WO2008104659A1

WO2008104659A1 - Method for preventing cumulative collisions

Info

Publication number: WO2008104659A1
Application number: PCT/FR2008/050125
Authority: WO
Inventors: Marc Heddebaut; Jean-Pierre Ghys; Jean Rioult; Fouzia Boukour
Original assignee: Inrets- Institut National De Recherche Sur Les Transports Et Leur Securite
Priority date: 2007-02-15
Filing date: 2008-01-28
Publication date: 2008-09-04
Also published as: DE602008002821D1; ATE483222T1; FR2912829B1; EP2118871A1; PT2118871E; FR2912829A1; ES2356047T3; EP2118871B1

Abstract

The invention relates to a method for preventing cumulative collisions on a traffic lane on which an incident has occurred, that comprises emitting a first radio-electric signal with a carrier at a first frequency towards said traffic lane, characterised in that it comprises the step of emitting, from an emitter located on said traffic lane and upstream from said incident, a second radio-electric signal with a carrier at a frequency equal to said first frequency, said second radio-electric signal having a power higher than the power of said first signal at said emitter.

Description

METHOD FOR PREVENTING OVER-ACCIDENT

The present invention relates to a method for preventing an over-accident on a taxiway, as well as to a device for implementing the method. It is known to broadcast information on the road traffic by FM radio on the frequency 107.7 MHz. Surveys by highway companies show that the time between the time an incident occurs on the network and the broadcast of information by radio may be less than 5 minutes. This result brings major progress in terms of limiting the risk of an accident, which constitutes a major element of road safety along an infrastructure where speed can be high.

A transposition from the time domain to that of distances shows that a user traveling at a speed of 120 km / h can therefore be warned as soon as the incident he is about to encounter has taken place a few kilometers ahead. him, for example 10 km for a diffusion time of 5 minutes. The user can then react and adapt his behavior.

For smaller distances, of the order of one kilometer, it has been found that the passage through the 107.7 MHz broadcast network does not have the required response time.

It is also known to set up optical markup before an incident, to prevent over-accidents. Figure 1 shows a typical situation. A patrol vehicle 1 is immobilized upstream of the incident. The patrol vehicle 1 comprises an optical information triangle 2 through which the incident can be visually signaled. Cones 3 define an open area of the taxiway.

The implementation of such optical tagging requires a relatively long time, during which the alert of the drivers is possible only by the only optical signaling boarded on board the patrol vehicle. Special conditions of reduced optical visibility, such as terrain topography, fog, snow, or grazing sun, may limit the effectiveness of this markup. The problem that the present invention aims to solve is to provide a method for preventing accidents that does not present at least some of the aforementioned drawbacks of the prior art.

The solution proposed by the invention is a method of preventing an over-accident on a traffic lane on which an incident occurs, a first radio signal having a carrier of first frequency being emitted towards said lane of traffic, characterized by the fact that it comprises the step of transmitting, from an emitter on said traffic lane upstream of said incident, a second radio signal having a frequency carrier equal to said first frequency, said second radio signal having a higher power the power of said first signal at said transmitter.

Thus, in a reception zone in the vicinity of the transmitter, the second signal has a carrier of the same frequency as the first signal and a larger power. A user located in this reception area and equipped with a receiver set to receive the first signal can be prevented by the second signal that an incident occurs. You do not need to set up visual markup before you can emit the second signal. The user can be warned quickly. In addition, the transmission of the second signal is not disturbed by particular conditions of optical visibility.

Preferably, the power difference between said second radio signal and said first signal at said transmitter is at least 6 dB. This difference is advantageously of the order of 40 dB.

Advantageously, the method comprises the steps of:

- measuring the power of said first radio signal at said transmitter,

- Adjust the power of said second radio signal according to the power of the first measured radio signal and a desired transmission distance.

Thus, it is ensured that the second signal has a power greater than that of the first signal up to the distance of desired transmission. The desired transmission distance may be predetermined or adjustable.

Preferably, said transmitter comprises a directional antenna having, in the direction of the lane, a front-to-rear ratio of at least 20 dB. More preferably, the front-to-back ratio is at least 30 or 40 dB. Preferably this antenna is located at a height less than that of the antenna for transmitting the first signal.

Thus, vehicles traveling in a first direction on the taxiway, and upstream of the incident and the transmitter, receive the second signal with a significant power greater than that of the first signal. Conversely, the vehicles traveling in the opposite direction, being on a part of the traffic lane not affected by the incident, do not receive the second signal before arriving at the level of the transmitter.

According to one embodiment, said directional antenna is a delta-loop antenna.

Such an antenna provides a high fore-and-aft ratio. Preferably, said transmitter is embedded in a vehicle, the method comprising the step of driving said vehicle to a marked area located on said taxiway upstream of said incident.

Advantageously, said vehicle comprises an optical information triangle, said transmitter comprising an antenna integrated in said optical information triangle.

Preferably, said first frequency is 107.7 MHz. According to one embodiment, said second signal comprises a traffic information marker. The marker may for example be an RDS-TA RDS tag. This increases the probability that the user receives the second signal.

