Method for alerting the driver of a vehicle

Abstract

Method for alerting the driver of a vehicle Method for alerting a driver of a first motor vehicle (V1), characterized in that it comprises:- detection (E11), by a detection means (3) embedded in the vehicle, of a lateral position of a second vehicle (V2) traveling in front of the first vehicle, then- detection (E2) of an erratic trajectory of the second vehicle as a function of its lateral position, then- generation (E3) of an alert message for the driver of the first vehicle, by a human-machine interface (4) embedded in the vehicle. Figure for the abstract: figure 3

Description

Title of the invention: Method for alerting the driver of a vehicle Technical field of the invention

[0001] The invention relates to a method for alerting a driver of a first motor vehicle, following the detection of an erratic trajectory of a second vehicle. The invention also relates to a motor vehicle configured to implement such an alert method. State of the prior art

[0002] To make driving motor vehicles safer, motor vehicles are fitted with driver assistance systems that alert the driver when a danger is detected. For example, driver assistance systems are known that are provided with a means for detecting the distance separating a first vehicle from a second vehicle positioned in front of the first vehicle. If the first vehicle gets too close to the second vehicle, that is to say if the distance separating the first vehicle from the second vehicle becomes less than or equal to a threshold, then an alert message is emitted by a human-machine interface. In practice, a sound is emitted and a pictogram is displayed on a dashboard in order to alert the driver of the first vehicle. The driver of the first vehicle is thus invited to re-establish a greater safety distance with the second vehicle.

[0003] According to another example, driving assistance systems are also known, also called fatigue detectors, capable of detecting a drop in the driver's attention. These systems may be based, for example, on the detection of the crossing of a traffic lane boundary or on direct observation of the driver. When a drop in vigilance is detected, these systems invite the driver to take a break.

[0004] The driving assistance systems known from the state of the art are nevertheless insufficient to ensure total safety for road users. Presentation of the invention

[0005] The aim of the invention is to provide a method for alerting a driver and a driving assistance system which overcomes the above drawbacks and improves the alert methods and driving assistance systems known from the prior art.

[0006] More specifically, a first object of the invention is a method for alerting a driver making it possible to alert a driver of a risk of collision with a second vehicle. Summary of the invention

[0007] The invention relates to a method for alerting a driver of a first motor vehicle, comprising: - detection, by a detection means on board the vehicle, of a lateral position of a second vehicle traveling in front of the first vehicle, then - detection of an erratic trajectory of the second vehicle based on its lateral position, then - the generation of an alert message for the driver of the first vehicle, by a human-machine interface on board the vehicle.

[0008] Detection of an erratic trajectory may include: - estimation of the amplitude of a lateral oscillation of the second vehicle, then - the comparison of said amplitude with an amplitude threshold, then - counting a first number of occurrences where said amplitude exceeds said amplitude threshold over a first duration, then - comparing said first number of occurrences to a first threshold of occurrences, the alert message being generated if said first number of occurrences is greater than or equal to the first threshold of occurrences.

[0009] Detection of an erratic trajectory may include: - the detection of a limit of a traffic lane on which the second vehicle is traveling, then - the estimation of an index of repetition of the crossing of said limit by the second vehicle, then - comparison of the repetition index with a repetition threshold, the alert message being generated if said repetition index is greater than or equal to the repetition threshold.

[0010] Detection of an erratic trajectory may include: - the detection of a limit of a traffic lane on which the second vehicle is traveling, then - the estimate of a second duration during which the second vehicle travels across the said limit, - the comparison of said second duration with a duration threshold, the alert message being generated if said second duration is greater than or equal to the duration threshold.

[0011] Detection of an erratic trajectory may include: - the estimation of a tracking time between the first vehicle and the second vehicle, then - comparing said tracking time to a tracking time threshold, then - counting a second number of occurrences where said tracking time exceeds said tracking time threshold over a third duration, then - comparing said second number of occurrences to a second threshold of occurrences, the alert message being generated if said second number of occurrences is greater than or equal to the second occurrence threshold.

