On the reserve capacities of priority junctions and roundabouts

The concept of reverse capacity of a whole junction has been used extensively in the design of signal-controlled junctions. This concept, however, has not been applied to priority junctions and roundabouts, probably because of the complicated demand and supply relationship. When the demands on the approaches to the junction increase, the capacities of those non-priority approaches reduce at different rates. This makes the calculation of reserve capacity of the whole junction not a straightforward task. Using the definition of reserve capacity of a whole junction in Allsop (1972; Transpn Res. 6, 245–255), explicit formulae for the estimation of reserve capacities of priority junctions and roundabouts are derived in this paper. Numerical examples are given to illustrate the usefulness of these formulae.