The growth in tourist numbers continued into the age of the motor car, when railways began to be closed or run down. The formation of the Lake District National Park in 1951 recognised the need to protect the Lake District environment from excessive commercial or industrial exploitation, preserving that which visitors come to see, without any restriction on the movement of people into and around the district. The M6 Motorway helped bring traffic to the Lake District, passing up its eastern flank. The narrow roads present a challenge for traffic flow and, from the 1960s, certain areas have been very congested.