Abstract:
Methods and systems for controlling vehicular traffic flow in a transport system are provided. The method includes defining a plurality of queues through the transport system, assigning each of a plurality of vehicles into one of the plurality of queues, determining a number of vehicles in each queue and a period of time each vehicle remains in the queue, and permitting traffic flow in at least one queue that facilitates reducing the congestion of the plurality of queues.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to methods and systems for controlling traffic flow and more particularly, to methods and systems for controlling traffic flow using RFID enabled devices. 
         [0002]    Traffic flow at street intersections is generally controlled with light signal systems. A light signal system includes a combination of light signal transmitters for various roads approaching the intersection and the required operating devices for controlling the traffic flow. A light signal transmitter may be a transmitting apparatus that transmits visible signals to the traffic participants such as a traffic light. A signal program executes in a local control device for the intersection, in which the signal times for the light signal system are fixed with respect to duration and assignment. At least some known light signal systems are fixed time controlled and others may use traffic-dependent methods for controlling the signal transmitters at an intersection. 
         [0003]    The fixed time signal control is a light-signal control with fixed signal times, without an influencing option for the traffic flow. This signal control is based on taking into account the long-term traffic situation at the intersection. The method uses signal programs, operating on the basis of fixed-time tables, with a rigid sequence of automatic operations. Fixed-time controlled methods are relatively inexpensive, but are not flexible over the short run or the long run with respect to changes in the traffic conditions at the intersection. 
         [0004]    Traffic-dependent methods take into account short-term traffic situations at the intersection and usually require several detectors, such as induction loops, infrared sensors, or radar detectors for each approach to the intersection. As a result, these control methods are very flexible in the short term, but have only an average flexibility for the long term, so that additional planning becomes necessary. On the whole, these traffic-dependent methods are expensive and require extensive pre-planning to implement. 
         [0005]    In addition, the known systems are not able to detect congestion at an intersection and therefore can not reduce congestion of traffic flow through the intersection. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    In one embodiment, a computer-implemented method of controlling vehicular traffic flow in a transport system includes defining a plurality of queues through the transport system, assigning each of a plurality of vehicles into one of the plurality of queues, determining congestion in each queue, and permitting traffic flow in at least one queue that facilitates reducing the congestion of the plurality of queues. 
         [0007]    In another embodiment, a radio frequency identification (RFID) enabled system for traffic flow control includes a plurality of vehicles including at least one RFID enabled device mounted thereon, a reader of the RFID enabled devices configured to determine a location of the RFID enabled device. The system also includes a processor communicatively coupled to the reader wherein the processor is configured to determine a plurality of queues through which the traffic flow is routed, assign each RFID enabled device to a queue, determine a congestion in each queue based on a number of vehicles in the queue and an amount of time the vehicle is in the queue, and control the traffic flow such that at least one of congestion in a queue and total congestion in a plurality of queues is facilitated being reduced. 
         [0008]    In yet another embodiment, a method of controlling vehicular traffic flow through an intersection of roads includes determining a queue for each possible track of travel through the intersection, determining congestion in each queue, and permitting flow in one or more queues such that congestion is facilitated being minimized. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a block diagram of an exemplary embodiment of a traffic control system in accordance with an exemplary embodiment of the present invention; 
           [0010]      FIG. 2  is a schematic diagram of an exemplary embodiment of a standard four way intersection including twelve queues for vehicles; and 
           [0011]      FIG. 3  is a flow diagram of an exemplary queue maintenance sequence that may be used with the system shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]      FIG. 1  is a block diagram of an exemplary embodiment of a traffic control system  100  in accordance with an exemplary embodiment of the present invention. In the exemplary embodiment, system  100  includes an RFID reader  102  capable of interrogating a plurality of RFID enabled devices  104  such as RFID tags coupled to a vehicle  106  to uniquely identify the vehicle to system  100 . In other embodiments, traffic control system  100  includes a real-time location system other than an RFID system that is capable of performing the functions described herein. In some instances, a non-participatory vehicle  108  such as a vehicle that does not include a RFID enabled device  104  or includes an RFID enabled device that is nonfunctional may be interspersed with vehicles  106 . Because vehicle  108  contributes to congestion but is unknown to system  100 , system  100  may include an algorithm to estimate or infer the presence of vehicles  108  and correct the control outputs of system  100  to account for the presence of vehicles  108 . 
