You can go and look in Google Earth, if you want to. I think they look a bit discoloured, but see no sign of rust coming through the paint. However, this one (image dated 5/2012) has an obvious watertightness problem.
They do have this rather odd arrangement of two access hatches, so sealing could be a design problem. They appear to be bolted to the flat bridge surface, so may well have a closed base and need a drainage hole, which could be blocked. Then there's what looks like a damp patch on the concrete round the lamp - that's the same on all of them. So there's quite a few things that could make them liable to fail.
Bolted base, could be a failure of the weld of the base plate to the post, could be rust from the inside out as Stuving has pointed out of access hatches leaking. Could also be the foundation bolts or the concrete foundation its self has failed
