Measuring delay and simulating performance at isolated signalized intersections using cumulative curves.

A new method for directly measuring total delay at isolated signalized intersections uses cumulative arrival and departure curves. This method of measuring total delay is an application of queuing theory that can be used for actuated and for pretimed signals. The data requirements of this method are greatly reduced by approximating the cumulative curves with piecewise linear curves and concentrating only on critical movements. As a result, a single observer can collect the data for all critical movements at an intersection, because only one critical movement occurs at a time. Plotting the data in the form of cumulative curves allows direct measurement of total delay, queue length, and percent of vehicles required to stop. The data collected for the delay measurement are used to simulate graphically the performance of a signalized intersection under different demand and control conditions. A set of cumulative arrival curves and a specified signal control strategy enable construction of cumulative departure curves for the critical movements. For actuated signals, the different critical movements must be simulated concurrently, because the timing for one movement influences the other movements. This graphical simulation method helps to visualise the flow behaviour at an intersection and provides an alternative to computer simulation methods, which remove the user from the underlying processes.