Final answer:
Returning to your lane after passing a vehicle, such as a semi-truck, is safe when you can see the entire front of the passed vehicle in your rearview mirror, often about three to four car lengths away.
Step-by-step explanation:
After passing another vehicle, such as a semi-truck, returning to your lane is considered safe when you can see the entire front of the vehicle you passed in your rearview mirror. By waiting until you can see the entire front of the other vehicle, you ensure that you have enough space to merge back into your lane without the risk of collision. This distance may vary based on speed and road conditions, but as a general rule of thumb, it is often about the length of three to four car lengths. When considering the safety of crossing multiple lanes on a freeway when a car is travelling in the furthermost lane, or gauging how many car lengths you need to consider before crossing a road, these distances provide a buffer that allows for reaction time and safe maneuvering.