The Regional Transport Officer (Enforcement) has identified three probable reasons that caused the horrific lorry-bus accident at Avinashi in the Tirupur district of Tamil Nadu on Thursday that claimed 19 lives.
The driver of the lorry lost control of the vehicle, which jumped over the divider and entered the opposite lane, and rammed into the Kerala State Road Transport Corporation (KSRTC) bus.
The accident happened around 3:15am on Thursday. The lorry weighed 9.52 tonnes and the container 25 tonnes, while the weight of the bus was 19 tonnes.
Understeering
About 100metres before the collision, the right tyre of the lorry climbed on to the divider. This happened because the lorry driver did not turn the steering sufficiently enough to navigate the steep curve on the National Highway, a flaw referred to as understeering.
With the front right tyre on the median and the rear-end tyres on the road, the lorry went 30 metres ahead at the same speed. During this time also, the steering wheel was not properly turned. This caused the rear-wheels on the right side to heat up due to increased pressure, resulting in one of the tyres getting thrown off the disk and the other bursting.
Lift axle
When heavy load is mounted on the lorry, two wheels in the front row at the rear-end, known as lift axle, have to be used. It is suspected that the lift axle was not used at the time of the accident. This is based on the finding that these tyres did not have damage in proportion to the intensity of the accident.
With one tyre coming off and another bursting, the wheel disk came in contact with the divider and was dragged along. The lorry travelled for a distance of 10metres in this manner before the entire vehicle was on the divider.
As the lift axle was kept raised and these tyres happened to be of the same height as that of the divider, they might have started rotating as the lorry climbed on to the divider and thus helping the lorry to cross the divider.
Though it is advisable to use lift axle when carrying heavy loads, most drivers keep it raised for ease of driving. If the lift axle had been used, chances are less that the lorry would have entered the divider.
Container lock
Container lock is used to fasten the container box on the platform. A broken lock was found from the accident site. Another lock was found fastened to the container platform.
Most portion of the lorry crossed over the divider and entered the opposite lane. The left rear tyres might have been on the median and the left front tyres in a raised position, when the bus coming from the opposite direction was sighted and the lorry driver attempted to serve out of a collision. As the container was already titled to the right after the tyre burst, the locks on the front side and left rear side of the container box gave away. The container box tumbled on to the road and crashed into the KSRTC bus.
The study was conducted by P Sivakumar (Enforcement RTO), motor vehicle inspectors P T Padmalal, S Biju, P Prashanth, C S George and assistant vehicle inspectors K Pradeep, A Anil Kumar, K Devidasan, and P V Sajeev,
