Title of Invention: TRAFFIC SIGNAL CONTROL SYSTEM AND

METHOD

Technical Field

[1] The present invention relates to a traffic signal control system and method; and, more particularly, to a system and method for intelligently controlling traffic signals based on traffic information reflecting various traffic and road conditions. Background Art

[2] As the number of automobiles, buses, trucks, or other types of vehicles around the world continues to grow, the task of solving traffic congestions caused by flooding of these vehicles has surfaced as a major challenge to today's societies.

[3] In efforts to attenuate the traffic congestion problem, there have been provided traffic signal control systems which purport to correct an imbalance between congested and less-congested roads.

[4] For instance, directional controls of conflicting traffic flows at an intersection may be made in a programmed sequence based on historical data accumulated through repetitive signal cycles. Such a history -based control system, however, is incapable of handling presently erupted anomalous traffic conditions and fails to alleviate traffic congestions caused thereby.

[5] Recently, the advancement in information and communications technologies has led to the advent of a traffic signal control system which acquires, manages and utilizes traffic information of a road based on the current positions of vehicles on the road, the vehicle positions being normally detected through the Global Positioning System (GPS). As is well known, however, GPS may not work in a tunnel or an underground road and may offer rather erratic information.

[6] Accordingly, there has existed a need for a traffic signal control system which is designed to operate, based on accurate traffic information provided even under adverse communications environments, to thereby effectively control traffic signals. Disclosure of Invention

Technical Problem

[7] It is, therefore, an object of the present invention to provide a traffic signal control system which acquires, manages and utilizes traffic information of a road section based on current positions of vehicles travelling on the road section and other traffic and road conditions thereof, thereby controlling traffic signals in an efficient manner and ameliorating traffic congestion.

[8] It is another object of the present invention to provide a traffic signal control method for intelligently controlling traffic signals on a road section based on traffic information derived from current positions of vehicles travelling on the road section and other traffic and road conditions thereof. Solution to Problem

[9] In accordance with one aspect of the present invention, there is provided a traffic signal control system for controlling a traffic signal for one or a plurality of vehicles travelling on a road section, comprising: an under-road communications unit for providing each of said one or plurality of vehicles on the road section with location information; a vehicle communications unit, installed in or attached to said each vehicle, for determining a position of said each vehicle based on the location information to generate travel information including the ID and the position of said each vehicle; a road-periphery communications unit, installed in a vicinity of the road section, for receiving the travel information to generate traffic information including the number of said one or plurality of vehicles travelling on the road section based on the travel information; and a traffic signal control unit for receiving the traffic information to thereby control the traffic signal based on the traffic information.

[10] In accordance with another aspect of the present invention, there is provided a traffic signal control method for controlling a traffic signal for one or a plurality of vehicles travelling on a road section, comprising the steps of: providing each of said one or plurality of vehicles on the road section with location information; determining a position of said each vehicle based on the location information; acquiring travel information including the ID and the position of said each vehicle; generating traffic information including the number of said one or plurality of vehicles on the road section based on the travel information; and controlling the traffic signal based on the traffic information. Brief Description of Drawings

[11] Fig. 1 shows a configuration of a traffic signal control system in accordance with an embodiment of the present invention and Fig. 2 is a schematic version thereof.

[12] Fig. 3 presents a traffic signal control system of the present invention which operates to control traffic flows at an intersection.

[13] Figs. 4 and 5 illustrate traffic flows controlled by the traffic signal control system of

Fig. 3 embodying the inventive features of the present invention.

[14] Fig. 6 provides a flowchart of an exemplary process which is performed in the traffic signal control unit of Fig. 3, in accordance with an embodiment of the present invention. Mode for the Invention

[15] Hereinafter, some of the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[16] Fig. 1 shows a configuration of a traffic signal control system in accordance with an embodiment of the present invention and Fig. 2 is a schematic version thereof.

[17] As shown in Figs. 1 and 2, the traffic signal control system 100 includes an under- road communications unit 101, a vehicle communications unit 102, a road-periphery communications unit 103, and a traffic signal control unit 104, all of which are discussed in detail below.

