes, from comfortable coaches to towering double-deckers. One of the best ways to increase a coach’s passenger capacity without adding height is to build the bus in at least two sections, adding a pivot point near the middle. The articulated bus is a common sight everywhere, but how they actually work, especially when they have a rear engine, is far more clever and interesting than you might think. A lot of these buses put brilliant engineering in plain sight. America’s largest train museum, the Illinois Railway Museum (IRM), hosts a special event each year to celebrate the transit bus, one of the greatest forms of public transportation that does not ride on rails. IRM is home to America’s largest collection of preserved buses, and most of the over three dozen trolley buses and motor buses in the museum’s hands do run and drive. This vast collection makes IRM the only railroad museum in America with a regular bus service. You might think it’s weird for a train museum to preserve so many buses across three warehouse-sized barns, but buses and trains complement each other in functional public transportation systems. One helps the other. I have not missed a single Bus Day since I started coming to the Illinois Railway Museum in 2022. This year’s Bus Day was the 11th running of the event, and in my experience, each Bus Day has been better than the last. This time, for example, there was a practical buffet of 13 buses to ride throughout the whole day. That Routemaster was the subject of one of my early RV articles at Jalopnik. Credit: AuthorOne of those buses was King County Metro No. 4020, a 1987 MAN SG-T310 articulated trolley bus. This unit usually gets to stretch its legs on every Bus Day, and it’s a favorite among visitors because everyone loves a fun “bendy bus.” As my wife published posts about our Bus Day at IRM, some followers and readers asked a curious question: Just how do articulated buses actually work? The answer to that question is more exciting than it would seem at first glance. Yes, a lot of bendy buses work exactly how you probably think they do. But others require quite a bit of clever engineering that you might not notice until after you read this. AuthorOver A Century Of Bending Let’s start at the beginning: the dawn of the articulated bus, because it’s important to see where we’ve come from before I show you where we are now. The articulated bus came early on in the development of the transit bus. Some of the first known internal combustion buses were built in the mid-1890s, and while those units were small, they wouldn’t be for long. As technology progressed, builders figured out how to stuff more people in a single bus. This was great for efficiency. It was cheaper and more practical to stuff one bus full of people than it was to run multiple smaller buses. Mechanics had fewer buses to work on, the transit district had fewer drivers to hire, and there were fewer engines to fuel. Daimler TruckHowever, a rigid bus can only get so long before making it any longer leads to diminishing returns. Super-long buses can carry more people, but have a harder time navigating city streets. Building up may also not be possible, as a double-decker bus might interfere with overhead infrastructure or fail to fit into tunnels. The solution was simple. Builders began assembling buses in two distinct sections. The second section of the bus would connect to the rear end of the coach’s front section through an articulating joint. The earliest example of an articulated bus I could find is this Dutch Ford Model T, which was built in the early 1920s. Check out how the interior of the rear section is paired with the front using an accordion-like central section: Public Domain via busbrief.nlThis wasn’t the only way to do it. An even simpler method to increase bus capacity was to make a single-unit bus or truck tow a trailer that had seats in it. A good example of this type of bus is the Officine Meccaniche bus truck from 1930, which is pictured below. The interior of the trailer was not connected to the main unit in any way. As a result, the trailer had its own entry doors. Often, buses like this had a conductor to signal to the driver when the bus was ready to get underway. Officine MeccanicheAs it happens, I’ve written about articulated buses before, and my story is a good primer: Of course, I cannot talk about towed buses without talking about the very fun trailer bus. Those weirdos are little more than tarted-up semi-trailers with seats and windows. But they aren’t really articulated buses, so I will talk about those buses on a different day. Articulated bus history starts getting really interesting in the late 1930s. Over in Italy, Alfa Romeo produced the pioneering 1937 Alfa Romeo 110 AM-Macchi. This bus, which Curbside Classic said carried up to 180 seated and standing