Microscopic traffic simulation models have advanced significantly in recent years and are now used extensively around the world for detailed traffic modelling where dynamic operations have to be represented. Whilst extremely powerful, these models can have substantial calibration requirements. This paper illustrates a new method of calibration of bus performance parameters as part of the ‘Gipps’ car-following model used within the microscopic simulation package Aimsun. This research looks at the impact of bus signal priority strategies on bus and traffic emissions. Calibration was undertaken using second-by-second bus performance data recorded automatically within the new iBus system in London. Results illustrate significant differences between some measured and default parameters, which in turn lead to some inaccuracies in emissions predictions for buses. Calibration is therefore essential and can benefit from the ever-increasing sources of automatic data emerging from new Intelligent Transport Systems applications.