SE533943C2 - Method and system for detecting the freezing of a liquid on a road - Google Patents

Description

Observing these two thermodynamic principles provides a model of road surface temperature while a freezing process of a road surface liquid is in progress. The delayed nucleation leads to the water being temporarily subcooled, but after the freezing process begins, the temperature rises rapidly to the freezing point. Theoretically, the water can reach a temperature colder than - 40 ° C with a freezing point of 0 ° C. This is only possible in extremely clean and calm water under laboratory conditions. Nevertheless, even on road surfaces, subcooling at fl your degrees has been observed.

Frozen liquid on a road surface is sometimes referred to as black ice. It is not really black but transparent. which makes it look black due to the asphalt. Unlike hoarfrost or snow, blacks are much harder to detect and resemble a wet road. Knowing where and when blackheads have formed is important information for both road users and maintenance personnel who can use chemicals, e.g. salt, to lower a freezing point temperature of liquid on a road surface and to avoid the formation of ice.

US5416476 and US2002 / 0075141 disclose a system and a device, respectively, which are vehicle mounted and measure a temperature of the road surface on which each vehicle travels. US'476 and WO'141 do not disclose detection of freezing of a liquid on a road surface.

US5313202 discloses a method and apparatus for detecting icing of bearing surfaces.

The temperature of different parts of a bearing surface is measured. The temperature of the different parts is compared and if a temperature difference is detected, ice growth is considered to have been detected.

US6456200 discloses a device for indicating icing on a surface. A temperature difference is measured by a sensor in the form of a Peltier element recessed in a road surface. A circular metal plate on an upper side of the device is located at the same level as the upper part of the road surface. The device can actively heat and melt an ice layer on the metal plate. No actual freezing point temperature is determined.

WO03 / 044508 discloses an active street paving sensor module provided with a sample well in which a Peltier cooler is arranged. Freezing of a liquid collected in the sample well is determined. 10 15 20 25 30 533 943 3 A system called Fensor ® developed by Saab / Combitech / Saab Technologies uses a peltier element for active heating and cooling of a liquid collected in a depression in a road surface to determine a freezing point for the liquid in the depression. A sensor head is arranged at the bottom of the recess.

The latter three prior art technologies, as shown in US'200 and WO'508 and the Frensor ® system, operate by utilizing a sensor in direct contact with liquid (or ice). Thus, heat transfer must take place between liquid (or ice) and a respective sensor in order for a change in liquid temperature to be sensed by the respective sensor. In themselves, therefore, these systems affect the freezing process because a certain mass of the sensor must assume a temperature of the liquid (or ice). Furthermore, these technologies work intennlttent because ice is melted and liquid is allowed to freeze again, respectively is actively frozen again. In addition, freezing of a liquid is not on the metal plate, or in the sample well or well. the same as detecting freezing on a wave surface.

Freezing conditions on the metal plate, in the test tubes or in the depression differ from freezing conditions on a road surface. Thus, these technologies do not provide information about a liquid on an actual road surface on which vehicles are traveling.

SUMMARY An object of the invention is to provide reliable information on the freezing of a liquid on a road surface.

According to one aspect of the invention, the object is achieved by a system for detecting freezing of a liquid on a road, which utilizes a release of latent heat from the liquid. The system includes a sensor for measuring a road temperature, and a processor connected to the sensor. The process is intended to monitor temperature changes over time measured by the sensor. The sensor comprises a measuring means arranged above and at a distance from a part of the wave surface in order to continuously measure a surface temperature over the part of the road surface. The processor is intended to determine the release of latent heat as an increase in the surface temperature corresponding to a differential ratio between the surface temperature and time and the differential ratio exceeding a threshold value. Since the measuring means is arranged above and at a distance from the part of the road surface, reliable temperature nets are made of the road surface and freezing of a liquid on the actual road surface is detected. The freezing of a liquid on an actual pavement is detected, i.e. do not freeze a liquid collected in a well or freeze a liquid on a metal plate. As a result, the above-mentioned object is achieved in a simple and reliable manner.

