WO2006035396A1

WO2006035396A1 - A road-marking system

Info

Publication number: WO2006035396A1
Application number: PCT/IB2005/053169
Authority: WO
Inventors: Antonius H. M. Raaijmakers; Egbert Lenderink
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-09-30
Filing date: 2005-09-26
Publication date: 2006-04-06

Abstract

A road-marking system comprising a light-emitting sign (12,17) on the surface (2) of the road, which sign (12,17) is made visible by means of light sources on the surface (2) of the road. The system furthermore comprises control means for adjusting the brightness of the light radiated from said light sources in order to create an appearance of said light emitting sign (12,17) that is similar to the appearance of an ordinary road-marking sign (11,16) on the surface (2) of the road. The control means comprise a detector (7), in particular a CCD-camera, for measuring the appearance, i.e. brightness and color, of said ordinary road-marking sign (16).

Description

A road-marking system

The invention is related to a road-marking system comprising a light-emitting sign on the surface of the road, which sign is made visible by means of light sources on the surface of the road, the system furthermore comprising control means for adjusting the brightness of the light radiated from said light sources in order to create an appearance of said light-emitting sign that is similar to the appearance of an ordinary road-marking sign on the surface of the road.

The expression Ordinary road-marking sign' indicates a road marking sign that is not provided with a light source, and that is visible because radiated light is reflected on it. Such radiated light can be diffuse light present in the daytime (daylight) and/or light radiation directly coming from the sun and/or light shining from the headlamps of vehicles and/or light radiated from stationary lamps near the road, etc. The ordinary road-marking signs may comprise a coating on the surface of the road, such as paint or a layer of white or colored material. The layer of material can also be embedded in the surface of the road, in order to create a flat surface of the road without bumpiness. A road-marking sign may be a sign to indicate a lane on the road, but it may also by any other road sign, for example a sign warning for a crossing ahead.

The expression 'light source' is defined as a unit, which emits visible light, whereby the origin of the light is not necessarily situated at the location of the light source. Light emitted by the light source may be generated at a remote location and be emitted to the light source, for example by means of optical fibers. The expression 'light source' does not refer to light generated by reflection of light, in particular light emitted by the headlamps of vehicles approaching the road-marking sign is meant.

The light sources can be located in the surface of the road, or can reach a little (one or more millimeters) above the surface of the road, just like a layer of material forming an ordinary road-marking sign. Then, when the tires of a vehicle make contact with the roadmarking sign, they will produce a sound that will draw the driver's attention. The light sources may be positioned at the upper side of small containers, which containers are embedded in the material of the road, so that said upper side is located level with the surface of the road or a little higher. The light sources may send the radiated light in substantially one direction at an angle with respect to the surface of the road, in the direction of the oncoming traffic.

The road-marking system can be used for marking traffic routes for vehicles, such as roads or lanes for cars and other road users, and runways for aircraft. The system may comprise permanent signs on the surface of the road as well as temporary signs. Temporary signs are in particular used in dynamic road-marking systems, for example where the direction of traffic of multi-lane roads is changed in one or more lanes in accordance with the direction of the main flow of traffic. In an alternative embodiment, the number of lanes available for road traffic is increased or reduced in dependence on the amount of traffic, for example from two lanes to three lanes and vice versa.

A road-marking system as described above is disclosed in US-A- 2002/0012244. This publication describes a system wherein the light sources are optoelectronic elements, each having a luminous flux of at least 5 Im during operation. Such optoelectronic elements may be LEDs, i.e. light-emitting diodes, wherein the LED is combined with a collimator for collimating light from the LED and for directing the light through an opening in the emission surface. The LEDs are electronically dimmable, so that the light emission of each LED can be easily controlled. There are LEDs of two or three different colors mixed over the surface of the road-marking sign, so that the color as well as the brightness (luminance) of the appearance of the road-marking sign can be varied by changing the brightness of the LEDs of each color.

By utilizing light sources of different colors, the light-emitting road-marking sign can be adapted to the desired appearance with respect to its brightness as well as its color. It is then important for the appearance of the light-emitting road-marking sign on the surface of the road to be as similar as possible to the appearance of an ordinary road-marking sign, in order to avoid confusion of the driver of a vehicle on the road. The appearance of an ordinary road-marking sign varies, in particular because it depends on weather conditions, on soiling conditions, on the radiated light that is present, etc. Thereby, diffuse light radiated on the one side and light radiated from a certain direction on the other side causes different appearances of the road-marking sign. The same applies for daylight and artificial light, and for different kinds of artificial light.

