The oversized problem that brings Sydney to a grinding halt

It's an oversized problem that can bring a city's early commute to a grinding halt.

Another overheight truck this morning forced the closure of the Sydney Harbour tunnel, disrupting the early commute. And 9NEWS can reveal 30 drivers every day are running the risk of being caught.

At 6.30am today, an overheight truck triggered an alarm on the southbound approach to the tunnel.

The driver given two chances to pull into a slip lane - but he doesn't - and Sydney traffic comes to a screaming halt once again. Cars are diverted as the offending truck is moved off the road.

"I find it really frustrating", says Bob Allen of the Sydney Harbour Tunnel.

"There's people out there taking risks every day that they're going to fit somewhere that they're not meant to be."

In this case, a piece of metal sticking out from the truck's trailer was the tipping point.

The driver now subject to $2000 fine, six demerit points and three months off the road.

"We've got the toughest fines, the toughest regime in the country. The community's over these idiots and so am I," NSW Roads Minister Duncan Gay said.