Case Study - Hindhead Tunnel 

The A3 Hindhead Tunnel is the Highways Agency’s longest road tunnel comprising two bores of 1.2 miles in length. 

The primary control system for traffic management including life-saving fast tunnel closures is via SSL’s tunnel subsystem (TSS).  The TSS communicates to IP message signs, tunnel lane control signals and speed limit repeater signs within the tunnel and communicates to fixed text message signs, barriers and wig-wag signals outside the tunnel.

This roll out of the TSS is the first without any need for a Signal Subsystem or Message Sign Subsystem as the TSS performs all the functions necessary to control all device types.

The Hindhead Operators use COBS WOIFs to view the tunnel and its vicinity and set pre-defined plans via the TSS menu.  The pre-defined plans include settings for tunnel lane control signals, tunnel message signs, speed limit repeater signs and diversionary FTMS at the same time.

The TSS has an independently verified IEC61508 SIL2 rating (Safety Integrity Level 2) together with comprehensive safety case and has built in redundant solutions.  Of primary importance are the two communication routes to devices, one via the traditional Transponder RS485 route and another IP route direct to the Transponders.  For IP devices, the TSS can communicate via two independent IP routes directly to the devices.

Barriers and Wig Wag signals are controlled via TR2095 devices and enable the Operators to bring down barriers across the A3 in the event of a tunnel closure or during a contraflow stage.

The TSS monitors tunnel SCADA devices such as cross-passage doors, fans, lighting, RADAR alerts (pedestrian, stopped vehicle, slow vehicle, oncoming vehicle, debris), emergency telephones, fog detectors, smoke detectors, fire detectors, intrusion detectors and many more.  This monitoring is achieved via a connection to the SCADA PLCs.

When the TSS receives alarms from these devices, the TSS will Pan, Tilt and Zoom a CCTV camera to allow the Operator to instantly see on their CCTV monitor the area in the tunnel where the alarm was initiated.  An example being if an emergency telephone is picked up by a stranded motorist, the Hindhead Operator, on accepting the TSS alarm, can instantly see the stranded motorist at the telephone point and take remedial action quickly.

In addition to SCADA plant monitoring, the Hindhead Operators, via the TSS, can play messages via the personal address system and radio re-broadcast systems in the tunnel.  Messages can be played to individual bores, individual cross passageway recesses or to all cross passages.

The TSS logs directly to HALOGEN device settings and faults including all SCADA settings.  The TSS also has the ability to continue to operate even on failure of the COBS as it has direct communication to all WOIFs.