Traffic congestion monitoring system

This invention relates to a traffic congestion monitoring system.

It is conventional to advise police or highway officials of traffic congestion upon main roads by monitoring such congestion visually or by closed-circuit television for example. It is also conventional to advise drivers of congestion locations by broadcasting details of such congestion locations on ordinary or special radio channels to which conventional vehicle radios can be tuned. A drawback of such conventional systems for the drivers is the time delay between the build-up of congestion at a location and the communication of that information to the driver, often with the result that he is unable to avoid that location. The time delay may be worsened by the facts that the broadcasting announcer naturally has to give information about the congestion locations in turn, which also means that the driver has to carry the information in his mind in order to be able to work out a route avoiding all of the congested locations. Moreover, only serious congestion locations may be identified in the announcement, to reduce the interruption of ordinary broadcasting. The transient and aural nature of the presentation of the information to the driver mean that if the driver is not listening to the broadcast or cannot hear the broadcast (for example because the vehicle is in a tunnel or because a passenger is talking to him) when the information is given, he has to await the next bulletin.

Another drawback is that the monitoring involves employing personnel continuously to watch the locations.

GB-A-2050767 discloses a traffic information apparatus comprising a radio receiver provided with a detector for separating received traffic information from other received radio signals, a store for the separated traffic information and a display device for presenting the traffic information. The traffic information may be phase modulated onto normal amplitutde modulated radio signals.

Three different radio-receive traffic information apparatuses are disclosed. In the first version the traffic information has stores associated with individual traffic regions, in which the traffic information associated with the different traffic region is stored and can be visually reproduced with the associated traffic region. The selection of the particular traffic region can be made with the aid of a control stage. This version is suitable for incorporation in, for example, motor vehicles. In the visual reproduction of the traffic information according to this version, reference is made to blocked motorway sections, for example by cross symbols thereon, where these symbols could also be coloured.

A second version is disclosed as an indicator board for the reproduction of the traffic information of an entire motorway network. Such a version is disclosed as being suitable for informing vehicle drivers at parking places, stopping places and in service areas as are to be found on motorways.

The third version disclosed speech-reproduction of the traffic information by a loudspeaker.

It also discloses that digitally coded traffic information can be transmitted from any type of existing radio transmitters wherein up to about 200 bits per second can be transmitted without leading to an adverse effect on the radio transmission proper. On the receiving side, normal radio receivers can be used which can be supplemented by a phase detector, a programmable switching stage, formed for example as a micro-processor, and an output unit provided with a videotext or viewing screentext decoder or a language computer. In so doing it is of advantage to incorporate stores in the output unit in which the entire motorway or road network is permanently stored so that only hold-ups or blockages need be transmitted as traffic information.

It further discloses that a narrow band width for the transmission of the traffic information is achieved when a batch of complete items of traffic information is repeatedly transmitted at predetermined time intervals and alterations in the batch of complete items of traffic information are continually transmitted.

EP-B-0029201 states that contemporaneously detectors at key positions in the road system were used to record the traffic situation by determining the number, direction, speed and, possibly, type of vehicles passing, and measuring time intervals and traffic density and that those figures allowed indirect conclusions to be drawn as to the volume of traffic on whole sections of road, although those readings only provided information on the traffic conditions of the narrow cross section measured; for example, a traffic obstruction between two measuring points some distance apart would not register providing the traffic kept flowing in front of and behind those measuring points.

EP-B-0029201 is directed to a system for collecting information about traffic congestion and based on the installation of guidance computers and their associated infrared transceivers, since it is the emission of signals from the guidance computers in the vehicles to roadside beacons that enables the system to monitor congestion levels.

