Sometimes a "bigger" stick might be needed for such accidents - a refresher test is like a little slap on the hand. Maybe, a demotion to a lower class position policy be included in there job description. Hitting building/crane columns is extremely serious business. Without a stiff penalty for such an negligent acts, it won't get through. Look what has happened in school no corporal punishment = todays kids out of control. Something to consider.
Well, every new driver must pass a training course. Classroom & practical tests along with so many hours being paired up with an experienced driver. Then they have to pass re-fresher training every year. If they do have an incident, they are pulled from the machine and have to review a training video and pass a test. So, I think we have the training covered. We have policies/procedures on moving vehicles which covers responsibilities and safe operation. But the issue still remains.
Sounds like you are taking precautions at your facility,maybe some retraining.Safe operating procedures,be aware of your surroundings and operator responsibilites for the safe operation of thier lift truck.Operator Refresher training I would think solve your problem. If not you might need some new operators. The very best of luck.