Uh, anyone that has ever been involved in a driver facing camera camera system says their decent at improving safety, if managed correctly.
I say this as the IT manager of the storage system for the camera data of a fleet of taxi's. You review the cameras for safety issues before an incident occurs. The personnel management at this particular company does a very good job at only using the camera reviews to look for safety issues, other issues seen on safety reviews do not get turned in to the HR department. These reviews have dramatically dropped cell phone usage in public transport vehicles while moving at this particular company. I don't have good accident statistics at this time to tell you if it has made a huge difference, and that can vary greatly by weather events per year (we had two extremely dry years, then this year has been very wet and was icy during the winter).