when are you allowed to wait on the yellow grid markings

You are generally not allowed to wait on yellow box (yellow grid) markings at all – except in a very specific situation: when you are turning right (or left, depending on the jurisdiction) and are blocked only by oncoming traffic and/or other right-turning traffic.

The core rule in plain English

Yellow grid markings (often called yellow box junctions) are there to keep the junction clear so traffic can flow. The basic rule is:

• Do not enter the yellow box unless your exit lane is clear and you can drive all the way through without stopping.

• You may wait on the yellow grid only when :
  • You are already in the junction to turn across oncoming traffic, and
  • You are blocked only by oncoming vehicles or other vehicles turning, so you must pause in the box while you wait for a safe gap.

In many multiple‑choice versions of this question, the officially correct answer is simply:

You are allowed to wait on the yellow grid markings when you are turning right (or left in some variations), not when going straight.

What this means in real life

Picture this:

• You are approaching a crossroads with a yellow grid.
• You want to turn right across oncoming traffic.
• The road you intend to turn into is clear, but:
  • There is steady oncoming traffic you must yield to.

You can legally:

• Move into the junction.
• Pause briefly on the yellow box while you wait for a safe gap in oncoming traffic.
• Complete your turn as soon as it’s safe.

You must not :

• Enter the box to go straight ahead if your exit is blocked by stationary traffic.
• Sit in the box “just in case” the traffic ahead moves.
• Use the yellow grid as a general waiting or queuing area.

Quick “do / don’t” checklist

Allowed:

• Entering and briefly waiting on the yellow grid:
  • When turning across oncoming traffic, and
  • When the only reason you’re stopped is oncoming traffic or other turning traffic.

Not allowed:

• Waiting on the grid when:
  • You’re going straight on and your lane ahead is not clear.
  • You’re queuing in traffic and your exit from the box is blocked.
  • You simply want to “hold your place” in the junction.

Why the rule exists

Yellow grid markings are designed to:

• Prevent junctions from being blocked by stationary vehicles.
• Keep cross‑traffic and pedestrians moving more smoothly.
• Reduce gridlock in busy urban areas.

So the law makes one narrow exception (waiting while turning across oncoming traffic) but otherwise expects you to stay out of the box until you can completely clear it. TL;DR:
You may only wait on yellow grid markings when you are already in the junction to turn across oncoming traffic and you are stopped only because of that oncoming traffic. At all other times, do not wait or stop on the yellow grid.

Information gathered from public forums or data available on the internet and portrayed here.