The driver of an overloaded dump truck was arrested yesterday on suspicion of dangerous driving after his vehicle hit a police motorcycle in Kowloon Bay, seriously injuring an officer. Police said a preliminary investigation indicated that tailgating was the cause of the accident. Acting Sergeant Ling Siu-ngai, 32, was on patrol on the eastbound lane of the Kwun Tong Bypass when the accident happened at about 10.25am. The truck, heading towards the Tseung Kwan O landfill, drove on to the elevated highway from the Kai Fuk Road slip-road and followed the motorcycle in the slow lane. Near the junction with the Wang Chiu Road slip-road, the motorcycle slowed but the truck failed to stop in time and ran into it, Chief Inspector Ho Chak-kan of Kowloon East traffic unit said. '[The truck] pushed the sergeant about 15 metres into the middle lane before it came to a stop. The officer was trapped under its left front wheel,' he said. 'Good-hearted motorists pulled over and offered help. They freed the officer by using jacks before firefighters arrived.' Police said there was a 30-metre skid mark behind the truck. Sergeant Ling suffered a crushed leg. He was taken to Queen Elizabeth Hospital, where he was in critical condition last night. The truck driver complained of chest discomfort and was later discharged from United Christian Hospital. He passed a breathalyser test and was granted police bail of HK$5,000. A police investigator said the truck was carrying about 36 tonnes of refuse - six tonnes more than the legal limit for the vehicle. The investigator said driving too close was the suspected cause of the accident. Drivers are urged to keep to the recommended braking distance of two seconds behind the vehicle in front. Police said the site of the accident was not a traffic black spot. The truck was towed to a government vehicle plant for examination. Traffic was disrupted for more than 2? hours. The road was reopened at 1.20pm. A car and a motorbike had collided in the eastbound lane of the bypass outside Enterprise Square, around 500 metres from the site of the later collision, at 6.50am. The motorcyclist, 38, was treated for minor head injuries at United Christian Hospital. Police figures show that 90 people died in 80 traffic accidents between January and July this year. Over that period last year, 104 people died.