Magic Roundabout (Hemel Hempstead) viaduct. The BP building was found to be unstable due to defective reinforced concrete and the exit had to be closed. The building was demolished but the original route was not restored, although a newer side exit from the roundabout replaced the junction with Marlowes off a side road. Magic Roundabout (Hemel Hempstead) The "Magic Roundabout" in Hemel Hempstead, Hertfordshire, England, is the familiar name given to the Plough roundabout. The familiar name comes from the children's television programme, and is also used for a similar junction in Swindon and the M40 junction in Denham. The official name relates to
Roundabout flow on bridges, which are two viaducts creating a roundabout suspended over the ring road. Signal controlled roundabouts are common in the United Kingdom, Ireland and Spain (mostly the city of Valencia), where they have been introduced in an attempt to alleviate traffic problems at over-capacity roundabout junctions or to prevent some flows of traffic dominating others (around the M50 in Dublin for example). The Cherry Street roundabout in Kowloon, Hong Kong is also one such example. "Magic roundabouts" direct traffic in both directions around the central island. They are officially known as "ring junctions". The first magic roundabout was