A small stretch of Rio de Janeiro's Santa Teresa Bonde tram system reopened for test runs on 27 July, four years after six people were killed and 50 others were injured in a deadly accident on the line.

That light rail system, known locally as the Bonde or Bondinho, was decommissioned after the deadly accident on 27 August 2011, which was blamed at the time on brake failure due to a lack of maintenance.

The Bonde was slated to reopen before the 2014 World Cup was hosted in Brazil but work to update the system suffered a series of setbacks frustrating neighbours who once relied on the system to bring them up and down the hillside neighbourhood.

Rio de Janeiro's state Secretary for Transportation, Carlos Osorio, recognised the delays in reopening the trolley while speaking to journalists.

"Look, first of all the state needs to recognise that we've had a lot of problems with this project. We've caused inconveniences for the residents of the Santa Teresa neighbourhood. We consider this opening, this start of service as a form of asking for forgiveness to the residents of the neighbourhood," Osorio said.

Passengers will be able to use just 900m of the newly laid magnetic tracks of the 10km system between the hours of 11am and 4pm.

The stretch of track opened on 27 July runs from downtown, over the landmark arches of Lapa to the Curvelo square in Santa Teresa. Up to 32 passengers can take ride the trolley free of charge on each of its runs during the initial test phase.

Osorio said the new trolleys were fitted with an emergency brake system to prevent an accident similar to the one that killed six people almost four years ago.

"This new trolley has four brake systems, the fourth is an emergency magnetic brake that can stop the trolley in any circumstance. It's like a magnet connecting the trolley to the tracks. And this emergency brake is only to be used at the last minute," Osorio said.

Other stretches of track are also being tested without passengers while construction in ongoing on much of the system.