When clearing vehicles read the weather

Snow and ice pose challenges to autonomous vehicles as well as conventional ones. Daimler recently presented a series of driverless and connected vehicles for winter road maintenance.

When the onset of winter comes unexpectedly, roadways suddenly become slippery and traffic signs and street markings are covered with snow. Drivers know they need to be careful. But how will the smart city deal with such situations in the future? After all, autonomous vehicles are expected to cope with all the challenges of modern traffic safely and confidently—with greater reliability than human beings are capable of today. That applies during winter weather as well.

This goal can only be reached when vehicles have learned to reliably assess dangerous road conditions—for example, by evaluating real-time data about weather-related local driving conditions that is available via data sharing with the infrastructure (V2X communication). In addition, the vehicles must be equipped with technology that will enable them to find their way around even under adverse conditions. This is important, because camera systems and lidar reach their limits when snow covers road markings, traffic signs and the optical systems themselves.

Testing under real-life conditions

That’s why researchers in the USA are developing solutions for autonomous mobility not only in California, where the weather is dry and warm, but also in places such as M-City on the campus of the University of Michigan. During Michigan winters, vehicles can be tested here very realistically in the snow, slush and ice that covers the road network of a simulated city almost 13 hectares in size.

Testing of this kind is highly relevant to the process of bringing autonomously driving vehicles to market maturity. After all, according to the Federal Highway Administration, 70 percent of all roads in the USA are located in regions that can be affected by snowfall and black ice. In central Europe, keeping roads safe in the winter is also an ongoing issue. Climate change is leading to an increase in the average annual temperature, but that doesn’t mean that sudden spells of severe winter weather—including short local ones—are becoming less frequent. According to the Potsdam Institute for Climate Impact Research, climate change can even cause a wider distribution of polar air, resulting in correspondingly low winter temperatures in temperate latitudes. This conclusion is confirmed by the study ‘More frequent weak stratospheric polar vortex states linked to cold extremes’, which was published in 2017 in the Bulletin of the American Meteorological Society. In addition, these events are becoming increasingly frequent. Freezing and snowy weather is becoming more common, but the snow and ice are also thawing faster.

How can automated mobility solutions deal with winter weather if conventional vehicle sensors are coming up against their limits?

Looking at other technical worlds

But how can automated mobility solutions deal with winter weather if conventional vehicle sensors are coming up against their limits? In this case, it’s helpful to take a look at other fields of technology with an open mind. That’s exactly what Mercedes-Benz demonstrated in the fall of 2017, using as an example the heavy-duty commercial vehicles that carry out winter ground maintenance at airports. In the Automated Airfield Ground Maintenance (AAGM) project, a convoy of four remote-controlled Mercedes-Benz Arocs semi-trailer trucks that are connected via Remote Truck Interface (RTI) clear an airfield with high precision. The ground-clearing routes have been previously defined in digital maps, and the convoy travels these routes with maximum deviations of 30 millimetres. The convoys can be expanded to include up to 14 vehicles in the future. The project was designed in close cooperation by Daimler Trucks Advanced Engineering, the Daimler innovation centre Lab1886 and Fraport AG. It took the partners about a year to implement the ideas in a reliably functioning application based on the Mercedes-Benz Arocs construction-site truck.

In the digitally supported agriculture known as ‘precision farming’, the process is already being applied with a precision of 20 millimetres

‘One of the technologies used here for navigation that is precise down to the centimetre is Differential GPS,’ says Martin Zeilinger, the Head of Advanced Engineering at Daimler Trucks. The system takes the GPS signal that is received from satellites and makes it more precise through corrective data received by radio. This data is provided by a network of permanently installed stations. The stations compare the regionally available GPS signal with their own precisely defined locations and then calculate their individual deviations. In the digitally supported agriculture known as ‘precision farming’, the process is already being applied with a precision of 20 millimetres. If the DGPS data are combined with highly detailed 3D maps of the road network, vehicles can use this technology to reliably determine their locations even under adverse environmental conditions. This is one possible response to the additional challenges that winter creates for autonomous mobility.

The AAGM project is initially focusing only on application in closed-off areas such as an airfield. That’s why it’s not so easy to transfer its results to traditional winter road maintenance in the public road network. However, the successful automation of the Arocs convoy demonstrates the potential of the new RTI interface for such applications as well. That’s because RTI can be used not only to connect vehicles with one another, as it was in the pilot project. It also enables external activation and data sharing with smart attachments.

Attachments such as snowploughs, snow cutters and, most importantly, road salting technology are essential for winter road maintenance. Today their precision and flexibility are greater than ever before, thanks to the use of electronic sensors and smart control systems. Ever since the invention of the spreading disk for spraying roads with hard salt granules in 1938, the technology has been significantly refined, according to the Road and Transportation Research Association (FGSV). For example, sodium chloride, the most important de-icing product used in Germany, is generally applied as a mixture of brine and damp salt. Alternatively, the vehicles may spray only brine. This damp salt 100 process (referred to in Germany as ‘FS 100’) makes it possible to precisely coat slippery road surfaces as a preventive measure.

Environmental and economic advantages

Precise data also makes it possible to decrease the amount of de-icing product that is used per application (besides sodium chloride, chlorides of calcium, magnesium and potassium are also used). The more often such de-icing procedures are used, the greater are the environmental and economic benefits. A look at the warehouses of winter road maintenance vehicles clearly shows the dimensions involved. In the UK alone, the road authorities warehoused approximately 1.3 million tons of salt after the snowy and icy winter of 2016/2017.