According to a particular embodiment, said second signal comprises a marker indicating the type and / or the position of the incident. The information transmitted by this marker may allow a controller on board a vehicle receiving the second signal to adapt the operation of the vehicle, for example to automatically brake the vehicle. The invention also proposes a device for implementing the method according to the invention, characterized in that it comprises an emitter capable of transmitting a second radioelectric signal having a frequency carrier equal to said first frequency, said second signal radio frequency having a power greater than the power of said first signal at said transmitter.

Preferably, said transmitter comprises a directional antenna delta-loop type.

Advantageously, said transmitter is able to measure the power of said first radio signal, and to adjust the power of said second radio signal as a function of the power of the first measured radio signal.

The invention will be better understood, and other objects, details, features and advantages thereof will appear more clearly in the following description of a particular embodiment of the invention, given solely for illustrative purposes and not limiting, with reference to the accompanying drawings. On these drawings:

FIG. 1 is a representation of a visual markup according to the prior art, with a view to preventing an over-accident on a taxiway; FIG. 2 is a schematic representation of the transmission of a first signal towards a traffic lane,

FIG. 3 is a graph representing the power received from the first signal, as a function of the distance to the transmitter pylon,

FIG. 4 is a graph representing the power received from the second signal, as a function of the distance to the transmitting vehicle,

FIGS. 5 and 6 represent the power received from the first and second signals, as a function of distance, FIG. 7 represents an example of an antenna that can be used in one embodiment of the invention, and

FIG. 8 represents a radiation diagram of the antenna of FIG. 7. FIG. 2 schematically represents a pylon 4 at the top of which is placed an antenna 5. The antenna 5 makes it possible to transmit a first FM radio signal on the antenna. frequency 107.7 MHz to route 6. The vehicle 7 on route 6 is equipped with an antenna 8 for receiving the first radio signal. Typically, the tower 4 has a height of 25 m and several pylons 4 corresponding are along the road 6, every 10 km, and the signals are synchronized.

The curve 9 of FIG. 3 represents the variation of the power of the first signal, received at the level of the antenna 8, as a function of the distance between the pylon 4 and the vehicle 7. The curve 9 represented was obtained by modeling theoretical simplified, and measurements have confirmed that the variation of the actual power actually had this type of pace.

Figure 4 shows a patrol vehicle 10 equipped with an on-board transmitter. The on-board transmitter comprises an antenna 11. The antenna 11 is a directional antenna configured to emit towards the rear of the patrol vehicle 10. The antenna 11 is typically located at a height of between 2 and 3 meters. The on-board transmitter makes it possible to transmit a second radio signal, also on the frequency 107.7 MHz. The curve 12 of FIG. 4 represents the variation of the power of the second signal, received at the antenna 8, as a function of the distance between the patrol vehicle 10 and the vehicle 7. As for the curve 9, the curve 12 represented was obtained by a simplified theoretical modeling, and measurements made it possible to confirm that the variation of the real power actually presented this type of pace. As the antenna 11 is located at a height lower than the antenna 5, the curve 12 decreases more rapidly than the curve 9.

If an incident occurs on the road 6, for example a plug or an accident, the patrol vehicle 10 is driven to a place a little upstream of the incident, and stops in a position in which the antenna 11 makes it possible to emit the second signal in the upstream direction. The on-board transmitter is then used to repeatedly send a short multilingual voice message, to warn drivers of vehicles 7 upstream.

If the on-board receiver of the vehicle 7, associated with the antenna 8, is already set to the frequency 107.7 MHz, it will demodulate the second radio signal. Indeed, because of the capture phenomenon of the FM demodulator, the receiver will only demodulate the most powerful signal, that is to say the second signal as explained below. Preferably, the second radio signal comprises a RDS-TA tag of the RDS protocol, or an equivalent tag. Thus, it maximizes the probability of notifying the driver of the vehicle 7 in the case where the on-board receiver of the vehicle 7 is not set to the frequency 107.7 MHz.

In one embodiment, the second signal comprises other markers, for example also according to the RDS protocol, which include information on the position and the type of incident. A controller embedded in the vehicle 7 can then control the vehicle 7 according to these markers. For example, the controller may implement automatic braking determined according to the type of incident, the position of the incident and the current position of the vehicle 7.

In radio transmission with FM modulation, the capture phenomenon of the demodulator corresponds to the fact that when a receiver receives two signals with different powers, it demodulates the most powerful signal. This phenomenon occurs when the power difference is greater than a given threshold of about 6 dB. Naturally, the invention is not limited to FM radio transmission. The invention can be implemented with another type of modulation in which there is a capture phenomenon, for example with digital radio DAB.

In Figure 5, there is shown the situation in which the patrol vehicle 10 is immobilized on the road 6 and sends the second radio signal. The curves 9 and 12 are superimposed. In an upstream zone 13, the curve 9 is greater than the curve 12 by more than 6 dBm. The receiver of a vehicle 7 situated in the upstream zone 13 thus demodulates the first radio signal coming from the antenna 5. near the point of intersection 14, the curves 9 and 12 have about the same amplitude, ie they differ by less than 6 dB. In this vicinity, the reception of the first and second radio signals is imperfect. However, because of the speed of movement of the vehicle 7 and the slope differences of the curves 9 and 12, this neighborhood is quickly crossed.

