As part of a project which deals with comprehensive free-flow toll systems for trucks and buses, a multi- agent based simulation model was developed. This model is used here to discuss the general development process for multi-agent based simulations which map real-world situations and whose results are the foundation for real-world decisions. It will be demonstrated that developing such models is a demanding task, requiring detailed understanding of the relevant reality and meticulous work. In addition findings from the model and their implication for planning and installing real world comprehensive truck toll systems will be outlined.