The new Hindhead Tunnel is the first in the UK to use radar-based incident detection. Paul Arnold, project manager with the Highways Agency, talks about the projectThe comparatively remote location of the A3 Hindhead Tunnel has resulted in it becoming one of the most sophisticated in the UK in terms of monitoring and control systems, according to Paul Arnold, project manager for the
The tunnel forms a part of the Hindhead bypass for the A3 in the county of Surrey, which replaces what was the last single-carriage stretch of the main, 64-mile road between the southwest of London and the city of Portsmouth on the south coast of England. In particular, it relieves congestion at a major choke-point on the route, the signal-controlled junction of the A3 and A287 roads in the village of Hindhead itself.
Local topography severely constrained the project. Generally the surrounding area is very hilly but to the north of the tunnel is the Devil's Punch Bowl, a designated Area of Outstanding Natural Beauty and also a site of Special Scientific Interest.
This led to the decision to build a tunnel rather than a road despite the greater expense. At its deepest point, the tunnel is 65m (200 feet) below ground level.
"Our starting point for the tunnel's design in 2001 was the BD 78/99 standard, although we also looked to second-guess where standards would progress to in coming years," says Arnold.
Remote locationThe remote location influenced the amounts of technology which have eventually been deployed; Hindhead is not an estuarial crossing where emergency services are routinely based, for instance.
Remote control of the tunnel from the Regional Control Centre (traffic management centre) at Godstone on the south side of the M25 London Orbital was considered as far back as 2002 but a number of factors led to this being abandoned.
These included the fact that Godstone's operations are focused on the M25 and that the HA's on-road Traffic Officer (TO) function does not extend as far along the A3 as Hindhead. Also, with the anticipated low rate of incidents it was felt that TOs would maintain sufficient levels of regular operational experience.
The solution therefore was a local control centre team, says Arnold.
"The challenge was how to connect the tunnel to the HA network," he continues. "UK Government fiscal stimulus work resulted in the National Roads Telecommunications Services [NRTS] network being extended south along the A3 and allows Hindhead to effectively become a remote outpost of the main network." NRTS extension was another best-value choice. Operationally, it will be much less costly than using leased lines from BT, the national telecommunications carrier, but by connecting the Hindhead control centre's telephones to the HA's own network much greater resilience is achieved. The ability to push out up to 10 switchable CCTV feeds into the NRTS network allows visibility elsewhere of what is going on locally and aids strategic management. NRTS also allows communication with remote signage, allowing tactical management of traffic in the nearby area as and when necessary.
Radar systems for tunnel monitoring
The Hindhead Tunnel uses a total of 12 Navtech Radar ClearWay systems. This is to take account of the tunnel's curvature but also provides a high level of redundancy, according to the company's Stephen Clark.
"With full line of sight, the ClearWay system can offer a range of 500m in each direction, giving 1km coverage in total, and in the Hindhead Tunnel it would be possible to lose 50 per cent of the radar systems and still retain perhaps 85 per cent of coverage," he says.
"The radar systems and the associated tracking software can generate a total of five alarm rules for the tunnel's operatives. These cover vehicles slowing, stopping or reversing, and pedestrian and lost cargo detection.
Operatives are automatically presented with images from the nearest CCTV camera when an incident is detected." The company's radar systems were first trialled in a tunnel setting in the UK in the Southwick Tunnel, near Brighton on the south coast of England, in 2008. They have also been trialled as a detection and monitoring solution for the Highways Agency's Active Traffic Management hard shoulder running system but have not as yet been taken forward for that application.
In Sweden, ClearWay systems are currently being trialled on Stockholm's Södra länken (southern link), a 6km route of which 4.7km is in tunnels. There, because the road geometry is less complicated, two systems provide coverage over 1km.
Two further systems are also deployed on Sweden's E4 motorway. Sited in the middle of the road, they provide 1.5km of coverage over all lanes on both carriageways.
"The Trafikverket [Swedish Transport Administration] has been very happy with the systems on the E4," says Clark. "Sweden offers a very challenging operational environment with long winters and high incidences of fog and snow. On the E4 where our systems are in use there are also reduced hard shoulders, so it's important to provide road users with timely warnings of stopped vehicles or other problems when there is poor visibility. Radar's detection range, reliability in all weathers and very low false alarm rate make it ideal for this sort of application.
"In the next six to 12 months, we're looking to add more capabilities to the ClearWay system. These will include software upgrades that will allow tailgating and illegal lane changes to be detected."
BD 78/99 governs all operations in the tunnel and its immediate vicinity.
There are variable message signs throughout the tunnel, fixed-text signs on the approaches and wigwag alternately flashing lights ahead of crossovers and barriers. Inside the tunnel, emergency roadside telephones are sited in recesses every 50m and there are cross-passage doorways every 100m. Each emergency point features a break-glass call point and fire extinguisher, and all extinguishers and cross-point doors are alarmed. The safety and emergency solutions include heat detection systems, radio break-in on all major channels, a PA system in the tunnel which features both pre-recorded and ad hoc messaging, directional sound beacons over each opening door, emergency backup lighting and photo-luminescent strips.The HA's Halogen fault-logging system is also installed.
Extensive testing was carried out both on-site and elsewhere. Balfour Beatty equipped the tunnel and provided the SCADA system, and contractor P. Ducker Systems Ltd mocked up the tunnel in its warehouse in Derby, in the East Midlands.
Generally, off-site testing has proven to be very useful, says Arnold.
Radar detectionThe incident detection system is the first in the UK to use radar (see Sidebar, 'Radar systems for tunnel monitoring').
Radar's performance allied to cost and pragmatism were drivers of system choice, says Arnold.
"We looked at using the
"Radar represented best value but that didn't overshadow performance: in tests in the Southwick Tunnel near Brighton two
"Hindhead is unique in the UK in terms of control systems. It's the first tunnel to use the full range of sub-systems 'as intended'; what we have here is akin to many miles of conventional motorway in terms of the technology deployed.
When it comes to traffic management I think we've pushed the boundaries in terms of the use of fixed-message signage, although similar levels of technology are now being deployed around the Holmesdale, Bells Common and Hatfield tunnels on the M25." With the tunnel just opening to traffic, it is too early to start discussions about future technological migration, although Arnold considers that there are local developments which will bring changes and improvements. More technology is expected to be deployed in and around Guildford, the nearest major town and the administrative headquarters of the southeast area of England, as efforts to increase capacity and management are realised.
For the moment, though, Hindhead will operate as a "mini-RCC" responsible for an isolated section of the HA network.