A couple and their two sons were killed in a road accident on Sunday when the motorbike they were riding was knocked down by some vehicle in Dhar district of Madhya Pradesh.Shobharam, 40, of Ghatabillod in Dhar district, his wife Kala Bai, 35, and sons Ayush, 12, and Akash, 10, were killed on the spot when a vehicle hit their motorbike on the Indore-Ahmedabad national highway. The family was going to Pariyal, Sadalpur police station chief Ramesh Chandra Awasiya told IANS.According to Awasiya, Shobharam's motorbike was hit twice by some bigger vehicle, after which its driver sped away.The four bodies have been to the hospital for the post-mortem examination, and the police are looking for the offending vehicle, Awaidiya said.