The report makes very sad reading my sympathies go to the families of those involved. The Chief Inspector certainly doesn't mince his words on this. Frankly it's one of the most strongly worded comments I have seen from the RAIB even the old HMRI reports that brought about major changes (in law in some cases) were not as strongly worded as this. I would be very curious how any railway employer going forward could suitably assess the fatigue risk of employees on zero hours contracts when the law states that such contracts cannot be exclusive or prevent people from taking up other work? Four and a half hours in the previous twenty four does seem like an incredibly low number. From personal experience I would struggle to perform the safety critical parts of my (non railway) job with that little rest.