There is a limit, both practical and desirable, as to the degree of protection one can give in such circumstances. My involvement with a much smaller museum than Didcot indicates that people often don't understand these days how mechanical things work and can cause injury. You can't put everything that moves behind guards, firstly because that would not allow people to see the working mechanism as it was in practice, secondly because it would take up excessive room and expense. Some things are discretely barriered off, but we either conduct people round our site so we can ensure their safety, but still let them have a close look at or to actually operate equipment, or on busy days station members around the site to explain things and keep an eye on the safety side.
I would expect that at Didcot the signalman or woman would check that people are clear of signal wires and point rodding before operating the same.