JPS5938640B2 - Vehicle group speed measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the speed of a group of vehicles, and more particularly to a method for obtaining a video signal of a traveling vehicle using an optical system and measuring the traveling speed of a group of vehicles from this video signal.

2. Description of the Related Art A vehicle speed measuring device is known that is provided with an optical system that is placed at a position overlooking a required detection point on a road and includes a light-receiving element that detects a vehicle at this detection point. In this type of measuring device, if the field of view of the light receiving element is set at a far distance, multiple vehicles will appear to overlap, so it is difficult to identify the signal waveform of each individual vehicle from the output video signal of the light receiving element. It is difficult. Therefore, for distant detection points, it is effective to consider a plurality of vehicles as a vehicle group and measure the speed of this vehicle group. However, since the length of the vehicle group changes depending on the flow of vehicles, the end points of the signal components representing the vehicle group in the video signal also vary. Because it is difficult to predict the length of a group of vehicles in advance, measuring the speed of a group of vehicles requires more complex processing than measuring the speed of individual vehicles. In view of the above-mentioned circumstances, the present invention provides a method that can measure the speed of a group of vehicles with extremely simple processing. Hereinafter, the content of the present invention will be explained in detail with reference to the drawings.

The example shown below is a case where a traffic flow measuring device installed in a position overlooking a road and having a large number of light receiving elements is used.

This device has the advantage of being able to collect vehicle information from multiple points on the road at one location and being easy to install. 1st
The figure shows how the camera of the traffic flow measuring device is installed.

The camera 1 is mounted at a required height position (for example, 6 m) above the road L using a support 3 or the like, and within a required range (for example, 6 m) in the length direction of the road L.
For example, it is installed so that it overlooks 100 meters).
As shown in FIG. 3, the camera 1 is equipped with an optical system 4 including a lens 5 and a large number of light receiving elements. In this example, within the field of view of the camera 1, there are six detection points P1 to P6 along the lane in which traffic flow is to be measured. A pair of light receiving elements DSl, dRl to DS are placed on the image forming plane of the optical system 4 in the camera 1 at locations corresponding to these detection points.
6, dR6 is placed. These light receiving elements are composed of photo diodes, for example. When measuring traffic flow in two lanes with one camera, a large number of light receiving elements are arranged in two rows on the imaging plane of the optical system 4.

At each detection point (represented by P), as shown in Figure 2,
A set area S and a set area R are set at a required interval l. A pair of light receiving elements (represented by DS and dR)
correspond to these regions S and R, respectively.

When the vehicle CA passes through the detection point P from the set area S toward the set area R, a vehicle location detection video signal shifted by a time t is output from the light receiving elements DS and DR, as will be described later. Then, the traveling speed of the vehicle is calculated based on this time t and distance l. vehicle speed, headway distance,
The degree of traffic congestion, the number of passing vehicles, and other traffic flow information are obtained by the processing device 2 based on video signals from the camera 1.

With reference to FIG. 3, each light receiving element DS, dR in the camera 1
The output signal is amplified by an amplifier 6 equipped with an automatic gain control function, and then sent to a multiplexer channel device 7, where the outputs of each of the 12 light receiving elements are sequentially switched and output from A to D. It is sent to converter 8. The AD converter 8 performs AD conversion on the input output of each light receiving element, and sends the result to a central processing unit (referred to as CPU) 11 . AD conversion of the output signal of each light receiving element is performed at a predetermined sampling period (4.8 mS in this example). The 12 light receiving elements are scanned by the multiplexer channel device 7 within this sampling period.

The processing device 2 is equipped with two CPUs 11 and 12.

Based on the data sent from the A-D converter 8, CPUll executes analysis processing of the output signal waveform of each light receiving element, as will be explained later, and also analyzes the output signal waveform of the multiplexer channel device 7 and the A-D converter 8. Converter 8 is controlled. The CPU12 calculates the running speed of the vehicle, detects the degree of congestion, and performs other traffic flow calculation processes based on the data obtained by the CPU11, and also creates necessary traffic flow information and sends it to the transmission unit (not shown). The data is then transmitted to the center. Each CPUll, l2 includes a program memory (not shown) storing an execution program, and local memories 13, 14 for storing data, respectively, and the processing device 2 includes both CPUll, l2. There is a shared memory 15 that can be accessed.

FIG. 5 shows an example of a vehicle video signal output from light receiving elements DS6 and dR6 that detect a vehicle traveling at a distant detection point, for example, detection point P6.

