The Space Envelope

The handbook's name for the room around your car is the space envelope. It has four sides, and they are not equal.

Ahead is the side you control completely. Your following distance is your choice, and Following Distance in Practice gave you the tool: the handbook's 4-second rule, measured against a landmark. It is also the side that protects the other three.

Behind is the side you can't set, because it belongs to the driver following you, but you can manage it. The handbook's advice: with someone following too closely, slow down earlier and more gently so they have more time to react. The Swedish Theory Book adds a quieter defence: leave a bigger gap ahead, so you never have to brake hard, and the tailgater is never tested. If they are still pressing, let them pass when there is a safe place.

The sides are the kerb and the next lane. On the left: parked vehicles whose doors may open (the handbook warns about opening doors and exiting passengers), pedestrians at the edge, and bodabodas filtering. On the right: the next lane, oncoming traffic, and vehicles overtaking you. Where you can, don't drive alongside another vehicle for longer than you need to, and give parked cars and cyclists a wide margin.

The trade between sides is the part that makes it a system. When one side shrinks, a lorry close alongside or a car sitting on your bumper, give yourself more room on a side you do control, usually ahead. You can't make the tailgater drop back. You can make sure you'll never need to stop suddenly in front of them.