According to a first aspect of the present invention, there is provided a traffic congestion information-supplying system, comprising transmitting means arranged to transmit signals representing information as to traffic congestion at a location through which a main road extends, and receiving means carried by traffic units and arranged to receive the transmitted signals and to present said information at the traffic units carrying said receiving means, characterised in that said system further comprises a multiplicity of electronic detecting means at respective locations through which said main road extends and serving automatically to detect speed of stationary or slow-moving traffic units at the respective locations and to emit said information in the form of varying information representing varying average speeds, including differing average speeds above zero, at said locations, whereby said system is adapted to monitor level of traffic congestion, in that said system is so arranged that said information is transferred from said detecting means to siad transmitting means, in that some of said detecting means are arranged to detect such traffic units travelling in one direction along said main road and others of said detecting means are arranged to detect other such traffic units travelling in the opposite direction along said main road; in that said transmitting means serves to transmit signals representing said information relating to the multiplicity of locations, and in that said receiving means includes presenting means arranged to present such varying information relating to the multiplicity of locations in a manner in which traffic congestion in said one direction is distinguished from traffic congestion in said opposite direction.

According to a second aspect of the present invention, there is provided a traffic congestion information-supplying method, comprising transmitting, by transmitting means, signals representing information as to traffic congestion at a location through which a main road extends, receiving the transmitted signals at traffic units and presenting said information at the traffic units, characterised in that said method further comprises monitoring level of traffic congestion by automatically detecting, by detecting means, speed of stationary or slow-moving traffic units at a multiplicity of locations and emitting said information in the form of varying information representing varying average speeds, including differing average speeds above zero, at said locations, with distinction between traffic units travelling in one direction along said main road and other traffic units travelling in the opposite direction along said main road, in that said information is transferred from said detecting means to said transmitting means, said transmitting consisting of transmitting signals representing said information relating to the multiplicity of locations, and said presenting consisting of presenting such varying information relating to the multiplicity of locations in a manner in which traffic congestion in said one direction is distinguished from traffic congestion in said opposite direction.

Owing to the invention, it is possible to obtain more accurate and reliable information as to traffic congestion on one or more main roads and to present that information more effectively to drivers of such traffic units. Moreover, personnel are not needed to watch the locations.

Further owing to the invention, the system and the method can be such that it is possible immediately, visually and during all the time period of relevance, to advise drivers of traffic units' average speed at a plurality of locations simultaneously.

In order that the invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- <ul id="ul0001" list-style="none" compact="compact"><li>Figure 1 shows diagrammatically a traffic congestion monitoring system,</li><li>Figure 2 shows diagrammatically electrical circuitry of one of a plurality of identical monitoring units of a traffic congestion monitoring system,</li><li>Figures 3a and 3b are a diagrammatic side elevation and a diagrammatic plan view, respectively, illustrating detection of vehicle speed by one of the monitoring units,</li><li>Figure 4 shows diagrammatically electrical circuitry of one of a plurality of identical paging units of the system,</li><li>Figures 5a and 5b are a front elevation of one of the paging units, with a screen thereof displaying the whole of the London motorway network and a North-Eastern quadrant thereof, respectively, and</li><li>Figure 6 shows a modified version of the monitoring unit.</li></ul>

The system of Figure 1 comprises three types of components, namely monitoring units 1 each as shown in Figures 1 and 2, a control centre 2 and paging units 3 each as shown in Figures 4 and 5.

Respective monitoring units 1 each as shown in Figure 1 are bolted to the sides of bridges 4 over one carriageway 5 of each of the motorways (M1 etc) shown on the screen 6 in Figure 5<u>a</u>. Although shown positioned over an intermediate - speed lane 5 in Figure 1, the unit 1 is preferably positioned over the highest-speed lane 5". Each monitoring unit 1 is compact (eg 400 mm x 280 mm x 150 mm). Access to the unit 1 for maintenance is from the bridge 4. Each unit 1 includes an active infra-red detector 7 and is connected to another detector in a remote housing (not shown) which is positioned above the other carriageway 8 to enable the unit 1 to report hold-ups in either direction.

