Initial plans for a Victoria line were made in 1937 but work on the first new underground line for 61 years began on 20th September 1968. It was built using new techniques including a drum digger (or rotary shield) and completed in record time. The first part (Walthamstow to Highbury and Islington) was opened in 1968. On 7 March 1969 the Queen opened the third stage (Warren Street to Victoria) and Princess Alexandra opened the final section (Victoria to Brixton) on 23 July 1971. In terms of passengers per mile, the Victoria Line is the busiest in London, carrying about 175 million over its 13.25 mile length each year.