Why should a driver slow down when entering or exiting a tunnel?

A driver should slow down when entering or exiting a tunnel primarily to adjust to the change in lighting. Tunnels can create a stark contrast between the bright daylight outside and the darker conditions inside. This sudden change in brightness can impair visibility and depth perception, making it essential for drivers to reduce their speed to comfortably adjust their eyes to the new lighting conditions. Slowing down ensures that drivers can safely navigate the tunnel, which may have limited visibility and potentially unexpected obstacles.

The other options, while they may present safety concerns in different driving situations, do not specifically address the critical need to manage the transition in visibility as one moves in and out of tunnels. This adjustment is particularly vital for maintaining control of the vehicle and ensuring safety in a confined and often high-traffic environment.