In the reception zone 15, the curve 12 is greater than the curve 9 by more than 6 dB. The receiver of a vehicle 7 located in this reception zone 15 thus demodulates the second radio signal coming from the antenna 11. Then, in the downstream zone 16, it is again the curve 9 which is greater than the curve 12.

Thus, the method according to the invention makes it possible to locally transmit a voice message to a driver, from an on-board transmitter upstream of an incident. Figure 6 is a view similar to Figure 5, with a reverse distance axis and on a larger scale. At this scale, curve 9 is approximately a horizontal curve at -40 dBm for the considered location. Curve 17 shown in broken lines corresponds to the threshold of 6 dB above curve 9. Reception zone 15 is therefore limited by the intersections of curve 12 with curve 17.

In the example shown, the receiving zone 15 has a length of about 500 m. For a given power of the transmitter on board the patrol vehicle 10, this distance depends on the power of the first radio signal, that is to say the height of the curve 9. In one embodiment, the patrol vehicle 10 is equipped with a sensor for measuring the power of the first radio signal, and the on-board transmitter is adapted to adapt its transmission power according to the measured power, in order to reach a given range. As can be seen in FIG. 6, the antenna 11 is a directional antenna, that is to say it emits the second signal towards the rear of the patrol vehicle 10, but not towards the front. . Thus, the vehicles traveling in the opposite direction, on a part of the road 6 not affected by the incident, are first in the zone 16 and do not receive the second signal before being at a distance from the patrol vehicle 10 allowing visual contact. The drivers of these vehicles are not disturbed by the second signal that does not concern them, before arriving in view of the patrol vehicle 10.

The antenna 11 can be made in many ways, so as to have a high directivity and a high front-rear ratio. Figure 7 shows a preferred example, where the antenna 11 is a delta-loop antenna. In this example, the antenna 11 comprises an emitter triangle 18 and a reflector triangle 19 composed of metal rods of length L equal to about one-third of the wavelength. The triangles 18 and 19 are arranged in two vertical planes at a distance x from each other, with one of the horizontal sides. This arrangement makes it possible to obtain a polarization adapted to the antennas 8 of the vehicles 7, which are generally vertical whisks. The signal to be emitted is injected at a lower corner 20 of the triangle 18, via a coaxial cable and an impedance matching device. In an optimized embodiment, the triangles 18 and 19 are made of aluminum tubes 12 mm in diameter, and the length L is 101.5 cm for the triangle 18 and 107.2 cm for the triangle 19. The distance x is 0.15 times the wavelength, i.e. 41.7 cm for a frequency of 107.7 MHz. Fig. 8 shows the azimuth radiation pattern of the antenna 11 in this optimized embodiment. It is found that we have the desired strong directivity, and in particular a front-rear ratio that can reach 40 dB.

The triangular shape of the antenna 11 makes it possible to integrate the antenna 11 into an optical signaling triangle like that of FIG. 1, which leads to a saving of space and to masking the antenna 11.

The transmission frequency of the second signal is not necessarily 107.7 MHz. The frequency is chosen so that it is probable that the receivers of the vehicles 7 are already tuned to this frequency. In one embodiment, the second signal is transmitted on the frequency 107.7 MHz, but also on one or more other frequencies corresponding to the local frequencies of the FM broadcasters.

Although the invention has been described in connection with a particular embodiment, it is obvious that it is not limited thereto and that it comprises all the technical equivalents of the means described and their combinations if they are within the scope of the invention.

Claims

A device suitable for carrying out a method of preventing an over-accident on a taxiway (6) on which an incident occurs, wherein a first radio signal having a first frequency carrier is transmitted to said taxiway, and which comprises the step of transmitting, from an emitter on said taxiway upstream of said incident, a second radio signal having a carrier of frequency equal to said first frequency, said second radio signal having a power (12) greater than the power (9) of said first signal at said transmitter, said device comprising a transmitter embedded in a vehicle (10) and adapted to transmit said second signal, characterized in that said transmitter comprises an antenna delta-loop antenna type directive, said vehicle comprises an optical information triangle, said antennas a directive being integrated in said optical information triangle.

2. Device according to claim 1, wherein said transmitter is adapted to transmit said second signal with a power such that the power difference between said second radio signal and said first signal at said transmitter is at least 6 dB.

3. Device according to one of claims 1 to 2, wherein said antenna (11) directive has, in the direction of the lane, a front-rear ratio of at least 20 dB.

4. Device according to one of claims 1 to 3, wherein said first frequency is 107.7 MHz.

5. Device according to one of claims 1 to 4, wherein said transmitter is adapted to transmit said second signal with a traffic information marker.

6. Device according to one of claims 1 to 5, wherein said transmitter is adapted to emit said second signal with a marker indicating the type and / or position of the incident.

7. Device according to one of claims 1 to 6, wherein said transmitter is able to measure the power of said first radio signal, and to adjust the power of said second signal radio frequency as a function of the power of the first measured radio signal.