         [0013]    System  100  uses an active RFID system with active RFID enabled devices  104 . RFID enabled devices  104  may be installed as an OEM system or could be installed on existing vehicles as an after-market accessory. In the exemplary embodiment, RFID enabled device  104  is attached to a windshield of vehicle  106 . In other embodiments, RFID enabled devices  104  may be formed into hood ornaments, appliques, decals, and other desirable fashion accoutrements and coupled to vehicle  106  by adhesion, magnetics, or fasteners. Because RFID enabled devices  104  transmit and receive radio frequency signals they can often experience interference in high metal density environments and therefore vehicle RFID enabled devices  104  are generally positioned on or near the windshield of vehicle  106 . Most vehicle glass atomic structure permits electromagnetic waves in the visible light spectrum and lower frequency waves such as radio frequency waves to pass through the glass unimpeded. 
         [0014]    A line of sight is not required between RFID enabled device  104  and an associated reader  102  for RFID enabled devices  104  to communicate with reader  102  and the active RFID feature of system  100  permits relatively greater accuracy and greater read distances, a weatherproof RFID enabled device  104  could be positioned on a exterior of vehicle  106  without interfering with driver vision. In another embodiment, exterior placement of RFID enabled devices  104  permits vehicle OEMs to preinstall RFID enabled devices  104  and hardwire them to a turn signal circuit  110  of vehicle  106  such that an intended track of vehicle  106  is capable of being transmitted to reader  102  with or without cosmetic changes. Forming RFID enabled devices  104  into marketable shapes and designs provides an opportunity to market RFID enabled devices  104  as desirable cosmetic additions to personal vehicles  106 . 
         [0015]    Reader  102  includes an electronics module  112  and at least one antenna  114 . In the exemplary embodiment, reader  102  includes one electronics module  112  and four antennae  114 . Other configurations of readers and antennae could be incorporated in other embodiments of the present invention. Reader  102  and associated antennae are mounted at predetermined positions at for example, an intersection  116  of roads. Placement of antennae  114  and readers  102  are determined by for example, readability. Antennae  114  and readers  102  are placed at various locations throughout an intersection based on locations that facilitate generating accurate readings of RFID enabled devices  104  in all directions. In addition consideration may be made to minimize the amount of hardware infrastructure used at each intersection. Generally the configuration is based on an empirical study of intersection  116 . Although unique characteristics of each intersection  116  generally preclude a single configuration for each intersection  116 , predetermined standards aid in hardware placement. Reader  102  includes a capability to network multiple antennae  114  coupled to reader  102 . Because only three antennae are necessary to triangulate a signal and determine a location of vehicle  106 , a single reader  102  is used at a typical four way intersection to determine the location of any vehicle within range. Using a single reader  102  when possible and multiple networked antennae provides a cost effective implementation and still permit additional antennae as required for customization of the environment at each intersection  116 . 
         [0016]    After placement of readers  102  and antennae  114 , reader  102  is communicatively coupled to all antennae  114 . Reader  102  is communicatively coupled to a server  118  through a communications link  120 . Link  120  may be a hardwired, wireless, or multi-mode link. Server  118  receives raw data and/or preprocessed information from each reader  102  communicatively coupled to server  118 . Server  118  executes traffic control application software that processes the raw data and/or preprocessed information to generate traffic control signals that facilitate reducing congestion of vehicles in a queue at each intersection, in the intersection as a whole, in a network of intersections. 
         [0017]    When installed, all hardware at an intersection is calibrated. Knowledge of vehicle  106  intended direction is an important feature of system  100 . Available RFID hardware is capable of locating active tags within a few feet. Accordingly an intended direction of vehicle  106  may be identified by its lane location. Calibration of system  100  hardware establishes how readers  102  are positioned about intersection  116 . For example, circumscribing a periphery of each traffic lane with a special calibration tag and noting each lane&#39;s designated direction such as a left turn only lane or choices of directions such as a right turn or straight thereby associating any vehicle within a lane with selectable destination choices. System  100  also ignores vehicles outside of boundaries of all lanes as non-participants in system  100 . For example, a vehicle parked at the side of the road or in a driveway is not counted as being in a queue. 
