RIVERHEAD - Police say several people were injured this afternoon when a tractor-trailer collided with a school bus in Riverhead.The crash happened at about 3:30 p.m. on Sound Avenue. Riverhead Police Chief DavidHegermiller says the bus and the tractor-trailer may have sideswiped each other.It remains unknown how many people were onboard the bus, or the nature of their injuries. Police say a helicopter is evacuating victims from the scene.