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
M25 motorway outside Heathrow Airport consistently records the highest number of daily traffic counts on the British strategic road network with a sample in 2017 measuring 211,059 counts (lower than the record peak measured in 2014 of 262,842 counts). This compares to 197,219 counts measured on the M1 motorway between junction 7 and 8 outside Hemel Hempstead in 2014, and 195,325 counts measured on the M60 motorway between junctions 12 and 13 in Western Manchester, also in 2014. The M25, plus the short non-motorway A282 which joins the two ends of the M25 across the River Thames using the Dartford Crossing, is