What are the correct line-handling techniques for effective communication in driving?

Line handling is the primary skill of the driver, equivalent to the seat, leg, and hand of a rider, and developing correct line-handling mechanics is foundational to effective communication with the driving horse. The driver's hands and arms are the only direct communication channel with the horse in driving — there are no leg aids, no seat adjustments, and no weight shifts that influence the horse — which makes the quality and sensitivity of the line handling more critical than in any riding discipline. The lines are held with the left line in the left hand and the right line in the right hand for single horse driving, with specific adjustments for pairs and teams. The hands should maintain a consistent, elastic contact with the horse's mouth through the lines — not a rigid, fixed contact that prevents the horse's natural head movement, and not a slack, loose contact that provides no communication. The elastic quality of correct driving contact is similar to the elastic rein contact of classical riding — following the horse's natural movement while maintaining the consistent connection through which communication travels. Direction is communicated through increases in contact on the turning side combined with a slight opening of that hand in the direction of the turn. The driver should feel the horse's response to each directional aid and release or soften the contact when the horse has responded correctly, reinforcing the correct response rather than maintaining constant pressure after the turn has been established. The whip is the driver's leg aid equivalent — used to reinforce the forward driving aids when the horse does not respond to the voice and line aids, not as a punishment. Correct whip position, movement, and use are specific skills that should be learned under instruction.