The report describes traffic flow observations made at five three-way major/minor priority junctions under conditions of heavy minor road demand. The results have been analysed by linear regression methods to determine the extent of the interactions between the major and minor road streams. Variations in the composition of major road traffic had no detectable effect on the total flow through the junction; effects due to variations in minor road composition were slight only. The relationships between the major and saturated minor road traffic flows are represented by linear equations which allow the minor road approach capacities to be calculated. The results provide a framework for predicting the practical capacities of three-way junctions. An extension to the four-way case is suggested.