What a dummy!

A Long Island man intent on driving in the carpool lane allegedly propped up a sunglasses-wearing mannequin in the front seat of his car to fool cops into thinking it was a passenger, authorities said Monday.

James Britt, 34, dressed the dummy in a baseball cap, jeans and a white T-shirt before tying it to the front passenger seat of his 2002 Saturn sedan with a blue hoodie and placing a couple of plastic water bottles in its lap, Suffolk County Police said.

But Highway Patrol Officer Andrew Spina became suspicious of the front seat passenger and stopped Britt, who had been traveling eastbound in the Long Island Expressway’s high-occupancy vehicle lane Monday around 4 p.m., cops said.

The Centereach man was issued a summons for the HOV occupancy violation.