I’ve been fiddling around with the data on serious hazardous materials spills, and I used R to make a graphic that shows the differences in spill frequency by class.
The serious spills are distributed among hazardous materials classes similar to the prevalence of their shipping, with one exception. Corrosive materials (Class 8 ) are somewhat more represented in serious spills than in the entire spills record. Because there are so few spills from water transport, those are not illustrated. Infrequent hazardous material classes are also omitted from the figures.
A contrast of the two mosaic plots shows that rail and air modes have caused proportionately more evacuation events than highway shipping for both flammable (class 3) and corrosive materials ( class 8 ). This result is likely due to the volumes that can be transported by these modes, relative to a single truck. The reverse is true for events causing environmental damage, which could be a result of separation of rail and air facilities from other land uses. This separation contrasts with highways, which are more geographically dispersed and come in closer contact with environmentally sensitive areas. Here again, however, corrosive materials are proportionately over-represented among serious spills.
The mosaicplots are made in the R package vcd.