Sensors and actuators for the tunnel

Actuators respond to changes in conditions within a tunnel in many ways.

Tunnel Sensors

Sensors take important measurements that provide data on the air quality, brightness, traffic volume and visibility in a tunnel.

They thus provide essential information for a smooth, safe flow of traffic. The information includes:

  • Ambient conditions  (CO2, nitrogen, light opacity),

  • Brightness

  • Fire

  • Traffic situation and

  • Failures.

Further important systems include video surveillance, emergency calling as well as overheight detection by means of infrared beams.


The level of lighting must adapt to the changing ambient light at the tunnel entrance and should neither dazzle drivers inside the tunnel nor allow the entrance to appear as a black hole.


The ventilation system provides fresh air in the tunnel. The capacity of the ventilation system must be sufficient to supply enough air when the vehicles in the tunnel are stationary.  In the event of a fire, the ventilation system should ensure that no smoke develops in the tunnel.

Variable Message Signs

Variable Message Signs (VMS and SLS) use LED technology to display text information or traffic signs. The LED elements are monitored by their controller to prevent disrupted, illegible or contradictory displays. An optional hardware lockout can also be installed. 

Lane Control Signs – LCS

Lane control signs use LEDs to display lane signals with arrows. By this means lanes can be opened or closed for traffic.

Traffic Light Signals

Traffic lights and Co for tunnels, using the latest LED technology. Traffic lights are located at tunnel entrances or, if tunnels are very long, also within tunnels. They are activated automatically, triggered by a detector if a vehicle exceeds the height limit or if another type of incident requires a tunnel to be closed.

The traffic lights can be activated automatically, but they can also be controlled manually.

Tunnel Barriers

Traffic light signals can be supplemented by barriers when tunnels have to be closed. They ensure that no more vehicles can enter the tunnel.

Lane Lights

Lane lights, based on LED technology, are set into the road surface and can be used either for dynamic lane assignment or for static marking of the hard shoulder.