Six people were killed and 37 others injured in a twin-bus accident on Turkey's Trans-European Motorway on Wednesday.The first bus, heading to Istanbul from Nigde province, overturned at the Bolu mountain tunnel, 300 km east of here, after the driver lost control, Xinhua reported, citing the semi-official Anatolia news agency. At least six people were killed in the accident besides several others receiving injuries.As traffic teams worked on the scene, a second bus hit roadside barriers, narrowly avoiding a collision with the already-crashed vehicle.The injured passengers from the second bus were evacuated by police and fire crew.