A popular city has locals taking to the streets to help crack down on the “tire traps” that are scattered across busy roads.

Volunteers in Jakarta, Indonesia, have been picking up nails, threaded bolts and scraps of umbrella frames, according to The Associated Press (AP).

It is thought the mysterious sharp metal pieces are intentionally left by vandals to damage the tires of vehicles on main roads. 

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What started as a few community members involved in addressing the issue has grown into a movement of locals cleaning the streets called “Sapu Bersih,” or the Clean Sweep.

Siswanto, a Jakarta resident, told AP he has been picking up metal for five years after his own encounters with the tire traps.

“From 2010 to 2016, we collected four tons of nail traps from Jakarta and other areas, like Bekasi,” said Siswanto.

“We collected them from the volunteers.”

Siswanto said many volunteers take turns picking up metal before or after work. This apparently occurs all over the city.

There were over 10 million people living in Jakarta in 2010, according to Jakarta Investment Center.

Jakarta Traffic Police Chief Komarudin told the AP he believes the metal is intended to force bikers to the side of a road with a flat — making riders more vulnerable to serious crimes like robbery.

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Some locals suspect the traps may have been set by tire repair shops, as metal was found in close proximity.

Motorbike taxi driver Pandu Dewanata told the AP he’s had at least three tires hit the traps in the past year.

“It is suspicious after hitting a nail trap — 100 meters from where we hit there was a tire patchier,” said Dewanata.

“That is suspicious. But I am not accusing, no.”

Police have found, while investigating the traps, that there are some nuts or bolts that could accidentally fall from passing vehicles — but many objects appear to be deliberately bent.

The Associated Press contributed to this report.