According to exemplary embodiments, the part of the road surface is located in an area of a wheel track in the road. In this way, the measuring means can be directed towards the road surface where vehicles are traveling and thus, freezing of a liquid on the road surface as such, on which vehicles travel, can thus be detected. A wheel track is a part of the scale where the vehicle's left or right wheels touch, and travel on, the road surface.

According to exemplary embodiments, the processor may be intended to recognize the increase if the surface temperature or an ambient temperature is below a threshold temperature. In this way, sudden temperature rises which occur at non-freezing temperatures will not be recognized as the freezing of a liquid.

According to exemplary embodiments, the processor may be intended to determine whether said increase has a duration of at least a minimum period. In this way, temperature increases due to, for example, passing vehicles such as freezing of a liquid are not recognized.

According to exemplary embodiments, the processor is intended to determine an actual freezing point temperature of a liquid on the part of the road surface determined by prevailing conditions affecting the liquid on the part of the road surface. Knowledge of the freezing point temperature can be used for many purposes. For example, the freezing point temperature can be used to decide if chemical treatment of the road surface to lower the freezing point temperature is necessary. For example, the processor may be intended to determine the actual freezing point temperature as a temperature reached after the increase. The liquid will substantially maintain the freezing point temperature for a period of time after the increase. According to exemplary embodiments, the measuring means may be an infrared thermometer. The infrared tin meter will provide contactless measurements of the surface temperature in a reliable and cost-effective way.

According to exemplary embodiments, a cooling element may be arranged below at least a part of said part of the road surface and the processor may be connected to the cooling element for controlling the cooling element. In this way, the part of the road surface can be actively cooled under the control of the process and thus the freezing point temperature of the liquid can also be determined when ambient temperatures are above the freezing point temperature of the liquid.

According to exemplary embodiments, the processor may be intended to communicate the actual freezing point temperature to a receiver. Such a receiver may be a road maintenance vehicle or a road information station. Other examples may be a general warning road sign or a monitoring maintenance statue for road maintenance or a road vehicle.

According to one aspect of the invention, there is provided a method for detecting freezing of a liquid on a road which utilizes a release of latent heat from said liquid in which: - a road temperature is measured. - changes in road temperature are monitored over time, - road temperature is a surface temperature continuously measured over a part of the road surface, - surface temperature is measured from above and at a distance from the part of the road surface, and - latent heat emission is determined as an increase in surface temperature surface temperature and time and the differential ratio exceeding a threshold value.

According to exemplary embodiments, the increase can be recognized if the surface temperature or an ambient temperature is below a threshold temperature.

According to exemplary embodiments, the method may include determining whether the increase has a duration of at least a minimum time period. According to exemplary embodiments, the method may include determining an actual freezing point temperature of a liquid on the portion of the road surface, determined by prevailing conditions affecting the liquid on the portion of the road surface.

According to exemplary embodiments, the actual freezing point temperature can be determined as a temperature reached after the increase.

According to exemplary embodiments, the method may include that at least a portion of the portion of the road surface is actively cooled.

Additional features of, and benefits of. The present invention will become apparent when the appended claims and the following description are studied.

Those skilled in the art will recognize that any features of the present invention may be combined to create embodiments other than those described below without departing from the scope of the present invention as defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS The various aspects of the invention, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which: FIG. 1 shows a system for detecting freezing of a liquid on a road surface according to exemplary embodiments, and Figs. 2 shows the freezing of a liquid on a part of a road surface.

DETAILED DESCRIPTION The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments are shown. However, this invention should not be construed as limited by the embodiments expressed herein.

Demonstrated features of exemplary embodiments can be combined as easily understood by those skilled in the art to which the invention belongs. The same number referred to the same element throughout. As used herein, the term "comprising" or "included" is open and includes one or more of the specified features, elements, steps, components or functions but does not exclude the presence or addition of one or more additional features. element, rose. components, functions or groups thereof.

