AIMSUN follows a microscopic simulation approach. This means that the behaviour of each vehicle in the network is continuously modelled throughout the simulation time period while it travels through the traffic network, according to several vehicle behaviour models (e.g., car following, lane changing).

The system provides highly detailed modelling of the traffic network, it distinguishes between different types of vehicles and drivers, it enables a wide range of network geometries to be dealt with, and it can also model incidents, conflicting manoeuvres, etc. Traffic equipment present in a real traffic network is also modelled in AIMSUN: traffic lights, traffic detectors, Variable Message Signs, ramp metering devices, etc.

One of the main new developments at the core of the simulator is the ability to use simulation steplengths as low as 0.1 seconds. It allows improvements such as the incorporation of variability in drivers' reaction times. The richness of other parameters available for characterising the different types of objects and traffic conditions means that the only limitation to the precision of the model is the quantity and accuracy of the data collected.