Don’t Neglect the Other Windows: Rear Windscreen Part Two
Likewise you can use the back window to see if other drivers are wanting to overtake you, and if you’re in the fast lane on the motorway and someone wants to go past it’s good etiquette to move over so that they can do so. This is especially important if an emergency vehicle such as a police car or ambulance is trying to get past (while to an extent the sound will warn us when one is near it won’t alert us to whether we need to pull it or it’s in an adjacent road). When we’re overtaking on the other hand, whether on the motorway or elsewhere, checking the back windscreen is important as a way to ensure you’ve fully overtaken a vehicle (or even a bike, pedestrian or inanimate hazard) before you pull back in in case you do so before they’re clear and hit them on the way back.
The final, and perhaps most obvious use for the back window is reversing. Here the rear windscreen takes on the role of the front windscreen behind the window to where you’re going. If you’re going to reverse around a corner then, or out of a drive or parking space, you need to look out of the rear windscreen before you do to check that the way is clear.