The intensity of its service was reflected in the 1,650 locomotives it owned – it was by far the most densely trafficked system in the British Isles with more locomotives per mile than any other company – and that one third of its 738 signal boxes controlled junctions averaging one every 3.5 miles (6 km). No two adjacent stations were more than 5.5 miles (9 km) apart and its 1,904 passenger services occupied 57 pages in Bradshaw, a number exceeded only by the Great Western Railway, the London and North Western Railway, and the Midland Railway. It was the first mainline railway to introduce electrification of some of its lines, and it also ran steamboat services across the Irish Sea and North Sea, being a bigger shipowner than any other British railway company.
The L&YR was incorporated in 1847, being an amalgamation of several important lines, the chief of which was the Manchester and Leeds Railway (itself having been incorporated in 1836).
The following companies, in order, were amalgamated into the L&YR. The dates shown are, in most cases, the Acts of Parliament authorising the incorporation and amalgamation of each company. In a few instances the effective date is used.
The system consisted of many branches and alternative routes, so that it is not easy to determine the location of its main line. For working purposes the railway was split into three divisions: