Blackwall Tunnel
Over Height Vehicle Warning

The Blackwall Tunnel gateway built in 1897.

The Blackwall Tunnel in east London was the longest underwater tunnel in the world when it was opened, but that was in 1897 long before the advent of double-deck buses and juggernauts.

The constraints of the original tunnel, which now carries northbound traffic only since the addition of a southbound tunnel in 1967, requires the imposition of lane and height restrictions to prevent the risk of damage to the tunnel.

Transport for London commissioned the design and installation of an over height vehicle warning system and Variable Message Signs was contracted by Serco to supply and install the system and coordinate the overall project.

Objectives of the project

  • Reduce over height vehicle (OHV) hits on the tunnel
  • Detect OHVs of 2.8m and 4.0m
  • Detect the lane the OHV occupies
  • Warn the driver to move into the correct lane
  • Record the vehicle number plate with automatic number plate recognition (ANPR)
  • Display the number plate on signs
  • Instruct driver to divert

The solution was to install an early warning system 3km before the south entrance to the tunnel to alert drivers of OHVs to the height restrictions ahead and guide them to alternative river-crossing routes.

System 1 - Early warning

  • Cross carriageway over height vehicle detector (OVD)
  • Over height vehicle lane detectors (OVLD)
  • Processor
  • ANPR Cameras
  • Pegasus continuous matrix variable message sign (VMS).

System 2 - Near tunnel entrance

  • Cross Carriageway detector
  • Lane detectors
  • Processor
  • ANPR Cameras
  • Two gantry-mounted Pegasus VMS signs

The second system is installed 500m before the tunnel entrance to reroute vehicles over 4m high away from the tunnel, and to ensure vehicles over 2.8m are diverted to the correct lane. The ANPR cameras detect the OVH and display its number plate with the appropriate message on the VMS displays.

David Hargreaves, VMS Principal Engineer on the project said, “The key of this system is the speed at which all equipment operates to enable appropriate information to be displayed in time for drivers to view it. The two-stage system adds extra security so that in the unlikely event of one system missing an OHV, the other will pick it up and alert the driver.”

As part of an earlier project VMS produced and installed lane control and message signs in the northbound tunnel.

Variable Message Signs

Monkton Business Park, Mill Lane, Hebburn, Tyne and Wear, NE31 2JZ, UK. Tel: +44 (0)191 423 7070
Griffin Lane, Aylesbury, Buckinghamshire, HP19 8BP, UK. Tel: +44 (0)1296 673000

Hill & Smith Ltd trading as Variable Message Signs |  Registered in England No: 01270322 | Registered office: Westhaven House, Arleston Way, Shirley, Solihull, West Midlands, B90 4LH