There is no limit to fantasies like this? Who will pay is the question? What if you have pay each time you avail this service thru GPS? Would you avail it? What if it costs you more than the benifit you are taking out of it, simply being more cautious, concisious and aware of the sign boards and remembering that Life happens only once and more so that you own this car you are driving.

You don't need GPS for that. GPS relays only geographic position.

You can use, at these points, micro transmitters which beacon things like that to a receiver box in the vehicle.

For speed limits, there could be maximum speed limits built into a vehicle's computer, but not tied to any outside source (such as the transmitter above).

The idea is that ground equipment (like the micro-transmitters) can be vandalised or tampered with, but the chances of this happening to GPS are remote. Again, the main override is in the car but the computer controlling this, in order to avoid hacking of any sort should be in a server-like location else on the ground communicating with the satelite. So basically after a car relays its speed, the necessary commands are sent back, necessitating either auto-speed, or whatever. Think of accident free roads. Google accident costs and then you will appreciate that this is not as expensive as it may sound. Plus prevention of loss of lives, priceless!! If a system is already there that knows how a section of the road is, why not use it? We have already navigation systems which utilizes the GPS quite favorable, the only missing thing being the software interaction with the vehicle.

I can imagine a national database that is updated hourly with work zone speed limits and such. Then broadcast speed limit and GPS references to an on-board computer. Tie the cruise control into the database so as you are cruising you don't miss any of the speed changes.

This concept has been documented at

Hands-Free Vehicle Operation