They're not running traffic directly on a road surface of styrofoam. A picture in the article shows a road embankment under construction, with a rebar mat on to

They're not running traffic directly on a road surface of styrofoam. A picture in the article shows a road embankment under construction, with a rebar mat on top of the geofoam blocks. This will have a concrete pad poured on it, which spreads the load of the road and traffic across the entire area of the embankment vs just point loading of the tires of the vehicles, so it can easily handle the weight.