[0012] The alert method may comprise a detection of the traffic lane on which the second vehicle is traveling, the second vehicle traveling generally on the same traffic lane as the first vehicle or on a traffic lane adjacent to the traffic lane on which the first vehicle is traveling, at least one threshold of the alert method being defined as a function of the traffic lane on which the second vehicle is traveling.

[0013] The alert method may comprise: - an estimate of a tracking time between the first vehicle and the second vehicle, then - comparing said tracking time to a tracking time threshold, the alert message being generated if and only if said tracking time is less than or equal to the tracking time threshold.

[0014] The alerting method may comprise: - a detection of the traffic lane on which the second vehicle is traveling, then - a calculation of said tracking time threshold, said tracking time threshold being equal to a first value if the second vehicle is traveling in the same traffic lane as the first vehicle, said tracking time threshold being equal to a second value if the second vehicle is traveling in a traffic lane adjacent to the traffic lane on which the first vehicle is traveling, the second value being different from the first value.

[0015] The alert method may comprise: - detection of the activation state of a flashing light of the first vehicle, - a calculation of said tracking time threshold, said tracking time threshold being equal to a first value if the second vehicle is traveling in the same traffic lane as the first vehicle, no flashing light of the first vehicle being activated, said tracking time threshold being equal to a third value if the second vehicle is traveling in the same traffic lane as the first vehicle, a flashing light of the first vehicle being activated, the third value being different from the first value.

[0016] The alert method may comprise, following the detection of an erratic trajectory of the second vehicle, an automatic slowing down of the first vehicle to increase the distance separating the first vehicle from the second vehicle or a deactivation of an adaptive cruise control.

[0017] The invention also relates to a motor vehicle equipped with a driving assistance system comprising a detection means, a man-machine interface, and hardware and software means configured to implement the alert process as defined above.

[0018] The invention also relates to a computer program product comprising program code instructions recorded on a computer-readable medium for implementing the steps of the alert method as defined above when said program operates on a computer.

[0019] The invention also relates to a data recording medium, readable by a computer, on which is recorded a computer program comprising program code instructions for implementing the alert method as defined previously.

[0020] The invention also relates to a signal of a data medium, carrying the computer program product as defined previously. Presentation of figures

[0021] These objects, characteristics and advantages of the present invention will be explained in detail in the following description of a particular embodiment made without limitation in relation to the attached figures among which:

[0022] [Fig.l] is a schematic view of a motor vehicle according to one embodiment of the invention.

[0023] [Fig.2] is a block diagram of an alert method according to one embodiment of the invention.

[0024] [Fig. 3] is a schematic top view of a first configuration in which the alert method is implemented.

[0025] [Fig.4] is a schematic top view of a second configuration in which the alert method is implemented.

[0026] [Fig.5] is a schematic top view of a third configuration in which the alert method is implemented. Detailed description

[0027] [Fig.l] schematically illustrates a first motor vehicle VI according to an embodiment of the invention. The vehicle V1 may be, for example, a private vehicle, a utility vehicle, or even a truck or bus. The first vehicle VI conventionally comprises control means intended to be controlled by a driver to guide the vehicle, in particular at least one steering wheel, an accelerator pedal and a brake pedal. The first vehicle V1 also has a driving assistance system 2. The driving assistance system 2 comprises a means 3 for detecting the environment of the vehicle, a human-machine interface 4, and an electronic control unit 5 electrically connected to the detection means 3 and to the human-machine interface 4.

[0028] The detection means 3 is configured to detect objects located in front of the first vehicle VI. In particular, the detection means 3 is configured to detect the position of a second vehicle V2 preceding the first vehicle VI. That is to say that the second vehicle V2 is positioned in front of the first vehicle VI. The detection means 3 is also configured to detect the position of traffic lane boundaries, in particular in the form of marking lines painted on the ground, for example in a continuous or broken line, for example in white or yellow. The detection means 3 may also be capable of detecting traffic lane boundaries in a different form, such as for example road surface boundaries, sidewalks, or even barriers. The detection means 3 may be for example a camera, a radar or a lidar.

