Researchers who work on driverless cars say we're still five to 10 years away from developing an all-weather self-driving capability. That's because there are a host of challenges when it comes to driving in bad weather that humans have learned to overcome - but computers have not. This issue has taken on even greater urgency given that an initial wave of high-tech cars, such as Tesla's sedans that can go on autopilot, are already on the road.