WO1990009014A1

WO1990009014A1 - Method and apparatus for surveying traffic conditions

Info

Publication number: WO1990009014A1
Application number: PCT/FI1990/000030
Authority: WO
Inventors: Heikki Saari
Original assignee: Valtion Teknillinen Tutkimuskeskus
Priority date: 1989-02-02
Filing date: 1990-01-29
Publication date: 1990-08-09
Also published as: FI83822B; FI890504A0; FI83822C; FI890504A

Abstract

A method and an apparatus for surveying traffic conditions. The conditions prevailing on the road are observed by means of optical radiation obtained from a radiation source (3) of a transmitter unit (1) so that at least one linear beam (5) is formed of optical radiation by means of a cylinder lense (4), which linear beam is placed at an oblique angle α with respect to the perpendicular (N) of the road surface. The radiation of the linear beam (5) scattered from the road or from above the road surface is observed by means of a detector unit (2) and on the basis of these observations, at least vehicles (A) and other heightwise changes in the road surface are detected, and the condition of the road surface is evaluated.

Description

METHOD AND APPARATUS FOR SURVEYING TRAFFIC CONDITIONS

The present invention relates to a method for surveying traffic conditions, defined in the introduσto- ry section of the first patent claim concerning method.

The invention also relates to an apparatus for surveying traffic conditions, according to the first patent claim concerning apparatus.

In the prior art there are known road traffic computation systems, where line loops are installed in the road, and by means of these line loops, on the basis of inductance changes, the surpassing vehicles are detected. By employing this kind of arrangement, it is possible to carry out traffic computation, but not any classification of vehicles moving on the road.

Moreover, the realization of such a system requires that the road surface be broken in order to install the line loops in place. What is more, the line loops are subjected to vibration and wearing, and in northern latitudes damages caused by soil frost.

The object of the present invention is to introduce a new method and apparatus for surveying traffic conditions, whereby road traffic and for instan¬ ce road surface conditions can be surveyed better than before. As for the characteristic novel features of the method of the invention, the first method claim is referred to, and as for the characteristic novel featu¬ res of the apparatus of the invention, the first appara¬ tus claim is referred to. Among the advantages of the method and appara¬ tus of the present invention, the following is pointed out. The method can be applied without breaking the road surface or the driveway at all. The apparatus is installed above the road surface, at a sufficient dis- tance from the road surface, and all observations are made by means of optical radiation. By employing this method and apparatus, the length and height and, if necessary, the speed of all vehicles moving on the road can be measured, as well as the condition of the road surface.

According to a preferred embodiment of the present invention, there is formed a number of linear beams, and these are arranged lengthwise side by side and transversally in a fan-shaped position, and they are directed, at certain intervals from each other, towards the road surface so that they cover an area of surveillance of a desired width on the road surface. By means of this method, road traffic can be controlled simultaneously along the whole width of the road.

In a method of the present invention, which is defined in the patent claim 3, the whole area of εur- veillance is scanned successively in a serial fashion. Thus the measuring of the radiation entering the detec¬ tor is carried out reliably, and the adjacent beams do not affect each other. At the same time the data processing is simplified, too. By means of the method defined in the patent claim 4, the condition of the road surface can be sur¬ veyed or evaluated. Depending on whether the road surface is dry, wet, covered with ice or snow, the road surface reflects radiation in a different way, and on the basis of this reflection, the state of the road surface can be evaluated, and if necessary, travellers can be for example warned of dangerous road conditions. According to the method defined in the patent claim 5, road traffic conditions can be observed at two different spots on the road, at given distances from each other. By means of this method, among others the speed and direction of the vehicles can be determined. The patent claim 7 introduces an advantageous apparatus for realizing the method of claim 2. The patent claim 8 introduces an advantageous apparatus for realizing the method of claim 3.

The patent claim 9 introduces a preferred embodiment of the invention, which apparatus is provided with a separate source of radiation, by means of which, together with the detector, particularly the presence of fog in the vicinity of the road surface can be detec- ted.

