"... this energy would be totally free because it is produced by the interaction between the vehicle and the road..."
This is not true. The magnetic force is not free. I am confident this mechanism will not be deployed until the power can be billed per watt, because it will cost money to create. Some means of quantifying the power drawn by vehicles must accompany the delivery of that power in order to bill vehicle owners nominally, and seems yet to be devised, just like aiming a bow is necessary to deliver arrows to targets.