If using your cell phone might cause tumors imagine what this might do. Wouldn’t you need some sort of filtering or lead shield to be safe?
Answer is no, as far as a magnetic field is concerned lead looks like air and does not alter the field. There is a material used to shield magnetic fields, its called Mu (pronounced 'meow', like a cat call) metal. It is notable for its high magnetic permeability. The high permeability makes mu-metal very effective at screening static or low-frequency magnetic fields. Another high permeability alloy is permalloy which has similar magnetic properties.
Before we go all nutso on shielding I should point out that the human body is subject to the earth's magnetic field every day and to much stronger fields when having a MRI scan. There are no side effects to such exposure unless of course you have a prosthesis made of hardenable stainless steel, then you might feel a sudden attraction!
Shielding the field defeats the purpose of generating it in the first place. The whole idea is to construct what amounts to a transformer with the primary coil buried under the pavement and the secondary under the bus. Whenever the bus stops over the primary the magnetic flux couples to the secondary and induces an electric current to charge the bus batteries. If someone put a coil under his Prius and tried to grab some free juice, he would have to park in a bus loading zone. It would seem wasteful to leave the primary energized whenever there was no bus present for charging and I would think that designers would include a "below the pavement sensor" (like they use for left turn sensing) to switch off the primary when no authorized vehicle was present.
The biggest problem I can see is that nearly all transformers are constructed around iron cores which have a permeability of several thousand compared to air which has a permeability of one. Permeability is a measure of a materials ability to support a magnetic field, it would be analogous to conductivity (1/r) in an electric circuit. If you put an iron core in both the primary and secondary coils the problem remains because the two cores are separated by two air gaps. Perhaps the best you could do would be to bring the primary core (pole pieces) as near to the surface as possible and design the secondary to lower itself into contact when properly aligned. This precludes charging on the go but that would be a tremendous waste of energy in any event.
It seems that a much simpler solution would be trolly buses (rubber tired vehicles) with an overhead trolly system to supply continuous power to series wound traction motors.
Regards,
GtG