The patent claim 10 introduces an advantageous apparatus for realizing the method of claim 5.

The invention is below described in more detail with reference to the appended drawings, where figure la is a schematical illustration of an apparatus according to the present invention; figure lb is a top-view illustration of the road surface, seen from the point of view of the detector of the apparatus; figure lc is an illustration of an enlarged detail of the apparatus; figure 2 is an illustration of another preferred embodiment of the invention; figure 3 illustrates the principles of the transmitter; figure 4 is a block diagram of the construction of the apparatus.

In figure la, the apparatus of the invention comprises a transmitter unit l and a detector unit 2, which are located at a distance di from each other. The transmitter unit l is provided with a infrared or IR radiation source 3, advantageously an IR-LED or IR semiconductor laser, and a cylinder lense 4. By means of the cylinder lense 4, the radiation sent by the radiation source 3 is formed into a linear beam 5. In cross-section, the linear beam 5 is on one side a strongly oblate ellipse, as is apparent from figure lb. The linear beam 5 is directed towards the roadway, so that the longitudinal axis 5a of its cross-section is advantageously converged, at least roughly, to the lengthwise direction B-B of the road, and is positioned at a predetermined oblique angle α with respect to the perpendicular N of the roadway. The detector unit 2 comprises an objective 6 and a detector 7. Advantageously the detector 7 is a CCD line detector, or a position-sensitive photodiode. In principle the visual field 20a of the objective is a conical area in front of the detector unit, which area falls within the scope of the detector either wholly or as a suitably limited section 20 in figure lb. The linear beam 5, which meets the vehicle A or the road surface T, is respectively formed into an image 5b or 5c on the surface of the detector 7 by means of the objective 6. The location of the image 5b, 5c of the beam 5 depends on the distance of the surface under surveillance, such as the vehicle A or the road surface T, from the objective 6. When the location of the beam scattered from the roadway surface, i.e. the beam image 5b, 5c, on the detector 7 is known, the vehicle A can be detected as a shift of the beam image on the surface of the detector. By means of a suitable data processing unit 8, such as a microprocessor, the necessary computa- tions are carried out, the principles whereof are set forth in the following.

The location of the center 5d of the beam 5 on the detector 7, as a function of the distance s bet¬ ween the surface Al of the vehicle A and the objective 6, is illustrated in figure la. The beam 5 and its optical axis la. are at an oblique angle α with respect to the perpendicular N of the roadway. The optical axis Io also is perpendicular to the roadway surface. The focal distance of the objective lense 6 is f. The center 5d of the beam 5 on the road surface T is located at a distance h from the normal N of the roadway, figured at the point of the transmitter unit. The center 5d' of the beam 5 on the surface Al of the vehicle A in turn is placed at the distance h_a from the said normal N. The image of the beam center falling on the road surface, received on the detector, is lo¬ cated at the distance ha.' from the optical axis Io of the detector, and the image of the beam center falling on the surface Al of the vehicle A, received on the detector, is at the distance h_a ' from the optical axis Io of the detector, as is apparent from figure lc. The transmitter unit 1 and the detector unit 2 are placed at the distance s_x above the road surface T.

The obtained location of the center 5d of the beam 5 falling on the road surface T on the detector is: (i) _hl ' = - l-_χ (h.-d,, = - §&. ₊ |& .

The obtained location of the center 5d' falling on the surface Al of the vehicle A on the detector is:

(2) h₂' = - |- (ha-da.) =

When we substitute h_a ₌ §2_l_

Formulas 1, 2 and 3 presuppose that Si » f and s_a » f, i.e., when the focal distance f of the objective 6 is remarkably smaller than the distance s_a of the vehicle A or the road surface T from the objective 6, the change of the location of the beam image on the detector only depends on the distance s_a of the vehicle A from the objective 6.