[18] As depicted in Fig. 1, the under-road communications unit 101 provides each vehicle

112 on a road section 122 with location information from which the position of each vehicle 112 can be determined.

[19] The under-road communications unit 101 may transmit the location information at a fixed time interval, regardless of the presence of a vehicle on the road section 122, or only when there is detected at least one vehicle passing over it.

[20] The inventive traffic signal control system 100 may be employed in a variety of traffic systems. For instance, it may be integrated into an electromagnetic induction- powered electric vehicle system, an example of which can be found in U.S. Patent No. 5,669,470. In such electromagnetic induction-powered electric vehicle system, a power supply line may be embedded under the road section 122 along the mid-line of each lane on the road section 122 for supplying power to an electric vehicle travelling thereover. The under-road communications unit 101 may include a magnetic inductor, which is operatively connected to the power supply line which supplies power to the electric vehicle through magnetic induction. By way of detecting a change in the magnetic inductance of the power supply line, it would be possible to determine whether or not an electric vehicle is passing over the under-road communications unit 101.

[21] The under-road communications unit 101 may employ any one of the available magnetic and/or electric field communications techniques that may be suitable for transmitting the location information. For example, a pulse- width modulation technique may be used to transmit the location information.

[22] As shown in Fig. 1, a plurality of under-road communications units may be embedded under the road section 122 along the mid- line of each lane on the road section 122, or along one side-line of each lane. Needless to say, other types of arrangements of the under-road communications units may be also possible.

[23] Still referring to Figs. 1 and 2, the vehicle communications unit 102 installed in or attached to each vehicle 112 receives the location information to determine the position of each vehicle 112, generates travel information including the position of each vehicle 112, and transmits the travel information to the road-periphery communications unit [24] The vehicle communications unit 102 can determine the position of each vehicle 112 based on the location information received from the under-road communications unit 101, by way of, e.g., comparing the location information with map data stored in the vehicle communications unit 102.

[25] The vehicle communications unit 102 generates the travel information which may include the ID, the position, and the travel speed of each vehicle 112. Further, in case each vehicle 112 is participating in a group-driving, by which it is meant a mode of driving engaged by a group of vehicles travelling in tandem on a road, while maintaining a safety distance therebetween, the travel information may include group- driving information, such as the group ID, the number of vehicles in the group, the ID of the leading vehicle in the group (i.e., the foremost vehicle in the travelling direction of the group), the average length of a vehicle in the group, the safety distance between two neighboring vehicles in the group, the speed of the group, and so on.

[26] The road-periphery communications unit 103, which may be installed in a vicinity of the road section 122, receives from the vehicle communications unit 102 the travel information of each vehicle 112, generates traffic information of the road section 122 based on the travel information and transmits the traffic information to the traffic signal control unit 104.

[27] The traffic information may include information on: the number of vehicles on the road section 122; inter- vehicular separation time, indicating the time required for a vehicle to reach a present position of an immediately preceding vehicle; and group- driving preservation information, indicating the time required for all of the vehicles engaged in a group-driving to completely pass the road section 122.

[28] The traffic volume information can be generated by way of counting the total number of vehicles currently on the road section 122. As stated above, travel information may include the ID of a vehicle on the road section 122. By way of counting the number of the distinct IDs included in the travel information, being transmitted from the vehicle communications unit 102 attached to or installed on each vehicle 112, the total number of vehicles currently on the road section 122 can be obtained. As an alternative thereof, or in combination therewith, the road-periphery communications unit 103 may count the number of vehicles per lane on the road section 122. In addition, the road-periphery communications unit 103 may classify the traffic volume information into a plurality of traffic volume levels N _q As the step size of the traffic volume levels is set to a smaller value, the traffic signal control unit 104 can reflect the current traffic condition of the road section 122 more accurately in controlling the traffic signals 105.

[29] The inter- vehicular separation time information, i.e., the time interval T _mter vai required for a given vehicle to reach a present position, e.g., the end point of a road section, of an immediately preceding vehicle, can be obtained with the following equation (1): [30] L interval

, ι \ _t - XJ' - ' V _! - \ _ϋ - _i - - : 2. - 2 ₃ l' \\

[31] where X _f is the X coordinate value of the preceding vehicle, Y _f is the Y coordinate value of the preceding vehicle, Z _f is the Z coordinate value of the preceding vehicle, X _b is the X coordinate value of the given vehicle, Y _b is the Y coordinate value of the given vehicle, Z _b is the Z coordinate value of the given vehicle, and V _b is the speed of the given vehicle.

