A Heavy Vehicle (prime mover and trailer) was travelling through a bend in a graded road when the driver fell asleep and veered onto the wrong side of the road where there was an oncoming Coaster bus which had 9 passengers on board. Both drivers had attempted to take evasive action, turning to their rights respectively, with the bus leaving the road onto the soft sand over a small windrow, however the HV struck the drivers side in the center of the Coaster bus resulting in minor damage to both vehicles.