The fight to lower the speed limit on an Adelaide Hills road has taken a strange turn, with a resident armed with a piece of plastic and a few screws taking the matter into his own hands.

A 60km/h sign on Ambleside Road in Hahndorf was switched to 50km/hwithout the knowledge of authorities.

“It’s bizarre and it’s illegal,” Transport Minister Tom Koutsantonis said.

“I know they’re well intentioned but we can’t have people doing that – it’s dangerous and inappropriate.”

While some locals have voiced concerns about speeding along Ambleside Road and support a reduction in the speed limit, they said any change needs to go through the proper channels.

“I don’t think we’ve really got the right to change signs on the road. It should be done through the right channels,” one resident said.

A man believed to be responsible for the alteration was approached for comment but declined to speak on camera.

“My very strong advice is to stop,” Koutsantonis said. 

“Yes, ingenuity yep, tick. Illegality? Unfortunately, yes, that is a tick as well, and you can’t do that.

“And if you get caught, you can go to jail.”

The fake speed sign has since been removed.

Meanwhile, it’s believed a load limit sign on the same road has also been tampered with.

It’s meant to say 15 tonnes, but the “1” has been removed.