Each vehicle enters the network from the upstream end of the first link on its path. Its initial position and speed are determined by the simulation step size, the driver's desired speed, and the traffic conditions on the loading segment. More specifically, if the necessary leading spaces are not available in the entrance links, vehicles are stored in a FIFO queue and wait to enter the network during subsequent time intervals; when vehicles can enter the network, they are pushed to positions with appropriate initial speeds that do not cause disturbance and artificial queues at the network ``entrances''.