The deadly device uses a pressure plate which explodes when a vehicle drives over it and is described as “very effective”, putting authorities on high alert.
It has already been used by the dissident republican group in February to target an off-duty police officer on the driveway of his Londonderry home.
Police Service of Northern Ireland Detective Superintendent John McVea said: "The pressure plate is a crude method of detonation.
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“So, not sophisticated, but a very effective means of detonation.
"The New IRA have access to high explosives - which is concerning.”
It comes a police are on high alert for more attacks from dissidents opposed to the peace process.
Crowds gather for bonfire in Londonderry, Northern Ireland
Mr McVea said the terror group had invented their new weapon to avoid the more common method of having to attach booby-trapped bombs to the undersides of cars.
That was historically done using magnets but modern cars are made using more plastic, Mr McVea said.
He said the bomb is a box of explosives wrapped in tape and placed beneath a car. The pressure plate detonator is activated when a car wheel drives over it.
The detective said: "It is concerning that they have access to high explosives and have the skills to develop their own homemade method of detonation by way of the pressure plate design."
Mr McVea said the method was used in February to target an officer but it failed to explode.
The bomb was discovered hours later on the driveway, detonating while it was being examined.
The only other case was in a linked attack at Ballyarnett village in Londonderry in October 2014 when a pressure plate was left under a mat in the hope of luring officers to stand on it.