[0029] The human-machine interface 4 is configured to transmit information to a driver of the first vehicle V1. In particular, the human-machine interface 4 may comprise a display means 41 and / or a loudspeaker 42. The display means 41 may for example be integrated into a dashboard providing other information useful for controlling the vehicle. It may also be integrated into a head-up display device for displaying information on a windshield of the vehicle. The display means 41 is capable of displaying at least one pictogram P, for example the symbol K21 according to the ISO2575 standard. The display means may furthermore display a brief text for the driver. The loudspeaker may be configured to emit a simple alert sound and / or a voice alert message.

[0030] The electronic control unit 5 is configured to receive signals from the detection means 3 and to transmit signals to the human-machine interface 4. The electronic control unit 5 is equipped with a microprocessor 51, a memory 52 and input / output interfaces 53 for exchanging information with the detection means 3 and the human-machine interface 4. The memory 52 of the electronic control unit 5 is a data recording medium on which is recorded a computer program comprising program code instructions for implementing a method for alerting the driver of the first vehicle V1 according to an embodiment of the invention. The microprocessor 51 is capable of executing this computer program.

[0031] A particular embodiment of the alert method will now be described in relation to Figures 2 to 5. Figures 3, 4 and 5 show a top view of the first vehicle VI on a road comprising two adjacent traffic lanes 11, 12, i.e. side by side. The traffic lanes 11, 12 are parallel and in the same direction of travel. It is possible for a vehicle to move from one traffic lane to the other. The traffic lanes are delimited by boundaries 13, 14, 15 such as marking lines in the form of dotted lines. The direction of travel is oriented from left to right and is represented by a vector X. A vector Y is perpendicular to the vector X. The vector Y is parallel to a transverse axis of the two traffic lanes 11, 12. The vectors X and Y are parallel to the plane in which the traffic lane extends.

[0032] A second vehicle V2 travels in front of the first vehicle VL. In particular, at least one point of the second vehicle V2 (for example, a rear edge of the second vehicle V2) is positioned in front of a front edge of the first vehicle VI in the direction of travel. The second vehicle V2 follows an erratic trajectory T. By "erratic", it is understood that the trajectory T is abnormal, irregular and / or unstable. In particular, the second vehicle V2 may have a fluctuating lateral position, that is to say a position relative to the vector Y that varies temporally. In other words, the second vehicle V2 successively moves away from and approaches the limits 13, 14, 15 while remaining at least generally in a traffic lane. The second vehicle V2 may also be driven eccentrically relative to its traffic lane.Alternatively or additionally, an erratic trajectory of the second vehicle may also be characterized by a fluctuating speed of that vehicle. A fluctuating speed may include unjustified accelerations and slowdowns of the second vehicle, in particular unjustified by a traffic jam situation. Typically, an erratic trajectory may be caused by a state of fatigue, by a state of great distraction, by a state of intoxication of the driver of the second vehicle V2, or by a malfunction of the second vehicle, such as for example a flat tire.

[0033] The trajectory T of the second vehicle can be represented by a line passing through a center of the second vehicle. Furthermore, in Figures 3, 4 and 5, the second vehicle is represented at two different times: at time t-1 and at time t. According to the configuration of [Fig. 3], the first vehicle and the second vehicle are traveling on the same traffic lane 12. According to the configuration of [Fig. 4], the first vehicle is traveling on the traffic lane 11 and the second vehicle is traveling on the traffic lane 12, adjacent to the traffic lane 11. Finally, according to the configuration of [Fig. 5], the first vehicle and the second vehicle are traveling on the same traffic lane 11, and the first vehicle has activated a flashing light 6 on the side of the traffic lane 12 because the driver of the first vehicle VI is preparing to overtake the second vehicle V2.The flashing light 6 is an intermittent warning light, manually activated by the driver of the first vehicle VI, and which signals to other road users an intention to change lane.

