Cars fitted with the system would have their speed automatically monitored by satellites, which would also be programmed with the speed limits for different roads.
Ah, but there are two problems with this.
The first is technology. The error in location for GPS various quite a bit (depending on the overhead satellite constellation). There will be times when the system cannot determine if the car is on the freeway or on the access road running right alongside it. This means that at some point a car driving on the freeway at 55 will suddenly slow to 35, much to the annoyance of the people following along behind.
Second, there are times when one has good reason to break the speed limit, such as getting a loved one to the hospital in a medical emergency, outrunning the waters from a dam burst, or escaping that meth head who has mistaken you for the guy who dropped a dime on him last week.
I for one do not speed. I barely remember the last time I was cited for a moving violation. But freedom means having the right to floor that accelerator if in my own judgment the circumstances warrant it.