You only need to derail ONE of the bogies/wheel sets of only one of the wagons for the train to be "derailed".
Yes, it looks like the train in the image jack-knifed, suggesting it probably isn't articulated. So the affected coach can be pushed off by itself, rather than being stabilised by the weight of the rest of the train.
There's already Essex, Middlesex, Sussex and Wessex, so all we need is a Norssex to ceate Sexland.