As is apparent from the above description, the location of the center 5d of the beam 5 on the detector 7 is comparable to the height Al of the vehicle A. It is clear that other heightwise changes in the road surface can also be detected. If for instance it is wintertime and the road surface is covered with snow, and the position of the beam on the detector has shif- ted for a relatively long time from the location corresponding to the road surface, it is obvious that a snowdrift has accumulated on the road. The state of the road surface can also be surveyed and observed by means of the apparatus desc¬ ribed above. The intensity of the radiation scattered or reflected from the road surface depends on the cha- racteristics of the road surface. In order to evaluate the state of the road surface, it is advantageous to divide the road surface condition for example to four classes: 1) the road surface is dry; 2) the road surface is wet; 3) the road surface is covered with ice or with black ice; and 4) the road surface is covered with snow. This is realized by comparing the intensity of the transmitted beam 5 and the intensity of the radiation scattered from the road surface, and the state of the road is evaluated on the basis of this.

In the above description, the linear beam is directed towards the road surface so that the longitudinal axis 5a of its cross-section is parallel to the lengthwise direction of the road, and generally to the direction of the vehicle transport. It is, however, possible to install the apparatus above the road, so that the longitudinal axis 5a is at an oblique angle with respect to the lengthwise direction of the road. This, however, somewhat decreases the sensitivity of the measurement.

A preferred embodiment of the apparatus of the present invention is illustrated in figure 2. The transmitter unit 1 and the detector unit 2 of the apparatus, as well as the connected data processing unit 8, are attached to a suitable support 9 at a desired distance Sa. above the road surface T. The transmitter unit 1 and the detector unit 2 are located at the distance dt from each other, the said distance being advantageously 0,5-1,0 . The transmitter unit 1 and the detector unit 2 are installed to the support 9 so that their optical axes I and I_β are at right angles to the road surface T. The principle of the transmitter unit 1 of the apparatus of figure 2 is illustrated as enlarged in figure 3. The transmitter unit l comprises a number of infrared transmitters 10, their number in this particular embodiment being 10. The infrared or IR transmitters 10 are formed of IR radiation sources 3, such as IR-LEDs, and of cylinder lenses 4, which are arranged in the housing 11 of the transmitter unit. The IR transmitters 10 are placed in the housing 11 of the transmitter unit so that they are located on a circle orbit 11a at a given distance from each other. In this case the IR transmitters 10 are also arranged so that the optical axes Ilo , In , ... , Ia.» of their beams 50, 51, 52, ..., 59 intersect the circle orbit 11a at the center O, symmetrically with respect to the center axis, i.e. the optical axis Ii of the transmitter unit 1.

The beam 50, 51, 52, ..., 59 received from each IR transmitter 10 is linear. The spread angle β of the beam is advantageously of the size 2-4" with respect to the transversal direction of the cylinder lense 4. In the longitudinal direction of the cylinder lense 4, the spread angle corresponds to the spread angle of the IR radiation source, or is somewhat limited therefrom. It can be within the range of 10-25°.

The housing 11 of the transmitter unit is placed within a protecting shield 12. The front plate 12a of the protecting shield 12 is adjusted to such a distance from the IR transmitters 10 that the optical axes of the beams intersect each other, i.e. in the vicinity of the center 0 of the circle orbit 11a. In the front plate 12a, at the said center O, there is arranged a slot or an aperture 13, wherethrough the beams proceed out of the transmitter unit 1. The aperture 13 can be provided with a filter or a protecting glass, whereby a certain radiation frequency range is excluded outside the beams, or in general the intrusion of for instance dust to inside the protecting shield is prevented.

From the transmitter unit 1 the beams 50, 51, 52, ..., 59 are directed, in a fan-shaped formation, towards the road surface T, as is illustrated in figure 2. Thus they cover a desired area D of surveillance in the transversal direction of the road. The apparatus can be installed for instance at the height s_x = 8-12 m above the road surface. Consequently the width D of the area of surveillance is within the range of 10-15 m. The beams 50, 51, 52, ..., 59 meet the road surface at given distances from each other, these distances being within the range of 1-2 m, and symmetrically on both sides of the optical axis la. of the transmitter unit 1.

