The reliability of transit modes is a crucial issue to guarantee their competitiveness and attractiveness. Experience shows that buses covering busy lines with short headways tend to arrive irregularly at their stops, often in bunches and therefore remarkably affecting the service. Hence, this work presents a stochastic model capable of representing the operational activity of a bus transit network and the service disruptions which eventually end up causing deviations from desired schedule. At the same time, the model is tested on an ideal route as a decision making tool.