There's a reason they do that. If the vehicles aren't moving at relative speeds, they will very quickly be very far away from each other (how long do you see a specific car going the opposite direction on the freeway, when traffic is moving well?). When they are separated by a long distance, then it's the distance, more than the location, that matters in the vast majority of circumstances, and the grid doesn't much matter.
If the two vehicles aren't competing, then specific relationships don't matter so much, and you don't need the grid anyway.
If they are competeing (a race, say) then either they are equal, near equal, or not near equal; if they are equal, then they won't be moving much in relation to each other; if they are near equal, there will only be a little movement in relation to each other; if they are not near equal, then the outcome is already decided, or near enough, and the specific positioning doesn't much matter.
If there is a running fight between two vehicles then, at any given time, either one or more will be trying to stay close (chasers - note that chasers become pacers in many instances), one or more will be trying to get farther away (runners), or one or more will be trying to maintain a particular distance (pacers). Whichever one is better at it will decide which occurs - if a runner is better at it, then the distance will increase to the point where it's separation that matters, not location; if a chaser is better at it, then distances will become very short, and likely stay that way... and it's back to close, relative movement (ditto for pacers, although for them, the distance is fairly set).