The results indicate that appreciable net benefits can be obtained when the degree of saturation is very high (over 90 per cent), the priority flow is high and/or there is a setback of optimum length. When the degree of saturation is low, there is likely to be no appreciable benefit or disbenefit when an optimum setback is provided, but when no setback is provided substantial disbenefits can occur even at low flows. Under ideal conditions (high degree of saturation, optimum setback) only a few buses an hour are required to justify provision of reserved lane, but under adverse conditions the required bus flow may well exceed the maximum practicable flow for a single lane