Yellow box junctions keep the junction clear for through-traffic to avoid traffic jams. They can also keep a road space free to ensure fire engines always have a clear exit from fire stations.
Yellow box junctions, loading bays and red routes are in place to keep traffic on the roads flowing.
Yellow box junctions are indicated by criss-cross yellow lines painted on the road. They are usually found at the junction of two or more roads and occasionally at roundabouts or outside fire and ambulance stations. A yellow box junction does not require any other signage.
You are not allowed to stop in a box junction. The only exception to the rule is when you are turning right and are prevented from doing so by oncoming vehicles or other cars waiting to turn right as well. More details can be found on the Traffic Signs Regulations and General Directions legislation pages.
The rules can be found in the Highway Code Rule 174. This states: “You must not enter the box until your exit road or lane is clear. However, you may enter the box and wait when you want to turn right, and are only stopped from doing so by oncoming traffic, or by other vehicles waiting to turn right. At signalled roundabouts you must not enter the box unless you can cross over it completely without stopping.”