The M1 was extended south towards London from its original starting point at Junction 5, in three stages. The first stage, opened in 1966, took the motorway south-east, parallel to the A41, to meet the A5 at junction 4 south of Elstree. The second phase continued east to Scratchwood (London Gateway Services occupies the location of the missing junction 3 from where an unbuilt spur would have connected to the A1 at Stirling Corner to the north-east). The M1 then runs south alongside the Midland Main Line towards Hendon, where it meets the A1 again at Junction 2 via a tightly curved flyover section. These flyovers connecting from the A1 were originally both for northbound traffic: the left one as the on-ramp to the M1, the right one going over the A1/A41 junction beneath to rejoin the A1 northbound.