Methodology for Timing and Impact Analysis of Signalized Intersections

A new Swedish capacity manual has been developed based on a major research project called METKAP. This paper is focused on the deterministic methods for calculation of signal timing and traffic performance measures for isolated, fixed time signalized intersections documented in the new manual (STA 2013a) and applied in the CAPCAL 4 software (Linse 2013). The use of the methods is mandatory in projects for the Swedish Transport Administration (STA). Special focus has been devoted to the following issues: 1) Modelling of saturation flow for opposed lanes. 2) Impact of short approach and exit lanes. 3) Iterative signal timing process based on critical conflict identification, intergreen and minimum green times. The deterministic methods can also be applied for selection of maximum green time for VA-controlled intersections, and as planning tool for analysis of the traffic performance alternative intersection types, designs. They can also be used to identify "bottleneck intersections" and for determination of minimum cycle time and required green time ratios for coordinated traffic signal systems. Micro simulation can be used as an alternative method, e.g. to model complex, signal control strategies and active priority of public transport vehicles. Need for simulation also arises if adjacent traffic facilities influence the studied system, and for animation purposes. However, micro simulation has important short-comings compared to deterministic methods. Simulation models require validated and detailed input data, e.g. regarding vehicle characteristics, arrival distribution, route choice and driver behavior. It is also difficult to estimate saturation flow, capacity and volume-to-capacity ratio since the simulated queue discharge is normally based on car-following models. Determination of optimal intersection design and signal timing requires a very large number of simulation runs and is therefore very time consuming and costly.