Apparently they tested just that -

Säll said: “There is no electricity on the surface. There are two tracks, just like an outlet in the wall. Five or six centimetres down is where the electricity is. But if you flood the road with salt water then we have found that the electricity level at the surface is just one volt. You could walk on it barefoot.”

They also mentioned they turn off each segment if there is not a car on it. Each segment is 50 meters.