Amsterdam was intended in 1932 to be the hub, a kind of Kilometre Zero, of the highway system of the Netherlands, with freeways numbered One to Eight planned to originate from the city. The outbreak of the Second World War and shifting priorities led to the current situation, where only roads A1, A2, and A4 originate from Amsterdam according to the original plan. The A3 to Rotterdam was cancelled in 1970 in order to conserve the Groene Hart. Road A8, leading north to Zaandam and the A10 Ringroad were opened between 1968 and 1974. Besides the A1, A2, A4 and A8, several freeways, such as the A7 and A6, carry traffic mainly bound for Amsterdam.