How do I get the trigger to only trigger when object comes from the left?

Can you make a one sided trigger? I have a game with a bicycle that runs on the road and I want to make a notification when the player cycles to far to the left on the road. This also needs to work for both directions of the player. Thats why I need a trigger that only triggers if you enter the trigger from the left.

This is not foolproof, but it should work for most occasions:

private void OnTriggerEnter(Collider c)
{
    //convert the playerposition into localposition for the trigger
    Vector3 localPosition = transform.InverseTransformPoint(c.transform.position);
    if(localPosition.x > 0)
    {
        //Player is on the left
    }
}

This assumes that the player has a centered collider.