Abstract
Probing a die-hard traffic congestion controversy, this paper scrutinises two key variables, density and flow, under equilibrium versus optimal states. Optimisation requires equilibrium flow to decrease under mild congestion, but increase under hyper-congestion. However, both increasing flow needed under hyper-congestion and decreasing flow needed under mild congestion should be accompanied by decreasing density. Thus, inflow of vehicles should always be discouraged to either increase or decrease flow of vehicles for economic efficiency. Moreover, even when optimal policy requires equilibrium flow to increase, the optimal flow itself must decrease eventually as demand increases beyond a critical level. (A)