The set signal is the output of the light receiving element DS6, and the reset signal is the output of the light receiving element DR6. Since multiple vehicles appear to overlap at a distant detection point, each signal contains the waveform of a vehicle group consisting of multiple vehicles, making it impossible to identify individual vehicles. Therefore, instead of measuring the speed of individual vehicles, the speed of a group of vehicles is measured. In measuring the vehicle group speed, it is necessary to determine changes in the output signal of the light receiving element.

The output signal of the light receiving element is A-D at each sampling period.
The data is AD converted by the converter 8, and the result of the current AD conversion is defined as the current data Dt. In order to determine whether the current data Dt is increasing or decreasing compared to the previous data, or whether it is in an equilibrium state of neither increase nor decrease, the deviation Δω between the current data Dt and the previous data is
It is necessary to ask for Previous data to be used for determining this deviation Δω is defined as preprocessed data DO. This preprocessed data DO is, for example, previously sampled data and is updated every sampling period.
Furthermore, for the above determination, the reference amount to be compared with the deviation Δω between the current data Dt and the preprocessed data DO is defined as a deviation reference amount ω0. If Dt-DO≧ω0, the state increases; if Dt-DO≦-ω0, the state decreases; 1Dt-D
If O<ω0, it is assumed to be in an equilibrium state. FIG. 4 shows how the change in the signal is determined for each sampling period in this manner. In order to detect the rising edge of a signal waveform, a flat reference level is required.

This level is called the equilibrium level LC. The equilibrium level LC is determined by the number of times the signal is in an equilibrium state (this is determined by the equilibrium judgment value CO).
) are updated when they occur consecutively. There are several equilibrium levels LC. One is the level LO at which the light receiving element detects the road surface (indicated by A in Figure 5); when the vehicle is not running, this road surface level LO
continues. The other level is the level at which a group of vehicles is detected (indicated by B in FIG. 5), and in this case, an equilibrium state continues at a level higher than the road surface level LO. Since the length of the video signal waveform of a vehicle group changes depending on the number of vehicles making up the vehicle group, it is impossible to predict in advance when it will end (fall).

Therefore, we introduce the concept of a prohibited time period T, and assume that one vehicle group has passed when this prohibited time period T has elapsed. This prohibited time period T starts from the rising edge of the signal. The speed of the vehicle group is calculated based on the time from the rising edge of the set signal waveform to the rising edge of the reset signal waveform (this is referred to as detection time t). That is, as will be described in detail later, the process of measuring the detection time t starts at the rising edge of the set signal and ends at the rising edge of the set signal. However, if the rising point of these signals is within the prohibited time period T that started from the previous rising edge, the measurement of the detection time t will not start from this point, and the measurement of the detection time t will not start from this point. It never ends. If the time point at which the signal rises is within the prohibited time zone T, the timing process for the prohibited time zone T will not start from this point. The timing process for the detection time t and the prohibited time period T is not affected by the falling signal. This makes it possible to measure the speed of one simulated vehicle group during the prohibited time period T. becomes.

The prohibited time period T is of course set to a time longer than the expected detection time t. Since the detection time t is the time required for the vehicle to travel between the set area S and the set area R (distance 2), the traveling speed V of the vehicle is determined by the following equation.

However, K is a constant. The distance that the vehicle actually moves during the detection time t varies slightly depending on the vehicle due to the influence of the vehicle shape, vehicle height, etc., and is actually not equal to the above-mentioned distance j.

However, by imagining a sensing surface at a position above the road surface by the required height, measuring the distance between both areas S and R on this sensing surface, and statistically correcting this distance, it is possible to increase the vehicle's running speed. It is possible to measure with high precision. CPU
The memories 13 and 15 are provided with areas for storing various data in order for the memory 11 to analyze the output signal waveform of the light receiving element.