As used herein, the term "and / or" includes any or all combinations of one or more of the accompanying listed items.

As used herein, the common abbreviation 'eg', which means 'for example', may be used to introduce or specify a general example or general examples of a previously mentioned item, and is not intended to be limiting of such item. If used herein, the common abbreviation “ie,” meaning “that is,” can be used to specify a particular item from a more general listing.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limited to the invention. As used herein, the slngular forms "en", "ett" and "den / det" are intended to include plural forms as well, unless the context clearly indicates otherwise.

Unless otherwise indicated, all teeth (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which the invention belongs. It is further to be understood that terms, such as those fi nienated in commonly used dictionaries, are to be construed as having a meaning consistent with their meaning in the context of the relevant technical art and should not be construed in an idealized or excessively formal manner unless expressly so fi niered herein.

It is to be understood that when an element is referred to as “connected” or “connected” to another element, it may be directly connected or connected to the other element or intermediate elements may also be present. However, when an element is referred to as 'directly connected' or 'directly connected' to another element, there are no intermediate elements present.

Well-known functions and constructions may not be described in detail in exchange for consistency and / or clarity. Fig. 1 shows a system 2 for detecting freezing of a liquid on a road surface 4 according to an exemplary embodiment. The system comprises a sensor comprising a measuring means in the form of an infrared (IR) thermometer 6 arranged on a post 8 next to a road, the road surface 4 of which is to be monitored with respect to the freezing of liquid.

The liquid on the road surface 4 may be water or brine containing water and a chemical agent for treating the road to prevent freezing of water on the road surface, e.g. salt (NaCl). In the case of water only on the road surface, it is generally known that the freezing point temperature of water is 0 ° C. However, on roads that are treated with chemicals during cold seasons to lower the freezing point temperature of the liquid on the road, the freezing point temperature is unknown, especially if a certain time has elapsed since a road section was treated. According to the system of the present invention, freezing of a liquid on a road surface 4 can be detected, and according to certain exemplary embodiments, the freezing point temperature can be determined. The 1R thermometer 6 is directed towards a part 10 of a road surface so that the 1R thermometer 6 can measure the temperature of the part 10 of the road surface or a liquid which at least partially covers the part 10 of the road surface. The part 10 of the road surface may be located in an area of the road where vehicles travel, such as an area for a wheel track. Part 10 of the road surface may have an area of about 20 square centimeters or may have another area. for example within the range of 5 - 30 or 1 - 50 square centimeters. Too large an area can make it difficult to determine a sudden increase in fluid temperature.

The IR tinometer 6 is connected to a processor or data collector arranged in a box 12 on said post 8. The processor is intended / programmed to use an algorithm for detecting freezing of a liquid on the part of the road surface, see below. The processor may be connected to an active road sign 14, a warning sign which is lit when a freezing of a liquid (formation of ice) is determined by the system 2. The active road sign may be located some distance before the 1R thermometer 6, e.g. 1 km. The processor may or may not be connected to a road maintenance monitoring station, e.g. a switchboard from which road maintenance vehicles are routed. Such a monitoring station may alternatively be a device mounted in a road maintenance vehicle. The processor can also be connected to a warning system, which draws the attention of vehicle drivers, e.g. via a GPS receiver; 10 15 20 25 30 533 943 9 on ice formation on a relevant road section. In an alternative embodiment, the processor is arranged at a location other than the IR thermometer 6. In this case, the box 12 may contain communication equipment for communicating temperature measurements from the IR thermometer 6 to the processor.

The processor can receive temperature locking from more than one measuring means. Either your IR thermometers 6 can be arranged on the post 8 and directed towards different parts of the road surface of a stand or measuring means. for example IR thermometers at different locations, send their temperature measurements to a centrally arranged processor.