In order to create an appearance of said light-emitting sign that is similar to the appearance of an ordinary road-marking sign on the surface of the road, the control means for adapting the light emission of the light sources of the road-marking sign may comprise a photocell to measure the daylight level and may comprise devices to detect fog and/or rain, in order to adjust the appearance of the light-emitting sign. Also, the length of the day may be programmed in the control means. However, in practice, it has turned out that such control of the appearance of the light-emitting sign is not always optimal. For example, it is difficult to detect from which direction the radiated light mainly comes. That direction varies depending on the time of day and the moment (season) of the year. The main direction of the radiated light has a substantial influence on the appearance of the road-marking sign. Furthermore, it appeared to be necessary that further adaptations in the control means be made from time to time by operating personnel, for example to compensate for degradation due to soiling and/or degradation of the LED dies themselves and/or coloring of plastic optical parts due to the influence of UV and/or the temperature dependence of the LEDs on flux and/or scratching of the optical parts and tarnishing of the surface of the optical parts by vehicles driving over them and/or frost in the cold seasons and/or damage to the light-emitting road-marking sign. The object of the invention is to provide a road-marking system comprising a light-emitting sign on the surface of the road, whereby control means effectively adjust the light radiated from the light sources in order to create an appearance of said light-emitting sign that is similar to the appearance of an ordinary road-marking sign on the surface of the road.

In order to accomplish this object, the control means comprise a detector for measuring the appearance of the ordinary road-marking sign, preferably an ordinary road- marking sign near the light-emitting road-marking sign. Such detection can be done from a direction and from a distance with respect to the ordinary road-marking sign, which is comparable to the direction and distance from which a driver looks at the road-marking signs. The brightness (luminance) of the appearance of the road-marking sign can be measured, but in a preferred embodiment, also the color of the appearance is measured, with the control means being able to adjust the color of the light radiated from said light sources. In that case two or three groups of light sources having different colors should be present in the light-emitting road-marking sign. They may be red, green and blue light sources, so that the light-emitting sign can emit light having any desired color. In case only a limited color variation is required, two different colors may be sufficient, for example blue and amber, whereby the color of the emitted light can vary between blue, white and yellow/orange. Such variation in color may be required to distinguish regular road-marking signs from road- marking signs that are temporarily present due to road construction works.

Each measured appearance may correspond with a predetermined setting of the light-emitting road-marking sign. The setting that belongs to a certain measured appearance can be found by visually and/or mathematically comparing the appearance of the ordinary sign and the appearance of the light-emitting sign under different weather conditions and different further circumstances, whereby the light-emitting sign is adjusted, so that it looks as similar as possible to the ordinary road-marking sign nearby. The setting belonging to each appearance of the ordinary road-marking sign can be programmed in the control means.

As said before, the luminance as well as the chromaticity can be measured and set by the control means. The color may vary depending of the kind of light around the road- marking signs. For example, diffuse daylight and artificial light at nighttime will cause different measured colors.

To determine the appearance of the ordinary road-marking sign, the control means may compare the detected appearance with a standard appearance of that ordinary road-marking sign, which standard appearance is stored in the control means. The standard appearance is for example measured by the same detector under clear and dry weather conditions with diffuse daylight, i.e. without sunshine. Then, the difference between the measured appearance and the standard appearance can be determined and used to set the light-emitting road-marking sign, whereby each measured difference corresponds with a certain setting of the light-emitting road-marking sign.

Preferably, the detector is a CCD-camcra by which the brightness and the color of a certain portion of the recorded image can be determined, which portion covers

(part of) the road-marking sign. Apart from the portion covering a part of the sign, i.e. an area of the surface of the road where there is paint or a colored layer on the road, another portion of the recorded image, covering a part of the surface of the road without any paint or layer, can be determined for analyzing the contrast between the sign and the surrounding road surface. In case the contrast is low, the brightness of the light-emitting road-marking sign can be increased, to ensure appropriate visibility of the sign.

In one preferred embodiment, the angle between the surface of the road and the direction in which the detector is directed towards said ordinary road-marking sign is between 0.2° and 45°, preferably between 8° and 30°, more preferably between 12° and 20°. Although a driver of a fast driving motor vehicle will mainly look to objects located more than 100 m ahead of the vehicle, measuring of the ordinary road-marking sign closer to the vehicle, i.e. at a wider angle with respect to the surface of the road, appeared to be adequate for measuring the appearance of the ordinary road-marking sign. Preferably, the detector is located above the surface of the road, for example attached to a gantry over the road. Such gantries are often present to support road signs or traffic lights. Thereby, the detector can take pictures of the road-marking sign at moments when there is no vehicle between the detector and the road-marking sign. The presence of a vehicle can be detected because of its motion, so in the period when no moving object is detected, the measurement can take place, or, as the case may be, a picture of the road- marking sign can be taken to be analyzed afterwards.

