The three were returning home after a marriage function when a speeding SUV hit them from behind, Karakat police station officer in-charge Pankaj Sharma said.
While two died on the spot, the third has been sent to Varanasi in a critical condition, he said.
The driver of the car fled leaving the vehicle after the accident, the OC said adding the vehicle has been seized.
The three are natives of Karakat bazar area of Bihar's Rohtas district headquarter, Sharma said.