Despite a lot of effort has gone into research on human-induced vibrations of footbridges in the last decade, there is still a lack of reliable models and adequate design guideline pertinent to dynamic loading due to multiple pedestrians. There are three key issues that a new generation of models should urgently address: (i) interaction between pedestrians and the structure they occupy and dynamically excite; (ii) pedestrian intelligent behaviour; (iii) inter-subject and intra-subject variability of pedestrian walking loads. This paper presents a model of pedestrian-structure dynamic interaction in the vertical direction which addresses the first two issues. The model comprises three sub-models: (1) a model of a footbridge featuring a SDOF system having the dynamic properties of an empty structure, (2) a microscopic model of multiple pedestrian traffic that simulates position and velocity of each individual pedestrian in space and time, and (3) a model of individual pedestrian actuator featuring a periodic force model coupled with a spring-mass-damper oscillator which move together along the structure. The proposed model is applied to a lively footbridge with known modal properties and results are compared to the measured vibration response due to a light pedestrian traffic.