The EDSMAC simulation model has been in widespread use by vehicle safety researchers since its introduction in 1985. Several papers have been published that describe the model and provide validations of its use. In 1997, the collision and vehicle dynamics models were extended significantly. The main control logic was also extended and generalized. The resulting model was named EDSMAC4. This paper describes the EDSMAC4 model with particular attention to the extensions to the original algorithms. The paper also provides a validation of the new model by direct comparison to staged collision experiments and the results from the previous EDSMAC model. Extensions found in the new algorithm include the ability to simulate articulated vehicle collisions, simultaneous collisions between any number of vehicles (the original was limited to two vehicles), the adoption of a more realistic force deflection model using A and B stiffnesses (as opposed to a single Kv stiffness that assumes the force-deflection curve goes through the origin), the ability to simulate vehicles with tandem axles and dual tires, and vehicle longitudinal and lateral load transfers. The validation study found differences in the results when compared to the previous EDSMAC program. New EDSMAC4 data sets were produced that reflect the changes to the model.