On the one hand, there is a tendency, as illustrated here, to want someone to blame, although often it's a bit more complicated than that. On the other hand, accidents such as these, where there is a big corporate body involved, it's easy to blame the workers and overlook the failings of management. See for example, Herald of Free Enterprise accident. Or, as in this case, blame no one, it falls between two stools as it were.
So the basic facts are these, to remind ourselves. A tram went around a tight bend 3 times too fast and derailed. 7 died, others were injured. There were no mechanical reasons for it, rather the driver was driving too fast of his own accord. The driver was seemingly disorientated, probably through tiredness from not getting enough sleep, and forgot to slow down for the bend coming up. You can't see it until the last second, you rely on track knowledge to drive it safely.
There were, however, some design flaws.
- There was no advance signage of the up-coming speed restriction, which would have been a good idea. The driver had to know to slow down in time. This change was made very quickly. A cheap and obvious thing to do.
- There is no automatic speed limiting system, comparable to the one that is a legal requirement on the mainline railway, in such locations. On the mainline, the TPWS system is present to slam on the brakes if the driver is approaching a speed reduction location too fast. This can be a red light or a speed-limited bend. There is a minimum speed reduction that applies. And temporary speed restrictions don't need it if they are sufficiently temporary.
- There was a history of drivers going rather too fast around the bend and getting away with it. But this was only discovered afterwards. No one was routinely analysing the data to see if drivers obeyed the speed limits, and analyse possible reasons for it.
- A disputed point is whether the shift patterns contributed to the driver's likely tiredness.
- Does the fact of the design faults absolve the driver of any blame for this?
- Are the design faults sufficient that TfL should be blamed, either alternatively, or in addition?
Also motoring background. Suppose someone failed to slow down for an unsigned concealed bend in their car, and crashed it and killed someone. Would/should they be found guilty of causing death by careless, or even dangerous, driving? I am aware of some cases like this where drivers did something quite like that, and were found not guilty of either offence. In one case a driver crashed their car into a ditch through taking a bend too fast on a mountainous single track road in the dark, killing some of the passengers. No other vehicles involved. The driver in effect admitted misjudging the bend. In the other case, a driver went around a blind bend 10mph over the speed limit, started to overtake some bicycles they encountered, and then a car came the other way. The driver cut in very close to the bicycles, one of them wobbled and came off, and was killed when the car struck them.