|Ringway 3 (Part)|
|From:||South Mimms (TL225001)|
|To:||Potters Bar (TL263002)|
|Length:||2.5 miles (4 km)|
|Met:||A1, A1081, A1(M), A6, A111, A1005|
|Now part of:||M25|
|Route outline (key)|
The Potters Bar southern bypass was planned as part of the M16 Ringway 3 and opened in the mid-1970s with the A1178 number. The road started on the A1 and A6 at South Mimms and headed east. A gap in the carriageway was where the mainline of Ringway 3 would have joined these slip roads, after which the road continued to end on the A111 east of Potters Bar.
In the early 1980s, with the plans for the Ringways having been considerably altered, the road was renumbered M25 and is now the section between J23 and J24. The space for the future western continuation via Borehamwood has not been used and is unlikely ever to be: the M25 to the west is an upgraded A6.