The detector unit 2 is formed of a CCD line camera comprising an objective 6 and a CCD line detec¬ tor 7. Instead of the said detector, there can be used some other suitable monodimensional detector which is sensitive to the employed radiation. Advantageously the detector unit 2 also includes a data processing unit 8, such as a microprocessor. In connection with the objective 6 of the detector unit 2, there is advantageously also provided a filter 14, whereby the amount of diffused light entering the detector is diminished, and in this case visible light is prevented from entering the detector.

The visual field 20 of the detector 2 is adjusted so that it covers the area D of surveillance. By means of the data processing unit 8, the linearly successive detector elements 7a of the detec¬ tor 7 are read, and the intensity and distribution of the received radiation in the lengthwise direction of the linear detector is registered. The measuring information is recorded in the memory 16 of the data processing unit 8 (cf. figure 5) .

The operation of the transmitter unit 1 is also controlled by means of the data processing unit 8. Each IR transmitter 10 of the transmitter unit 1 is connected to the switching unit 15. The switching unit 15 comprises a number of switches, advantageously electronic switches, by intermediation of which each IR-LED is connectable to the power source U. The data processing unit 8 is connected to the switching unit 15 so that by means thereof, any one of the IR-LEDs 3 can be chosen to operate by manipulating the correspond- ing switch in the switching unit 15.

In principle the apparatus of the invention, illustrated in figures 2, 3 and 4, is operated as follows. By manipulating the switching unit 15 by means of the data processing unit 8, the IR transmitters 10 of the transmitter unit 1 are made to operate one at a time. Thus one of the beams 50, 51, 52, ..., 59 at a time is directed from the transmitter unit 1 towards the road surface T. If the area of surveillance is being traversed by a vehicle with a height Al or A2 (figure 3), the location of the beam 50, which is nor¬ mally hi on the road surface, has shifted towards the optical axis Ix of the transmitter unit 1, and is lo¬ cated at the distance h_aa. or h_aa therefrom. This is detected in the detector unit 2 as a corresponding transversal shift on the surface of the detector 7, i.e. hi' and ha' or h_a' ' respectively, which can be substituted in the above formulas 1 and 3. Thus, by means of the data processing unit 8, among others the height Al or A2 of the vehicle, i.e. Si - s_a, can be calculated.

The area D of surveillance is covered one beam 50, 51, 52, ..., 59 at a time, and the location of the beam on the road, or on the surface of the vehicle moving in the area of surveillance, is defined by means of the detector unit 2 and recorded in the memory 16 of the data processing unit 8. When the locations of all beams in the area D of surveillance are defined and recorded in the memory 16, they are compared to the locations of the beams on the surface of the road T as previously recorded in the memory. Any deviations from the previous locations on the road surface, i.e. h - h_aι or hi - h_aa respectively, mean that a vehicle or the like appears at the location of the said beam. On the basis of the size of the deviation, the height of the vehicle at this particular beam can be defined. Because the direction and location of each beam with respect to the optical axis I_β of the detector unit 2 is known, the width and location of the vehicle on the roadway can be defined, when the changes in the posi¬ tions of the beams, with respect to the positions cor¬ responding to the road surface, are known on the detec- tor 7.