[0034] The alert method mainly comprises a first step E1 during which, with the detection means 3 on board the vehicle VI, a road configuration in which the first vehicle VI is located. In particular, the different traffic lanes 11, 12 and their limits 13, 14, 15 are detected, as well as the second vehicle V2. The first step notably comprises a first sub-step El 1 in which the lateral position of the second vehicle V2 on its traffic lane is detected. This lateral position can be expressed as a distance along the vector Y of the second vehicle V2 relative to a given point on the traffic lane on which it is traveling. More precisely, the lateral position can be equal to the distance from the center of the second vehicle V2 to the right or left limit of its traffic lane. The lateral position of the second vehicle is preferably calculated in the reference frame of the traffic lane on which it is traveling.Alternatively, the lateral position of the second vehicle could be calculated in the frame of reference of the first vehicle, i.e. the movements of the second vehicle would be quantified with reference to the first vehicle. This would allow the alert method to be implemented even when no traffic lane boundary is detected.

[0035] In a second sub-step E12 of step El, a tracking time is determined between the first vehicle VI and the second vehicle V2. The tracking time between the first vehicle and the second vehicle designates the time required for the first vehicle to reach the position of the second vehicle. It may be equal to the distance separating the first vehicle from the second vehicle divided by the speed of the first vehicle.

[0036] Then in a third sub-step E13 of step E1, the previously calculated tracking time is compared with a given tracking time threshold. The tracking time threshold may be for example less than or equal to five seconds, for example between one second and four seconds. Advantageously, the alert method is only continued if the calculated tracking time is less than or equal to the tracking time threshold. Thus, if the second vehicle is sufficiently far in front of the first vehicle, relative to the speed of the first vehicle, no driver alert is then generated. Sub-steps E12 and E13 are optional and may not be implemented.

[0037] The tracking time threshold may be equal to a value defined by parameterization. Advantageously, this tracking time threshold may also be calculated during a sub-step El4, in particular as a function of the road configuration in which the first vehicle VL is located.

[0038] Thus, the first step E1 may also comprise a sub-step E15 in which the traffic lane on which the second vehicle is traveling is detected. In particular, it is detected whether the second vehicle V2 is traveling on the same traffic lane as the first vehicle VI, or on an adjacent traffic lane, to the right or left of that on which the first vehicle is traveling.

[0039] The first step El may also comprise a sub-step El6 in which the activation state of the flashing light 6 of the first vehicle VI is detected. The activation of the flashing light may be detected by an electronic control unit of the vehicle itself connected to the electronic control unit 5 so as to transmit to the latter the activation state of the flashing light.

[0040] In sub-step E14 during which the tracking time threshold is calculated, the following calculation rules can be applied: - the tracking time threshold may be equal to a first Talertel value if the second vehicle V2 is traveling in the same traffic lane as the first vehicle VI and no flashing light of the first vehicle is activated; - the tracking time threshold may be equal to a second value Talerte2 if the second vehicle V2 is traveling in a traffic lane adjacent to the traffic lane on which the first vehicle is traveling; - the tracking time threshold may be equal to a third value Talerte3 if the second vehicle V2 is traveling in the same traffic lane as the first vehicle VI, a flashing light of the first vehicle being activated; Advantageously, the three values ​​Talertel, Talerte2 and Talerte3 can be different from each other. For example, the value Talertel can be less than or equal to the value Talerte2 and / or the value Talerte3. For example, the values ​​Talertel and Talerte2 can be equal to two seconds. The value Talerte3 can be equal to three seconds.

[0041] As we will see in more detail later, the traffic lane on which the second vehicle V2 is traveling, detected in E15, and / or the activation state of a flashing light of the first vehicle V1 detected in E16, constitute information which can also be used in the rest of the alert method to adapt different thresholds.

[0042] Then, in a second step E2, an erratic trajectory of the second vehicle V2 is detected as a function of its lateral position. More detailed embodiments of this detection will be detailed in the remainder of the description.

[0043] Then, in a third step E3, an alert message is generated for the driver of the first vehicle, by means of the human-machine interface on board the vehicle. In particular, a pictogram such as the symbol K21 according to the ISO2575 standard can be displayed on the display screen 41 and / or a message inviting the driver to increase the distance separating him from the second vehicle can be displayed. Alternatively or additionally, an alert sound and / or a voice alert message can be produced by means of the loudspeaker 42.