         [0018]    Mathematical models are idealized representations expressed in terms of mathematical symbols and expressions. If there are n related quantifiable decisions to be made, they may be represented as decision variables (x 1 , x 2 , x 3  . . . xn) whose values must be determined. A measure of performance may then be expressed as a mathematical function of these decision variables and is called an objective function. Restrictions to these decision variables may also be expressed mathematically and are called constraints. A process called sensitivity analysis is usually performed to determine how the model would change as the values assigned to the decision variables were changed to other feasible solutions. 
         [0019]    System  100  is a traffic flow optimization solution that utilizes active radio frequency identification technology along with linear programming and statistical routines to minimize vehicle wait time at intersections, increase road capacity and consumer fuel economy, reduce vehicle congestion and pollution caused by congestion, and provide vehicle data for future planning using existing technology with minimal infrastructure investment and consumer expense. 
         [0020]    In a typical RFID system such as reader  102  and RFID enabled device  104 , individual objects are equipped with a small, inexpensive tag containing RFID enabled device  104 . The tag contains a transponder with a digital memory chip that stores an electronic code that is unique to that tag. Reader  102  includes one or more antennae packaged with a transceiver and a decoder, emits an electromagnetic signal that activates RFID enabled device  104  by passing over its antenna and generating a return radio frequency electromagnetic signal that can be interpreted by reader  102 . Reader  102  decodes the data encoded in the tag&#39;s integrated circuit and the data is passed to server  118 . Application software on server  118  processes the data, and may perform various filtering operations to reduce the numerous often redundant reads of the same tag to a smaller and more useful data set. 
         [0021]    Passive RFID tags have no internal power supply. The electrical current induced in the antenna by the incoming radio frequency signal provides enough power for the integrated circuit (IC) in the tag to power up and transmit a response. Most passive tags signal by backscattering the carrier signal from the reader. This means that the antenna is designed to both collect power from the incoming signal and also to transmit the outbound backscatter signal. The response of a passive RFID tag may include a unique ID number and data that may be stored in a nonvolatile EEPROM. Lack of an onboard power supply means that the device can be quite small. For example, some known RFID ICs measure 0.15 mm×0.15 mm, and are less than 7.5 micrometers thick. RFID tags are inexpensive as well, costing only a fraction of a dollar. The addition of the antenna creates a tag that varies from the size of a postage stamp to the size of a post card. Passive tags have practical read distances ranging from about 4 in. up to a few dozen feet depending on the chosen radio frequency and antenna design/size. Due to their simplicity in design antennas may be manufactured through a printing process. Passive RFID tags do not require batteries, can be much smaller, and have an unlimited life span. Non-silicon tags made from polymer semiconductors are also available. 
         [0022]    Unlike passive RFID tags, active RFID tags have their own internal power source which is used to power any ICs that generate a transmitted signal. Active tags are typically much more reliable than passive tags due to the ability for active tags to conduct a “session” with a reader. Active tags, due to their onboard power supply, also transmit at higher power levels than passive tags, allowing them to be more effective in “RF challenged” environments like water (including humans/cattle, which are mostly water), metal (shipping containers, vehicles), or at longer distances. Many active tags have practical ranges of hundreds of meters, and a battery life of up to 10 years. Active tags typically have much longer range (approximately 300 feet) and larger memories than passive tags, as well as the ability to store additional information sent by reader  102 . 
         [0023]      FIG. 2  is a schematic diagram of an exemplary embodiment of a standard four way intersection  200  including twelve queues for vehicles. In the exemplary embodiment, intersection  200  includes a North to South queue  202 , a North to East queue  204 , a North to West queue  206 , a East to North queue  208 , a East to South queue  210 , a East to West queue  212 , a South to North queue  214 , a South to East queue  216 , a South to West queue  218 , a West to North queue  220 , a West to East queue  222 , and a West to South queue  224 . For purposes of some calculations the intersection itself may be considered a queue. The number of queues for an intersection of any number of two way origins and destinations can be represented by the equation [X number of directions * (X number of directions −1)]. 
