M3 Junction 6 Black Dam Roundabout Improvements

Project status:   Current

Start date:   October 2014
End date:  Autumn 2015

Type:   Improvement Scheme
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Improvement Scheme

Part of our programme of improvements (generally with value <£10m)

Cost:  £10 million

Managed by:   Area 3


Work is progressing well on-site, with construction of the northbound carriageway through the existing roundabout underway. However, we currently expect the work to be completed in October, due to delays in the relocation of a gas main and other utilities within the extents of the work site.



What is happening?

Following completion of vegetation clearance from the work site, the relocation of public utilities is being carried out in advance of the main improvement works beginning in August.

We will be carrying out work to reduce congestion and improve the flow of traffic at the M3 Junction 6 Black Dam Roundabout. This will include:

  • construction of a four-lane northbound carriageway through the roundabout
  • widening on the eastern side of the gyratory to provide four lanes
  • widening on the north-eastern section of the gyratory to provide five lanes

M3 Spur Road:

  • widening to provide three lanes southbound from Black Dam roundabout to the M3 junction 6 roundabout

A339 Southbound:

  • widening to provide four lanes approaching the roundabout

A339 Northbound:

  • widening into the central reserve to provide four lanes to the A3010 Churchill Way diverge

A30 Ringway South:

  • widening to provide three lanes on approach to/from the roundabout
  • provision of two lanes onto the A339 northbound carriageway

A30 London Road:

  • widening to provide two lanes to the roundabout and two lanes to the four-lane northbound carriageway through the roundabout
  • widening to provide two lanes off the exit from the roundabout.
  • installation of a refuge island for cyclists and pedestrians on the A30 opposite Redbridge Lane

  • Associated works will include the following:
  • realigning all approaches to the roundabout
  • installing new traffic signals
  • installing new streetlighting
  • installing new traffic signs to advise motorists of the revised layout
  • renewal of road markings

These works are part of the national pinch point programme. The pinch point programme forms part of the UK Government's growth initiative, outlined during the Chancellor’s Autumn Statement in November 2011.

When and where is this happening?

The main construction work started in October 2014 and will be completed by Autumn 2015. The project is located at the Black Dam roundabout in Basingstoke where the M3 spur meets the A339 ring road and the A30.

Why is this happening and what will it cost?

The M3 junction 6 experiences congestion which regularly results in traffic queuing on the exit slip-roads during peak periods. This problem is connected to the Black Dam roundabout, located on the A339 approximately 350m north of M3 junction 6, which is currently operating above capacity.

Basingstoke & Deane Borough Council, supported by Hampshire County Council (HCC) and the Highways Agency have been working in partnership to address the congestion issues at both the M3 junction 6 and the Black Dam roundabout

The works are estimated to cost £10 million.

How will the scheme be carried out?

The works will transform Black Dam roundabout into a fully-signalised junction with a dual four-lane carriageway through the centre of the roundabout. This will involve:

  • realigning the approaches to the roundabout
  • constructing a retaining wall to accommodate carriageway widening
  • installing new traffic signals
  • improving routes for pedestrians and cyclists


What are the benefits?

As part of the pinch point programme, this scheme aims to:

  • help to reduce daily congestion especially during peak times
  • reduce journey times for the travelling public 
  • improve safety
  • boost the economy

Traffic flows across the Black Dam roundabout will be improved through the widening of the approaches to and exits from the roundabout as well as the construction of a northbound four-lane carriageway through the roundabout.

How do I find out more information ?

More information will be posted on this project page as it becomes available. You can subscribe to be alerted when updates are made.

If you have any queries about this project you should contact the Highways Agency Information Line by emailing ha_​info@​highways.​gsi.​gov.​uk or calling 0300 123 5000.

Other works are planned for Basingstoke during summer 2014, to find out more, please visit: http://​www​.basingstoke​.gov​.uk/​b​r​o​w​s​e​/​t​r​a​n​s​p​o​r​t​-​a​n​d​-​s​t​r​e​e​t​s​/​h​i​g​h​w​a​y​-​w​o​r​k​s​.​htm

Details of scheduled roadworks are provided to help you plan your journey. Please note that works are weather- and resource- dependent and may need to be cancelled at short notice. This information is not updated in real time so please check Traffic England for current traffic conditions. Diversion timings are approximate and act as a guide only.

Will there be roadworks?

Roadworks will be needed to carry out this scheme safely and efficiently. Due to the scale and location of the works, delays are expected during the construction period and we advise that you allow extra time for your journey.

We recommend that you avoid this route during the construction period if possible.

We will continue to work on refining the traffic management to minimise disruption to road users, local communities and businesses.

By installing narrow lanes and a speed limit work can be carried out close to the carriageway without the need for full closures.


We will be closing the M3 Spur northbound, from junction 6 to the Black Dam roundabout, and reducing the Black Dam roundabout to a single lane over two full weekend closures. This will allow the construction of a new splitter island at the northern point of the M3 Spur.

The work will take place from:

10pm on Friday 19 June until 5.30am on Monday 22 June


10pm on Friday 26 June until 5.30am on Monday 29 June

At this time, diversion routes to Junctions 7 or 5 will be in place.


Signed diversion routes will be in place at these times, and please allow additional time for your journeys while these works take place

Road Works

DateDurationDetailsAllow an Extra
Monday 13 July to Thursday 16 July10pm to 05.30 am each nightClosure of the A339 southbound (from the Eastrop roundabout to the Black Dam roundabout)Please allow extra time for your journey
Friday 17 July to Sunday 19 July10pm to 05.30 am each nightClosure of the A339 northbound (from the Black Dam roundabout to the Eastrop roundabout)Please allow extra time for your journey

How will you manage traffic?

Traffic will be managed by the installation of narrow lanes with a 30mph speed limit through the work site.

We expect to close each approach road for one night during the work to install overhead sign gantries. The roundabout will also be closed in sections overnight to allow resurfacing. All closures will be advertised in advance and signed diversion routes will be in place.



Will there be diversions?

A signed diversion route via the A3010 Churchill Way and A30 Ringway South with be in place during the closures.



M3 Junction 6 Black Dam Junction Improvement Frequently Asked Questions
M3 Junction 6 Black Dam Junction Improvement Frequently Asked Questions
Black Dam Improvements M3 Junction 6 - Exhibition imagery
The Black Dam Roundabout is a vital junction to and from Basingstoke.
Black Dam Improvements Exhibition Panels
Black Dam improvements M3 Junction 6 - Exhibition Panels



M3 Junction 6 Black Dam Roundabout Improvements - Environmental Covering Note
Summary note describing environmental assessments required for this scheme.
M3 Junction 6 Black Dam Roundabout Improvements - Surface Water Drainage
Summary of results from surface water drainage investigation carried out as part of scheme design.
M3 Junction 6 Black Dam Roundabout Improvements - Summary of Environmental Results
Summary of results following investigation of environmental aspects affected by this scheme including air quality, visual impact and wildlife.