System 2 can be installed as part of an existing WiS, (see below regarding WiS station). This can have the advantage that the same processor or data collector can be used for other WiS functions and the system according to the present invention, and that no new location needs to be prepared. The IR tennometer feeds the data collector with a signal that is analyzed. In the event of an ice alarm, a message is sent to a decision support system used by maintenance personnel together with traditional data such as wind, air temperature and humidity which are normally measured at a WiS station. The staff can either receive a message about a freezing point temperature or an alarm about freezing, i.e. isblldning. System 2 can alternatively be installed separately from an existing VViS station.

Below the part 10 of the road surface, a cooling element can be arranged to actively cool the part 10 of the road surface to determine a freezing point temperature of a liquid even when the ambient temperature is above the freezing point temperature of the liquid. The cooling element is controlled by the processor.

Fig. 2 shows the freezing of a liquid on a part of a road surface. The curve shows how the temperature of the liquid changes as measured by a measuring means arranged above the road surface. First, the temperature gradually decreases until it reaches 2 degrees Celsius, at which point freezing of the liquid begins and its temperature increases rapidly to the prevailing freezing point of the liquid, -0.5 degrees Celsius. The liquid remains at this temperature until all the liquid has frozen. Thereafter, the temperature of the ice continues to fall.

Embodiment examples of the freezing detection system include a contactless thermometer, e.g. an IR tennometer (infrared thermometer), and a processor connected to the thermometer. The processor is programmed with a detector algorithm. The processor may include or may be connected to a memory. The memory can be used to store e.g. the detector algorithm. The processor and memory can alternatively be called a data collector.

According to an exemplary embodiment, the system may comprise a cooling element, e.g. a Peltier element was sold forming an active system. The cooling element can be mounted below the road surface in order to be able to cool the wave surface above the cooling element. It is to be understood that 'below the road surface' also includes cooling elements embedded in a road surface (eg asphalt or rough asphalt) only the cooling element is covered by the road surface. The cooling element is connected to the processor and is controlled by the processor. Thus, the processor can use the cooling element to cool the road surface above the cooling element to a temperature below its current temperature given by ambient conditions. Thus, the freezing point temperature can be determined even before it has been reached naturally. The processor may be programmed to cool the asphalt until its liquid then freezes. The actual freezing moment can be detected by the 1R tennometer and a freezing point temperature can be calculated. This can ensure that an actual freezing point temperature is determined before the liquid on the asphalt freezes naturally. With the cooling element, the system can be considered active in the sense that the cooling element actually freezes a liquid on a part of the road surface. If the cooling element is switched off, the system could be considered passive and be able to detect ice that is formed naturally and can only calculate a freezing point temperature when freezing occurs.

According to exemplary embodiments, a passive system without the cooling element can provide sufficient information for many applications. In this case, the road surface does not need to be manipulated.

According to exemplary embodiments, the system could be integrated in or be connected to already existing road measuring stations, these are usually called "Road Weather Information Systems" (VViS). At present, a representative WiS measures temperature and humidity but cannot induce bleeding. Alternatively, the system for detecting freezing of a liquid may be arranged in a dedicated station at a fixed location by a road or a vehicle. In the latter case, it should be noted that the vehicle must stand still to use the detector algorithm since detection of freezing of a liquid on a road surface according to the present invention must be performed on a part of a road surface. 10 15 20 25 30 533 943 11 A passive system can be upgraded to an active system by adding a cooling element. The IR thermometer and the black ice detector algorithm are used in both the active and passive systems. The IR thermometer may have a time resolution of 0.5 - 50 Hz, e.g. a time resolution of 10 Hz can be used. It can be connected to a data collector in the WiS station where the black ice detector system can be integrated. Alternatively, a stand-alone system can be built with a data collector that only handles the IR thermometer. This can be useful if stand-alone systems will be installed more frequently than existing WiS stations, for example at bridges or other areas exposed to ice formation.