The memory 13 is provided with an area for storing the current data Dt, the preprocessed data DO, the deviation Δω, and the previous pattern of the set signal indicating whether the change in the previous signal is increased, decreased, or balanced. In addition, there is an area used as a prohibition time counter C1, a balance counter C2, and a vehicle group speed counter C3. The prohibited time counter C1 measures the passage of the prohibited time period T. The equilibrium counter C2 counts the number of consecutive equilibrium states, and the vehicle group speed counter C3 measures the detection time t. Furthermore, the memory 13 includes an area for storing the equilibrium level LC and an area used as the measurement flag F1. The measurement graph F1 is turned on by the rise of the set signal and turned off by the rise of the reset signal. The memory 15 stores in advance various constants, namely, the deviation reference amount ω0, the inhibition time T, the equilibrium judgment value CO, the abnormal feed count number CM, and the rising detection reference amount L1. The abnormal count number is a value corresponding to a speed smaller than the lowest expected vehicle speed, and is a value that is caused by noise contained in the set signal etc.
This is to prevent the switch 1 from remaining on for a long time without being turned off. Rising detection reference amount L1
is a reference value for detecting whether the signal has risen from the equilibrium level LC. Moreover, in the memory 15,
There are an area for storing the change pattern of the signal waveform for each sampling period, an area for storing the final contents of the vehicle group speed counter C3, and an area used as the collection flag F2. The collection flag F2 is turned on when the measurement of the vehicle group speed is completed, and the CPU 12 reads the state of this flag F2 and reads the data in the vehicle group speed data area. FIG. 6 shows the procedure of waveform analysis processing of the set signal by CPUll.

This process is executed every 4.8 mS. First, check whether the content of the prohibition time counter C1 is O (step 2).
1). A prohibition time T is set in the prohibition time counter C1 when a rising edge of the signal is detected, and its contents are decremented by 1 for each process. When the content of the counter C1 is O, it is outside the prohibited time period T. If the content of the counter C1 is not 0, the content of the counter C1 is decremented by 1 (step 22), and the preprocessed data DO is subtracted from the current data Dt to obtain the deviation Δω (step 23). Then, it is checked whether this deviation Δω is greater than or equal to the reference amount ω0 (step 24).
), if Δω≧ω0, it is an increase, so the equilibrium counter C
2 (step 25) and store the increased pattern in the pattern storage area of the memory 15 (step 26).
. Then, it is checked whether the previous pattern was an increase in calories (step 27). If the signal was balanced or decreased last time, there is a possibility that the signal rose, so the level difference Δω1 is calculated by subtracting the balanced level LC from the current data Dt (step 28), and this level difference Δω1 and the rising detection reference amount are calculated. It is compared with L1 (step 29), and if Δω1≧L1, it is regarded as a rising edge. Then, the content of the prohibited time counter C1 is checked (step 30), and if it is outside the prohibited time period T, the process proceeds to step 31 to measure the speed of the vehicle group, and if it is within the prohibited time period T, speed measurement is not started. When measuring the speed, first set the prohibition time T in the counter C1 (step 31), and turn on the measurement flag F1 (step 32).
), clear the vehicle group speed counter C3 (step 3
3). The contents of this vehicle group speed counter C3 are incremented by 1 each time a reset signal is processed, which will be described later, and the detection time t is counted. Then, this time data Dt is converted into preprocessed data D
The preprocessing data is updated as O (step 34), and the current pattern (power increase 0 in this case) is stored in the previous pattern storage area of the memory 13 (step 35), and the process ends. If YES in step 27 and NO in steps 29 and 30, the process immediately moves to step 34. If NO in step 24, the process moves to step 36 and compares the absolute value of the deviation Δω with the reference amount ω0 to determine whether the current pattern is decreasing or balanced.

In the case of a decrease, the balance counter C2 is cleared (step 37), the decrease pattern is stored in the pattern storage area of the memory 15 (step 38), and the process moves to step 34.
In the case of equilibrium, the equilibrium pattern is stored in the memory 15 (
After incrementing the contents of the equilibrium counter C2 by 1 (step 40), it is checked whether the contents of this counter C2 have reached the equilibrium judgment value CO (step 41).
.

If the content of the counter C2 is equal to or greater than the judgment value CO, the current data Dt is set as the equilibrium level LC and the equilibrium level is updated (step 42), and the process moves to step 34.

If NO at step 41, the process directly advances to step 34. FIG. 7 shows the procedure of waveform analysis processing of the reset signal by the CPUll. This process is also executed every 4.8 mS. First, the content of the prohibition time counter C1 is O.
(Step 51) If the content of the counter C1 is not O, the content of the counter C1 is decremented by 1 (Step 52), and it is checked whether the measurement flag F1 is on (
Step 53). If this flag F1 is on, measurement has already started, so the vehicle group speed counter C
Add 1 to the contents of 3 (step 54) and set this counter C.
3 and the abnormal speed count number CM are compared (step 55). If C3≧CM, flag F1 has been set for longer than the expected maximum detection time, so it is determined that there is an abnormality, measurement flag F1 is turned off (step 56), and counter C3 is cleared (step 56). Step 57). If NO in step 53, proceed to step 5.
If the result in step 55 is NO and it is determined to be normal, the process proceeds to step 58 without performing the processes in steps 56 and 57. In step 58, the preprocessed data DO is subtracted from the current data Dt to obtain the deviation Δω.
and checks whether this deviation Δω is greater than or equal to the reference amount ω0 (step 59). If Δω≧ω0, it is an increase, so the balance counter C2 is cleared (step 60), and the increase pattern is stored in the pattern storage area of the memory 15. Remember(
Step 61).

