The loading gauge is small compared to those of newer metro systems (but comparable to that of early European metros), with capacities of between about 560 and 720 passengers per train on Lines 1–14. Many other metro systems (such as those of New York and London) adopted expanded tunnel dimensions for their newer lines (or used tunnels of multiple sizes almost from the outset, in the case of Boston), at the cost of operating incompatible fleets of rolling stock. Paris built all lines to the same dimensions as its original lines. Before the introduction of rubber-tire lines in the 1950s, this common shared size theoretically allowed any Métro rolling stock to operate on any line, but in practice each line was assigned a regular roster of trains.