The data collector with the algorithm software may be remotely located, i.e. the data collector is located in a place other than the IR tin meter. The main reason for using a data collector near the IR thermometer is that the continuous temperature measurements do not need to be communicated, instead the temperature measurements can be analyzed on site and signals can be sent to other places or devices e.g. In case of ice detection or to communicate freezing point temperature values. With a sufficiently high data transfer rate, a remote data collector can be realized.

According to exemplary embodiments, a Quixote Surface Patrol Model 999.1 iR tennometer can be used. It works well measured from a static position.

The signal from the IR thermometer is sent to a data collector where an algorithm analyzes the signal in a directly connected manner. The IR thermometer signal is interpreted by a detector algorithm. The algorithm specifies a few conditions for the signal that may correspond to a freezing moment. Preferably, the algorithm may be insensitive to disturbances such as passing traffic. The fundamental basis of the algorithm is the calculation of the differential ratio between surface temperature and time, AT / At. To exclude sudden disturbances of the temperature signal, such as trafik. from being interpreted as freezing, At is set to a constant value k. (seconds) longer than the time step used, e.g. longer than 0.1 second in the case of temperature measurements at 10 Hz. The size of k, is a matter of optimization where too small values will trigger alarm isltuatloner that are not related to the freezing process. k, can for example be set to a value of 10 seconds or 20 seconds or even 90 seconds. Other values can also be used, e.g. 10 15 20 25 30 533 943 12 during experiments, a value of k, = 30 seconds has shown good performance for detecting ice with few incorrect detections. Too large a k would make the algorithm less sensitive to changes and miss freezing traps, so k can be seen as a sensitivity parameter for the system.

The ratio is calculated for each step of the signal, which means that the algorithms run about ten times per second in the case where a 10 Hz signal is used. In order for the algorithm to detect a freezing event, the differential ratio must exceed a predetermined threshold value, Tdw.

The basic condition for freezing then becomes: BT _ _> AT ï> kt * r Tdth, A high threshold value can exclude the fl slowest climate-related variations of the surface such as heating from solar radiation. The algorithm may also include a condition that requires a number, n, of n + m calculated ratios to be above the threshold value, Tdw, to ensure that temporary erroneous temperature values do not affect the detection of ice formation on a portion of a road surface. Td fl, can be determined at a location for a system for detecting freezing or a fixed value can be set, e.g. to Tdm, = 1/60 'Clsecond.

Other care at Td fi., Can alternatively be used, e.g. within the range 1/120 to 1/20 'C / second.

In order to avoid that disturbances at higher temperatures are incorrectly interpreted as freezing times, the road surface temperature or ambient temperature may be required to be below a maximum value of Tm.,. Tmu may, for example, be 0.5 ° C, 5 ° C or 10 ° C or any other suitable temperature, which gene 11- "arr> k, - ~ 'ram AND T <' rum THEN [F] = [fl <1) Where [F] is a vector that saves time for freezing times.

The algorithms described so far are sufficient, for example, to control information that ice has formed into active road signs or otherwise indicate that ice has formed. To provide information about a freezing point temperature of a liquid on a road surface, e.g. 10 15 20 25 30 533 943 13 for road maintenance personnel, the system must also save the freezing points. Since the freezing point temperature (T The vector saved in equation (1) can then be extended, for example, to: 'i [F] = [fn] then, j; = lnaxcrrr- 1zoj = m + 300)) (z) In this example, Tf will be the highest temperature reached 120 seconds before the freeze 'a'r registered to 300 seconds after, the algorithm looks for the highest temperature instead of the instantaneous temperature. Time limits other than 120 seconds and 300 seconds can of course be used to indicate an interval during which the highest Tf has been registered. For example, the time limit before freezing (sudden increase in surface temperature) can be set to 0 minutes and the time limit after freezing is selected within the interval 20 - 180 seconds.

A freezing point temperature may alternatively be defined as a temperature within a temperature range of a temperature reached at the end of the sudden increase of the road temperature, e.g. a range of 1 degree Celsius.

