Optimal signal settings over transportation networks

Several recent papers have discussed the shortcomings of a simple approach for determining traffic signal settings over a network. This procedure iteratively sets signal timings at each intersection to minimize delay, holding flows constant. Flows are then adjusted to a new user equilibrium, and the process is repeated until both flows are at equilibrium and signal timings are optimal given the flows. This paper reviews the shortcomings of this procedure and describes an algorithm for small networks which overcomes these shortcomings. This new algorithm is used to quantify the errors in the simpler approach. Also, conditions under which both procedures would produce the same solution are discussed.