Three members of a family were injured after a speeding Mercedes, allegedly being driven by a 17-year-old boy, rammed into a car inside the Coastal Road tunnel in South Mumbai, police said.The accident occurred in the early hours of Sunday.The D B Marg police have registered a case against a businessman from the Agripada area, the Mercedes owner, his 18-year-old granddaughter and the latter’s 17-year-old male friend, who was driving the luxury car, an official said on Monday.The accident took place inside the tunnel on the road when the speeding Mercedes, going towards South Mumbai, rammed into another vehicle from behind. The high-end four-wheeler then hit another car going ahead, he said.Three members of a family, including a senior citizen woman, suffered injuries when the Mercedes hit the second car, the official said.During the probe, it came to light that the Mercedes was being driven by a 17-year-old boy. He lost control of the vehicle inside the tunnel, leading to the accident, the official stated.