One by one they crossed the tarmac, their tails trailing behind them as they left the safety of one forest to reach the other patch of green across Old Upper Thomson Road.
A camera watched their every move. As it detected the animals' presence, lights flashed under a sign that read "Animals Ahead".
A car nearing the flashing sign slowed, and the troop of long-tailed macaques raced into the safety of the forest.
For the first time, the authorities are leveraging technology to better protect Singapore's native wildlife as the animals make their way from forest to forest to find food or mates.
This novel roadway animal detection system was unveiled by the National Parks Board (NParks) yesterday, during the opening of the new Thomson Nature Park, which was built on the site of a former Hainan village and rambutan plantations.
The $400,000 system was co-funded by NParks and the Land Transport Authority (LTA), and is part of a year-long pilot that aims to reduce wildlife-vehicle collisions along Old Upper Thomson Road.
LTA chief executive Ngien Hoon Ping said the agency has been working closely with NParks to safeguard the environment and to mitigate the environmental impact when embarking on infrastructural developments. He said: "Joint efforts, such as the one on the roadway animal detection system, help us understand how technology could be deployed to achieve our aims."
Biodiversity surveys and "clues", such as track marks, droppings and claw marks on trees, had shown that native animals, including critically endangered ones such as the Raffles' banded langur - found only in Singapore and southern Peninsular Malaysia - often cross this road to get from forest to forest.
The 3km-long Old Upper Thomson Road separates the new Thomson Nature Park from the eastern end of the Central Catchment Nature Reserve.
Ground-dwelling and arboreal animals can also cross Old Upper Thomson Road safely via the five underground culverts and two overhead rope bridges - a ladder rope bridge, and a single rope bridge - that NParks installed.
NParks also collaborated with LTA to convert the dual-lane road into a single one-way lane with a park connector since June last year. There are also plans to close the road to vehicular traffic between 7.30pm and 6am daily, although more details on this will be provided later.
NParks director for conservation Sharon Chan said Thomson Nature Park is a unique place.
"It has many critically endangered species, like the Raffles' banded langur, slow loris and lesser mousedeer... With all this biodiversity here, we thought it is important to build this place sensitively, so animals can continue to find a home here."
Dr Andie Ang, a primate scientist and chair of the Raffles' Banded Langur Working Group, welcomed the installation of the rope ladder, saying it was placed in a location where it was needed as the langurs have been spotted in the area.
On the other hand, it would take time for animals like the langurs to get used to artificial structures and so long-term monitoring is necessary, she added.
But she lauded the initiatives to reduce vehicular traffic on Old Upper Thomson Road. "Cars will have to slow down, making it safer for the animals to cross, and also for the people using the park connector," she said.