Ice warning system
An ice warning system ( GMA for short ) is a device for recording or forecasting black ice or the risk of black ice on roads . Such systems are installed on many high-level roads (expressways and motorways) but also increasingly on roads in the subordinate road network ( state road / state road , district road ).
A road ice reporting system usually consists of a central unit and at least one, but mostly several measuring stations (so-called road weather measuring points, road weather stations) that send measured data to the central unit at regular intervals (typically every ten minutes). It is therefore a technical aid for the coordination and control of winter service .
function
In order to be able to technically detect smoothness, various measurement data must be recorded. Important measurement data are:
- Freezing temperature
- Road surface temperature
- Residual salt
- Water film height on the road
- Precipitation type
- Rainfall intensity
- Air temperature
- Relative humidity
Additional parameters can optionally be recorded:
- Wind direction and wind strength
- Road surface temperature (typically at a depth of 30 cm)
- Air pressure
- Visibility
- Radiation balance
To determine the freezing temperature, the road surface temperature, the amount of residual salt and the height of the water film on the road, it is necessary to install a probe in the road. This is a mostly cylindrical body, the top of which is set flush with the roadway and can thus record the measurement data directly in the roadway.
Freezing temperature
The freezing temperature in particular is of particular importance. This value can be used to determine when the liquid currently on the roadway starts to freeze and would therefore become slippery. A distinction is made between direct and indirect measurement methods.
Direct measurement method
In the direct or active method, the freezing point is determined by cooling and then heating the probe. The cooling or heating capacity is recorded over time together with the road surface temperature. If the liquid on the probe freezes, it continues to give off heat, but the temperature does not change during freezing and does not decrease further until the liquid is completely frozen. During the subsequent heating, the opposite occurs and the temperature remains at the melting point until the liquid has completely melted. This method is able to determine the melting point comparatively precisely, but has difficulties when vehicles drive on the probe. The tires of the vehicles exert pressure on the water film, the tires push the water to the side and bring heat into the measuring area. These influences make a measurement inaccurate. In order to reduce the interference, the measuring probe can be installed in the center of the lane with less traffic.
Indirect measurement method
In the indirect or passive method, the freezing point is determined from the height of the water film on the road, the road surface temperature and conductivity. The conductivity allows conclusions to be drawn about the salt content and, in conjunction with the road surface temperature and the water film height on the road, can be used to estimate the melting point. This method has the advantage that no process has to be observed, but that all parameters can be determined at one point in time. The measurement methods used are also largely insensitive to rolling tires. This means that it is less precise than the direct method, but the probe can measure the condition directly in the lane.
Measuring points
Road weather stations are positioned at intervals of 5 to 20 km, depending on climatological and topographical conditions. The sensors of road weather stations are often installed in the area of bridges. This is to ensure that the coldest point of a route section is recorded. Modern methods of locating measuring points use the so-called "thermal fingerprint" method. "Thermal fingerprint" means that the road surface temperature along the route is measured under significant weather conditions (e.g. on a cold, starry winter night). With the help of this method, meteorological and topographical aspects as well as the experience of the winter service personnel responsible for winter service, optimal locations for measuring points can be determined.
Plant engineering
camera
In some cases, ice warning systems are equipped with cameras . In addition to normal camera technology, night vision-capable cameras with infrared spotlights are also being used more and more frequently in order to be able to deliver images at night as well. The images are usually sent to the server every ten minutes.
Data transfer
The data transfer from the ice warning system to the server takes place in different ways. The information can be transmitted to federal highways via the administrative network available there. Alternatively, information from ice warning systems can also be transmitted via the cellular network.
Power supply
Similar to data transmission, ice warning systems are powered in different ways. The energy required on federal motorways can also be obtained from the administration's own power grid available there. Alternatively, a network connection can be established for ice warning systems. Another alternative is self-sufficient power supply via photovoltaics , fuel cells , a wind turbine or a combination of the systems mentioned.
Norms and standards
Germany
- 15518-1 DIN EN 15518-1: Winter service equipment - Road condition and weather information systems - Part 1: General definitions and components
- 15518-2 DIN EN 15518-2: Winter service equipment - Road condition and weather information systems - Part 2: Road weather - Recommended observation and forecast
- 15518-3 DIN EN 15518-3: Winter service equipment - Road condition and weather information systems - Part 3: Requirements for measured values of the stationary systems
- 15518-4 DIN EN 15518-4: Winter service equipment - Road condition and weather information systems - Part 4: Test methods for stationary equipment
- Technical delivery conditions for outstations, edition 2012
Austria
ÖNORM EN 15518-1 to 4: Winter service equipment - Road condition and weather information systems - Part 1 to 4
RVS 12.04.14: Black ice early warning systems and road weather information systems (November 1, 2014)
