M25 motorway re-examined as a motorway route in Sir Charles Bressey's and Sir Edwin Lutyens' "The Highway Development Survey, 1937". Sir Patrick Abercrombie's "County of London Plan, 1943" and "Greater London Plan, 1944" proposed a series of five roads encircling the capital. The northern sections of the M25 follow a similar route to the World War II Outer London Defence Ring, a concentric series of tanks and pillboxes designed to slow down a potential German invasion of the capital. Little was done to progress these plans until the 1960s when the Greater London Council developed its London Ringways plan consisting of four
London Underground infrastructure in 1999, and key interchange stations such as King's Cross St. Pancras, Victoria station and Green Park becoming step-free. Over 28 stations will become step-free over the next 10 years, taking the total step-free stations to over 100. In October 2015, TfL installed the first incline lift on the UK transport network, at Greenford station. The London Underground comprises eleven lines. London Underground trains come in two sizes, larger sub-surface trains and smaller deep-tube trains. Since the early 1960s, all passenger trains have been electric multiple units with sliding doors and a train last ran with a guard in 2000.