Bendy-buses: the Marmite product of London. Mothers with pushchairs love them; cyclists hate them.
However, despite the aversion many people have towards the bendy-bus (also known as ‘articulated-buses’, ‘accordian-buses’ and ‘jointed buses’ in other countries) they currently make up an essential part of the London transport network.
In 2004, a report by TfL found that more than a third of visitors to the city centre arrive by bus. With bendy-buses capable of carrying 60 passengers more than a double-decker bus and improved disabled access it is obvious to see why they were originally implemented. They also offer several other great advantages: a higher maximum speed, increased stability (thanks to their lower centre of gravity) and a lower roadwheel pressure.
In keeping with the transport theme of my recent blog post, here’s a little look at the engineering behind the bendy-bus.
A typical London bendy-bus – here the 207 which runs between Hayes-By-Pass and White City. Image by Chloé Sharrocks
Their Construction
Previously illegal on British roads until 1980, bendy-buses of around 60 feet are now observed throughout Britain, and especially in London where in 2008 there were over 380 bendy buses in operation.
Fitted with an extra set of wheels compared to a normal bus, some models of articulated buses have a crab-like steering arrangement. In this case, the steering arrangement on the rearmost of the 3 axles turns slightly in opposition to the front steering axle allowing it to negotiate bends more easily.
A heavy pivot pin below the floor level joins the two halves of the bus and a turntable arrangement is constructed inside the vehicle to give a continuous floor, whilst ‘bellows’ seal the interior from the external environment.
The Folding Bellows
The concertina portion of a bendy-bus can be made from a hypalon-coated synthetic fabric or polyurethane. They are often furnished with additional properties such as UV resistance and low and high temperature insulation, to optimise fire resistance. The fabric is rubber-coated to protect the bellows from salt, grit, petrol, oil and stones. A key feature of the design is that despite being flexible they must also allow for a high-degree of road clearance.
The bellows can be produced using a vulcanisation process in which layers of elastomer-coated fabric are bonded together under intense heat and pressure which causes polymer molecules to link together with strong atomic bonds. Aluminium binding is also used within the bellows to help reinforce their shape. This prevents distortion from automatic vehicle-washers and damage from everyday wear and tear.
The Future of the Bendy-Bus?
In 2008, Mercedes-Benz were awarded the DEKRA Environmental Award for their new design of a hybrid bendy-bus.
Image of the new hybrid bendy-bus courtesy of the Mercedes-Benz website
Although the new Citaro bus has a diesel engine this does not power the vehicle itself, only acting as a generator, producing power which is stored in lithium-ion batteries stored on the roof of the bus. The batteries however, are not only charged by the diesel generator, but also when the bus brakes. This process, known as recuperation, means that each time the bus brakes when in traffic or nearing a bus-stop, energy is stored for use when the vehicle subsequently pulls-away and accelerates. This means that when in use, the bus produces virtually no emissions as well as little noise.
Despite Mercedes-Benz’s hard work, it would appear that the bendy-buses might not have a future if Boris Johnson is successful in phasing them out.
So do you agree with Boris’s opinion that they are “jack-knifing, traffic-blocking, self-combusting, cyclist-crushing bendy buses” or can you see them as a useful addition to a busy transport network?
Many cyclists have an aversion to the bendy-bus amid fears that the driver may not always see them on their nearside, especially when over-taking and subsequently pulling-in. Image by Chloé Sharrocks