Every Who down in Who-ville knows you need more than one person to drive in the carpool lane – but cops in Arizona say an inflatable Grinch simply will not do.

A trooper in the western US state noticed something amiss last week as a car sailed past carrying a blow-up Dr Seuss character.

The law enforcement officer "spotted a driver in the high-occupancy vehicle (HOV) lane with a Seusspicious-looking 'passenger,'" the state's Department of Public Safety tweeted.

"The trooper stopped the driver and determined the grumpy green guy was, in fact, an inflatable Grinch. (No other passengers.)"

The Grinch, whose mission in the Dr Seuss tale is to steal Christmas from the Whos in Who-ville, does not count as a legitimate passenger under Arizona law, the department said.

"While we appreciate the festive flair, this is illegal and the driver received a citation for the HOV violation."

In the children's book, the Grinch's distaste for Christmas – attributed to his heart being two sizes too small – is overcome when he sees Who-ville celebrating, even without the presents he stole from them.