Rule 173
Dual carriageways. When crossing or turning right, first assess whether the central reservation is deep enough to protect the full length of your vehicle. If it is, then you should treat each half of the carriageway as a separate road. Wait in the central reservation until there is a safe gap in the traffic on the second half of the road. If the central reservation is too shallow for the length of your vehicle, wait until you can cross both carriageways in one go. Rule 173: Assess your vehicle’s length and do not obstruct traffic