Black Dam Roundabout
| Black Dam Roundabout | |||
| Location Map ( geo) | |||
| |||
| Location | |||
| Basingstoke | |||
| County | |||
| Hampshire | |||
| Highway Authority | |||
| National Highways | |||
| Junction Type | |||
| Roundabout and Spur | |||
| Roads Joined | |||
| M3, A30, A339 | |||
| Junctions related to the A339 | |||
Black Dam Roundabout is the roundabout at the north end of the spur from junction 6 of the M3, though the name is commonly applied to both this junction and the main roundabout under the M3.
The junction started out as a T junction between London Road and Coronation Road (later called Grove Road). By the 1960s, the A30 had been diverted down Grove Road, and this junction became a large T-junction with priority towards Grove Road. The A339 now took the old route into Basingstoke.
When the M3 opened, the main Black Dam Roundabout was built. The A339 moved onto a new route heading north from here. A smaller T-junction remained in place to the west. To the east, it has been pointed out that a seemingly random section of dual carriageway was provided in just the right place for a future flyover to land here - this may have been the intention.
Within a couple of years, Ringway South had been built. Both Grove Road and the old London Road route into Basingstoke were disconnected from the main junction, and traffic for those roads now had to use the new junction to the west. Ringway South had space for a flyover.
High traffic levels have been a common problem for this junction. In 1989, an improvement proposal titled "A339 Black Dam GSJ" added to the Trunk Road forward programme, with an expected cost of £5 million; which had risen to £7.6 million for a 1.0 mile D2 scheme by 1994. It was withdrawn from the programme in the November 1995 review along with a large number of other schemes.
During 2016, the northern roundabout was majorly reconfigured. The junction was fully signalised and there was an additional road added to the middle of the roundabout that allows traffic from the M3 and A30 westbound to avoid going around the roundabout, turning the junction into a hamburger.
Routes
| Route | To | Notes |
| The SOUTH WEST, Southampton, Winchester | ||
| London, Guildford, Farnham | ||
| Basingstoke (A339), Alton (A30), Reading (A33) | spur to Black Dam Roundabout | |
| The SOUTH WEST, London | spur to M3 | |
| Ring Road (N), Town centre, Newbury, Reading (A33), Daneshill, Chineham, Houndmills | ||
| Ring Road (S), Alton (A339), Viables | ||
| Old Basing |
