CERN just managed to transport antimatter via truck, and people are asking what happens if it gets into an accident. the answer is... a car accident.
the energy equivalence of antimatter is huge โ 10ยนโทJ/kg, but the amount is tiny โ 92 protons. it's so tiny that if i placed all 92 in your hand, the destruction and release of energy would feel less warm than mere sunlight, by a factor of at least a few thousands.
i'd be more worried about the 2-ton magnetic containment machine in that truck.