Providing priority to buses plays an important role in protecting bus services from the effects of traffic congestion and in improving speeds and reliability. Among the measures available, bus priority at traffic signals is the most relevant where opportunities for segregated systems are not available and/or where numerous traffic signals exist. Again, there is scope for many forms of bus priority at signalised junctions. One such method is differential bus priority in which buses are given different levels of priority according to their individual requirement. This method allows a range of priority strategies to be implemented, depending upon the lateness of buses and junction capacity constraints. Exploring the performance of different priority strategies within this method has been the main aim of this research. The literature review showed that there is a need for a model for modelling differential priority in detail. Hence, a microscopic simulation model SIMBOL (Simulation Model for Bus priority at traffic signal) was developed. SIMBOL simulates a bus route in a field situation, taking account of the characteristics of buses, bus stops, traffic signals, the AVL system and differential bus priority systems. The model was calibrated and validated with the field data from a bus route in Southampton. The validated model was then used to formulate 7 different types of priority strategies and to simulate them under various scenarios. These strategies varied in terms of the level of priority to be provided, based on the lateness of the buses. The different scenarios in which these strategies were simulated included: the present field condition, different types of bus generation, holding early buses, potential errors in location systems and changes in bus operations. The performance of these priority strategies was evaluated using the output results from the model. The simulation results showed that all bus priority strategies simulated give benefit to a bus system including buses and passengers. However, the type of benefits and their magnitude differ from one strategy to another. The results illustrated the strength and weaknesses of different priority strategies under different field conditions. This showed that the selection of a best-suited priority strategy depends upon the aim of a priority scheme in terms of total benefit or punctuality. Research included the development, modelling and recommendation of a new mixed priority strategy giving good benefits across a range of scenarios. The research also demonstrated the usefulness of SIMBOL as a valuable tool for modelling differential bus priority under different field conditions and as a basis for further research.