The ripped carcass of the school bus involved in a horror highway crash has become the focus of a massive investigation to determine where the blame lies.

The vehicle, hired by Grayston Preparatory School to take 43 children and two teachers on a field trip, was involved in an accident on the M1 South in Sandton on Wednesday.

Initial unconfirmed reports indicate that the bus was travelling in the middle lane when a tyre burst, causing the driver to veer across the right lane into the centre concrete barrier.

The bus hit a lamppost, which tore it open, and the front right wheel went into an uncovered stormwater drain, causing the front axle to snap.

The 42-year-old driver, Patrick Mamburu, was killed. His body was flung from the bus, over the barrier and into oncoming traffic.

Two teachers and three children were still in hospital on Thursday night.

The bus has been impounded by metro police accident investigators, who are examining the wreck. They will focus specifically on the tyres and the broken front suspension.

Acting MEC for Community Safety Ayanda Dlodlo has issued a directive to the department of traffic management to investigate the accident.

"In addition, the department will also audit all the roads in the province to improve road safety," said spokesperson Phumla Mthala.

This would include monitoring highway stormwater drains, which were supposed to be fitted with metal covers.

Mavela Dlamini, managing director of the Johannesburg Roads Agency (JRA), said while he was aware of the missing stormwater drain grate along the M1 South, the problem did not fall under his jurisdiction.

The Ben Schoeman Highway from Pretoria to Southgate fell under three different authorities. From Pretoria to the Buccleuch interchange it was the responsibility of the National Roads Agency, from Buccleuch to Corlett Drive it was managed by the Gauteng Roads Directorate and from Corlett to Southgate it fell under the JRA.

"We have noticed those missing drain covers and reported them to our counterparts, but we are not responsible for that stretch of road."

Generally speaking, said Dlamini, the concrete blocks along the centre of the highway were designed to bounce cars back into their path of travel and stop them passing into oncoming traffic.

It was possible the bus might not have bounced off the barrier because the wheel stuck in the 300mm uncovered stormwater drain.

"Our experience is that these grates are susceptible to theft and are regularly stolen."

The fact that a relatively short stretch of busy road fell under three different authorities led to breakdowns in communication and people passing the buck.

"It's unfortunate that it takes an accident like this to be a wake-up call," he added.

Paul Nucci, managing director of Arrow Coaches, the company which leased the bus to Grayston Preparatory, was still waiting to hear a professional opinion on what went wrong.

He said that every Monday all vehicles were inspected, including all tyres.

The company has been in operation since 1968 and regular clientele includes 200 schools.