I have an EDSMAC4 simulation where the vehicle starts from a stop and accelerates and turns left. I notice that the vehicle is experiencing an unexpectedly high lateral acceleration at the beginning. Why?

If you were trying to address this initial starting condition by reducing the Integration Timestep for Vehicle Trajectory, it will have no effect whereas the Vehicle Separation timestep will. The design of EDSMAC and EDSMAC4 uses the setting for the Vehicle Separation timestep as the starting Integration Timestep.  If a collision is detected within the first 100 timesteps, then the Vehicle Collision timestep will be used.  If not, then the Vehicle Trajectory timestep will be used until a collision is detected.  Basically, after the initial 100 calculations it switches to the appropriate time step, whether that be collision or trajectory.

If you’d like to learn more about the internal workings of EDSMAC and EDSMAC4, attend the EDC Simulations course or download the EDC Simulations Training Manual, Publication 1055, in the Technical Reference Library of the EDC website.