Whilst this is only partly relevant to the story, I thought it might be interesting to some non Europeans.
A popular trend in the UK at the moment for young drivers is to have their car fitted with a "black box" by the insurance company. The idea behind this box is that it monitors the "g-forces" it is exposed to, to gather an idea of how safely the owner is driving the vehicle. Throughout the year, the owner is graded on various aspects of their driving based on this telemetry. Also, I believe that the insurance companies can penalise the owner for driving at certain times, e.g. after 10pm on a friday night. The idea behind this is that the insurance company can charge the owner less, and if they do well after one year, the price drops dramatically.
Additionally, if the black box experience a very high braking force, it will automatically trigger the insurance company to ring your mobile to ask if you're okay, and if you need any help exchanging insurance details with any other drivers involved.
Anyway, back on point, I imagine it wouldn't be too difficult to add GPS facilities to these devices, and receive speed limit information based on location similarly to have satnav's currently do so. Obviously, for various reasons already mentioned by other posters, you would not want any restrictions to be physically enforced, but it could serve as a guide, or notice, to the driver.