The third generation

In my opinion, the history of the British half-cab double-decker can be summarised in three generations. First generation – establishing the format and the main components. Second generation – refining the design to create a comfortable and efficient vehicle. Third generation – embodying new technology to optimise the design.

The first-generation half-cab double-deckers

Half-cab double-deckers came about after the First World War. Operators wanted to increase the seating capacity downstairs and so manufacturers moved the driving position from behind the engine to beside it.

The first examples of this first generation looked pretty cobbled together, with high chassis frames, a driving position open to the weather, crude running units and solid tyres. Incremental improvements were made, like full-width bodies, partially enclosed cabs, and early pneumatic tyres, but it took a bit of a revolution in the late 1920s to take us to the second generation.

The second generation

Bringing novel ideas back from his time in America, John Rackham designed the Leyland Titan, which was introduced in 1927. It had a low-swept frame, welcoming interior and advanced power train. The rakish body made earlier buses, and especially trams, look utterly outdated.

Rackham was enticed to join AEC, where he created the Regent, which emulated and improved upon the Titan. Other manufacturers were forced to produce more modern models – the Albion CX series, the Bristol K series, the Crossley Condor, the Daimler COG series, the Dennis Lance, the Guy Arab and so on.

By the end of the 1930s the configuration of the typical second generation British half-cab double-decker was pretty well settled.

Diesel fuel had superseded petrol, but manual gearboxes prevailed (semi- and fully-automatic transmissions didn’t catch on). The engine was hidden beneath a narrow sheet metal bonnet, that met the cab on one side and an open mudguard on the other. Springs were steel and brakes were vacuum. The upper deck extended all the way forwards over the cab and bonnet.

The entrance was almost always a rear open platform. The chassis height was just low enough to permit access to the lower saloon by a single step. The body was smooth sided, with large windows and gentle curves to the front and rear roof domes. The bodywork was attached to the chassis but carried no dynamic loads, and the body frame was made from some combination of steel and timber, with steel or aluminium panelling.

If the bus had to ply routes with reduced clearances like some railway bridges, the upper deck was arranged in a lowbridge pattern. This involved a side gangway on the off-side and a step up to transverse bench seats that could take four passengers. Very cramped, and awkward when someone sat by the window needed to get out.

The arrangement was pioneered by Leyland in the 1920s to get the height of a double-decker down to a reasonable level. Improved designs meant this was no longer necessary by the late 1930s, except on buses destined to operate in areas with low clearances.

Against that general pattern some outfits took a maverick approach. One was the Birmingham and Midland Motor Omnibus Company (BMMO), better known as Midland Red.

Midland Red was one of very few operators that designed and built its own vehicles. Under the technical leadership of its chief engineer, Loftus George Wyndham Shire, in the 1930s it decided that a forward entrance, behind the front axle, was the better layout for a double-decker. It was a pioneer in other ways, able to take advantage of close links with the automotive component suppliers that serviced the huge West Midlands car, lorry and bus building firms.

By 1939 the second-generation double-decker was reaching a high level of refinement. The apotheosis was undoubtedly the London RT, a bus designed by an in-house team at the Chiswick engineering headquarters, with a chassis built by AEC as a variant of the Regent, and body to an advanced standard design that could be built by a number of bodybuilders.

But the Second World War brought an end to such progress. Instead, design went backwards as firms that were allowed to continue building buses had to embody heavier materials, cruder components, starker interiors, and none of the curved panels and graceful lines that marked out the best of the 1930s products.

When peace returned the demand for new buses was enormous – partly to replace vehicles destroyed in the conflict, partly to allow thousands of utterly worn-out buses to be scrapped (whose working lives had to be extended through the war), and partly to service new housing estates that saw towns and cities expand considerably.

The second-generation half-cab double-deckers saw further refinements, like air brakes instead of vacuum, but the basic formula stayed the same. AEC improved the Regent, and its RT variant was produced in staggering numbers for London Transport. Leyland updated the Titan and adapted it to meet London’s insatiable appetite for buses with the RTL and RTW types.

The various manifestations of the RT family eventually added up to what was, in the late 1950s, the largest fleet of buses to a standard design anywhere in the world – almost 7,000.

At this time the bus operating industry basically split into five segments. There were dozens of municipally-owned fleets – some huge, some tiny. There was the Tilling Group, whose constituent companies ran a mixture of urban and rural services across England and Wales. Then came British Electric Traction (BET) which did the same. Scottish Motor Traction (SMT) ran large parts of the Scottish bus network. And then there were lots and lots of independent operators, the biggest of which had fleets running into the hundreds.

Bus operators in the Tilling Group found themselves nationalised in 1948, and restricted to buying KSW double-deckers from Bristol and Eastern Coach Works, who were prohibited in return from catering to the open market.

At the same time, the SMT companies in Scotland were nationalised and their ownership transferred to Scottish Omnibuses. They were also allowed to buy Bristol and ECW equipment, but could also buy from other manufacturers.

BMMO evolved its double-decker design into the D5 in 1948. To an observer, its most striking feature was a bonnet that enclosed the radiator and the front near-side wheel and gave the front of the bus a more integrated appearance.
Soon other operators persuaded their preferred manufacturers to cloak their engines in a similar fashion and big city fleets especially tended to favour this layout, even if it made engine access a bit more awkward.

The third generation

Moving into the 1950s, and behind the scenes, bus makers and operators were contemplating new approaches, approaches that would take us to the third-generation half-cab double-deckers we are going to compare, from AEC-PRV, BMMO and Bristol-ECW.

These three outfits were convinced the immediate future lay in persevering with front-mounted engines, which required a two-person crew but offered very quick boarding and unloading times with an open rear platform. By contrast the other two big players in the market, Leyland and Daimler, were quietly investigating the potential of a rear-engined layout.

What made these new half-cabs different from the second generation was the adoption of significant new technology to improve performance, reduce weight and increase passenger appeal. London Transport and Bristol had both been involved in aircraft production during the Second World War and became aware of the possibilities of new materials and ways of manufacturing. BMMO was able to take advantage of the improved equipment coming from automotive suppliers which had also been enlisted to make components for the war effort.

These bus builders also took advantage of changes in regulations that allowed a bus to be 8 feet wide (from 1948) and up to 30 feet long (from 1956).