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Frequently Asked Questions

1. Why are the works being carried out?
The tunnel's mechanical and electrical equipment installed at the time of construction is reaching the end of its design life and needs to be replaced in line with current standards.
2. What is involved
The existing lighting, power supply, and emergency equipment will be replaced. We will also be upgrading the ventilation system using portal fan stations and installing new safety and monitoring equipment. This will be linked to new control systems in the Highways Agency's Regional Control Centre at South Mimms.
3. How long will the work take and is there anyway it could be carried out more quickly?
The programme is to start major construction works in Autumn 2008 and should be completed by March 2010. The works are similar to the recent refurbishment of Holmesdale Tunnel which was completed in a similar time. We will again use 24 hours a day, 7 days per week working where practicable to minimise the works period.
4. Who is paying for the work to be done?
The Highways Agency is funding the £90.4 million major maintenance scheme.
5. What are the impacts on this section of M25
Three lanes in each direction will remain open during day time hours. They may be fewer lanes open during the night when traffic flows are lighter. Junction 27 with the M11 will remain open at all times.
6. What are you doing to publicise this scheme to users of the M25?
We mounted a campaign during the summer to alert the public to the forthcoming works. Start of works exhibitions were held on Friday 3rd - Saturday 4th October 2008. We will produce newsletters and regular updates during the works. We will also be updating this website regularly with detailed information as it becomes available.
7. What are the key messages to users of the M25?
  • Plan your journey before setting off,
  • Consider alternative routes,
  • Allow extra time for your journey,
  • Drive safely and obey the temporary speed limit that will be in place for both the safety of road users and the workforce.
8. If you don't do the work now what would be the safety implications?
The tunnel safety equipment will become increasingly difficult to maintain. This will result in unplanned maintenance closures.
9. Why can't the work be carried our overnight and at weekends?
The scale of the work is too great.
10. How much extra time should we allow for journeys?
Allow around an additional 15 minutes at peak times through the works.
11. Will you remove work and restrictions at bank holidays?
The scale of the works involved means that restrictions will remain in place at bank holidays.
12. What other works are being carried out on M25 during the same time.
Subject to satisfactory completion of the procurement process M25 Widening Junctions 16 - 23 is likely to start in spring 2009.
13. What if there is a major incident?
Emergency plans would be implemented in a similar way to the current operating arrangements. The tunnel will remain closed until it is safe to reopen.
14. What are the emergency plans for getting traffic away from the area?
The existing plans will be implemented.
15. Who is the contractor?
Costain Ltd has been appointed to complete the detailed design and construction of the scheme.
16. Where will the contractor's compound and office be sited?
Bell Common Tunnel Project, Site Compound, Great Cambridge Road, Waltham Cross, Enfield, Middlesex, EN8 8EX
17. Why is tunnel ventilation needed?
Under normal conditions the tunnel ventilates through the action of passing vehicles. When traffic is slow moving the air quality can deteriorate and in these conditions mechanical ventilation is required.

In the event of an incident involving a tunnel fire, the ventilation system will be required to keep smoke and hot gasses away from tunnel users whilst the tunnel is being evacuated.
18. Will the new ventilation change air quality adjacent to the tunnel?
There will be no changes in ambient air quality levels as a result of the scheme. Air will be pushed through the tunnel in a similar way to the current ventilation system.
19. What about the future widening of M25 to Dual four lanes and why can't the work be delayed until the widening is carried out?
The project is compatible with the proposed M25 Widening and no further major works will be required at the tunnel. M25 improvements are programmed for the period of approximately 2009 -2016. The tunnel is between junctions 26 and 27 and as this is part of improvement section 5 which is likely to be delivered towards the end of this period, the refurbishment of the tunnel cannot be postponed this long. Construction of M25 widening Junctions 27 - 30 is planned to start in 2010 subject to the Secretary of State deciding to proceed with the scheme.