JPH0321959B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a traffic flow measuring device used for monitoring vehicle traffic on roads and road networks.

Configuration of conventional example and its problems Figure 1 shows a conventional traffic flow measuring device.
The configuration of this conventional example will be explained below with reference to FIG. In FIG. 1, 1 is a vehicle sensor connected to an ultrasonic transceiver 2, and 3 is a vehicle sensor connected to an ultrasonic transceiver 4. Ultrasonic transceiver 2, 4
is installed on the side strip of the road, facing approximately sideways, or above the center of the lane on the road, facing approximately downward, and detects vehicle travel by emitting ultrasonic signals in the direction of the vehicle travel zone within the lane. It is something. Also,
The vehicle detectors 1 and 3 are housed in a casing or the like attached to a roadside belt, as necessary. The vehicle sensor 3 is installed on the downstream side in the vehicle traveling direction, and the vehicle sensor 3 is installed on the upstream side in the vehicle traveling direction. 5 is a speed calculation unit, 6 is a modulation device,
Reference numeral 7 denotes a demodulating device, and 8 denotes a central device, which are connected to each other as shown in the figure to constitute a traffic flow measuring device.

Note that the speed calculation section 5 and the modulation device 6 are attached to the roadside belt section, and are connected to the demodulation devices 7 and 7a and the central device 8 installed in the traffic control center via a communication line.

Next, the operation of the conventional example having the above configuration will be explained. As shown in the timing chart of the above-mentioned conventional example in FIGS. 2A to 2C, the rising edge of the vehicle presence pulse c of the upstream vehicle sensor 3 is detected by the speed calculation unit 5,
Raise the speed pulse e. Further, by similarly detecting the rising edge of the vehicle presence pulse d from the downstream vehicle sensor 1 in the speed calculation unit 5, the speed pulse e is lowered. Therefore, the pair of vehicle sensors 1
The speed of the vehicle can be detected from the installation distance of 3 and the duration of the speed pulse e. Further, the number of vehicles and the occupancy time can be obtained from the vehicle presence pulse c. That is, the vehicle presence pulse c and speed pulse e are connected to the central device 8 via the modulation device 6 and the demodulation device 7, thereby forming one signal transmission system.
A large number of demodulators 7a and signal transmission systems are connected to the central device 8.

The vehicle detectors 1 and 3 transmit ultrasonic signals T at sampling time intervals of 60 mseo, for example, as shown in FIG. 3A. The ultrasonic signals transmitted from the vehicle sensors 1 and 3 are reflected by the vehicle, and the reflected waves are received by the vehicle sensors 1 and 3 within a predetermined time range, as shown in FIG. 3B. When the reflected wave R is detected within a predetermined time range, a presence pulse _c1 of a predetermined time length (60 msec) is generated after the predetermined time range has elapsed, as shown in FIG. 3C. This operation is performed every 60 msec, and when the reflected wave from the vehicle is always detected, the third
As a result of the occurrence of c ₂ , c ₃ , c _{4 .} . . as shown in FIG. A speed pulse e is set by detecting each rising edge of the vehicle presence pulses c and d. Therefore, the speed pulse e also has a pulse configuration with a sampling time interval of 60 msec. In this way, the vehicle sensor 1,
3 uses an ultrasonic sampling method at regular intervals,
The presence of a vehicle is detected, and therefore it is measured as data in multiples of the sampling period with respect to the continuously changing true vehicle presence signal or speed signal. That is, with respect to the true vehicle presence signal length d _R shown in Fig. 3 d, the measured presence signal length Cm has the measurement value given by ε = τ - (ta + tb) from the ultrasonic period τ and times ta and tb. This inevitably results in an error ε. This also applies to the speed signal determined from the vehicle presence signal. If we convert this further into a statistical formula, we get
The speed measurement error ε is expressed by the following equation from the number of measured vehicles N, the vehicle running speed V, and the ultrasonic transceiver installation interval _L0 .

That is, when the number of measured vehicles N〓 is constant, the higher the vehicle speed, the shorter the ultrasonic transceiver installation interval _L0 , and the longer the ultrasonic period τ, the more the measurement error tends to increase. However, in current traffic flow measurement devices, the ultrasonic period τ is substantially restricted by the road width configuration or the mounting height above ground.
Normally, a value of about 60 msec is commonly used. or,
The vehicle running speed V and the number of vehicles to be measured N〓 are determined by the traffic situation and are the objects to be measured. Therefore, the ultrasonic transceiver installation interval L ₀ remains a factor that improves speed measurement accuracy, but usually
L ₀ will be fixed at approximately 5 meters. This is to prevent multiple vehicles from entering between a pair of ultrasonic transceivers, especially during rush hours.

As is clear from the above, in current traffic flow measurement devices, the installation interval of ultrasonic transceivers is fixed, and the sensitivity to changes in vehicle speed and tolerance for error are narrow, resulting in large reading errors and problems. I was getting used to it.

Purpose of the Invention The present invention eliminates the drawbacks of the above-mentioned conventional example, and even if the ultrasonic transceiver installation interval is fixed,
It is an object of the present invention to provide an excellent traffic flow measuring device that can have a wide sensitivity to changes in vehicle speed and a wide tolerance range for errors, so that even when the vehicle speed is high, the reading error is small.

Composition of the Invention In order to achieve the above object, the present invention arranges a second ultrasonic transceiver on the downstream side, which has a wider installation interval with the upstream transceiver, in a pair of upstream and downstream ultrasonic transceivers. Depending on the average speed of the vehicle, the first ultrasonic transceiver installed at normal installation intervals is used when the vehicle is running at low speeds, and the second ultrasonic transmitter and receivers installed at widely spaced intervals are used when the vehicle is running at high speeds. Since the switching section is provided, highly accurate speed measurement can be achieved even when the vehicle speed becomes high.

