Why must drivers slow down before entering tunnels?

Drivers must slow down before entering tunnels primarily to adjust to dark adaptation, which is crucial for maintaining visibility and safety. When a vehicle approaches a tunnel, the light levels suddenly change from bright daylight to a darker environment. The human eye takes time to adjust to these changes in lighting, sometimes referred to as dark adaptation.

By reducing speed before entering the tunnel, drivers give themselves a better chance to see clearly and to respond appropriately to any obstacles or changes in the roadway conditions inside the tunnel. This transition helps in preventing disorientation that could lead to unsafe driving situations, such as misjudging distances or failing to notice other vehicles and pedestrians.

In addition, slowing down helps ensure that drivers remain alert and attentive, which is especially important in enclosed spaces like tunnels where visibility and reaction time can be compromised. Being cautious can help prevent accidents and enhance overall road safety in these environments.