It is a brilliantly sunny afternoon, you are wearing sunglasses, and the road ahead disappears into a tunnel. What three things does the Driver's Handbook tell you to do?

Correct answer: A. Slow down to let your eyes adjust, remove your sunglasses, and turn on your headlights

Slow down, take the sunglasses off, and switch your headlights on: "When you enter a tunnel on a bright day, slow down to let your eyes adjust to the reduced light. Remove your sunglasses and turn on your headlights." All three deal with the same problem from different angles. Your eyes need several seconds to adapt from bright sun to tunnel gloom, and slowing down buys you that time; the sunglasses make the gloom darker still; and your headlights are for the drivers already inside, who are looking out at a bright entrance and cannot see much. Glare is not only a night-time problem — the Handbook notes it is a problem on sunny and overcast days alike, depending on the angle of the sun.

Source: MTO Driver's Handbook: Driving at night and in bad weather — Glare, entering a tunnel on a bright day