The condition of the road surface is surveyed, by means of the above described apparatus, in the following manner. The intensities of the beams transmitted in successive pulses by the IR transmitters 10 of the transmitter unit 1 are adjusted on the basis of the reflectory capacities of the road surface T, so that the signal of scattered radiation obtained in the detector unit is maintained sufficiently strong in order to be clearly perceived. By means of the data processing unit 8, it is possible for example to adjust the power fed to the IR transmitters 10 via the switching unit 15 by using a separate adjusting unit 17. These preset adjustments are recorded for example in the memory 16 of the data processing unit 8. The beams 50, 51, 52, ..., 59 directed from the transmitter unit 1 towards the road surface T meet the road surface at _.varying but defined angles r , and similarly the meeting angle with respect to the optical axis I_β of the detector unit 2 varies. While the road surface changes, radiation is scattered therefrom in a different fashion, which is observed in the detector unit 2. Because respective reference readings for each beam in given conditions of the road are recorded in the memory 16, the changes in the state of the road can be observed immediately. For example, reference readings for four different classes of road surface can be recorded in the memory, as was explained above, and the obtained measuring results can be compared to these reference readings, and consequently the state of the road surface can be inferred. At least two apparatuses of the present invention can be arranged in connection with a road, parallel to the road and at desired distances from each other. The data processing units 8 of these devices can be connected to each other. By employing two separate devices, the velocity and direction of the vehicles is found out. By means of the data processing units 8, it is possible to examine whether a vehicle appears near either one of the devices. When a vehicle is detected at one of the apparatuses, the data proσess- ing unit 8 measures the time that passes between this moment and the moment when the second apparatus detects the same vehicle. The direction of the vehicle is inferred according to which apparatus first detects it. This kind of apparatus can be used for surveillance and computation of traffic in both directions, as well as for speed control.

The transmitter unit 1 of the apparatus can be provided with an extra IR transmitter 10a, comprising an IR radiation source 3a, advantageously an IR-LED or an IR semiconductor laser, and a lense 4a, advantageous¬ ly a cylinder lense as is apparent from figure 3. The optical axis lax of this IR radiation source 3a advan¬ tageously forms an angle δ of about 30° or larger with the optical axis I of the detector unit 2 (cf. figure 2) . By means of the radiation source 3a and the detec¬ tor unit 2, the existence of fog above the roadway can be detected. The beam 60 of the radiation source 3a traverses the visual field 20 of the detector unit 2, and in case of fog the radiation beam 60 scatters radia¬ tion which is detected by the detector unit 2. The IR radiation source 3a is employed in the same fashion as the other radiation sources 3 of the transmitter unit 1₇ and in structure it can be completely similar to them.

For detecting fog, the rest of the IR transmitters 10 of the transmitter unit 1 can also be employed, as well as the beams 50, 51, 52, ..., 59 formed by them. For instance, the distribution of the radiation scattered from the beam 50 can be examined at the successive elements 7a of the detector 7 of the detector unit 2 (cf. figure 4) . Outside this radiation intensity distribution, obtained from different detec¬ tor elements, there can be excluded the known scattering location on the road surface, and the areas immediately above the road surface. If the intensity of the radia¬ tion scattered from other areas surpasses a given limit, the obvious conclusion is that there is fog on the road. In the above description it is suggested that one or several infrared radiation sources be employed in the apparatus of the present invention. It is, howe¬ ver, clear that the radiation frequency range can be generally within the wavelength range of optical radiation, i.e. within the wavelength range of visible light, as well as within the wavelength range of infrared radiation. The use of infrared radiation is, however, advantageous, because in the daytime the brightness of the surroundings interferes with the measurements.

In the above specification the invention has been described with reference to a few preferred embodiments only, but it is obvious that the invention can be modified in many ways within the scope of the inventional idea defined in the appended patent claims.

Claims

PATENT CLAIMS

1. A method for surveying traffic conditions, c h a r a c t e r i z e d in that according to the method, the conditions prevailing on the road are observed by means of optical radiation so that

- at least one linear beam (5) is formed of optical radiation;

- the linear beam is placed at an oblique angle (α) with respect to the perpendicular (N) of the road surface;

- the radiation of the linear beam (5) scattered from the road or from above the road surface is observed, and on the basis of these observations, at least vehicles (A) and other heightwise changes in the road surface are detected, and the condition of the road surface is evaluated.

2. The method of claim 1, c h a r a c t e ¬ r i z e d in that - there is formed a number of linear beams (50, 51, 52, ..., 59); and that

- the beams are arranged lengthwise adjacently, and transversally in a fan-shaped formation; and that

- the beams are directed towards the road surface, at given distances from each other, so that they cover an area of surveillance (D) of a desired width on the road surface (T) .

