Police said on Tuesday that track workers were to blame for the train crash on Sunday night as they did not send signals to stop the approaching train, causing it to collide with six cars, killing two and injuring 24.
The accident happened when a northbound train crashed into six cars stuck on the Ghenh Bridge in the southern province of Dong Nai.
The narrow bridge, reportedly built more than 100 years ago, handles both car and train traffic.
Track workers in charge of the railway gate failed to stop cars from entering the bridge, leading to a serious traffic jam, police said.
They did not signal to stop the train from running into the cars either, they added.
Police said they are looking into pressing charges of irresponsibility in the accident.
Seven people have been detained so far, including the driver and the conductor of the train as well as the track workers.
The accident, a Lunar New Year tragedy, has raised concerns about similar accidents that could happen at junctions around the country where train paths run through roads used by cars and motorbikes.
Transportation officials said it has become necessary now to separate car and train traffic by building elevated train lines at such sites.