Equation (2) can be used in an active system with a cooling element. The system will then cool the road surface with the cooling element until it freezes. Freezing point temperature will be saved. The set freezing point temperature can be used by maintenance personnel to evaluate whether more brine is needed or whether the latest application is still effective. If the ambient and / or wave surface temperature approaches the freezing point temperature, the cooling element can be switched off to use the system in the same way as the passive system without the cooling element to detect freezing on the road surface caused by a natural drop in ambient temperature.

According to an exemplary embodiment, a method for detecting freezing can be described which uses the following steps: - Read a length value corresponding to the temperature of the road surface. 10 15 20 25 30 533 943 14 - Compare the value with the value registered 30 seconds earlier.

- If the temperature has risen rapidly (faster than Tdw) and if the temperature is below 0.5 'then save the time as a freezing event.

- Look for the highest temperature a tldslnterval before and after the freezing event.

- Register this temperature as the freezing point.

If an active system is used, the cooling element can be activated several times per hour, e.g. 2- 10 times / hour: According to exemplary embodiments, the system may comprise: - An IR thermometer - The detection algorithm - A cooling element ~ A processor or data collector for data processing, running algorithm and sending out icebreaking information, i.e. information for vamingsskyitar, wave maintenance personnel, car navigators etc.

The cooling element may be a peltier element in an aluminum cylinder. The element needs a 12V voltage. The aluminum cylinder would be embedded in the road and connected to a power supply. An active system can detect freezing point temperatures at any time compared to a passive system where a freezing point can be calculated after a natural freezing event.

According to exemplary embodiments, a major application of the system may be to monitor a road network to detect icing and estimate at least one freezing point temperature. The system can either be integrated in one or your existing WiS stations or installed as a stand-alone system. Other applications may include ice detection on aerodrome runways, the terms road, road surface and part of the road surface shall in this context be interpreted as a runway, runway surface or part of the runway. 10 15 20 25 30 533 943 15 According to the embodiment example, the system can make it possible to assess when and at what temperature freezing actually occurs. The system can consequently enable safer roads with cattle accidents. In addition, the system can enable more efficient and optimized road maintenance because the results of road treatment with de-icing and anti-icing can be monitored if they have had any impact. This will lead to less salt being used. get trucks deployed for road treatment and thus cost savings, environmental benefits and safer roads.

According to an exemplary embodiment, the increase in temperature can be used as an indicator of ice formation and thus enables the detection of ice that is formed. for example on a road.

The phenomenon of an increasing temperature of the freezing water-ice mixture can be measured with a sufficiently high resolution. During field observations, the increase in temperature has lasted for about 30 - 90 seconds. Thus, as part of a criterion, a duration of the increase can be chosen to be e.g. 10, 20, 30 or 40 seconds. The temperature can be measured ten times every second to be sure of capturing the sudden temperature changes. However, the temperature can be measured with a different frequency, e.g. 1 Hz or 3 Hz. The measurement requires a thermometer of a kind that does not resist rapid changes in the environment, i.e. a classic thermometer probe will have a mass that must adapt to the environment to represent the true temperature. This effect will even out rapid temperature changes. An iR terrain meter that measures infrared radiation from the part of the road surface without any contact does not suffer from this effect. This contactless method of measuring temperature makes it possible to capture rapid temperature changes. The concept of making high-frequency measurements with a contact thermometer makes it possible to observe rapid temperature changes that occur during the course of freezing of a liquid on the part of the road surface.

According to exemplary embodiments, the proposed system can monitor the portion of the road surface and can detect rapid temperature changes that indicate that a liquid is freezing and ice formation was sold. Consequently, the proposed system may involve maintenance personnel and road users on slippery road conditions. To do this, the high frequency temperature signal can be analyzed by a real-time algorithm. The algorithm detects patterns of the temperature signal that may correspond to a freezing event and triggers an alarm when freezing occurs. The alamite may, for example, contain three types of information: the time of the alarm, the location of the IR tennometer in question and the freezing point of the surface which corresponds to a temperature reached during the freezing process.

