the cars will still try to go in the same direction
In case you are moving them to position, the problem might be that they did not reached their position so they keep trying and the two event to move object to position and separate two object are in conflict because the object trying to move to position but the separate two object prevent it and so it keep trying. So what you might want to do is set a new target position until find one that can be reached and as Lizard-13 suggested use the separate two object event to make sure the cars don't run over each other in the process or accidentality stop on top of each other. You can also use pathfinding to make them a bit smarter to find destination. Pathfinding allow you to easily check if a destination can be reached or not, if not, pick an other (random) position within a radius or something.