Something you'll find on roads in Britain, A box junction is a grid of yellow lines, occupying the space where two roads intersect. Box junctions are often used at the intersection of major roads, in conjunction with traffic lights.

            |          |
            | Road     |
            |          |
            |          |
            |==========|
____________|==========|_____________
          = =\/\/\/\/\/= =
 Road     = =/\/\/\/\/\= =     Road
          = =\/\/\/\/<-------'Box'
          = =/\/\/\/\/\= =<----Pedestrian crossing                             
__________=_=\/\/\/\/\/=_=____________
            |==========|
            |==========|
            |          |
            | Road     |
            |          |
            |          |
            |          |

Traffic is not allowed to stop on the box, nor to enter the box when the way out is blocked. The box junction is intended to prevent drivers from obstructing the flow of traffic by becoming stuck on the intersection when the lights change. If you're driving following the highway code, you will never be stranded in a box junction, as you will never have entered one when the exit wasn't clear.

In a driving test, not checking to make sure the exit is clear before entering a box junction is a major fault, and will result in an immediate fail. Despite this, many drivers ignore box junctions. This leads to traffic congestion and road rage, as when the lights change, traffic cannot start moving because some plonker is stuck in the middle of the junction. Perpendicular to the flow of traffic, he can't get off the junction because traffic in front of him is not moving. Had he simply waited for the exit to clear before entering the box, he wouldn't be stranded, and creating an obstruction. In Edinburgh, I've seen double decker buses doing this. In Glasgow's city center, ignoring box junctions would seem to be the rule, rather than the exception - traffic enters the junction the moment the lights change, and any cars that are stranded wait in the middle of the junction, while traffic from the side attempts to drive around them.