The dash cam footage shows a driver turning around and driving the wrong way in a 110km/h zone on the Hume Highway near Marulan.

The motorist drove in front of a fast-approaching truck before it narrowly missed a ute.

Southern Highlands Police officer-in-charge Inspector John Klepczarek said the manoeuvre was a "stupid act by someone who's not fully aware of the conditions".

"It was quite clear they weren't in a section of road that was designed for that purpose," Inspector Klepczarek said.

"They've actually crossed a painted median strip to conduct the U-turn.

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"While it appears on initial view the driver was assuming they were turning onto the highway to go in the other direction, he clearly had no awareness of his situation.

"His reckless actions put himself and clearly another road user in immediate danger. It was only through good luck this was not a fatality."

The driver submitted the near-miss video to the Dash Cam Owners Australia Facebook page.

The post received more than 2700 likes, 3600 comments and 950 shares.

"U-turned into oncoming traffic going 110," the driver wrote to the Facebook page in their submission.

"Thought I was turning into highway going the other direction which was further ahead."

The dash cam video shocked fans of the popular Facebook page.

"First you did it, then you shared it? I have no words," one user said.

"This sort of thing just terrifies me that we are forced to share the roads with these sort of people," another said.

Inspector Klepczarek said if drivers were unsure of the road conditions, it would be best to "pull over or slow down and fully assess the situation before proceeding any further".

"The footage shows a driver who did none of that," Inspector Klepczarek said.

"He did not assess the road conditions before making his decision. His behaviour and assumptions put lives at risk.

"This type of driver behaviour continues to frustrate police who are out there trying their best to reduce the road toll."