When entering a tunnel on a sunny day, what is the safest action to take?

When entering a tunnel on a sunny day, slowing down to allow your eyes to adjust is the safest action to take. This is important because the transition from bright sunlight to the darker environment of a tunnel can be disorienting. The sudden change in lighting levels can impede your ability to see clearly and react appropriately to any hazards inside the tunnel. By reducing your speed, you give your eyes time to adapt to the lower light conditions, improving your visibility and reaction time.

Maintaining a moderate speed also helps you to better gauge the environment around you, such as the distance between vehicles and any potential obstacles or hazards that might be present. It is crucial to ensure that you can respond to any unforeseen changes, such as approaching vehicles or pedestrians, with adequate attention and care. Therefore, adjusting your speed and allowing time for your eyes to adapt is a vital safety measure in this scenario.