Most of the film is set during a heavy rainstorm but some scenes are filmed in bright sunlight with the ground obviously dry.
At the start of the film, Johnny Chicoy is shown getting under the front of the bus, but the close-up of him working shows that he is near the back wheel.
The condition of the bus is not consistent with its journey; for instance sometimes later in the film there is less dirt splattered on the side of the bus than earlier and the rear bumper is sometimes hanging loose and sometimes fixed in place.
When the bus is descending the dirt road, the sound of screeching tyres can be heard, but on soft ground such as this, there would be no screeching sound.
The interior of the bus obviously is a built set as one can tell by the outside dimensions that do not match up.
When the bus looks to be out of control coming down the dirt road, it can be seen that there are no passengers on board.
When Johnny Chicoy is working under the bus, tightening the brake-line connector, he uses only one spanner which allows the connector to turn with the nut; this means that the connector never achieves a proper seal. As the person responsible for the mechanical safety of the bus, he should have known this.