The detectors 7 are mounted about 35ft above the traffic. Each detector 7 produces two obliquely downwardly directed beams 7' and 7" of infrared radiation each extending across the width of the lane 5'. As a vehicle V travelling in the direction A of traffic flow intercepts the first beam 7', the detector 7 emits a first electrical signal which is passed via a line 8 to a computer kernel 9 and, as the vehicle intercepts the second beam 7", the detector emits a second signal which is again passed via the line 8 to the kernel 9. The kernel 9 includes a data logger 10 comprising a 256K byte RAM backed by a battery 11 through a power supply unit 12. The kernel also includes a timer which measures the time interval between the two signals, such time interval naturally representing the speed of the vehicle V, and, if the time interval is greater than a threshold value corresponding to, say, 25mph, in other words the speed is less than 25mph, as an average for the vehicles passing during a given time period of, say, three minutes, the kernel 9 sends a message to a modem 13 the output of which is connected by a telephone line 14 to the control centre 2. The timer is adjustable to set the threshold value. Connected to the kernel 9 is a bank 15 of identify (ID) switches and each monitoring unit 1 has its own individual identity given by selection of an individual ID switch. The first part of each message emitted by the kernel 9 is the address of the individual unit 1 as determined by the selected switch. Also connected to the kernel 9 is a tamper sensor 16 which causes the kernel 9 to send an alarm message to the control centre 2 if the unit 1 is tampered with. By way of a line 17, the kernel 9 monitors the output voltage of the battery 11 and, if the voltage falls below a desired level, the kernel sends a warning message to the centre 2.

In an alternative version (not illustrated), each monitoring unit 102 employs, instead of active infra-red detectors, a passive infra-red detector 103 which thus detects motor vehicles stationary or moving at or below, say, 15 mph from the infra-red radiation emitted by the vehicles. The detector 103 detects a radiation with a wavelength of approximately 9 Microns in three zones. Each detector 103 when operated closes contacts to provide current from a 12v battery 104 to energize a timer 105. The timer 105 not only detects the time interval between infra-red radiation pulses provided by respective passing motor vehicles, and thus the pulse frequency, but also emits a signal when the pulse frequency falls below a threshold value for a set time period. The timer is adjustable to set the threshold value and the time period, and thus the sensitivity of the unit 102 to the degree of congestion,. The timer 105 can handle simultaneous signals from the detector 103 and the remote detector (not shown). When the timer detects that the threshold value has been undershot for the set time period, it acts to energize a relay 106 to close the relay contacts to energize a cellular telephone transmitter 108, for example. The respective outputs from the timer are connected to a signal generator 107 and a remote signal generator (not shown). Coded messages are sent by the signal generators via the transmitter 108 to the control centre 2.

For the remote detector, a different identifying signal is employed. Should there be congestion in both directions, two differing signals are emitted or transmitted.

The control centre 2 in this example covers the London area motorways. Up to 100 units 1 may be deployed in this area. Messages will be transmitted by the telephone lines 14 from the monitoring units to the control centre. At the control cente 2 is a control operator 18 watching a VDU (Visual Display Unit) 19. As an address/speed message arrives at the centre, the address, the speed and the time of day are displayed upon the VDU screen and are logged into a computer data base at the centre 2.

The address enables the operator 18 to identify the monitoring unit that is reporting to him. Upon receipt of the message and by way of a keyboard 20, the operator keys into a direct input paging service computer 21 stating the location of the traffic hold-up. The paging service computer immediately emits messages which are transmitted via VHF to the units 3.

In an alternative version, the messages received at the control centre may be used automatically to operate the paging service, an operator possibly maintaining merely a supervisory role.

The messages transmitted by the paging service each comprise firstly a code to activate all of the units 3, secondly a code representing the hold-up location and thirdly a code representing vehicle speed.

