Highways Agency

The Current Project

On 5th March 2007 we implemented a change to the road layout designed to try and reduce overall delay at junction 12 of the M25.

The Highways Agency has now reviewed the results of the two year trial road layout at this junction and, in order to maintain the improved journey times this has achieved, permanent white lining and signing is now being implemented to make the layout permanent.

Consultation Process

The trial has shown a significant journey time reliability improvement, therefore we have decided to make the scheme permanent. However, the final decision about making the trial permanent, including the implementation of the 50 mph speed limit, will be subject to a statutory consultation, which is currently taking place. If successful the cones and temporary signs will be replaced with permanent signs and markings.

A copy of the Consultation Letter is available in the Publications page.

Decision to Proceed

Following the Statutory Consultation Process, the final decision has been made to start construction work on a scheme to make the current layout permanent in early summer 2009. A report on the consultation process can be viewed in the Publications page.

Start of Works Date

Work began on the night of 26th May 2009 to make the trial permanent. The duration of construction is 16 weeks.

The Revised Layout

Records showed that high volumes of traffic wishing to join the M3 westbound from the M25 anticlockwise at peak periods caused congestion and tailbacks onto the M25. In the evening peak period, approximately double the volume of traffic joins the M3 westbound from the M25 clockwise and anticlockwise than is already on the M3 westbound (from London).

On a typical weekday 32,000 vehicles travel on the M25 and join the M3 Coast bound, compared to 20,000 vehicles travelling on the M3 past the M25/M3 junction.

To improve these conditions, the revised layout provides an upgraded entry slip onto the M3 westbound. This consists of two dedicated lanes for traffic joining from the M25 and a single lane for M3 westbound traffic.

Therefore, at the merge the single lane of the M3 is joined by two dedicated lanes from the M25. After this point, the M3 westbound continues as a three lane motorway.

Throughout the revised layout there is a speed limit of 50 mph and average speed cameras are in effect for your safety. The reduced speed is necessary over the length to the east and west of the scheme to enable vehicles to move safely into the required lane. In addition, a vehicle activated sign has been erected on the M3 to warn drivers of the approaching 50 mph speed limit.

Whilst some congestion on the M3 approach to the new layout has been generated in the evening peak period, traffic monitoring and analysis carried out since implementation has confirmed that this is far outweighed by the reduced congestion on the M25 anticlockwise approach.

Following suggestions from our customers we have added 'merge in turn' signs on the M3 westbound carriageway. This is to ensure a smooth transition from two to one lane by reminding customers to give way to traffic merging from the right.

Overall, the revised layout has delivered a net journey time benefit of 297 Vehicle Hour Delay (VHD) saving hours per weekday or 77,000 VHD per year saved over the original layout. The results of the independent customer satisfaction survey (353KB PDF) have confirmed more road users being in favour of the revised layout than the original layout.

To deliver benefits to road users, the revised layout has been marked out in traffic management. This has not only provided immediate delivery but also allowed us the option of reinstating the original layout. We are currently in a transition phase and moving towards the permanent solution.