Four persons were killed and one injured in a road accident when a car rammed in to a state transport bus from behind along the Greater Noida Yamuna Expressway early Saturday, the police said.The collision of the car and truck at 6.45 a.m. was of such intensity that the crash left the front portion of the car completely flattened.The victims travelling in the car belonged to Agra, Ghaziabad, Haryana, Maharashtra while the injured person is a resident of Faridabad.According to police the spot was nearly one-and-a-half kilometres before the zero point near the HP petrol pump along the expressway line from Agra to Greater Noida at the Beta-2 police station area. All four deaths took place on the spot while the fifth is critical.