Patent Description:
Traffic light control is the most important and efficient method for controlling traffic in urban areas. There are three categories of traffic light control strategies: fixed-time control, traffic actuated control and traffic adaptive control. In fixed time control each traffic light has a predefined duration for allowing traffic to flow. The controller cycles between all the traffic signals. In this manner each lane gets a predefined duration of a green light and flow of traffic. As the rate of flow of traffic increases, the fixed time control may not provide the optimal division of time between the different lanes and traffic congestion may arise.

A remedy to the inefficiencies of fixed time traffic light control is to measure the traffic flow and change the traffic light duration according to measured traffic flow. Examples of measuring traffic flow include; wire loops embedded in the road which generates a current when a car passes over them; pressure sensitive devices embedded in the road; acoustic devices to measure traffic flow; and image based systems to measure traffic flow. Examples of existing algorithms are given in <NPL> and<NPL>. <CIT> discloses an exemplary method of controlling traffic signals of traffic lights.

Existing solutions focus on the static measure of traffic. For example, a green traffic light is provided if the traffic sensor indicates the existence of a car in the relevant lane. To assess the amount of traffic in the lane these solutions require additional sensors which increases the cost of deployment and significantly increases the cost of operation. The required computing resources for some algorithms are not supported by existing traffic light controllers, so a deployment of some systems requires an overhaul of the existing infrastructure. Furthermore, the cited examples which dynamically change the traffic light duration based on static measurements also change the cycle of the traffic signal. Changing the cycle of the traffic light disrupts the flow of traffic and induces congestion across the road system. In some examples of state of art solutions, the applied methods can only reduce the preplanned maximum time for each light. In one example, if <NUM> seconds are allocated for a green light than the state of art method will reduce the allocated time from <NUM> seconds to a smaller number. Hence this will shorten the allocated green time to a specific lane, without an increase in green light time to other lanes. The inability to increase the allocated green light time to more than <NUM> seconds results in traffic congestion as demonstrated in this example. Assuming traffic is congested and requires <NUM> seconds to pass through the junction. If only <NUM> seconds are allocated than the remaining <NUM> seconds of traffic would be stopped for next green light cycle. In the next green light cycle, there will now be <NUM> seconds of traffic plus the <NUM> seconds from the previous cycle. Thus the traffic flow is impeded and congestion arises rapidly.

Hence an alternative algorithm is required. The desired algorithm should provide the following features:.

Can be implemented in the existing infrastructure of controllers and single sensor per lane.

Maintains the traffic flow cycle to prevent disruption to traffic.

In some examples, the proposed algorithm can also increase the allocated green time beyond the static allocated green time.

An algorithm and method is disclosed according to the features of claim <NUM>, for optimizing traffic light duration in a desired direction/lane and which overcomes the deficiencies of existing algorithms and methods. <FIG> is an example of a traffic intersection according to the invention having the features of claim <NUM>. The intersection is the area where two or more roads intersect. Road (<NUM>) and road (<NUM>) are examples of roads which intersect. In one example the traffic flow through the intersection is controlled by traffic lights (<NUM>). The traffic light (<NUM>) directs the traffic through the use of pre-designated signals such as light colors, or light shape. The traffic light (<NUM>) lighting pattern is designed so that at any given time, the traffic emanating from one lane would not intersect with traffic emanating from another lane. In a further example, traffic sensors (<NUM>) register the passage of an automobile over the sensor. Examples of traffic sensors (<NUM>) include; induction loops which generate current when a metal body such as an automobile passes over the sensor; Pressure or shear sensors which measure the weight of deformation caused by the passage of an automobile; Acoustic sensors which sense the passage of an automobile; Or image sensors which record and analyze the flow of traffic.

<FIG> is an example of a graph of sensor signal over time. The "x" axis depicts the time, while the "y" axis depicts the sensor signal. In one example, when an automobile traverses the sensor, the sensor will emit a signal event (<NUM>) which corresponds to the time of traversal. The period of a green signal, the green light time (<NUM>) is depicted as a dashed line. During the time the traffic light is green, several cars may traverse the sensor, hence <FIG> depicts several signal events (<NUM>), each signal event (<NUM>) corresponding to one automobile traversing the sensor. The "usage time" is defined as the sum of all signal events (<NUM>) in a lane. The "usage percentage" is defined as the "usage time" divided by the green light time (<NUM>).

