記事掲載日: 2009/01/28
記事更新日: 2011/08/22

Background of developing ROAD SURFACE SENSOR

What is difficulty you face when you drive a car in winter season ?
We think it is an accident by a natural event such as freezing and snowfall that cannot be seen in other seasons.

The freezing and snowfall, which are winter’s feature, are necessary for the water circulation on the earth. On the other hand, as the frozen and snowfall cause a slip and a stuck, they trouble car-driver.

Therefore, a road supervisor adopts the following methods to avoid the freezing.
a) Road heating by heat source to prevent the freezing.
b) Sprinkling.
c) Generation of heat or fall of freezing point by sprinkling solution.
In addition, the methods to avoid snow accumulation are as follows.
d) Removing the snow by snow-plow-car.
e) Road heating or sprinkling for snow-melting.

Automatic operation control system is introduced to these works in order to make the works efficient. Especially, a sensor to detect freezing and snow cover is needed for the automatic operation control system of road heating facilities, sprinkling facilities and fixing sprinkling solution facilities

For representative examples of conventional sensors, there are snowfall sensor, accretion of snow sensor, and road surface temperature sensor, etc. The merit of such kind of sensors is inexpensiveness because of its limited function. But, these sensors cannot measure the freezing of road or the situation of snow cover because these sensors do not measure the situation of the road while actual road surface is influenced by terrestrial heat and car tire. That is the demerit of conventional sensors which detect the road surface indirectly.

Instead, is there any possibility of a way to measure the road surface by a monitor camera? Such a monitor camera has not yet had a technique to make use of a natural event like snow cover as a picture data for the control, although it can see the situation of road surface.

So, we would like to present a way of measurement by a desirable sensor which detects precisely the weather and road surface.
Let us show the example.
“Suppose, the snow starts falling. At this time, conventional snowfall sensor asks snow-melting facilities to start automatic operation. But the situation of road surface is not yet frozen but wet due to terrestrial heat and car tire.

Suppose, next, time passes and snow keeps falling.
Conventional sensor still asks snow-melting facilities to keep operation.
The road surface is still influenced by terrestrial heat and car tire, but gradually the snow on the road is changed to sherbet or snow cover.” If the automatic operation start at this time, the cost of operation is cheaper than the one of conventional sensor.

In addition, especially in Hokuriku area (an area with lots of snow in Japan), to save the water is very important matter because the use of underground water for the snow-melting by the sprinkling causes the land subsidence.

On the other hand, after the snow stops falling, the road surface is changed as follows.
Conventional sensor asks snow-melting facilities to stop operating, but non-melted sherbet or snow cover still remains on the road.

For safe driving, the sensor should ask the snow-melting facilities to keep the operation until the road surface is changed to wet or light sherbet.

To solve the problem above, it is the most desirable that there is a sensor which can measure directly the situation of road surface including snow accumulation, freezing and temperature of road.

Development and Technology for ROAD SURFACE SENSOR

There are some ways to directly measure the situation of the freezing and snow cover on the road. One of the ways is the under-road -type sensor, of which the merit and demerit are following.

The structure is simple so there are few errors of measurement.
The frequency of damage and trouble is high due to car tire.
The sensor must be replaced at the time of renewal of paving.

The best way is to measure the road situation by the ray and the sound from upper side (above the road).

The way of measurement by road surface sensor is as follows.
・Red visible ray is used. Red visible ray outputted from road surface sensor returns back after reflecting to the road surface.
・The sensor recognizes that the “snow” is on the road when the reflection rate is high, and it judges that no snow is on the road (the situation is “dry or wet”) when the reflect rate is low.
・Furthermore, the sensor can recognize “snow or ice” is on the road in case of below 0 degree C by using the road surface temperature measured by radioactive thermometer of road surface sensor.

As above, the situation of road surface can be classified and judged as “snow cover”, “freezing”, “sherbet”, “wet”, “dry” according to the minimum value of measured reflect rate and road surface temperature.

