NIRMAL : Four persons were killed and 15 injured in two separate incidents involving Telangana State Road Transport Corporation (TSRTC) buses in Nirmal and Medak districts on Friday. In Nirmal district, a motorist was killed and 15 passengers were injured when an RTC bus turned turtle on old NH 7 near Dyangapur village of Sarangapur mandal after the driver of the bus lost control of the vehicle and hit a car stranded on the roadside and then hit a motorist standing on the footpath, killing him instantaneously. The bus, travelling from Hyderabad to Adilabad, had 33 passengers on board. Meanwhile, in a similar accident in Medak, an RTC bus rammed into two motorcycles killing three at Kasila Farms under Narsapur police station limits on Friday. The bus was coming from Banuswada to Hyderabad.