[0044] Furthermore, in a fourth, optional step E4, the first vehicle VI can also be automatically slowed down so as to increase the distance separating from the second vehicle V2. In such a case, the first vehicle VI can advantageously be equipped with an adaptive cruise control coupled with the detection means 3. The adaptive cruise control is capable of controlling an engine of the vehicle and / or braking means of the vehicle in order to maintain a given distance with the second vehicle, called the safety distance. The electronic control unit 5 can send an instruction to the adaptive cruise control in order to increase said safety distance. Alternatively, the adaptive cruise control could be deactivated during this fourth step

[0045] Step E2 of detecting an erratic trajectory of the second vehicle V2 may comprise different sub-steps E21, E22, E23. These three sub-steps each define a condition independent of the other two which, if verified, lead to the generation of an alert message in step E3. Alternatively, the alert method could comprise only two sub-steps or a single sub-step among the three sub-steps E21, E22 and E23.

[0046] In a first sub-step E21 of step E2, an amplitude of a lateral oscillation of the second vehicle is first estimated, in E211. That is to say, the lateral position difference between two extreme positions of the oscillation movement of the second vehicle is estimated. Then, in E212, said amplitude is compared to an amplitude threshold Aseuill. This amplitude threshold Aseuill may, for example, be between one meter and three meters, in particular equal to two meters or any other value defined by parameterization. The amplitude threshold Aseuill may also be equal to a given percentage (for example 50%) of the width of the traffic lane on which the second vehicle is traveling. Then, in E213, the number of occurrences where said amplitude exceeds said amplitude threshold over a first duration Dseuill is counted.The first duration Dseuill can be for example between five seconds and thirty seconds, in particular equal to ten seconds or any other value defined by configuration. Then, in E214, the said number of occurrences is compared to a first occurrence threshold Xseuill. The first occurrence threshold Xseuill can be for example between two and five, in particular equal to three or any other value defined by configuration. Finally, the alert message is generated in E3 if the said number of occurrences is greater than or equal to the first occurrence threshold Xseuill.

[0047] In a second sub-step E22 of step E2, a limit of the traffic lane on which the second vehicle V2 is traveling is first detected at E221. Then, at E222, a repetition index of the crossing of the limit detected at E221 by the second vehicle is estimated. This repetition index can be calculated in particular by counting the number of times the second vehicle crosses or enters said limit over a given period, for example a period equal to the first duration Dseuill. A limit crossing can be proven as soon as the second vehicle has a wheel on either side of said limit. Then, in E223, the repetition index estimated in E222 is compared to a repetition threshold Fseuill. The repetition threshold can be, for example, between once per ten seconds and five times per ten seconds, for example, equal to three times per ten seconds or any other value defined by configuration. Finally, the alert message is generated in E3 if the repetition index estimated in E222 is greater than or equal to the repetition threshold Fseuill.

[0048] In a third sub-step E23 of step E2, a limit of a traffic lane on which the second vehicle is traveling is first detected at E231. Then, at E232, a second duration is estimated during which the second vehicle is traveling astride the limit detected at E231, i.e. it is traveling with at least one wheel on either side of said limit. This second duration can be calculated over a predetermined period. This period can be equal to the first duration Dseuill. Then, at E233, the second duration estimated at E232 is compared to a duration threshold Dseuil2. The duration threshold Dseuil2 can be, for example, equal to 50% of the first duration Dseuill, for example between three and ten seconds, in particular equal to five seconds or any other value defined by parameterization. Finally, the alert message is generated in E3 if the second estimated duration in E232 is greater than or equal to the duration threshold Dseuil2.

[0049] Optionally, the step E2 of detecting an erratic trajectory of the second vehicle V2 may also comprise a substep E24 in which an erratic speed of the second vehicle is detected. For example, in the fourth substep E24, a tracking time between the first vehicle and the second vehicle is first estimated, in E241. This step may be implemented as in the step E12 described previously. Then, in E242, said tracking time is compared to a tracking time threshold Tseuill. This tracking time threshold Tseuill may be defined by parameterization. Then, in E243, a second number corresponding to the number of occurrences where said tracking time exceeds said tracking time threshold Tseuill over a third duration Dseuil3 is counted. The third duration Dseuil3 may, for example, be between five seconds and thirty seconds, in particular equal to ten seconds or any other value defined by parameterization.The third duration Dseuil3 can be equal to the first duration Dseuill. Then, in E244, the said second number of occurrences is compared to a second occurrence threshold Xseuil2. The second occurrence threshold Xseuil2 can be for example between two and five, in particular equal to three or any other value defined by configuration. The second occurrence threshold Xseuil2 can be equal to the first threshold Xseuill. Finally, the alert message is generated in E3 if the said second number of occurrences is greater than or equal to the second occurrence threshold Xseuil2. Finally, this fourth sub-step E24 makes it possible to detect an erratic speed of the second vehicle, leading to a measurement of a variable tracking time.

