|Location Map ( geo)|
|From:||Potters Bar (TL259008)|
|Distance:||7.5 miles (12.1 km)|
|Meets:||A111, A1000, A1081, M25, B5378, A5183|
|Former Number(s):||A111, A6, B555|
|Route outline (key)|
The present B556 is a cross-country road, mostly in Hertfordshire. It starts in Potters Bar, at traffic lights on the A111 and A1000, and heads west signposted South Mimms into Mutton Lane. This is a largely straight suburban road which zigzags over the East Coast Main Line just south of Potters Bar station.
Presently we reach open country and soon cross a bridge over an unclassified road (the erstwhile A1 bypass) and the adjacent A1(M). Not long afterwards we reach South Mimms where we bear right at a roundabout to join the dead-straight St Albans Road. After reentering open country we meet the M25 and divert from our line to pass beneath the motorway.
After the road straightens out again, the B556 and M25 run adjacent as far as the next roundabout, which is part of junction 22. Here we meet the anticlockwise offslip and the A1081, which runs via the clockwise slip roads into London Colney. At the next roundabout the anticlockwise onslip turns off and we then continue close to the motorway, leaving it behind after we cross the B5378. The road continues westwards along Harper Lane past Harperbury Hospital. After going over the Midland Main Line the road ends immediately afterwards on the A5183 (former A5) north of Radlett.
The route's present designation came into first use on 1 April 1935 when the B555 from Hatfield to Radlett had its number changed to B556 – probably to avoid confusion with the Barnet Bypass (completed in 1926) which was renumbered A555 on the same date.
The northern end of the road, in Hatfield itself, was downgraded following the construction of the New Town in the 1960s.
Construction of the A1(M) and M25 in the 1980s then changed the route of the B556 completely. The road was severed by the new A1(M) and so the old road through Colney Heath was declassified following a short period as the B197. However, instead of having its eastern end on the A1081 at London Colney the road was extended east along the former A6 as far as South Mimms, then the A111 from there to the A1000 in Potters Bar, giving the road its present length.