<FIG> is an example of an algorithm for optimizing the traffic flow and which does not suffer from the deficiencies of state of art algorithms. Block (<NUM>) of the algorithm initializes all the variables required for the algorithm. Examples of variables include; a counter for the traffic lights (e.g. "i"); a timer; a green light time (<NUM> in <FIG>) for each traffic light. Block (<NUM>) sets the traffic light counter (e.g. "i") to the first traffic light. This facilitates the main loop to start the traffic light cycle. Block (<NUM>) activates the designated traffic light (e.g. traffic light "i"). In one example, the activation is composed of a sequence of lights leading from a red light to a green light. In addition block (<NUM>) starts a timer circuit <NUM> (<FIG>). The timer circuit or timer is used to limit the green light in the traffic light to the green light time (<NUM> in <FIG>). Block (<NUM>) measures the traffic through the sensor which is relevant for the designated traffic light (e.g. traffic light "i"). If the sensor measurement is positive then block (<NUM>) adds the time the sensor is positive to the usage time. If the sensor measurement is zero, then no time is added to the usage time. Block (<NUM>) compares the timer time to the green light time (e.g., time on, <NUM> in <FIG>) of the designated traffic light (e.g. traffic light "i"). If the elapsed time is shorter than the green light time (<NUM> in <FIG>), block (<NUM>) is executed and the sensor is measured. If the elapsed time is greater than the green light time (<NUM> in <FIG>) the designated traffic light (e.g. traffic light "i") is deactivated (block <NUM>). In one example, the deactivation is a sequence of light signals starting with green light and ending with a red light. Block (<NUM>) checks if the active traffic light is the last of the traffic lights. If the active traffic light is not the last, the traffic light counter (e.g. "i") is changed to reflect the next designated traffic light (e.g. traffic light "i+<NUM>") (block <NUM>). The algorithm then executes the loop again for the next designated traffic light (e.g. traffic light "i+<NUM>"). If the active traffic light is the last traffic light in the sequence than block (<NUM>) is executed and the green light time (<NUM> in <FIG>) duration for each traffic light, is amended based on the usage time measurements.

In one example the usage time is changed by the following procedure. For the traffic light with the maximum usage percentage increase the green light time (<NUM> in <FIG>) by one unit. If there is more than one traffic light with the same usage percentage as the maximum usage percentage, than randomly choose one of the traffic lights with the maximum usage percentage. For the traffic light with the minimum usage percentage decrease the green light time (<NUM> in <FIG>) by one unit. If there is more than one traffic light with the same usage percentage as the minimum usage percentage, than randomly choose one of the traffic lights with the minimum usage percentage. The above described procedure ensures that the total green light time of all the traffic lights is constant, which maintains traffic flow across multiple intersections. One example of a time unit is one second. Another example of a time unit is <NUM> seconds.

Hence one example is a method for controlling traffic signals comprising: a green light time for each traffic light; measuring usage percentage for each traffic light; increasing the green light time of the traffic light with maximum usage percentage; and reducing the green light time of the traffic light with minimum usage percentage. In another example above method is continuously repeated. In another example the increase in green light time is a fixed duration. In a further example the fixed duration is one second. In an alternative example the fixed duration is between one second to five seconds. In another example the reduction in green light time is a fixed duration. In an embodiment the increase and reduction in green light time are equal and of a fixed duration.

In another example the device for measuring traffic usage comprising of; a traffic sensor; wherein said sensor provides a signal when a vehicle is present in the vicinity of the sensor; a timer device; wherein said timer device provides an electrical signal at a fixed interval; and wherein the output signal of the device is proportional to the duration that a vehicle was present in the vicinity of the traffic sensor to the duration that no vehicle was present in the vicinity of the sensor. In a further example the device output is an analog signal. In a further example the device output is a digital signal.

The algorithm balances the usage for each green light by passing time units from the minimum used direction to the maximum used direction. The algorithm changes only the green light duration plan of a traffic light junction, and does not change any other aspect of the junction control, thus do not impair safety of passengers in the junction. Common Traffic Light Junctions have one or more predefined green light duration plan which can change according to the time of the day. This algorithm manages and changes the plan continuously to find the plan that optimizes the traffic flow for any predefined green light duration.

The above described method can be implemented in a traffic intersection. In one example a traffic intersection comprising; two or more intersecting roads; two or more traffic lights; a traffic light controller executing a method for controlling traffic signals comprising: a green light time for each traffic light; measuring usage percentage for each traffic light; increasing the green light time of the traffic light with maximum usage percentage; and reducing the green light time of the traffic light with minimum usage percentage. In a further example the method for controlling traffic signals is continuously repeated. In a further example the increase in green light time is a fixed duration. In a further example the reduction in green light time is a fixed duration. In an embodiment the increase and reduction in green light time are equal and of a fixed duration.

The described algorithm expands on the state of art and resolves the deficiencies of existing solutions namely; the algorithm can be implemented in the existing infrastructure of controllers and single sensor per lane, and the algorithm maintains the traffic flow cycle to prevent disruption to traffic. It is clear that in the implementation of the apparatus and method, many modifications could be made to the system that carries out the described algorithm. It should be considered that all modifications and alterations of the system and algorithm are falling within the scope of this document.

Claim 1:
A method for controlling traffic signals of traffic lights (<NUM>), each traffic light having a sensor (<NUM>) for registering each signal event (<NUM>) corresponding to an automobile traversing the sensor and a green light time, the method comprising the steps of:
measuring usage percentage for each traffic light, wherein the usage percentage is the sum of all signal events in a lane registered by the respective sensor, divided by the green light time (<NUM>);
increasing the green light time of the traffic light with maximum usage percentage by a duration;
reducing the green light time of the traffic light with minimum usage percentage by the duration;
wherein the increase and reduction in green light time are equal and of a fixed duration;
whereby the total green light time of all the traffic lights remains constant and wherein the method is continuously repeated.