Three people were killed and 22 others were injured when a bus plunged off a highway into a canal in Thailand.

The shuttle was transporting more than 20 workers of the Wellgrow Industrial Estate when it crashed into a road barrier and fell off the Rattanakosin 200 Years Road in Samut Prakan province on February 3 evening.

The bus flipped over and fell into a canal, killing at least three passengers and wounding 22 others, including the severely injured driver.

They were rushed to the Ruamchai Pracharug Hospital, Princ Hospital Suvarnabhumi, Chularat 9 Airport Hospital, and Bangbo Hospitals for treatment.

Police Major General Wichit Boonchitwuthikul, commander of the Samut Prakan Provincial Police, conducted an investigation and said the road was being expanded to add two more lanes.

The accident has been blamed on poor lighting and the lack of proper road markings separating the lanes.

Police Major General Wichit said: 'After the inspection, the contractors were ordered to immediately add more barriers and install sufficient lighting along the entire road to prevent further accidents.'

Police Colonel Chairat Rungruang, superintendent of Bang Bo Police Station, said the bus typically picked up the workers from Bangkok to take them to the Wellgrow Industrial Estate in Chachoengsao province.

He added the driver may have been inexperienced as the road was not on the shuttle's usual route.

Police said the unnamed driver will be charged with reckless driving causing death and injury. He will be questioned when his condition has improved.

Meanwhile, the bodies of three casualties were at the Ramadhibodi Chakri Naruebodindra Hospital awaiting retrieval by their relatives for funeral arrangements.

Thailand has one of the world's worst road safety records. Ministers have set the goal of reducing fatalities from 32.7 deaths per 100,000 people to 12 per 100,000 people by the year 2027.

However, a lack of road safety education in schools along with notoriously easy driving tests, police failures to enforce road laws, and chronic under-investment in infrastructure, all appear to hamper the efforts.