If a loaded transport vehicle is destroyed them carried infantry unit are automatically unloaded next to the transport.
The unit doesn´t suffer any damage not even a morale loss.

Riding on trucks in the middle of a battlefield and having your transport blown up is surely make bad news for the occupants...infantry in trucks and half-tracks usually got out of their vehicles long before engaging the enemy.
I would suggest for the next update that units loaded on a transport that is destroyed would automatically be unloaded AND supressed. More reallistic IMHO.