[32] If the time interval T _mterval is greater than a predetermined threshold value T ₁₁₁ , the traffic signal control unit 104 can assume that there would be no vehicle passing, e.g., the end point of the road section 122 within the next T ₁₁₁ time interval; and, therefore, can control the traffic signals 105 accordingly, as will be described in detail later.

[33] As stated above, the group-driving information included in the travel information, which is transmitted from the vehicle communications unit 102 installed in or attached to each of the vehicles engaged in a group-driving, includes the group ID, the number of vehicles in the group, the ID of the leading vehicle in the group, the average length of a vehicle in the group, the safety distance between two neighboring vehicles in the group, and the speed of the group, etc. The road-periphery communications unit 103 may estimate the time T _gn ,^ required for all of the group-driving vehicles to pass the end point of the road section 122, as given by the following equation (2): X ^Λ + ' r ¹ ^> group W/' ^γ group?

[35] where N _grO up is the number of vehicles in the group, L _group is the average length of a vehicle in the group, D^ _p is the safety distance between two neighboring vehicles in the group, and the V _group is the speed of the group. Then, the road-periphery communications unit 103 generates group-driving preservation information including the time Tgroup and transmits it to the traffic signal control unit 104.

[36] The road-periphery communications unit 103 may provide the traffic signal control unit 104 with the traffic information periodically with a specified period T _u As the time period T _u is set to a smaller value, the traffic signal control unit 104 can reflect the current traffic conditions of the road section 122 more precisely in controlling the traffic signals 105.

[37] The traffic signal control unit 104 receives the traffic information, which may include the traffic volume information, the inter- vehicular separation time information and the group-driving preservation information, from the road-periphery communications unit 103, and intelligently controls the traffic signals 105 connected thereto based on the traffic information. [38] For example, the traffic signal control unit 104 may dynamically set the turn-on duration of the green light to be in proportion to the number of vehicles on the road section 122 based on the traffic volume information.

[39] Further, if the traffic volume information indicates that no vehicle on the road section

122 waits for the green light, the traffic signal control unit 104 may flexibly control the turn-on duration of the green light, while overriding a history -based traffic signal control program.

[40] Although all of the above embodiments of the present invention have been explained under the assumption that the road section 122 forms a part of a one-way road where all of the vehicles travelling thereon are heading to one direction, it should be understood by those skilled in the art that the traffic signal control system of the present invention can be equally applied for a bidirectional road and also an intersection, as further explained in conjunction with Figs. 3 to 6.

[41] As shown in Fig. 3, the traffic signal control system of the present invention can be used for controlling the traffic signals 105a to 105d at an intersection 220 of bidirectional road sections 222a to 222d.

[42] Referring to Fig. 3, vehicles on each of the road sections 222a to 222d may be passing through or stopped before the intersection 220 depending on the status of the traffic signals 105a to 105d controlled by the traffic signal control unit 104.

[43] As shown in Fig. 3, the traffic signal control unit 104 may receive from road- periphery communications units 103a to 103d traffic information of the road sections 222a to 222d, respectively, to thereby intelligently control the traffic signals 105a to 105d. In addition, the traffic signal control unit 104 may periodically receive the traffic information from the road-periphery communications units 103a to 103d at an interval of, e.g., the time period T _u .

[44] Figs. 4 and 5 illustrate traffic flows controlled by the traffic signal control system of

Fig. 3 embodying the inventive features of the present invention.

[45] As shown in Fig. 4, assuming that a right-turn at the intersection 220 is always allowed and a U-turn at the intersection 220 is always prohibited, eight traffic flows Tl to T8 are taken into consideration for preventing vehicles which may enter the intersection 220 from colliding. Also, as shown in Fig. 3, the traffic signals 105a to 105d may include eight green lights, each of which permits the forward movement of each of the traffic flows Tl to T8.

