A card implanted on the license plate is not a realistic solution. That would make a cop finding out if a car is speeding a lot harder. Not only would they have to clock the speed of the car, they'd then have to chase it down to see if that speed is 'speeding' via the license plate, and then pull the car over to make sure the registered owner is driving. Not to mention, the time/cost needed to test everyone, re-test regularly (reaction times do change), etc. We cant even get people 80+ years old to take sight tests regularly to insure safety, you want this to apply to everyone, just so some people can drive faster than others? And, reaction time isn't even half the story of what makes a certain speed safe, personal decision making certainly factors in. Lastly, traffic flow would be ridiculous, with so many people having so many different legals speeds on the same stretch of road. Not even close to realistic, or simple to implement.