A few weeks ago, Google announced it had put up more than 140,000 road miles on its driverless test cars including the Toyota Prius hybrid and Audi TT. The underlying technology consists of a combination of radar and laser technology, GPS and video cameras. And while Paris Hilton isn’t driving one of them yet it has been hailed as a boon for car safety.

The modified cars’ were recently observed in Ireland in October and its most noticeable feature is a rotating sensor on the roof that scans 360 degrees for more than 200 feet in diameter, creating a 3D map of the car’s location.

The left rear wheel has a sensor which measures the car’s movements in detail and helps locate it on the map. Near the rearview mirror a camera locates and monitors pedestrians, cyclists, traffic lights and obstacles in the rod and sends that data to a computer onboard the vehicle. There are also radar sensors at the front and back which help locate more distant objects.

Google says the cars have tackled many challenging terrains such as San Francisco’s Golden Gate Bridge, the Pacific Coast Highway and around Lake Tahoe.

However, while the car is technically driven ‘driverless’ there is – at all times – a trained safety driver behind the wheel and a trained software operator in the passenger seat. Presumably this satisfies concerns which law enforcement authorities would otherwise have with a driverless vehicle.

There are videos on the web of the driverless cars in action. Good Morning America also test drove the Google car.  Finally, see our earlier blog on automated car technology.