The winter road maintenance trucks are also used for tree care operations in warmer weather. Especially for municipal road services, it’s important to have carrier vehicles that can be used very flexibly. The Mercedes-Benz Unimog is this kind of vehicle. For over half a century, the extremely diverse model series of this universal motorized vehicle have been performing a broad variety of tasks. The Unimog used to be built in Gaggenau, but now it is manufactured in Wörth. Unimogs are also used for various winter road services, ranging from spraying FS 100 brine to clearing away meter-high masses of snow along mountain roads. In addition, road maintenance services often use heavy-duty Mercedes-Benz trucks as base vehicles for de-icing and clearing roads.

Sensors have long played a key role in winter road maintenance services in particular. That’s because they measure ‘road weather’ and make it possible to treat road surfaces in ways that are adapted to local conditions

In winter maintenance vehicles, the attachments for clearing roads and for spreading or spraying de-icing materials are of course especially important. Daimler has cooperated for many decades with various manufacturers to develop such devices. During this period, the technology has become increasingly intelligent. Sensors have long played a key role in winter road maintenance services in particular. That’s because they measure ‘road weather’ and make it possible to treat road surfaces in ways that are adapted to local conditions.

For example, the MARWIS system from Lufft collects, as often as 100 times per second, information about factors such as the dew point temperature, road surface temperature, relative humidity above the road surface, thickness of the water film and the condition of the roadway (dry, wet, damp, frozen, snow/ice, critical wetness). This extremely precise road weather information, which is collected in real time, is most valuable. It is not only used by individual vehicles but also transmitted via the V2X communication network and used for up-to-the-minute analyses of the status of the entire road network.

The smart city becomes weatherproof

Thanks to IT solutions, this information can be used to derive not only dynamic deployment strategies for winter road maintenance but also automated traffic warning signals and local speed limits. This digital dimension of road clearing and de-icing technology, along with traffic control, will be a special focus of the 15th International Winter Road Congress in February 2018. The motto of this meeting of the World Road Association (PIARC), which will be held in Gdansk, will be ‘Providing Safe and Sustainable Winter Road Service’.

There will be a particular emphasis on the collection of road weather information and its use by smart software to support deployment planning (maintenance decision support systems, MDSS). According to information released before the congress, the use of innovations in this area is expected to strengthen the resilience of traffic infrastructures against severe winter weather. The discussions will focus on MDSS, measurement by mobile and stationary sensors and data sharing.

Non-contact measuring sensors

‘The use of this data offers tremendous potential,’ confirms Dr. Martin Nicklas, the aerospace engineer who is the Managing Director of the measurement technology company Lufft. He puts his faith in the connection of measurements recorded by mobile devices with measurements made by stationary sensors. Stationary measurement equipment of this kind has already existed for quite some time. Back in 2006, Germany's Federal Highway Research Institute (BASt) pointed out its significant role in predicting the occurrence of icy roads as early and as precisely as possible. At that time, the BASt defined the key measurement data as road surface temperature, precipitation intensity, thickness of the water film and freezing temperature. It should be pointed out that some versions of measuring technology must be integrated into the roadway itself. As a result, the installation and maintenance of this technology is expensive and complicated.

Today, however, non-contact measuring sensors are available. They are based on technologies that are also used in the automotive industry. If they are used as part of a dense network of sensors for smart cities, they can lead to considerable cost savings. But when will automatically driving trucks be clearing snow and spraying de-icing materials on the streets of such smart cities? Daimler’s RTI interface is basically creating a new level of assistance systems in commercial vehicles, because driving functions can be influenced via the interface—for example, by means of the data from attachments.

At airports and container terminals

However, the Daimler development unit is initially focusing on solutions for automated driving in normal main road traffic. ‘These solutions will relieve pressure on drivers and significantly enhance safety,’ says Martin Zeilinger. By contrast, more complex applications are mainly being developed for closed-off areas. A good example of this is ground clearance technology for airports. Other examples cited by Zeilinger are driverless manoeuvering procedures in container terminals and transportation inside mines.

Incidentally, in the future communication networks consisting of vehicles, sensors and control elements, the role of the infrastructure will not be limited to collecting data and acting as an interface. In the future, the road network of the smart city will be able to act on its own to improve driving conditions, particularly in areas that are especially at risk of icy roads. Temperature-controlled road surfaces have been a subject of research for several years, especially on bridges. In October 2017, the Federal Highway Research Institute commissioned the new duraBASt research institute in the state of North Rhine-Westphalia. In the testing ground near the Köln-Ost motorway junction, various options for controlling the temperature of road surfaces are being investigated. The necessary heat energy is obtained and stored by solar collectors during the summer. In the winter, this energy is available for de-icing processes—ideally, exactly at the time and in the amount that is predicted as necessary by the sensors of the smart city.


De-icing salts lower the freezing point of water on road surfaces. The use of these salts helps to prevent icy roads in the winter. Damp salt is the form that is most often used today. In this process, crushed and sifted sodium chloride (common salt) is mixed with a liquid salt solution that may consist of chlorides of sodium, calcium or magnesium, depending on the application. Just before the spraying begins, the attachment of the winter road maintenance vehicle mixes the two components on the spreading disk in the rear of the vehicle, which then sprays out the mixture in a fan-shaped pattern. The most frequently used mixture in Germany is FS 30, consisting of 70 percent salt (which the manufacturer K+S delivers for winter road maintenance in grain sizes of up to 5 millimetres) and 30 percent brine (which includes sodium chloride in 21 or 26 percent concentrations or magnesium chloride in 20, 25 or 30 percent concentrations). Between FS 30 and pure brine (FS 100), there are still other mixture proportions such as FS 50 and FS 70. Thanks to real-time road weather information, intelligent winter road maintenance vehicles can dose and spray their salt solutions with extreme precision.

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