Traffic laws already limit how you are allowed to use your own car. This just prevents you from breaking the law. Your freedom ends where the freedom of another person to live a safe life begins.
> Also I don't understand what does this have to do with climate change?
Speeding cars make it a lot more difficult for other means of transport to share the road. In Europe many urban areas are limited to 30km/h (19mph). This allows sharing the street with bicycles, pedestrians and playing children. Speeding cars (speed limits are often seen as minimum speeds) make this impossible.
So the climate will come from people moving to other means of transport that are becoming viable and safe. Also public transport will be more attractive if taken a car takes longer. Europe tries to make its cities more live and loveable.