In its latest monthly report on the autonomous automobiles, Google lays out some of the challenges that bad weather presents, as well as some ideas about how it's going to develop a car "that will be able to drive come rain, hail, snow or shine".

"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," reads the report. "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."

Whatever the weather

Fortunately radar isn't affected by rain or clouds of exhaust gas but some of the other sensors are, and that's a problem for Google's engineers to get around. At the moment the self-driving cars pull over to the side of the road if they encounter particularly stormy conditions.

There's still a lot of work to do, but Google's software has been trained to take more care in the rain, just like human drivers. As ever, test drivers are on hand to take manual control if necessary.

"As we're developing the technology, we've made sure our cars are aware of how rain may affect their ability to drive," says Google. "Our cars can determine the severity of the rain, and just like human drivers they drive more cautiously in wet conditions when roads are slippery and visibility is poor."