The innermost ring-road, the M-30, is the only one with its path strictly located within the Madrid municipal limits. It is owned by the Madrid City Council and operated by Madrid Calle 30, S.A. It is the busiest Spanish road, famous for its traffic jams. A significant portion of the southern part runs underground parallel to the Manzanares, with tunnel sections of more than  in length and 3 to 6 lanes in each direction.