LUCKNOW, Oct. 3 -- A total of four passengers were killed and four others critically injured when an air-conditioned private sleeper bus carrying around 50 people collided with a trailer on the Gorakhpur Link Expressway in Uttar Pradesh's Ambedkar Nagar district early on Friday, police said. According to police, the crash occurred at around 5.15 am in the Jaitpur police station area, around 50 km from the district headquarters. The bus was travelling from Delhi to Darbhanga in Bihar when it collided with the trailer, which was carrying tiles from Rajasthan to Bihar. The impact was so severe that the left side of the nearly 40-foot-long bus was completely mangled, trapping several passengers inside. Most of the passengers were asleep when the accident occurred, triggering panic and screams inside the bus. Police, assisted by passers-by, cut open the damaged portion of the bus to pull out the trapped passengers. The rescue operation continued for around 40 minutes, after which the injured were taken to hospital. Ambedkar Nagar additional superintendent of police Tejveer Singh said the preliminary investigation indicated that the bus driver may have dozed off at the wheel, leading to the collision. He said the bus, operated by Tighra Express Travels, was reportedly travelling at close to 100 kmph....