A box junction is a yellow box with yellow crosses printed on the road. You will find the yellow box at junctions, usually a crossroad but also sometimes at T-junctions.
How to approach a box junction
You should not enter the box junction unless your exit is clear. Be sure to look ahead and if the car in front has moved forwards enough for you to cross the yellow box and not stop within it, then proceed.
Stopping in a box junction
The only time you should stop in a box junction is if you want to turn right, but cars coming the other way are stopping you, as they have priority over you. In this instance, you can wait in the box junction until there is a safe enough gap in the traffic to cross them.
