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Dashing through the snow? How driverless cars handle bad weather

Gothenburg: where self-driving cars will have to deal with winter (Photo: iStock)

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Gareth Watson
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There will come a day when automated driving technology steps out of the controlled testing environments and into the real world. For Volvo, that day will arrive in 2017. But are self-driving cars ready to face the elements?

Volvo describes its upcoming Drive Me project as “the first real world trial of autonomous cars.” Yes, there are currently self-driving cars circulating the streets of San Francisco and other locations. But the difference with Drive Me is: these will not be test vehicles. These will be production XC90s with real customers behind the wheel. In 2017, Volvo will start to lease 100 SUVs equipped with IntelliSafe Autopilot which will take to the suburban roads of Gothenburg, Sweden. The technology will finally allow them to experience fully automated driving (SAE Level 4) while on some of the city’s main highway-like commuter routes.

Real world testing is an important step in the journey towards safer roads – as Dr Erik Coelingh, Senior Technical Leader for Safety and Driver Support at Volvo explains: “Drive Me is not just about developing a demo car or concept car; it is about developing something that ordinary people can use in their daily lives on the roads as we know them today.”

Dr Erik Coelingh, Volvo’s self-driving technology expert (Photo: Volvo)

But with the real world roll-out comes a real world problem: the weather. “When you go and deploy the technology in the real world, you have to be able to deal with all weather conditions that may occur,” Coelingh says, and concedes: “We also know that the technology will not work in all weather conditions – so we have to prepare for that. It might be different in the long-term future, but on day one there will be limitations as to what the car can and cannot deal with.” 

Prevailing problems

So what are these limitations? As drivers, most of us don't like seeing a weather report that reads: "Heavy snow throughout the day. Motorists advised to take extreme caution." Driving rain or a blanket of snow on the ground suddenly makes driving a whole lot harder. Dealing with poor visibility, loss of traction and buried reference points test even the best drivers. But this is not only the case for humans. Such conditions also challenge the sensors that are fundamental to automated driving.

Typically, LiDAR sensors, which emit short pulses of laser light, co-operate with cameras to sense nearby objects and allow the automated vehicle to create a real-time, high-definition 3D image of its surroundings. This works extremely well in fine weather. But what happens when the cameras and sensors can't see the road markings because they are buried in snow? What if the sensor lens is covered by dirt or the snowflakes are mistaken for objects? Then, the autonomous technology has a real problem. Not usually an issue in sunny California, of course - but Gothenburg has been known to host some harsh winters.

Since safety is paramount for the Drive Me project, Volvo's approach is to know its enemy. "Knowing the limitations of the technology, you have to get information about the weather conditions - lighting conditions, visibility conditions etc. - in order to answer the question: should the self-driving mode be made available, yes or no?" Dr Coelingh explains.

Snowy, with a chance of driverless cars

Dr Coelingh’s team has therefore created a mechanism by which the Drive Me cars will make this decision. “We have designed it so that each car will make an assessment to see if the conditions are ok for self-driving. That assessment will then be sent via a connectivity link to the Volvo cloud. Here, data from all cars will be aggregated and a decision is made if the weather in Gothenburg is appropriate for self-driving or not.”

Dr Coelingh goes on to explain how self-driving mode will be allowed if an approval signal is sent back to the car after which, the driver is offered autonomous mode via the interface. This signal will only be sent when several elements align: the car must have the correct map versions and connection to the server. The traffic and weather conditions must be within scope. “The challenge then becomes making that scope sufficiently big. That means being robust in different weather conditions,” Coelingh explains.

For this, often the simple ideas are the best: “One thing we have already done for the new XC90 is to place the main radar behind the windscreen so that the area in front will always be cleared by the wipers.” But there are more ways to make the car more weather-resistant: “We will have active cleaning on the sensors on the outside of the car to keep them free from any dirt or debris. Moreover, the XC90 will have optimized cameras which will mean a better performance in low light.”

Self-driving mode only available after weather assessment (Photo: Volvo)

The extended forecast

One fact remains: at present, there is no state-of-the-art automated driving technology that works well on snow-covered roads. Yet the ability to do so is something that will become absolutely necessary if automated driving is to prevail. “Ultimately, the solution will lie in vision – improving how well the sensors and cameras ‘see’ in snow,” Coelingh predicts.

It is exactly this challenge that Ford have recently accepted. They have teamed up with the University of Michigan to test solutions for the snow blindness problem. As it turns out, the answer may lie in the maps. Since detecting on-road markers becomes extremely difficult in snowy conditions, Ford claim to have found a promising solution: they use ‘above road’ features to localize. The vehicles create highly detailed 3D maps as they drive in favorable weather by logging all road information and ‘furniture’ i.e. signs, trees, buildings, landmarks and topography. In adverse conditions the vehicle can then use these landmarks to pinpoint itself before continuing to use the map to navigate. On top of this, vehicle-to-X communication could play a role in overcoming localization problems by helping vehicles pinpoint through direct communication to other vehicles or infrastructure.

Knowing where you are is one thing. Getting the car to adjust its driving style intelligently to bad weather and low friction is another. As Dr Coelingh says: “That is perhaps the more difficult challenge.” For example when travelling in heavy snowfall, lane markings may become irrelevant – because the best strategy is to drive in the tracks of the preceding car: “They become your guiding lights.” Now we just have to teach the cars how to follow them.

About our expert:

Dr Erik Coelingh is Senior Technical Leader for Safety & Driver Support at Volvo with 15 years’ experience of developing active safety systems. He is deeply involved in the Drive Me project, mainly with the design of the self-driving features of the XC90.

Looking at Dr. Coelingh's explanations, do you think you'll see fully automated driving on the highway in snowy conditions in 2025? Would you entrust an autonomous car with your life in such weather? Leave your thoughts in the comments!

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