Compared to existing technologies for detecting ice on a road surface, the present system has the advantage of being simple and inexpensive. The passive version requires no modeling or installations on the road surface, no traffic will be obstructed and the lR thermometer is small enough not to disturb road users. The present system can offer a low cost option that can be installed in many places. If active weighing signs are used with the system, these signs can replace passive signs.

A commercially interesting application of exemplary embodiments may be to install a large number of sensors in a road network of a country or region of a country to inform road maintenance personnel of the time and place of freezing events. The information may also include freezing point temperatures at different locations. Optionally, detected icing can be discharged via active wave signs.

Those skilled in the art will appreciate that exemplary embodiments may be combined.

Although the invention has been described with reference to exemplary embodiments, many various changes, modifications and the like will be apparent to those skilled in the art.

Therefore, it is to be understood that the foregoing illustrates various exemplary embodiments and is not to be limited to particular embodiments shown, and that modifications of the illustrated embodiments. combinations of features of illustrated embodiments as well as other embodiments are intended to be included within the scope of the appended claims.

Claims (1)

A system (2) for detecting freezing of a liquid on a road which utilizes a release of latent heat from said liquid, the system comprising a sensor for measuring a road temperature, and a processor connected to said sensor and intended to monitor temperature changes over time measured by said sensor, characterized in that said sensor comprises a measuring means arranged above and at a distance from a dei (10) of the road surface to continuously measure a surface temperature above said part ( 10) of the road surface, and wherein said processor is intended to determine said release of latent heat as an increase of said surface temperature corresponding to a differential ratio between said surface temperature and time and said differential ratio exceeding a threshold value. The system (2) of claim 1, wherein said processor is for recognizing said increase if said surface temperature or an ambient temperature is below a threshold temperature. The system (2) according to any one of claims 1 and 2, wherein said processor is intended to determine if said increase has a duration of at least a minimum time period. The system (2) according to any one of the preceding claims, wherein said processor is intended to determine an actual freezing point temperature of a liquid on said dei (10) of the road surface determined by prevailing conditions affecting said liquid on said part (10) of the road surface. The system (2) according to claim 4, wherein said processor is intended to determine said actual freezing point temperature as a temperature reached after said increase. The system according to any one of the preceding claims, wherein said measuring means is an infrared tennometer (6). The system (2) according to any one of the preceding claims, wherein a cooling element is arranged below at least a part of said part (10) of the road surface and said processor is connected to said cooling element for controlling said cooling element. The system (2) according to any one of claims 4 and 5, wherein said processor is intended to communicate said actual freezing point temperature to a receiver. The system (2) according to claim 8, wherein said receiver is one of a general warning road sign (14) or a monitoring station for Road Maintenance or a road vehicle. A method for detecting freezing of a liquid on a road which utilizes a release of latent friend from said liquid, wherein: a road temperature is measured, changes in said road temperature are monitored over time, said road temperature is a surface temperature continuously measured over a part of the road surface . said surface temperature is measured from above and at a distance from said part of the road surface, and said latent heat accumulation is determined as an increase of said surface temperature corresponding to a differential ratio between said surface temperature and time and said differential ratio exceeding a threshold value. The method of claim 10, wherein: said increasing is recognized if said surface temperature or an ambient temperature is below a threshold temperature. The method of any of claims 10 and 11, wherein: determining whether said increase has a duration of at least a minimum time period. 533 943 19 13. The method according to any one of claims 10 - 12, wherein: an actual freezing point temperature of a liquid on said part of the road surface, determined by prevailing conditions affecting said liquid on said part of the road surface, is determined. The method of claim 13, wherein: said actual freezing point temperature is determined as a temperature reached after said increase. The method according to any one of claims 10 to 14, wherein: at least a portion of said portion of the road surface is actively cooled.