[0050] The sub-steps E21, E22, E23 and E24 are based on the use of parameters or thresholds Xthreshold, Xthreshold2, Dthreshold, Dthreshold2, Dthreshold3, Tthreshold, Fthreshold. Advantageously, these parameters or thresholds can be adapted according to the road configuration in which the first vehicle VI is located, in particular according to the traffic lane on which the second vehicle is traveling as detected in E15 or according to the activation state of a flashing light of the first vehicle as detected in E16.

[0051] As a note, the terms "first", "second" and "third" appearing in this document do not characterize any order relationship between the objects to which they relate but simply aim to define different objects.

[0052] The method which has just been described is now illustrated with different configurations all leading to the generation of an alert message so that the driver of the first vehicle increases the safety distance separating him from the second vehicle.

[0053] In a first configuration, illustrated in [Fig. 3], the first vehicle VI follows, with a tracking time less than or equal to two seconds, the second vehicle V2. The second vehicle V2 begins to oscillate by more than two meters, three times in less than ten seconds.

[0054] In a second configuration, also illustrated in [Fig. 3], the first vehicle follows, with a following time less than or equal to two seconds, the second vehicle V2. The second vehicle crosses a road marking line more than three times during the last ten seconds.

[0055] In a third configuration, also illustrated in [Fig. 3], the first vehicle follows, with a following time less than or equal to two seconds, the second vehicle V2. The second vehicle crosses a road marking line for more than five seconds out of the last ten seconds.

[0056] In a fourth configuration, illustrated in [Fig. 4], the first vehicle drives on the traffic lane 11 and the second vehicle drives on the traffic lane 12. The first vehicle follows, with a following time less than or equal to two seconds, the second vehicle V2. The second vehicle V2 crosses a road marking line for more than five seconds.

[0057] In a fourth configuration, also illustrated in [Fig.4], the first vehicle drives on the traffic lane 11 and the second vehicle drives on the traffic lane 12. The first vehicle follows, with a following time less than or equal to two seconds, the second vehicle V2. The second vehicle crosses a line or a road marking more than three times during the last ten seconds.

[0058] In a fifth configuration, illustrated in [Fig. 5], the first vehicle V1 follows, with a following time less than or equal to three seconds, the second vehicle V2. The second vehicle V2 begins to oscillate or to cross a marking line on the ground as explained previously. If the driver of the first vehicle V1 activates his indicator, then the first vehicle generates an alert message so that the driver of the first vehicle increases the safety distance separating him from the second vehicle. The driver of the first vehicle then understands that it is preferable not to overtake the second vehicle because a collision could occur if he gets too close to it.

[0059] These different configurations are not limiting and other configurations could be proposed. In particular, the invention can very well be implemented on a road comprising any number of traffic lanes. The traffic lanes can be straight or curved. The method could also be implemented when at least a third vehicle is interposed between the first vehicle and the second vehicle, provided that the lateral position of the second vehicle is still detectable.

[0060] Thanks to the invention, the driver of a vehicle is warned when another motorist is exhibiting risky driving. He can then increase the distance separating him from this vehicle and reduce the risks of having an accident.

