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M25 J25


Graham Construction


Enfield and Broxbourne, England

Key services

Highways Engineering, Intelligent Transport Systems, Transport Modelling, Transport Planning & Assessment

UN Sustainable Development Goals

8, 9, 11, 15, 17

Our Guide To The UNSDG goals

Read Guide

Project Overview

We are the lead designer for GRAHAM on the new £8.7bn Highways England regional delivery framework and our partnership won the first collaboration award at Highways England’s annual Regional Investment Programme conference in 2019.

The Challenge

Junction 25 is a nationally and regionally important road, connecting the M25 with the A10. Up to 6,300 vehicles per hour currently travel through the junction 25 roundabout at peak times, causing congestion and regular delays. The A10 southbound approach into the junction is also a congestion hotspot in Broxbourne.

The junction itself is a 4-arm signalised roundabout with 3 lane approaches for the northbound and southbound A10.  The eastbound and westbound M25 slips roads are 2 lanes for most of their lengths, flaring to 3 lanes at the stop lines. Much of the circulatory carriageway varies between 2 and 3 lanes wide, with a 4 lane section on the south-eastern side.  During peak times, traffic on the M25 westbound exit can end up queuing back to Holmesdale Tunnel.

Research shows that traffic in the area is expected to increase by around 20% by 2037 and without intervention, congestion could get worse and delays could double.

Our Approach

  • Co-locating our leaders, selected for their behavioural maturity, skills and experience. This provided the foundation for long term relationships and insight of one another’s ways of working which enabled effective and efficient resolution of blockers and decision making.
  • Leading integration by facilitating workshops ensuring buy-in for our strategy to deliver a common shared objective to achieve start of works dates for all four partnerships. By sharing responsibilities for the preparation of programme critical key deliverables we secured time and cost savings to meet all dates.
  • Knowledge-sharing of our successful approach in the south-east region to drive performance improvements nationally.

The Solution

The preferred option will provide extra lanes on the roundabout, widen the A10 southbound approach and the M25 approaches, and provide a free-flow left turn from the M25 eastbound to the A10 northbound. A new at-grade NMU route will be provided with toucan crossings enabling more convenient and direct north/south movements whilst minimising the perceived safety concerns associated with the existing subways.

Upon contract commencement in March 2020, the priority goal was to establish an integrated team that could achieve a construction start date of 4 January 2021. This objective, which was met, coincided with the onset of the Covid-19 pandemic. Remote working and an innovative approach to communication and partnership-working had to be fully adopted.

We embraced digital technologies such as Teams and Skype and hosted a Virtual Consultation Event to improve communication and strengthen the integration of the team. To complement the formal meeting programme, regular lessons learnt sessions, online design reviews and workshops also helped promote diverse opinions, skills and ideas that informed decision-making.

Watch the M25 Junction 25 Improvement Scheme animation here: https://highwaysengland.co.uk/our-work/south-east/m25-junction-25-improvements/


Delivering value engineering

Design changes identified collaboratively at construction preparation stage provided a platform of knowledge sharing and teamwork focus, delivering high level requirements without compromising safety. As an example, the M25 25 westbound-offslip was shortened (150m to 120m) from the preliminary design by using refined traffic modelling. Further value engineering solutions developed in partnership also supported the timely agreement of departures from standard, increasing the scheme benefit-to-cost-ratio by 28%.


Collaboration with Thames Water resulted in the efficient resolution of statutory diversion issues. We also established a strong working relationship with the Operations Directorate and the DBFO responsible for the Holmesdale Tunnel, a partnership defined by early engagement.


Despite consistent Covid-19 challenges, and a stand-down period at Christmas, the site was mobilised and ready for construction to begin in January 2021.

It demonstrates true collaboration that the integrated project team (Highways England, GRAHAM, Sweco and WSP) delivering the scheme overcame significant challenges to start on site in nine months.

The Result & Benefit to Client

We met all key programme milestones and delivered within budget. With the scheme under construction, on completion the benefits for Highways England’s customers are:

  • reduction in congestion and delays at junction 25 between the M25 and the A10
  • increased capacity by widening both the roundabout and the A10 southbound approach
  • improved safety and traffic flows on the roundabout by redesigning the layout
  • supported future traffic demands enabling development and economic growth
  • maintained access for pedestrians and cyclists and improved conditions
  • minimised environmental effects on local air quality and noise

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