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
Denham Roundabout round it clockwise in the usual way, but as traffic volumes built up, the layout was altered so that the traffic moved round the roundabout in both directions, making it a ring junction with mini-roundabouts at the points that other roads join the main roundabout. Denham Roundabout The Denham Roundabout is where Western Avenue, the A40, flows into the M40 motorway. The roundabout below facilitates junction 1 (J1) of the motorway to connect with the westbound continuation of the A40, together with the intersection of the road from Uxbridge (A4020) and the road from Slough to Watford (A412). When the