Why can the screen effect occur in tunnels but not the tunnel effect?

Driving through a tunnel requires us to be even more careful while driving. Within these spaces there are certain characteristics that we must take into account for greater road safety. Firstly, the road usually has less grip with respect to the outside and there is less visibility, so it is imperative that you increase the safety distance with respect to the vehicles in front.

You should also remove your sunglasses when entering the tunnel. And, if you are stopped inside the tunnel for more than two minutes due to a traffic jam or an accident, you must turn off the engine, activate the emergency or warning lights and keep the position lights on. This is stated in the General Traffic Regulations and, in case of non-compliance, you are exposed to a penalty.

But apart from these maxims, we must know two phenomena whose names can lead to confusion: the tunnel effect and the screen effect. You have to know what both consist of and how to prevent them, for the sake of your safety on the road.

It is paradoxical that the so-called tunnel effect does not take place precisely in tunnels. What does affect you when driving through a tunnel is the screen effect. To know why this happens, we must stop and explain what each one consists of.

The tunnel effect refers to a loss in the driver’s peripheral field of vision, which happens when we drive at high speed or under the influence of alcohol. When driving at high speed, we lose visual clarity around us, so we stop perceiving the environment around us: other vehicles, pedestrians, animals, traffic signs, etc. Our angle of vision closes, until it feels like we are traveling through a tunnel, even though we are in an open space.

For its part, the screen effect occurs on days with strong gusts of wind. When you pass a truck or bus, leave a tunnel or pass a building, the force of the wind can propel your vehicle and move it, breaking into the opposite lane or causing you to leave the road. To avoid this ‘push’, we must anticipate and foresee the strength of the wind. Whether exiting a tunnel or passing a truck after overtaking it, you must hold the steering wheel firmly and turn it slightly towards the direction in which the wind is blowing, in order to keep your path fixed despite the momentum of the air.

That is why the tunnel effect does not happen in tunnels, while the screen effect does, because the air surprises you when you leave the tunnel. Likewise, when leaving a tunnel you have to be careful with glare from natural light.