Priority over oncoming vehicles' Supplementary Plate - Post Mount Dia. 811.1 R2/RA2This supplementary plate details that drivers have priority over vehicles coming towards them. These are often seen in built up areas in the suburbs where traffic calming measures are in place to reduce speeds. They can also be seen frequently in seaside towns where narrow roads are not sufficient for two vehicles to pass. You will always see this sign used in conjunction with the main plate diagram 811 which we have available in our post mounted