I'm guessing that, at the time the road signs were originally commissioned, the 8052 was probably 'state of the art'?
And these days, the old adage - 'if it ain't broke, don't fix it,' may still apply?
I remember a project - not that many years ago - where a client had had such a bad time using 8048/8051 microcontrollers in previous projects, he absolutely banned their use for his new project.
In fact, he went further. He insisted on a 'hardware only' control system for his new project!
Interesting challenge, bi-directional data comms with no processing power at all, but we did it! (Only minimal data transferred required, I hasten to add!).
I'm thinking PICs are probably easier, and more reliable to use, than these older microcontrollers? -
Or maybe that one client had just been really unlucky, with the quality of his 8048/8051 project designs??
As Nigel says, PICs are everywhere now. I can't imagine anyone doing a 'hardware only' control system for virtually anything, other than hobby projects, these days.