In one preferred embodiment, a second detector is present for measuring the appearance of the light-emitting sign, which second detector is also preferably a CCD- camera. By measuring the appearance of the ordinary road-marking sign as well as the appearance of the light-emitting road-marking sign, the two appearances can be compared, in order to adjust the appearance of the light-emitting road-marking sign to the appearance of the ordinary road-marking sign by means of a feedback control process. As a result, the appearance of the light-emitting sign is varied by the control means till it looks as similar as possible to the appearance of the detected ordinary road-marking sign. The second detector can measure the appearance of the light-emitting road-marking sign in the same way that the other (first mentioned) detector measures the appearance of the ordinary road-marking sign.

In one preferred embodiment, a third detector is present for measuring the appearance of the surface of the road without a road- marking sign, which third detector is also preferably a CCD-camera. The appearance of the road surface without a sign on it can be compared to the appearance of the light-emitting sign, in order to determine the contrast (difference) between the two appearances, i.e. to determine the visibility of the light-emitting sign. The brightness of the light-emitting sign can be increased in case the visibility is too low. The invention furthermore relates to a method of controlling the appearance of a light-emitting sign on the surface of the road, which sign is made visible by means of light sources on the surface of the road, whereby control means set the brightness of the light radiation from said light sources in order to create an appearance of said light-emitting sign that is similar to the appearance of an ordinary road-marking sign on the surface of the road, and where the control means comprise a detector that measures the appearance of said ordinary road-marking sign. Preferably, the control means also set the color of the light radiated from said light sources. The invention will now be further elucidated by means of a description of a road-marking system comprising a light-emitting sign on the surface of the road, and control means for adjusting the brightness and the color of the light radiated from the light sources, which form the light-emitting road-marking sign, while reference is made to the drawing comprising figures, in which:

Fig. 1 shows a CCD-camera detecting a road-marking sign, and Fig. 2 shows the surface of a road with road-marking signs.

Fig. 1 is not to scale; in particular the dimensions in horizontal direction are small compared with the dimensions in vertical direction. The figure shows diagrammatically a road surface 1 provided with road-marking signs 2, being stripes parallel with the direction of the road. The road-marking signs 2 are present between two adjacent lanes on the road and, in general, indicate that a vehicle may change lanes. The side of a lane abutting an emergency lane or the shoulder or verge of the road is often indicated by an uninterrupted line. Vehicles are not allowed to cross that line.

A commonly used road-marking configuration is shown in Fig. 2. The length of each road-marking sign 2 is 3 m, and the mutual distance between two subsequent signs 2 is 9 m. A gantry 3 has a horizontal part 4 above the road and two vertical supporting parts 5 on either side of the road. The horizontal part 4 of gantry 3 carries a road sign 6 located above the road. The horizontal part 4 of the gantry 3 furthermore carries a CCD-camcra 7 being directed to one of the road-marking signs 2. The angle between the road surface 1 and the direction of the CCD-camera is indicated with arrow 8 and is in this example about 15°. The CCD-camera 7 is directed to one of the road-marking signs 2, so that the appearance, i.e. brightness (luminance) and color of it, is observed and can be recorded by means of the CCD-camcra 7. The CCD-camera observes the road-marking sign 2 from substantially the same direction that the driver of a vehicle 9 looks to the sign 2, so that the CCD-camera records the real appearance of the road-marking sign 2.

Fig. 2 is a perspective view of the road surface 2, seen from a position above the road, i.e. from the horizontal part 4 of the gantry 3 in Fig. 1. The road surface 2 is provided with different kinds of road-marking signs. On the left side of the road there is an uninterrupted line 11 and on the right side of the road an uninterrupted line 12. Three drive lanes 13,14,15 are present between these two uninterrupted lines 11,12. Between lanes 13 and 14 there are road-marking signs 16 and between lanes 14 and 15 there are road- marking signs 17, both road-marking signs 16,17 are individual stripes positioned in two arrays parallel with the direction of the road.

The uninterrupted line 11 on the left side of the road is painted on the road surface 2 by means of white paint. Such painted road-marking sign is indicated as an ordinary road-marking sign. Other ordinary road-marking signs are the stripes 16 forming the interrupted line between lane 13 and lane 14. Between lane 14 and lane 15 there are light- emitting road-marking signs 17, also forming an interrupted line on the road surface 2. The uninterrupted line 12 on the right side of the road is also a light-emitting road-marking sign.

