When is it legal to drive in the left lane of a highway?

Driving in the left lane of a highway is primarily permitted for specific reasons that enhance road safety and traffic flow. The correct choice reflects that it is legal to use the left lane when passing another vehicle, as this promotes smoother and faster movement for those needing to overtake. Additionally, if the left lane is designated for turning, utilizing it for that purpose aligns with traffic regulations and helps prevent congestion that might occur if everyone were to remain in the right lane for turning.

In terms of traffic legality, the left lane is often referred to as the "passing lane." Staying in this lane while not actively passing can impede traffic, lead to frustration among drivers, and potentially create dangerous situations as other vehicles attempt to navigate around a slower driver. Thus, understanding the proper context for using the left lane—such as for overtaking vehicles or preparing for a left turn—is essential for safe and lawful driving practices.