The fire hydrant knocked over by the elephant was clearly a prop, as the elephant's trunk would not have sufficient strength to knock a real hydrant over.
While an acetylene torch could heat up a barrel containing flammable materials and cause an explosion, the other barrels were too far away to explode. Additionally, a rail car would not be abandoned containing flammable material- the contents would have been sold and offloaded prior to it being disposed of at the scrap yard.
While pursuing their stolen truck on a 2 lane road, Will says they are barreling down the Interstate. Interstate highways are multilane divided highways with paved shoulders. They were on some type of secondary road, not an Interstate highway.