CLOSE to 700 people took part in a safety exercise that saw a fiery four-vehicle 'collision' in the underground Kallang-Paya Lebar Expressway (KPE) on Saturday.

To make it more realistic, 120 cars driven by staff of the Land Transport Authority replicated a tunnel jam tailing back several hundred metres from the 'crash site'.

Traffic marshals on their distinctive three-wheel scooters, however, arrived quickly on the scene to direct motorists out of the affected tunnel via emergency escape staircases that lead to the surface. There are 41 such staircases along the KPE's 9km tunnels.

Singapore Civil Defence Force fire and rescue vehicles arrived within minutes through a crossover door separating the two carriageways of the KPE.

Crossover doors, 4m wide and 4.5m high, are situated at 1.5km intervals along the tunnels. They allow emergency vehicles to reach an accident site via an unaffected carriageway.

SCDF rescuers attended to and evacuated 40 'casualties' in the exercise, including extricating two who were trapped in an overturned car.

Apart from staff and officials from the LTA, SCDF and Police, participants of the exercise included 200 grassroots leaders and 40 students from St Gabriel's Secondary School.

Transport Minister Raymond Lim, who witnessed the swift 'rescue' operation, said the event is an important one leading up to the full opening of the KPE - South-east Asia's longest underground road - on Sept 20.

'It ensures that we have the systems and procedures in place to detect and respond speedily and effectively should an emergency occur in the tunnel,' he said. 'The exercise shows that our teams and systems are ready.'

After the exercise, he officially opened a new pedestrian bridge across Pelton Canal (which the KPE runs under). The old bridge was removed during the construction of the expressway.

He also gave out prizes to 18 winners of a mural competition. The winning designs will adorn the exterior walls of KPE escape staircases between Stadium Walk and Eunos Road.

The first prize of $3,000 went to Tampines Junior College student Ek Xin Rong, 16.