Question

Give an example and explain in detai lwhat measures you would undertake to calibrate and validate your mode lin SIDRA.

Answer 1

SIDRA traffic analysis is used for modelling individual intersections and is not suitable for all analytical tasks requiring computer based modelling of traffic operations.

For SIDRA models calibration shall comprise checks of the input data to ensure that the base case (i.e. the latest valid data representing the existing intersection) data is adequately represented in the model. The calibration process should be based on various traffic data, including surveys and site observations. This data, for traffic signals shall principally include traffic flow, saturation flow, traffic signal phase sequences, phase green time splits, traffic signal timing settings for yellow, all red and pedestrian phases, and geometric parameters.

Validation shall provide an additional check, independent of the calibration. Validation shall use the calculated values in the base case model to check that the results are representative of the observed situation. The principal values to be used shall be the Degree of Saturation (DoS) and the calculated 95%ile queue length on the approaches. Where approaches are known to be over-saturated in peak periods and the models reflect this by calculating values above 95% DoS, it should not be necessary to undertake site surveys to establish the measured DoS values. At unsaturated sites, on-site measurements of degrees of saturation may be necessary in order to validate the model.