3. The method of claim 2, c h a r a c t e ¬ r i z e d in that - one beam (50, 51, 52, ..., 59) at a time is set to operation;

- the intensity of the radiation scattered from the road surface (T) or from a vehicle (A) is measured and that - the obtained readings are recorded in a memory (16) ;

- after all beams have been operated in turns and the measurements have been carried out, the obtained results are compared to the corresponding earlier intensities of radiation scattered from the road surface, and a possible appearance of a vehicle is determined on the basis of horizontal deviations.

4. The method of any of the preceding claims, c h a r a c t e r i z e d in that the intensity of the transmitted beam (5; 50, 51, 52, ..., 59) and the intensity of the scattered radiation are compared to each other, and on the basis of this comparison the state of the road surface and/or the weather above the road surface are evaluated.

5. The method of any of the preceding claims, σ h a r a c t e r i z e d in that by means of one or several linear beams (5; 50, 51, 52, ..., 59), the road surface is observed at two different locations in the lengthwise direction of the road, at given intervals from each other.

6. An apparatus for surveying traffic conditions, c h a r a c t e r i z e d in that the apparatus comprises a transmitter unit (1) and a detec¬ tor unit (2), which transmitter unit (1) is provided with at least one radiation source (3) transmitting optical radiation, and a cylinder lense (4) whereby the radiation transmitted by the radiation source is formed into a linear beam (5) , and the said beam (5) is directed towards the road surface, so that it is in the lengthwise direction positioned at a predetermined oblique angle (α) with respect to the normal (N) of the road; and which detector unit (2) is provided with an objective (6) and a detector (7) , as well as a data processing unit (8) , such as a microprocessor, by means of which microprocessor (8) and the intensity and/or location of the radiation scattered from the road surface (T) and/or the vehicle (A) and received in the detector (7), at least vehicles and other heightwise changes in the road surface, as well as the state of the road surface, can be detected.

7. The apparatus of claim 6, c h a r a c ¬ t e r i z e d in that the transmitter unit (1) comprises a number of optical radiation transmitters (10), which are formed of radiation sources (3) and cylinder lenses (4) , and the said transmitters (10) are arranged in the housing (11) in a formation corresponding to a circle orbit (11a) at a distance from each other, so that the beams (50, 51, 52, ..., 59) can be directed in a fan-shaped formation towards the road surface (T) , in such a fashion that they cover a desired area (D) of surveillance on the road surface (T).

8. The apparatus of claim 7, c h a r a c ¬ t e r i z e d in that the transmitter unit (1) comprises a switching unit (15) which is connected to each transmitter (10) and is controlled by means of the data processing unit (8) , so that only one transmit¬ ter (10) at a time is set to operation, and that the location and/or intensity of the radiation transmitted by the beam (50, 51, 52, ..., 59) of the respective radiation source and scattered from the road surface or from the vehicle is measured by means of the detector (7) of the detector unit (2) and recorded into the memory (16) , and that on the basis of the obtained measuring results, and by comparing them with earlier measurements, the traffic conditions prevailing on the road are defined.

9. The apparatus of any of the preceding claims 6, 7 or 8, c h a r a c t e r i z e d in that the transmitter unit (1) of the apparatus also is provided with an additional, separate optical radiation transmitter (10a) , which is formed of a radiation source (3a) , and of a lense, advantageously a cylinder lense (4a) , and that the optical axis (I ) and beam (60) of the said radiation transmitter (10a) advantageously form an angle (δ) of 30° or larger, together with the optical axis (Io) of the detector unit (2) , and that by means of the said radiation source (10a) and the detec¬ tor (7) of the detector unit (2) , the existence of fog can be detected.

10. The apparatus of any of the preceding claims 6, 7, 8 or 9, c h a r a c t e r i z e d in that the number of employed apparatuses is at least two, and that they are arranged in connection with the road, in the direction of the road and at given inter¬ vals from each other.