M3 Junction 6 Black Dam Roundabout Improvements

Project status:   Current

Start date:   October 2014
End date:  March 2016

Type:   Improvement Scheme
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Improvement Scheme

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

Cost:  £11.246 million

Managed by:   Area 3


The Black Dam Roundabout will be fully open by Spring 2016.
Rather than a partial opening of the roundabout in November 2015, which would have affected traffic flows and driver behaviour, we have decided with our partners in Hampshire County Council and Basingstoke and Deane Borough Council to maintain the existing road layout until the junction can be fully opened.
Partial opening of the junction in November would have opened two lanes of the northbound carriageway through the roundabout, along with the two lane section from the A30 London Road westbound to the A339 northbound. The approach roads would have retained the current number of lanes. With shorter daylight hours and the increased number of journeys over the Christmas holiday season, the preferred option to delay the full opening until the New Year will be safer for road users and construction workers.
We will pause construction between Wednesday 23 December and Monday 4 January during which time existing lanes will be kept open and traffic management (cones) will be removed except where necessary for safety reasons. There are no planned weekend closures. Highways England are working closely with Hampshire County Council, Basingstoke and Deane and the Enterprise M3 Local Enterprise Partnership (representing business interests) to look at further mitigation to reduce the impact on residents, road users and the local economy.

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 March 2016. 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 Highways England 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 junction with traffic signals and 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.

For other works planned for Basingstoke 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

Please note that due to an ongoing technical error, the Highways Agency Information Line is still displaying the old email address and we are hoping to resolve this problem as soon as possible. In the meantime the old email ha_​info@​highways.​gsi.​gov.​uk is still working and you can also use our new email address info@​highwaysengland.​co.​uk


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.

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

In September we will be making the following closures to allow installation of overhead gantries:

How will you manage traffic?

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



Will there be diversions?

It is currently expected that the sign gantry over the A30 London Road will be installed in December.


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.