Trans-Pennine transport transformers
Sixty years after their introduction as the centrepiece of a service revamp, DAVID CLOUGH charts the career of Britain’s most iconic first-generation diesel multiple units - the ‘Trans-Pennine’ Class 124s
The British Transport Commission (BTC) took the first steps towards the use of lightweight diesel railcars several years before the 1955 Modernisation Plan was conceived, but these were primarily for rural services.
The idea was not new and mirrored the construction of diesel-mechanical railcars for such work by the Great Western Railway (GWR) during the 1930s. The GWR’s first fullblown application of this type of train was also in the 1930s, for a premium service between Birmingham Snow Hill and Cardiff that proved very popular, despite a supplementary fare. This was the first use of diesel power for a UK inter-city service.
BTC’s application of the diesel railcar concept evolved quite quickly, with the decision in 1954 to build trainsets for express services between Glasgow Queen StreetEdinburgh Waverley and Birmingham Snow Hill-Swansea.
These three-car sets used a power train comprising two British United Traction (BUT, an alliance of Leyland Motors and AEC)
150hp diesel engines coupled to a four-speed gearbox, and two of the three cars each had one power train. This provided 600hp for a three-car set and maximum speed was 70mph. Service introduction commenced from January 1957.
On April 29 1955, BTC’s Technical & Development Committee discussed traction options for a modernised inter-city transPennine service between Liverpool Lime Street, Manchester Exchange, Leeds City and Hull, to replace a long-established steamhauled operation.
While the first part to Manchester is level after the initial climb out of Liverpool, the section over the Pennines between Manchester and Leeds is very difficult, with steep gradients as well as many slowings over junctions and curves. The principal climbs are one mile at 1-in-47/59 getting away from Manchester, seven miles at 1-in-125/175 from Stalybridge to the summit at Standedge Tunnel, and seven miles at 1-in-96/105 westbound from Huddersfield to Standedge Tunnel.
The committee was not in favour of a power car for the new trainsets, preferring the use of an underfloor-mounted power train.
One proposal was to use a 450hp Paxman 6ZHX diesel, which would have meant a total of 2,250hp across five power cars in a six-car formation. Each engine would be married to a main generator that would then power two traction motors on one bogie.
Using the available power at rail, rather than the installed figure, the power-to-weight ratio worked out at a respectable 7.2hp per ton. Provision of power of this magnitude would have meant a 1-in-70 gradient could be climbed at 60mph and the maximum speed would have been 90mph, which would have enabled journey times to be cut by 25 minutes.
Derby Works produced a two-car prototype unit from two 1920s carriages, suitably converted with driving cabs at one end of each coach. This emerged in 1956 and ran extensive trials, but it failed to win wider support and never ran in service. The decision not to pursue this option was probably fortunate, because the Paxman engine was likely to have suffered reliability issues.
The consensus of the Technical Committee was that using the new standard-pattern powertrain, incorporating two 150hp BUT engines, would give roughly the same power-to-weight ratio - after allowing for the inherently higher transmission efficiency of mechanical over electrical drivetrains and their lower weight, which meant lower overall vehicle weights.
As the sponsoring Region for the proposed revamped service, the North Eastern Region was unhappy. It considered that more power was needed than could be delivered by the BUT engines and wanted to await the availability of a new Albion (part of Leyland Motors) engine of 230hp.
It took until April 9 1959 for the Commission to provisionally sanction the project at a cost of £ 948,600 as part of the 1960 building programme, although it was unhappy about the number of spare vehicles requested.
The order comprised 17 Driving Motor composites, 17 Motor Brake Seconds, nine Trailer Seconds and eight Buffet Firsts (a total of 51). These were to form seven six-car rakes that comprised two each of the driving and non-driving motor coaches and one each of the trailers and buffets.
With three of both the driving and the nondriving coaches spare, it is clear why BTC felt there was over-provision. It seems to be the case that eventually eight sets were assembled, because the original request for 51 vehicles was agreed in the end.
Design and construction was the responsibility of Swindon Works under Lot numbers 30603-6, with input from the BR Design Panel. The latter produced a handsome front end, clearly based on the Glasgow suburban ‘Blue Train’ electric multiple units, with wrap-around windscreens.
The front end panels were made from glass-fibre, rather than steel, and included a four-character route indicator panel. Livery was standard British Rail green for the bodysides and grey for the roof, relieved by light grey bands at cantrail height and below the windows.
Ted Wilkes (of Wilkes & Ashmore), who advised on the styling of several diesel locomotive designs including Class 47s, was consulted on styling.
The Motor Brake Second vehicles had accommodation in compartments, whereas the Trailer Seconds had open seating. The leading section of the driving vehicles comprised a First Class compartment, with a Second Class open saloon behind. Seating
On weekdays, five trains ran coast to coast (up from three), with a further four between Leeds and Liverpool and one from Leeds to Manchester. Fortyfive minutes was saved and the fastest through service took 2hrs 48mins for the 125 miles, at 44.6mph.