Detailed design approaches
Normally, rail systems are cheaper when placed in a cutting than on a deck. Hence, it is more common to find light rail taken at high level and buses (and sometimes traditional tram systems) at street level, all existing above the rail network. In cities, heavy rail has to pass beneath or above the road network, which often pre-exists the age of railway construction. However, the question of cross-city movement around interchanges imposes a discipline upon the whole transport system, especially as the weight of political argument and, hence, public investment shifts from road to rail. Low-level railway lines result normally in interchanges at street level, possibly with elevated light rail operating above bus, cycle and taxi levels. Railways at street level normally employ an elevated concourse where it forms a bridge over the tracks (as at Croydon near London) or a low-level one as at Leiden in Holland. Whatever the arrangement in plan and section, the structural engineering of the interchange will be a significant factor in giving the spaces their architectural character.