[46] In the description given below, the traffic flow which is indicated by Tl shall be referred to as the first traffic flow Tl, and the green light allowing the first traffic flow Tl shall be called the first green light. The other traffic flows T2 to T8 and their respective green lights shall be called in the like manner.

[47] Referring to Fig. 4, as indicated by stars, there may occur a collision in the event that, e.g., both the second traffic flow T2 and the fourth traffic flow T4 are permitted to move forward at the same time. Therefore, it is necessary to inhibit the second green light from being turned on if the fourth green light is kept turned on, and vice versa. In such a case, a traffic flow inhibition table as shown in Fig. 5 may be referenced, the table indicating which of the traffic flows should not be permitted simultaneously.

[48] Fig. 6 provides a flowchart of an exemplary process which is performed in the traffic signal control unit of Fig. 3, in accordance with an embodiment of the present invention.

[49] Referring to Fig. 6, a program 400 may be executed at one or more central processors of the traffic signal control unit 104. Data may be read from and/or written into a memory of the traffic signal control unit 104 in the course of the program execution by the one or more central processors.

[50] At first, referring to Fig. 6, the variables i, j and k are set equal to one, two and three, respectively, in step S410.

[51] For the sake of convenience, the traffic flow corresponding to the variable i is referred to as the i-th traffic flow, the green light allowing the i-th traffic flow as the i- th green light, and the turn-on duration of the i-th green light as the i-th turn-on duration. With respect to the other variables j and k, like designations shall be made. It is noted, referring again to Figs. 4 and 5, that both the first traffic flow Tl corresponding to the initial value of i and the second traffic flow T2 corresponding to the initial value of j can be permitted to move forward at the same time.

[52] In step S411, the i-th turn-on duration is determined based on the traffic information of the corresponding road section from which the i-th traffic flow terminates and the i- th green light is turned on for the determined i-th turn-on duration. Similarly, the j-th green light is turned on in step S421, as performed in parallel with the step S411.

[53] Next, in step S412, it is decided whether the i-th turn-on duration has expired or not.

[54] If the i-th turn-on duration has not yet expired, the i-th turn-on duration can be regulated based on the newly received traffic information in step S413. For example, if the inter- vehicular separation time information indicates that no vehicle is expected to travel along the i-th traffic flow for the period of T^ the i-th green light may be turned off prematurely. As another example, the i-th turn-on duration may be properly adjusted, based on the traffic information including the group-driving preservation information, for maintaining the speed of the group-driving vehicles. Thereafter, the process returns to the step S412.

[55] If the i-th turn-on duration time has lapsed, the i-th green light is turned off and it will be decided whether or not the k-th traffic flow is permitted while the j-th green light is kept turned on, in step S414. At this time, the traffic flow inhibition table as shown in Fig. 5 may be referenced. [56] If the j-th traffic flow and the k-th traffic flow are not permitted at the same time, the variable k is represented in modulo N arithmetic (i.e., k is set to the remainder of division of k by N), where N is the total number of the green lights, and then increased by one, in step S415. Thereafter, the process returns to the step S414.

[57] If the k-th traffic flow is permitted while the j-th green light is still kept turned on, the variable i is set equal to the value of k and the variable k is then represented in modulo N arithmetic before it is increased by one, in step S416. Next, returning to the step S411, the i-th turn-on duration is determined and the i-th green light is turned on for the determined i-th turn-on duration, as mentioned above.

[58] Steps S422 to S426 for the j-th green light may operate similarly.

[59] In addition, the steps S411 to S416 for the i-th green light and the steps S421 to S426 for the j-th green light may be performed in parallel. For example, in the one or more central processors of the traffic signal control unit 104, both of the thread executing the steps S411 to S416 and the thread executing the steps S421 to S426 may run, sharing the variables i, j and k. It should be noted, however, that the execution of the steps S414 to S416 and the execution of the steps S424 to S426 are mutually exclusive because the former thread may be changing i and/or k in the steps S414 to S416 and the latter, j and/or k, in the steps S424 to S426. Thus, a mutual exclusion (MUTEX) algorithm may be adopted to guard against concurrent access and manipulation of the variables i, j and k.

[60] While the invention has been shown and described with respect to some of the preferred embodiments only, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.