Why should a driver slow down at the entrance or exit of a tunnel?

Slowing down at the entrance or exit of a tunnel is important primarily due to the transition between different lighting conditions. As a driver approaches a tunnel, the surrounding environment changes from well-lit outside conditions to the darker interior of the tunnel. This dramatic shift can temporarily impair a driver's vision and may reduce their ability to recognize hazards, other vehicles, and road signs. Adjusting speed during this transition helps ensure that a driver has adequate time to adapt to the new lighting, enhancing safety for themselves and other road users.

Considering the other options, while traffic patterns and the chance of accidents are factors to keep in mind in general driving situations, they do not specifically address the critical need to adjust for lighting changes when entering or exiting a tunnel. Additionally, the merging of vehicles may occur but is less relevant to the immediate need for a speed adjustment related to visibility issues.