What is the function of daytime running lights?

Answer: B — They come on when the engine is running

Daytime running lights (DRLs) are designed to enhance the visibility of vehicles during the daytime to improve safety on the road. Specifically, their primary function is to activate automatically when the engine is running, regardless of the main headlights being turned on. This feature helps increase the vehicle’s presence on the road, making it more noticeable to other drivers, pedestrians, and cyclists in various lighting conditions. While daytime running lights can be beneficial, they are not as effective as headlights for illumination at night, which is why the function of DRLs is to assist in daytime visibility only. The fact that they turn on automatically provides drivers with the convenience of ensuring visibility without needing to manually engage them, thereby reducing the risk of driving without lights during daylight conditions.