Claims

Claims

1. Method for alerting a driver of a first motor vehicle (VI), characterized in that it comprises: - a detection (El 1), by a detection means (3) on board the vehicle, of a lateral position of a second vehicle (V2) traveling in front of the first vehicle, - a detection (E15) of the traffic lane (11, 12) on which the second vehicle is traveling, then - a calculation (E14) of a tracking time threshold, said tracking time threshold being equal to a first value (Talertel) if the second vehicle is traveling in the same traffic lane as the first vehicle, said tracking time threshold being equal to a second value (Talerte2) if the second vehicle is traveling in a traffic lane adjacent to the traffic lane on which the first vehicle is traveling, the second value being different from the first value, - an estimation (E12) of a tracking time between the first vehicle and the second vehicle,then - the comparison (El3) of said tracking time with the tracking time threshold, then - a detection (E2) of an erratic trajectory of the second vehicle as a function of its lateral position, then - the generation (E3) of an alert message for the driver of the first vehicle, by a man-machine interface (4) on board the vehicle, the alert message being generated if and only if said tracking time is less than or equal to the tracking time threshold.,

2. Alert method according to the preceding claim, characterized in that the detection of an erratic trajectory comprises: - the estimation (E211) of an amplitude of a lateral oscillation of the second vehicle, then - the comparison (E212) of said amplitude with an amplitude threshold (Aseuill), then - the counting (E213) of a first number of occurrences where said amplitude exceeds said amplitude threshold over a first duration (Dseuill), then - the comparison (E214) of said first number of occurrences with a first occurrence threshold (Xseuill), the alert message being generated if said first number of occurrences is greater than or equal to the first occurrence threshold.

3. Alert method according to one of the preceding claims, characterized in that the detection of an erratic trajectory comprises: - a detection (E221) of a limit (13, 14, 15) of a traffic lane (11, 12) on which the second vehicle is traveling, then - the estimation (E222) of a repetition index of the crossing of said limit by the second vehicle, then - the comparison (E223) of the repetition index with a repetition threshold (Fseuill), the alert message being generated if said repetition index is greater than or equal to the repetition threshold.

4. Alert method according to one of the preceding claims, characterized in that the detection of an erratic trajectory comprises: - a detection (E231) of a limit (13, 14, 15) of a traffic lane (11, 12) on which the second vehicle is traveling, then - the estimation (E232) of a second duration during which the second vehicle is traveling astride said limit, - the comparison (E233) of said second duration with a duration threshold (Dseuil2), the alert message being generated if said second duration is greater than or equal to the duration threshold.

5. Alert method according to one of the preceding claims, characterized in that the detection of an erratic trajectory comprises: - an estimation (E241) of a tracking time between the first vehicle and the second vehicle, then - the comparison (E242) of said tracking time with a tracking time threshold (Tseuill), then - the counting (E243) of a second number of occurrences where said tracking time exceeds said tracking time threshold (Tseuill) over a third duration (Dseuil3), then - the comparison (E244) of said second number of occurrences with a second occurrence threshold (Xseuil2), the alert message being generated if said second number of occurrences is greater than or equal to the second occurrence threshold (Xthreshold2).

6. Alert method according to one of the preceding claims, characterized in that the second vehicle is traveling generally on the same traffic lane as the first vehicle or on a traffic lane adjacent to the traffic lane on which the first vehicle is traveling, at least one threshold of the alert method being defined as a function of the traffic lane on which the second vehicle is traveling.

7. Alert method according to one of the preceding claims, characterized in that it comprises: - a detection (El6) of the activation state of a flashing light (6) of the first vehicle, - a calculation (E14) of said tracking time threshold, said tracking time threshold being equal to a first value (Talertel) if the second vehicle is traveling in the same traffic lane (11, 12) as the first vehicle, no flashing light of the first vehicle being activated, said tracking time threshold being equal to a third value (Talerte3) if the second vehicle is traveling in the same traffic lane as the first vehicle, a flashing light of the first vehicle being activated, the third value being different from the first value.

8. Alert method according to one of the preceding claims, characterized in that it comprises, following the detection of an erratic trajectory of the second vehicle, an automatic slowing down (E4) of the first vehicle to increase the distance separating the first vehicle from the second vehicle or a deactivation of an adaptive cruise control.

9. Motor vehicle (1) equipped with a driving assistance system (2) comprising a detection means (3), a human-machine interface (4), and hardware means (5) and software configured to implement the alert method according to one of the preceding claims.

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