Road competition was also increasing with over 20,000 surplus military vehicles being sold cheaply after the First World War. Many went to demobilised army trained drivers, who set themselves up as small haulage contractors. In 1920, the Roads Act had introduced a tax on mechanical vehicles, which was paid into a Central Fund to pay for improvements to roads and highways and in 1925, the Road Improvement Act introduced powers to remove obstructions from roads and to widen streets. The road administration was also centralised and roads were classified into four divisions depending upon their importance. Grants from the Central Fund were then allocated to improve roads and bridges depending upon their classification. In addition by 1926, 25% of scheduled road maintenance was also being paid for by the Central Fund. With the improved roads came the Motor Omnibus which started to provide reliable rural bus services in direct completion to the railway passenger services.
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Despite the economic situation there was an appetite for speed and in 1927, the Great Western Railway introduced the Super Castle King Class passenger locomotives. The design had originally been proposed in 1919, but the 20.5ton axle weight exceeded the permanent way capabilities, however by 1927, bridges on the major routes had either been reinforced or replaced (see ) or reassessed following the findings of the Bridge Stress Committee. This committee finally reported in 1928, but the Great Western Railway civil engineers had been intimately involved in much of the testing allowing them to more accurately calculate bridge capabilities. In particular, it was found that the reduced hammer-blow from a balanced four cylinder locomotive meant that a locomotive with 2.5ton more static axle load could be accommodated. The catalyst for the Kings was the introduction of the Lord Nelson class by the Southern Railway, which had a marginally higher tractive effort than the Castle Class. The first engine of the new class King George V No 6000 was another publicity triumph, when it represented Britain on the Baltimore & Ohio Railroad Centenary Exhibition. Back in the UK the King Class started to haul the crack London to Birmingham two hour passenger expresses (see ).
They were taken around the period from 1882 to 1966
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The Bridge Stress Committee report also affected other Railways. For many years the Midland Railway had refused to allow engines larger than 4-4-0 to cross the Stonebridge Viaduct in Gloucestershire and this limited the locomotives that could be used on the Great Western Railway's Birmingham to Bristol expresses as they used running rights over the Midland's line. In 1927 the viaduct was replaced with an embankment and reassessed to carry 4-6-0 locomotives at a maximum speed of 15mph. This resulted in 4-6-0 Star and Hall class locomotives displacing the 4-4-0 locomotives on this route.