The brake system is one of the most critical components of a motor vehicle that ensure its safe operation. Current heavy commercial vehicles commonly use a S-cam air brake system, where compressed air is used as the medium to transmit the energy needed for braking. An Antilock Braking System (ABS) is an important safety device that ensures the stability and steerability of vehicles during braking in emergency situations, poor road/weather conditions, etc. The objective of this paper is to develop a mathematical model for the overall longitudinal dynamic response of a commercial vehicle equipped with an electropneumatic braking system. This will provide better insight into the performance of the vehicle and open room for improvements. This model will be ultimately used for the analysis of various schemes that can be used for ABS development. Such a model based approach will allow for computer based analysis of commercial vehicles equipped with ABS which may result in a reduction of expensive and time consuming experimental development trial runs.