I don't think I've ever seen mobile/crawler cranes here in Paris. All of them seem to be tower cranes and the structures seem quite stable (I couldn't find death by crane stats with a quick google). These tower cranes I see everywhere are on fixed construction sites... I suppose the use of mobile cranes is more for renovations -- and yes they seem very dangerous in comparison to a fixed-base crane. But still, when one is going to the effort of building/renovating something of such magnitude, why can't a fixed-base crane be used ? If done right it shouldn't be too hard to mount and dismount a modular tower crane -- maybe there's a market for this sort of thing...