Then check whether the previous pattern was an increase (
Step 62). If the previous data was balanced or decreased, the level difference Δ is calculated by subtracting the balanced level LC from the current data Dt.
ω1 is calculated (step 63), and this level difference Δω1 is compared with the rising edge detection reference amount L1 (step 64).
If Δω1≧L1, it is regarded as a rising edge. Then, the content of the prohibited time counter C1 is checked (step 65), and if it is outside the prohibited time period T, the process proceeds to step 66 for vehicle group speed measurement processing, and if it is within the prohibited time period T, the speed measurement process is not performed. When measuring the speed, first check whether the measurement flag F1 is on (step 67). If flag F1 is on, the set signal has already risen and speed measurement has continued, so to end this, flag F1 is turned off (step 68) and the contents of vehicle speed counter C3 are set as speed data. Vehicle group speed data in memory 15
Transfer to Elijah (step 69). After this transfer process, the collection flag F2 is turned on (step 70). Upon seeing that the collection flag F2 has been turned on, the CPU 12 takes in this speed data and executes processing for calculating vehicle group speed, detecting the degree of congestion, and creating other traffic flow information. When the speed data is captured, the collection flag F2 is turned off. Step 6
2: YES, steps 64, 65, 67: NO
In this case, the process immediately moves to step 71. After the above processing, the preprocessing data is updated by using the current data Dt as the preprocessing data DO (step 71), the current pattern is stored in the previous pattern storage area of the memory 13 (step 72), and the processing ends. If NO in step 59, the process moves to step 73, where the absolute value of the deviation Δω is compared with the reference amount ω0, and it is determined whether the current pattern is decreasing or balanced.

In the case of a decrease, the balance counter C2 is cleared (step 74), the decrease pattern is stored in the pattern storage area of the memory 15 (step 75), and the process moves to step 71.
In the case of equilibrium, the equilibrium pattern is stored in the memory 15 (
Step 76), after incrementing the contents of the equilibrium counter C2 by 1 (steps J and V), it is checked whether the contents of this counter C2 have reached the equilibrium judgment value CO (step 78).
.

If the content of the counter C2 is equal to or greater than the judgment amount CO, the current data Dt is set as the equilibrium level LC and the equilibrium level is updated (
Step 79), then proceed to step 71. If NO in step 78, the process directly advances to step 71. As explained in detail above, according to the present invention, when measuring a group of vehicles in the distance by using an optical system and detecting the rising edge of the video signal, the speed of the group of vehicles is measured by starting from the rising edge of the image signal. It is assumed that the signal of the vehicle group continues during this prohibited time period, and even if the video signal rises during this prohibited time period, it is ignored, so the terminal Even if the vehicle group signal waveform is unpredictable, it is possible to accurately measure the speed of each simulated vehicle group by the prohibited time period.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the installation status of the camera of the traffic flow measurement device.
Figure 2 is an enlarged view of the detection point, Figure 3 is a configuration and block diagram showing the inside of the camera and processing device, Figure 4 is an explanatory diagram showing how the waveform pattern is detected, and Figure 5 is vehicle group speed measurement. 6 and 7 are flow charts showing the vehicle group speed measurement processing means.〇4... Optical system, P1 to P6...
・Detection point, S...Set area, R...
Reset area, DS1 to DS6... Light receiving element, T
...Prohibited time period.

Claims (1)

[Claims] 1 A set area and a reset area are set at a required distance from a predetermined detection point on the road, and a pair of light-receiving elements are placed at a position overlooking the road and detect vehicles in the set area and reset area of the detection point. A method for measuring the speed of a group of vehicles based on the difference in time between the rises of the output video signals of these light receiving elements, the method starts from the rise of the output signal of each light receiving element, and measures the speed of one vehicle group. Set the time required to pass through each area and a simulated prohibited time period,
A vehicle group speed measuring method that measures the vehicle group speed when the rising edge of the output signal of each light receiving element is detected outside the prohibited time period.