Actually lap only belts are almost as bad as no belts.
The injuries caused by lap belts are quite different. With the lap belt the upper body is unrestrained while the hips are restrained and this itself causes BIG problems.
- For the driver the upper body pivots at the hips and this brings the forehead down onto the steering wheel and significant risk of skull fractures and cervical spine injuries - death.
- For all lap only belt wearers the contents of the abdomen are squashed into the thoracic cavity: lung injuries, liver and spleen lacerations, rupture of the stomach with emptying of stomach or bowel contents into the thoracic cavity and lacerations to major blood vessels.
- Whiplash injuries are also worse because of the extra momentum of the upper body (which would otherwise be restrained by the sash belt).
Without any belt the driver's chest and abdomen absorbs the energy as it folds around the steering wheel. The potential for fatal consequences of an unrestrained driver hitting the steering wheel is probably less than for lap belt restrained driver.
In any case I would not fit lap only belts to any vehicle I own. There are always options for 3 or 4 point harnesses.
Diana