Indonesia has come up with another bizarre plan to keep commuters from riding on the roofs of trains: Swat them with brooms drenched in putrid goop.

“For anyone who is still up there, it'll be like a whip,” said Ahmad Sujadi, of the state-run railway, PT Kereta Api Indonesia. The contraptions will be installed at select crossings on Monday.

Indonesia has tried just about everything to keep passengers from clamouring to the roofs of trains that crisscross its main island of Java, spraying them with paint guns, calling in sniffer dogs, and asking for help from Muslim clerics.

But it wasn't until last month that one of their tactics actually worked.

In a few places along the track, grapefruit-sized concrete balls have been suspended on chains from a frame that looks like a soccer goal. “Rail surfers,” realising they could be knocked in the head or even killed, quickly called it quits.

Buoyed by the success, railway officials decided to try the brooms as well.

They'll start setting them up around midnight on Monday along the line linking the capital, Jakarta, and the West Java town of Bogor.

Sujadi said he was unaffected by criticism for all the strange and strict security measures.

“Some people say its inhumane, but that's fine,” he said. “Because letting them ride on the roofs is even more inhumane.”

Hundreds have clamoured to the roofs of trains in the past because they want to escape overcrowded carriages, can't afford the price of a ticket, or, simply, because it's more fun.

But dozens are killed or injured every year, falling off the train or being electrocuted by the power lines above. - Sapa-AP