Think Big. Move Fast.

Cool concept. My concern is that people will change their driving style to achieve better feedback and it could be dangerous to other drivers. I used to drive an EV1 and it had a kinetic charger that could be switched on manually. I used to slowly coast into stop light and only accelerate to the minimum velocity needed to make it to the next light, all to save batteries and extend my range. I did this because the damn thing would run out of batteries if you drove it anywhere near the maximum stated range.
However, I could tell this type of driving practice was frustrating to other drivers and am worried that there are safety concerns that go along with encouraged unnatural driving habits. People going way to slow end up causing traffic jams, road rage and, consequently, wrecks as others try to scramble around them. It is more energy efficient to smoothly accelerate and regulate top speed but it is not how human drivers operate and will, therefore, have pronounced negative effects on traffic flow.
Overall it is a cute idea that needs to be thought through a little better.

Applying Game principles to traffic control

In some construction zone where the speed limit is 40kph, digital display board provides instant feedback of actual speed of drivers entering such zone. The board displays messages such as “Thank you! Your speed is 34kph. Well done!”

The “compliance” has been good, compared with similar speed limit in school zone, where drivers routinely ignore similar speed limit sign.