Traffic laws must be strictly adhered to in tunnels or underpasses on account of the increased risk factors involved in this type of road route, with attention specifically to such matters as using headlights, observing speed and safe distance requirements and not stopping, parking, changing direction or reversing. When approaching most tunnels a blue rectangular sign provides some key information about the tunnel, such as the name and the length, as well as details about emergency help points within. The speed limit in tunnels is controlled with the R-301 mandatory maximum speed limit sign (a red circle with the speed limit in the centre), although many also have an advisory maximum speed limit, indicated by the S-7 blue square with white numbers. Before entering the tunnel we will also see the R-413 sign, a blue circle with a headlight pictogram in the centre, telling us that it is mandatory for us to use headlights at all times. There may be other signs on the entry to tunnels such as the R-306 which prohibits heavy goods vehicles over 3,500 kg from overtaking. Some tunnels have indicators above the carriageway which shows if the lane is open or closed. This is sometimes by means of a standard red or green traffic light and sometimes by means of a green arrow or red cross. These indication signs must be observed at all times. All signs, whether fixed or temporary, visual or audible, must be adhered to at all times. In tunnels or underpasses where the traffic flows in both directions, overtaking is prohibited, unless an additional lane or lanes are provided for this. A safe distance must always be maintained from the vehicle in front, with a minimum of 100 metres being required between each vehicle, the equivalent of a 4 second gap. Some tunnels have markings on the lanes to assist in keeping this distance. For those with no markings the four second gap can be monitored by counting the time between the vehicle in front of you passes a fixed point and the time it takes your vehicle to pass that same place. In the case of vehicles with a maximum authorized mass exceeding 3,500 kg, the safe distance is increased to at least 150 metres or a minimum interval of at least 6 seconds. Tunnels of some length will have pedestrian exits and help points which are for use in emergencies only. The exits are indicated by the universal emergency exit signs of a pictogram of a figure about to leave a door, and often accompanied by the words “Salida” or “Salida de Emergencia”. The location of the closest emergency point is indicated by arrows on the wall of the tunnel. In the event of an emergency access point being in both directions, often a larger arrow will indicate the direction to the nearest emergency point or exit, which may be in front or behind. In the event of being involved in an emergency in a tunnel, you must: Switch off the engine, switch on emergency hazard lights and leave your vehicle lights on. If the emergency makes it impossible for the vehicle to continue, try to steer the vehicle to the area reserved for emergencies in the direction of travel, such as the hard shoulder if available, or an emergency layby. In the absence of these features, you must try to stop your vehicle as close as possible to the right side of the edge of the roadway. Use your emergency triangles to indicate your vehicle is creating a hazard. All vehicle occupants must leave the vehicle and proceed to the nearest evacuation emergency exit. In case of fire, the driver must make every effort to ensure vehicles do not block the path of the emergency vehicles attending. Turn off the ignition, leaving the key, and leaving the doors open. All vehicle occupants must leave by the nearest available exit in the opposite direction to the fire. Hopefully our passage through the tunnel will be without incident and as we leave the tunnel, we will see more signs. As well as the S-6 sign indicating the end of the tunnel and subsequent restrictions, we sometimes a change in the speed limit but always a reminder about our headlights. This S-24 sign is different to the R-413 as it is a blue rectangle which displays a pictogram of the headlights along with a question mark. Whereas it is mandatory to switch lights on when entering a tunnel, it is not necessarily mandatory to switch them off, as it could be night time or during a period of poor visibility, so this sign is an informative version reminding us to check if we need to continue with our headlights illuminated.