In addition, snowfall makes tire track on the road. To understand the part of tire track precisely, the road is measured transversely by rotating the sensor horizontally.

The information on measurement by road surface sensor can be distributed by way of Internet. This information can be used as ITS (Intelligent Transport System by Ministry of Land, Infrastructure, Transport and Tourism).


Road surface sensor measures following items at the same time every 10 minutes (interval changeable).

1) Temperature (℃). *It can be used as thermometer (permitted by the Meteorological Agency).
2) The situation of road surface (“snow cover”, “freezing”, “sherbet”, “wet”, “dry”). *It can be used as snowfall sensor, accretion of snow sensor, and freezing sensor.
3) Road surface temperature sensor (℃) for 50 points of the transverse direction on the road. * It can be used as thermometer for road surface.
4) The depth of snow cover (mm) for 50 points of the transverse direction on the road. * It can be used as snow cover sensor and snow cover depth meter (permitted by the Meteorological Agency).
5) Picture of road surface (still picture). * It can be used as monitor camera.

One Road surface sensor has same functions as above 5 conventional sensors.

In addition, it has following CONTROL functions.
1) Snow-melting facilities (road heating facilities, sprinkling facilities)
2) Freezing prevention facilities (road heating facilities and fixing sprinkling solution facilities)

The measured information can be used as ITS.

Actual result of ROAD SURFACE SENSOR

The automatic operation of Road surface sensor combined with Weather sensor for winter season brings 48% of saving of electric power for snow-melting, compared with conventional snowfall sensors, road surface sensors and accretion of snow sensors.


Fukui prefectural government
Other prefectural government
Fukui city government
Other city government
NEXCO (East Nippon Expressway Co., Ltd. Central Nippon Expressway Co., Ltd. West Nippon Expressway Co., Ltd.)
JR west


The situation of freezing and snow cover on the road is always changing according to terrestrial heat and car tire. Therefore, to understand the detailed situation of road surface is important for economical automatic operation of snow-melting facilities.

1) Our product can directly measure the road situation above the road.
2) Our product can measure transverse direction (tire track, non tire track).
3) Car driver, snow-ice supervisor and ITS can make use of detailed measurement information at 50 points.
4) Our product can economically operate snow-melting facilities and freezing prevention facilities with automatic control.
5) Our product has same functions as 5 difference kinds of conventional sensors.
6) Other functions:
・thermometer (permitted by the Meteorological Agency)
・snowfall sensor
・accretion of snow sensor
・freezing sensor
・thermometer for road surface
・snow cover depth meter (permitted by the Meteorological Agency).
* It can be used as monitor camera.


  • There is the possibility that the snow accretes on the sensor due to its complex shape (but snow-melting heater is installed).

  • Periodical maintenance is needed for moving parts and optical lens (but periodical maintenance is needed for conventional sensor as well).

Product Spec

Road surface sensor has 3 types of instrumentation function as follows.


1) type A : thermometer, snow cover judgment, snow-melting control
2) type B : type A + road surface meter, road surface judgment, defreeze control
3) type C : type B + camera picture, snow cover depth meter

Products Q & A

Is the sensor available not only in the daytime but also at night?

Yes. It is available through a day. The brightness does not influence instrumentation.

Does a terrible weather like snowstorm influence instrumentation?

Yes. There is the possibility that very strong snowstorm and snowfall might influence instrumentation. In this case, the sensor judges the situation “snow cover”.

Does the reflect of sunlight influence instrumentation?

No. A filter which cuts a wavelength of sunlight is installed to avoid the influence against instrumentation.

How does the sensor measure in case there is an obstacle in measurement area?

The point of an obstacle is canceled from measurement area. Horizontal turning angle of the sensor can be set optionally. Also, optional points can be canceled from 50 measurement points.

Does a passing car in measurement area influence the sensor?

Yes. The reason is because the sensor measures road surface by using a reflection. To prevent the sensor from taking white-colored car as snow cover, the sensor has a function to cancel a moving object.