As shown in Fig. 2, the road can have three lanes 13,14,15, with no emergency lane being present. However, as an alternative, the road can have two lanes 13,14, with lane 15 being used as an emergency lane. In that case, the light-emitting road-marking sign 12 (uninterrupted line) is switched off, so that the line 12 disappears from the sight of the drivers of the motor vehicles. Thereby, the array of stripes 17 is converted into an uninterrupted line. This is possible because the stripes 17 shown in Fig. 2 are light-emitting portions of an uninterrupted stripe of LEDs in the road surface 2. The LEDs can show an array of individual stripes (figure 2), whereby a portion of the LEDs emit light, and the LEDs can show an uninterrupted line, whereby all LEDs are emitting light (not shown in the Figures).

The road shown in Fig. 2 can have two lanes 13,14 and one emergency lane 15 when the number of vehicles on the road does not exceed a certain number per kilometer. However, in case there is more traffic, the road can temporarily be converted into a road having three lanes 13,14,15, whereby there is no emergency lane. In addition, breakdown bays for emergency stops can be present at several locations along the road.

For safety reasons, it is important for the drivers of the vehicles not to see substantial differences between the appearance of the light-emitting road-marking signs 12,17 and the appearance of the ordinary road-marking signs 11,16. In order to adapt the appearance of the light-emitting signs to the appearance of the ordinary signs, the brightness as well as the color of the light emitting signs can be adjusted by control means, as is described in US-A-2002/0012244.

The control means comprise three CCD-cameras located above the road surface 2 and attached to the horizontal part 4 of the portal 3, as shown in Fig. 1. The first CCD-camera is directed to the ordinary road-marking sign 16 in rectangle 21 in Fig. 2. The second camera is directed to the light-emitting road-marking sign 17 in the rectangle 22 in Fig. 2, and the third CCD-camera is directed to the road surface in rectangle 23 in Fig. 2. A portion of the image of each CCD-camera is analyzed by the control means, on which portion a part of the stripe 16,17 is present (first and second CCD-camera) or a part of the road surface is present (third CCD-camera). Thereby the brightness as well as the color is detected. Then the brightness and the color of the light-emitting signs 12,17 are changed, so that their appearance looks as similar as possible to that of the ordinary sign 16 recorded by the first CCD-camera. The control can be a continuous feedback process, so that the adjustment of the light-emitting road-marking signs 12,17 is always adapted to the changing weather conditions and other circumstances.

To ensure an appropriate visibility of the light-emitting road-marking signs, i.e. sufficient contrast with respect to the surrounding road surface, the third CCD-camera analyzes the appearance of the road surface without any road-marking sign. In case the analyzed appearance is too similar to that of the light-emitting sign, the brightness of the light-emitting sign can be increased.

The embodiment of the road-marking system as described above is only an example; a great many other embodiments are possible.

Claims

CLAIMS:

1. A road-marking system comprising a light-emitting sign (12,17) on the surface (2) of the road, which sign (12,17) is made visible by means of light sources on the surface (2) of the road, the system furthermore comprising control means for adjusting the brightness of the light radiated from said light sources in order to create an appearance of said light- emitting sign (12,17) that is similar to the appearance of an ordinary road-marking sign (11,16) on the surface (2) of the road, characterized in that the control means comprise a detector (7) for measuring the appearance of said ordinary road-marking sign (16).

2. A road-marking system as claimed in claim 1 , characterized in that said control means can adjust the color of the light radiation from said light sources.

3. A road-marking system as claimed in any one of the preceding claims, characterized in that said detector is a CCD camera (7).

4. A road-marking system as claimed in any one of the preceding claims, characterized in that the angle between the surface (2) of the road and the direction (8) in which the detector (7) is directed towards said ordinary road-marking sign (21,16) is between 0.2° and 45°, preferably between 8° and 30°, more preferably between 12° and 20°.

5. A road-marking system as claimed in any one of the preceding claims, characterized in that the detector (7) is located above the surface (2) of the road.

6. A road-marking system as claimed in any one of the preceding claims, characterized in that a second detector is present for measuring the appearance of said light- emitting sign (22,17), which detector is preferably a CCD-camera.

7. A road-marking system as claimed in any one of the preceding claims, characterized in that a third detector is present for measuring the appearance of the surface (23) of the road without a road-marking sign (11,12,16,17), which detector is preferably a CCD-camera.

8. A method of controlling the appearance of a light-emitting sign (12,17) on the surface (2) of the road, which sign (12,17) is made visible by means of light sources on the surface (2) of the road, whereby control means adjust the brightness of the light radiated from said light sources in order to create an appearance of said light-emitting sign (12,17) that is similar to the appearance of an ordinary road- marking sign (11,16) on the surface (2) of the road, characterized in that the control means comprise a detector (7) that measures the appearance of said ordinary road- marking sign (16).

9. A method as claimed in claim 8, characterized in that said control means adjust the color of the light radiated from said light sources.