passengers, had a novel way of articulation. Unlike today’s articulated buses, which articulate horizontally and vertically like a trailer, the Alfa Romeo had only vertical articulation. Having the center section articulate up allowed the bus to drive up grades without getting stuck. The Alfa Romeo 110 AM-Macchi. Credit: ATM via eBayIn 1938, the city of Baltimore put America’s first articulated bus into service. The Twin Coach Super-Twin was similar to the Alfa Romeo in that it articulated only vertically. To permit sharp turns, Twin Coach, like Alfa Romeo, designed a rear-wheel steering system. While extremely weird, there was some logic to this. Per Twin Coach, because its bus articulated only vertically, the bus floor is straight from front to rear. The Twin Coach’s articulation was more of a transitional technology. After World War II, bus builders largely switched to the more modern articulation system that we know of today. Here’s America’s first fully articulated highway bus, the 1946 Kaiser built for the Santa Fe Trail Transportation Company. Santa Fe Trail Transportation Co.How To Make A Bus Articulate Today, there are generally four ways to achieve an articulated bus. Two concepts that I explained earlier, the trailer bus and the bus that tows a trailer, remain in operation today. Trailer buses can still be found in Cuba, and they’re glorious in their simplicity: A trailer bus in Cuba in 2006. Credit: Panther – CC BY-SA 3.0Meanwhile, over in Munich, Germany, the Münchner Verkehrsgesellschaft runs the Busanhänger (bus train), which is a bus that tows a separate trailer that is also a bus. These were built in just 2022 by Sono Motors: Sono MotorsHere in America, you’ll generally find two kinds of articulated buses. The first, and older type, is the puller. In puller designs, the front section of the bus is a complete vehicle. The engine will usually be located towards the rear of the front section and under the floor. Only the rearmost axle of the front section (typically the middle axle of the whole bus) is powered. A great example of this design is the Crown-Ikarus 286, a bus jointly developed by the Crown Coach Corporation of America and the Ikarus Body and Vehicle Factory of Hungary: The Crown-Ikarus 286. Credit: Crown-IkarusBuilt from 1980 to 1986, these buses feature a Cummins 855 cubic-inch NHHTC straight-six mounted under the floor near the rear axle of the bus. That engine drives the rear wheels through either an Allison HT740 automatic or a Voith D864.2 automatic, both featuring four speeds. Puller buses usually connect to their rear sections through a somewhat complex articulation joint. PEI Mobility W695P puller bus articulation joint. Credit: PEI MobilityThis unit consists of a front and rear subframe that connect to the front section and the rear section, respectively. They meet in the middle, where they ride on a ring of bearings. These bearings allow the front and rear sections to turn relative to each other. In other words, it functions like a joint. In a puller configuration, the rear section of the bus straightens itself out as the front section pulls the bus forward. It’s like a semi-truck trailer, but with a few extra steps. These joints tend to be made out of materials like welded steel or cast iron. From here, a bus builder will place a turntable on top of the articulation joint, bellows to seal the bending path between the two bus sections, and flexible cabling to provide power to the rear of the bus. Bellows of an articulated bus. Credit: HUBNERThe benefit of the puller bus is that it’s technically a simpler design. The rearmost axle isn’t powered, and the articulation joint needs fewer components to get its job done. Anecdotally, some bus drivers I’ve spoken to prefer puller buses in snowy situations, since the powered axle is ahead of the articulation joint. Articulated buses also have a limited amount of vertical flexibility, permitting them to climb city streets. The articulation joint of a New Flyer bus. Credit: Goodshoped35110s – Public DomainHowever, puller-type articulated buses have one main drawback, and it’s that, generally, the floor cannot be lower than the engine that lives right in the middle of the bus. Some puller-type articulated buses manage to have a low floor by moving the engine to a side of the bus and having the lower floor go around the engine. The Van Hool AG300 has this design, and while it has a low floor, the large engine takes up a vast amount of space that could be used for seating. Check it out: The engine is under that gray block of plastic in the center of the image. Credit: Autoline ListingHow A Rear-Engine Articulated Bus Works The preferred solution to this problem is to place the engine at the very rear of the bus, where it won’t gobble up valuable passenger volume. Yes, a rear-engine bendy bus!