Geneva is a city used to organise international events like for example the International Motor Show which takes place every year. Most of these events are hold on the Palexpo area, a group of buildings situated near the Geneva airport. Both places are closely connected to the city ring highway. Traffic generated by this type of events obviously implies a totally different demand distribution shape compared to usual days. In addition, traffic volumes recorded during the event peak hours, (usually observed around the opening and closing hours), can reach up to the double of the ones ordinarily experienced. Given that the road network has not been design to handle this type of demand, important congestions are consequently observed during event periods implying important accidents risk, parking lot saturation and an overuse of the local network provoking annoyances for residents. In order to minimize these problems, the Geneva Transport Office asked Arx iT and CITEC (both local consultancy companies) to develop a method for supporting traffic management on the ring road. The basic concept is to implement in the Geneva highway traffic centre an on- line traffic data analysis tool which is able to, depending on the traffic situation (data coming from loop detectors and cameras) and parking lots occupancy, suggest a set of recommendations to be provided to road users through variable message signs. The whole process mainly relies on comparisons between the current network status and historical situations already observed during past events. For each of these situations correspond a traveller information scenario which has been designed based on empirical experiences. Although this tool has been offering reasonably good results for three years, situations without clear correspondence with past conditions are still frequently observed and the lack of experience on this particular cases lead sometimes to erroneous information scenario selection. Of course, facing these new situations allows traffic operators to increase their human knowledge, on which mainly relies the current AGIR process. Nevertheless, need for more systematic analysis process has been clearly identified. Reproducing various traffic situations without having to wait them to occur in reality is one of the major purposes of using traffic simulation tools in transportation studies. Thus, EPFL (Swiss federal Institute of Technology) has been in charge to assess the current AGIR system performances and to improve the knowledge data base through artificial experiments using a microsimulation model of the Geneva ring highway and part of the local network. For this task, EPFL has been helped by TSS, the company developing AIMSUN NG, the traffic simulator used for this analysis. The use of microsimulation offered the possibility of dynamically study the network’s traffic reaction to the information provided to simulated drivers by the AGIR system. This reaction implying new traffic data outputs, which are used as input for the AGIR process, the time dependent interaction between traffic situation and information system is fully captured. As simulation models offer statistical traffic outputs for each network element, global performance indexes could be computed offering a more realistic assessment of situation that only relying on traffic detection data. This complementary approach has been shown to be particularly efficient to improve current process and offer better answers to non frequent situations. Currently done off- line, possible integration of the simulation tool for on- line decision process is discussed for the future.