"We have no idea at this stage, inquiries are obviously continuing. It's a bit of a blank canvas... until we talk to all the witnesses we don't know."
Police would speak to several "witnesses" who had passed the scene of the crash, and others who had called in reporting hearing motorbikes in the area, Mr Metcalfe said.
"Obviously at the moment our priority is at the scene and getting that cleared so we can open the roads.