My sister-in-law followed a car with a trailer carrying a quite few hives, really they were just the honey boxes. The car/trailer hit a few road works where it had to stop. While stopped a cloud of bees circled around the road workers and my sister's car.
She was concerned with the hazard the bees were to workers and other motorists.
The second concern she had was with Varoa other other diseases, weren't those escaped bees spreading any diseases that the hives on the trailer had?
When transporting bees the hives should be secured and strapped. The hives also should be sealed, but have ventilation, so that no bees can escape. If the truck/trailer tips over then it prevents the bees from adding to the problem. Police, fire and ambulance will not attend where they are loose bees.
Having said all that I know that a few bees will always hang around the honey supers when it is loaded.