Subscribing drivers would receive accurate, immediate congestion information through paging units 3 linked in a pager network. Motoring organisations and police could also have access to the information from the control centre 2.

Referring to Figures 4 and 5, each paging unit 3 is mounted immediately in front of a driver of a vehicle, for example either at the dashboard or at eye level, and in the embodiment shown is a portable unit. Each unit 3 includes an antenna 22 of a VHF receiver 23, the output from which is fed to a POCSAG decoder 24. The output signals from the decoder 24 are fed to a computer kernel 25 supplied with power by a power supply unit 26 containing a rechargeable battery. Connected to the kernel 25 are an operating key pad 27 and a liquid crystal display device 28 including the screen 6. The pad 27 and the device 28 both have electroluminescent back lighting arrangements for night-time use and powered through a common line 29. The line 29 and a power supply input line 30 have input terminals in a plug 31 insertable into a fixed socket 32 and thereby connectible with a main battery of the vehicle via a backlight driver 33 and a battery charging control device 34. Connected to the kernel 25 is a battery temperature sensor 35 which monitors the state of charge of the battery in the unit 26 and causes the kernel 25 to produce a warning on the screen 6 in the event of it falling below a desired minimum. Also connected to the kernel 25 is a temperature sensor for the device 28, whereby the kernel 25 automatically varies the display contrast with temperature variation. By way of a line 36, the kernel 25 monitors the output voltage of the battery in the unit 26 and, if the voltage falls below a desired level, the kernel causes a warning to appear upon the screen 6.

The paging unit 3 carried by each motor vehicle emits an audible tone when the information is received. It then displays simultaneously on the illuminated screen 6 the locations of particular hold-ups to enable the driver to take avoiding action. The display consists of the outline map of the motorway network. Any area of congestion is illuminated to warn the driver immediately. A different colour illuminates depending on which carriageway is affected. The map in Figure 5<u>a</u> is divided into four quadrants, marked NW (North-West), NE (North-East), SW (South-West) and SE (South-East), which are stored in the kernel 25 and any one of which can be brought to occupy the whole screen 6, as in Figure 5<u>b</u>, automatically or manually. In automatic display of a single quadrant, once a location of congestion has been illuminated on the whole map in Fig. 5a, after a short time, say four seconds, the quadrant containing the congestion location replaces the whole map in the display. In manual display of a single quadrant, any one of four keys 37 arranged in a pattern and an orientation corresponding to those of the quadrants can be depressed to bring the corresponding quadrant to occupy the screen. At the illuminated congestion location on the screen 6, there is displayed the vehicle speed at that location, as shown in Figure 5<u>b</u> where the framed numeral 20 represents 20 mph. Various officially numbered junctions (J7, etc.) are also shown to enable the driver to judge more reliably at which particular junctions to leave or join the motorway to avoid the congestion location.

Included in the keypad 27 is an on/off key 38, upon the operation of which to switch on the paging unit 3, the whole map appears upon the screen 6, a standby key 39 whereby the unit can be caused to store congestion information from received messages but not to display the same, whereby battery power which would otherwise be used to energize the display device 28 is saved, and a message key 40 whereby, if the paging service additionally transmits personal messages to the driver in a conventional manner, these messages can be displayed upon the screen 6 in place of the traffic congestion information. In this personal message mode, the four keys 37 are operable to cause the screen 6 to display an index of stored personal messages (INDEX), to enable the driver to review selected ones (REVIEW), to enable the driver to delete selected ones (DELETE) and to enable the driver to protect oldest personal messages against automatic deletion (PROTECT), such key functions being conventional in conventional personal message paging units.

