Uh, why should the lifespan of a roadsign be only ten years? Unless they're really, really shoddily manufactured?
It could be that the printing of the name on the background takes a beating and the letters either darken or peel off.
Or the supports start to rust; remember they're out in all weathers.
They'd have to be pretty damn sh!tty manufacture for that to happen this quickly. Seeing as they're not in contact with
the earth.
More likely it's some set date at which there's a reasonable chance they might conceivably need replacing even without having suffered a major accident ... carved into by-law as an "average" by some greedy manufacturer with an inside track to the bureaucracy. It's the way of the world.
We actually had a similar issue in Germany recently. There'd been minor to middling changes to the design of a large number of roadsigns (not street name signs)... not sure of the exact year, round about 1989 I think. Of course the old signs remained valid for an undetermined "interim".
And a propos of the official abolution of a few obsolete signs this year, bureaucrats thought it cool to terminate that "interim" rule. Had to eat their words on that after a storm of protest from the municipalities who would have had to foot the cost - only West German municipalities, btw - the east has post-88 signs, obviously. As does any road built afterwards in the west, or where traffic directions changed. But not many outside of that, as traffic signs can actually last nigh-on forever. Though the federal bureaucrats apparently had some figure of a 15 years lifetime.
I also found an article from the city of Düsseldorf stating that their streetname signs hold "15 to 30 years on average"... or rather the ones they used til 1995 did, the current issue ought to have a slightly longer life expectancy.