DESCRIPTION OF EMBODIMENTS The configuration of an embodiment of the present invention will be described below with reference to the drawings. FIG. 4 is a block diagram of a traffic flow measuring device according to an embodiment of the present invention, and FIG. 5 is a graph showing the effects of this embodiment.

In FIG. 4, reference numerals 11 and 12 indicate ultrasonic transceivers, which are connected to the downstream vehicle sensor 9 via a switching unit 10. The first ultrasonic transceiver 11 is located downstream in the traveling direction of the vehicle 13 with respect to the upstream ultrasonic transceiver 4.
For example, it is arranged at a position of 5 meters in the same manner as before. The second ultrasonic transceiver 12 on the downstream side is disposed further downstream of the first transceiver 11, for example, at a position 15 meters from the transceiver 4. In FIG. 4, 14 is a speed calculation section, which is a conventional speed calculation section 5 (third
Although the configuration is substantially the same as that shown in Figure), in this example, the speed pulse e is set according to the transmitter/receiver installation interval of 5 meters and 15 meters for the same sampling time interval of 60 ms. Note that the demodulators 7, 7a and the central device 8 are the same as those of the prior art. Reference numeral 10 indicates a switch between the ultrasonic transceivers 11 and 12.

Next, the operation of the above embodiment will be explained.
When the average running speed of the vehicle 13 is low,
The switch 10 is set on the contact 10a side as shown in FIG. 4, and the transmitter/receiver 11 disposed at a position 5 meters from the upstream transmitter/receiver 4 is used. Furthermore, when the average running speed of the vehicle is high, the switch 10 is set to contact 1.
0b side, and use the handset 12 located 15 meters from the handset 4.

In order to make it easier to understand the effects of the present invention, the operation will be explained with reference to FIG. FIG. 5 is an explanatory diagram of the embodiment shown in FIG. 4, and shows the relationship between vehicle running speed and speed measurement error with the ultrasonic transceiver installation interval L ₀ as a parameter when the number of measured vehicles N is constant. shows. As shown by the broken line in the figure, in the case of the conventional system where the installation interval L ₀ = 5 meters, the error increases significantly as the vehicle speed increases, whereas in the embodiment of the present invention, when the vehicle speed is low In the case of , when the high speed is on the contact 10a side of the switch 10,
By operating on the contact 10b side, it is possible to improve the measurement accuracy in the high speed range as shown by the solid line in the figure.

Note that the operation of the switching unit 10 may be switched based on the average speed of the vehicle 13, or may be switched based on the occupancy time (occupancy) of the vehicle.

Effects of the Invention As is clear from the above embodiments, the present invention provides a pair of upstream and downstream ultrasonic transceivers with a second downstream ultrasonic transceiver whose installation interval with the upstream transceiver is set wider. Depending on the average speed of the vehicle, the first ultrasonic transceiver installed at normal installation intervals is used when the vehicle is running at low speeds, and the second ultrasonic transmitter and receivers installed at widely spaced intervals are used when the vehicle is running at high speeds. Since the switching section is provided, it has the effect of realizing highly accurate speed measurement even when the vehicle speed becomes high.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional traffic flow measurement device.
FIG. 2 is a timing chart explaining the operation of a conventional example, FIG. 3 is an explanatory diagram of conventional vehicle presence pulse generation, FIG. 4 is a block diagram of a traffic flow measuring device according to an embodiment of the present invention, and FIG. 5 is a graph showing the effect of this example. 3... Upstream vehicle sensor, 4... Upstream ultrasonic transceiver, 6... Modulator, 7... Demodulator, 8...
...Central device, 9...Downstream vehicle sensor, 10...
Switching unit, 11, 12... Ultrasonic transceiver, 13...
Vehicle, 14...speed calculation section.

Claims (1)

[Claims] 1. Upstream vehicle sensor 3, downstream vehicle sensor 9,
The upstream vehicle sensor 3 includes a speed calculation unit 14, a modulation device 6, a demodulation device 7, and a central device 8, and is installed around the road.
It has an upstream ultrasonic transceiver 4 that transmits and receives ultrasonic waves to and from the vehicle traffic zone, and the downstream vehicle sensor 9 is installed downstream of the upstream ultrasonic transceiver 4 with respect to the traveling direction of the vehicle and transmits ultrasonic waves. a first downstream ultrasonic transceiver 11 that transmits and receives
A second downstream ultrasonic transceiver 12 that is installed further downstream from the first downstream ultrasonic transceiver 11 and transmits and receives ultrasonic waves, and these first and second downstream ultrasonic transceivers 11 and 12 The speed calculation unit 14 calculates the time difference between the output signals of the upstream ultrasonic transceiver 4 and the downstream ultrasonic transceiver 9. The modulation device 6 inputs the output signals of the speed calculation unit 14 and the upstream vehicle sensor 3 and modulates them into signals that can be communicated to the communication line. The demodulation device 7 The central device 8 is to demodulate the signal of the line, and the central device 8 is to aggregate the data signals of the demodulator 7. The speed calculation unit 14 is to operate the switch 10 when the average speed of a plurality of vehicles is lower than the reference value. A traffic flow measurement device that connects a switch 10 to a first downstream ultrasonic transceiver 11 and connects a switching device 10 to a second downstream ultrasonic transceiver 12 when this average speed is faster than a reference value.