The communication arrangements are as follows:- <ul id="ul0002" list-style="none" compact="compact"><li>1. Any monitoring unit 1 or the control centre 2 may initiate communication.</li><li>2. A reply is expected to any communication.</li><li>3. Every monitoring unit is assigned a unique addres.</li><li>4. Every monitoring unit 1 may be fitted with two detectors 7, one for the Northbound (or Eastbound) lane, the other for the Southbound (or Westbound) lane.</li><li>5. Communication of a message in either direction takes the form:-    STX, ADDRESS, COMMAND, DATA (2 bytes), ETX, LRC</li><li>6. The LRC is the Exclusive OR of all data bytes inclusive kof STX and ETX.</li><li>7. The communications operate at 600 or 1200 baud.</li><li>8. Data Communications. <ul id="ul0003" list-style="none" compact="compact"><li>a) Status Test - the control centre 2 to a monitoring unit 9:- The control centre 2 interrogates the monitoring unit; the monitoring unit replies. <ul id="ul0004" list-style="none" compact="compact"><li>The monitoring unit checks the transfer for errors and accepts or rejects the transfer by sending a message reply or by sending NAK. If the mmonitoring unit sends NAK the interrogation is repeated. The process is repeated up to three times before disconnecting the line.</li><li>The control centre checks the transfer for errors and accepts or rejects the transfer using ACK or NAK. If the control centre sends NAK the transfer is repeated.</li><li>The process is repeated up to three times before declaring a link error at that address.</li><li>If the monitoring unit NAK'ed three times, it disconnects the line.</li><li>If the monitoring unit fails to reply within a specific time, a time-out error is declared at that address.</li><li>If a connection is established but a transfer is not completed, the monitoring unit disconnects the line after a time-out.</li></ul></li><li>b) Transfer from a monitoring unit 9 to the control centre 2:- <ul id="ul0005" list-style="none" compact="compact"><li>The monitoring unit initiates the transfer and the control centre replies.</li><li>If a monitoring unit attempts to make a connection to the control centre but finds the control centre's line busy, then it releases the line and repeats the attempt after a random time not exceeding two minutes.</li><li>The control centre checks the transfer for errors and accepts or rejects the transfer using ACK or NAK. If the control centre sends NAK the transfer is repeated.</li><li>The process is repeated up to three times before declaring a link error at that address.</li><li>If a monitoring unit is NAK'ed three times, it disconnects the line and repeats the attempt after a random time not exceeding two minutes.</li><li>If the monitoring unit fails to reply within a specific time, a time-out error is declared at that address.</li><li>If a connection is established but a transfer is not completed, the monitoring unit disconnects the line after a time-out.</li></ul></li></ul></li><li>9. Monitoring Unit <ul id="ul0006" list-style="none" compact="compact"><li>The monitoring unit monitors the infra-red detector for correct operation. If one sensor consistently fails to operate an error code is included in the reply to the Status Test.</li><li>The speeds for Northbound and Southbound lanes are included in the reply to the Status Test and speeds of 0 to 70 mph are identifiable in 5 mph increments.</li><li>Vehicle speeds are computed in one minute increments. The average speed is computed over the three minutes, to give a rolling average of the last three minutes.</li></ul></li></ul><ul id="ul0007" list-style="none" compact="compact"><li>10. Control Centre <ul id="ul0008" list-style="none" compact="compact"><li>Each time a monitoring unit 9 reports that speeds are below the threshold, a message is displayed on the VDU screen and on a printer.</li><li>The control centre undertakes a Status Test to each monitoring unit periodically at a desired frequency.</li><li>Each time a Status Test is sent to a monitoring unit and error conditions are detected, a message is displayed and printed.</li><li>Failure of the communications link results in a message being displayed and printed.</li><li>The control centre holds on disc a site history for each monitoring unit, the site history containing two separate files: <ul id="ul0009" list-style="dash" compact="compact"><li>vehicle speeds vs calendar time</li><li>errors and fault logging.</li></ul></li></ul></li></ul>

The system hereinbefore described has the advantages that reliable reports of traffic delays are immediately given to drivers, so that they have sufficient warning to take avoiding action, and that the system can be installed and maintained without excavating the carriageways and causing further congestion.