The mine's owner, Peabody Energy, applied to increase its yearly trucking rate of coal from 120,000 tonnes to 170,000 tonnes and in turn, introduce a daily cap on truck trips to the Corrimal and Coalcliff cokeworks - 25 and 30 trips respectively.

The department approved the changes, saying the increase would "not be likely, in itself, to result in an increase in traffic impacts".

But Ms Watson and Ms Merrin remain sceptical. The Wollongong council candidates say Helensburgh's main street is turning into a coal truck highway.

"The lack of good freight rail services in the Illawarra means both public health and the environment are suffering from noise, air pollution, increased road accident risks and road congestion," Ms Merrin said.

Ms Watson, a Helensburgh resident herself, said: "You only have to stand near the intersection of Parkes and Walker streets at Helensburgh, or watch the drivers' expressions when a laden coal truck is bearing down on them on Lawrence Hargrave Dr to know the negative impact these giant noisy vehicles have on our suburban streets."

But Peabody spokeswoman Jennifer Morgans said the company was focused on adhering to the needs of the community.

"We've constructed a paste plant that puts coal reject back underground and has in three months removed more than 250 truck movements from the road," she said.

Ms Watson also raised concerns over whether the mine would comply with its approval conditions, after the department's assessment report revealed the mine had trucked 150,000 tonnes of coal off site last year - 30,000 tonnes more than authorised.

But Ms Morgans said the mine did not knowingly exceed its limit, labelling the 120,000 limit "an error on the application".

"Peabody became aware of it halfway through the year and reapplied to increase the limit," she said.