Indonesian authorities are trying out a new method to deter people from riding on the roofs of trains - installing brushes suspended above the track to douse so-called "roof surfers" with foul-smelling liquid.
The system is initially being installed on the line between Jakarta and the town of Bogor.
In another initiative to discourage the practice, authorities have also experimented with grapefruit-sized concrete balls set up to hit any roof travellers on the head.
The BBC says other initiatives, already tried but found wanting, include spraying the roofs of the trains with paint, spreading oil on carriages and hiring musicians to perform safety songs.
Officials say dozens of people die each year while travelling on the roofs of trains.
Some are electrocuted by overhead power cables, while others are killed when they fall from moving trains.