Lowbridge double-deck bus
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A lowbridge double-deck bus is one which has an asymmetric interior layout, enabling the overall height of the vehicle to be reduced compared to that of a conventional double-decker bus. Usually, the upper deck gangway is offset to one side of the vehicle, normally the offside (or driver's side), and is sunken into the lower deck passenger saloon. Low railway bridges were the main reason that a reduced height was desired.
A major disadvantage of this layout was the inconvenient seating layout, with four-abreast seats upstairs making it difficult for passengers to manoeuvre past each other if they needed to alight in a different order from that in which they had boarded. A few buses were built with a gangway along both sides of the upper deck to mitigate the problem, but this was not a popular solution, as it resulted in a reduction in the seating capacity of the bus.
A second disadvantage was the restricted headroom for passengers on the offside of the lower deck, as a result of the encroachment of the upper deck gangway. It was often the case that passengers would bump their heads on it when standing up to alight.
[edit] Origins
The lowbridge design was introduced and patented by Leyland in 1927 on their Titan TD1 chassis. Early examples were delivered to Glasgow Corporation amongst other operators. One of the Glasgow vehicles is preserved.
[edit] Alternatives
At first, there was no viable alternative to the lowbridge design, apart from the use of single-deckers. However, the type started to become obsolete when low-height chassis were developed, which used a dropped-centre rear axle to enable the lower deck gangway to be lowered. This enabled a low-height vehicle to be built without the need for the cumbersome seating layout upstairs. The first such design was the Bristol Lodekka which was introduced by Bristol in 1949. It had a height of around 13' 6" (4.11m) compared to a typical height of around 14' 6" (4.42m) for a conventional highbridge double-decker. It was however only available to nationalised bus companies (Bristol itself being part of the state-owned sector at that time). Other lowheight double-deckers included the Dennis Loline (a version of the Bristol Lodekka built under licence); the AEC Bridgemaster and Renown; and the Albion Lowlander (a low-height version of the Leyland Titan PD3). The rear-engined Daimler Fleetline and Bristol VR were also low-height chassis. Nonetheless, despite the advent of the low-height chassis, the last lowbridge double-decker was not built until 1968.
When the rear-engined Leyland Atlantean was first introduced in 1958, it did not have a dropped-centre rear axle, even though the prototype had featured one. As a result, some Atlanteans were built to a "semi-lowbridge" layout, with the front half of the upper deck laid out conventionally, and a side gangway with raised seating area towards the rear.
A special situation existed in Beverley, in the East Riding of Yorkshire, where buses had to pass under the arched structure of Beverley Bar. To facilitate this, East Yorkshire Motor Services had a number of double-deckers built with special roofs of severely arched profile to match the shape of the bridge.
[edit] Notable vehicles
A notable lowbridge bus is Barton Transport's no. 861, registered 861 HAL. It is unique in combining a low-height chassis (Dennis Loline II) with lowbridge bodywork, built by Northern Counties. With the combined effect of both these height reduction techniques, the height of the vehicle is less than 12' 6", which remains the lowest ever for a British closed-top double-decker.
The last lowbridge double-decker to be built was bought by Bedwas and Machen UDC, a small municipal bus fleet in south Wales, in 1968. It is a Leyland Titan PD3 with bodywork built by Massey of Wigan, and is registered PAX 466F. Following its sale by B&MUDC's successor, Rhymney Valley District Council, it was operated by Stevensons of Uttoxeter, and subsequently by MK Metro of Milton Keynes.
