You don't get much rainfall in California, where Google is road testing its fleet of driverless cars, but the web giant wants its vehicles to be equipped for use whatever the weather. That's why the firm is taking steps to ensure that its autonomous motors are fit to handle rain, hail, and snow, Digital Spy said.

Google has outlined some of the measures it has put in place to weatherproof the vehicles, like adding sensors to the sensor equipment to keep them clear in the rain.

"Driving in rain makes many human drivers nervous due to reduced visibility, and some of our sensors - particularly the cameras and lasers - have to deal with similar issues," notes Google in its latest monthly report on driverless cars.

"For example, we've had to come up with our own equivalent of a windscreen wiper on the dome to ensure our sensors have the best view possible."

Just like human drivers, Google's self-driving cars are more cautious in the rain. At present, they are programmed to automatically pull over if a storm is severe enough.

Google is yet to announce when its autonomous cars might be commercially available, but reports suggest that it is on the verge of partnering with Ford to bring the technology to market.