         [0024]    System  100  comprises a solution to an increasing number of vehicles on the roads using growingly insufficient roadway capacity. When system  100  is activated a vehicle queue sequence is started. The vehicle queue sequence is responsible for transmitting appropriate data to the optimization and statistical sequences. As described above, the hardware may be calibrated upon start-up to establish roadway boundaries. As a vehicle approaches intersection  200  RFID enabled device  104  transmits an identification unique to that devise  104 . The vehicles current location and intended direction are determined through either location and turn signal, or lane location as it approaches intersection  200 . For any standard four way intersection there are a finite number of possible origins and destinations. As shown in  FIG. 2 , each arrow represents a potential origin and destination and therefore a potential queue of vehicles. 
         [0025]    Once the queue system is no longer null (has values &gt;0) the following variables are continuously calculated: 
         [0026]    Time of vehicle i (v i ) in queue x i =Tv i    
         [0027]    Sum total vehicles for each x i =Nx i    
         [0028]    Sum total time for each x i =Wx i    
         [0029]    Calculate average time between arrivals=λ i    
         [0030]    Upon detection, a vehicle is placed in a first queue associated with its determined location and all variables are calculated. When the vehicle passes into the intersection it is logged as being in the intersection queue. When the vehicle passes through the intersection it appears in a different lane and its location is determined and it is placed in a second queue. However, the queue system continuously checks for vehicles with multiple records by looking for an identical identification number on any new entry. When an identical number is found, the vehicle has passed through the intersection and all associated data may be deleted for v i  in all x i  and all variables re-calculated. An exception to this rule is made for the intersection queue which is necessary to execute a Grid-lock function as described below. In this sequence duplicates may exist in the intersection queue until a vehicle&#39;s tag identification is placed in multiple x i . 
         [0031]      FIG. 3  is a flow diagram of an exemplary queue maintenance sequence  300  that may be used with system  100  (shown in  FIG. 1 ). System  100  steps through queue maintenance sequence  300  to determine when vehicles and their associated data are added and removed from system  100 . 
         [0032]    Upon successful start-up  302  of system  100 , the program will run through a continuous loop of sequences, each customizable for a community or environment. Queue maintenance sequence  300  includes a default sequence  304  that initiates certain parameters and ensures continuous operation despite any potential software or hardware failures. These parameters may be customized, however conditions that may initiate default sequence  304  include: 
         [0033]    System  100  is available but the Department of Transportation does not yet want to begin the optimization and statistical routines. 
         [0034]    System  100  has detected corruption in its data and while it clears and replaces data from the queues must resort to a traffic pattern routine. 
         [0035]    A power save sequence  306  is customizable, however conditions that may initiate power save sequence  306  include: 
         [0036]    The average time between arrivals, λi is sufficiently low such that it is not necessary to run lights continuously, rather it would be possible to flash red and yellow on some non-continuous frequency. 
         [0037]    The average time between arrivals, λi is sufficiently low such that it would be possible to avoid using additional turn signal lights. 
         [0038]    The energy savings from using power save sequence  306  on any individual intersection is small but collectively over an entire geographic area is potentially significant. 
         [0039]    An over-ride sequence  308  is reserved for emergency and select public vehicles. System  100  permits police, ambulance, and fire vehicles to pass through intersections unimpeded by transmitting a signal that is received through an existing receiver at the intersection or directly from the emergency vehicle in one embodiment system  100  is linked to a satellite navigation system (not shown) that coordinates emergency vehicle destinations with over-ride sequence  308  to identify the fastest route to the destination and sequence traffic control devices to permit unimpeded passage through all intersections. 
         [0040]    An anti-grid lock sequence  310  determines when vehicles are blocking an intersection and will permit the blocking vehicles to clear the intersection before permitting traffic to resume travel through the intersection. System  100  is calibrated to identify vehicles in their approaching lanes and determine an amount of time the vehicle remains in that lane. System  100  also determines when vehicles enter the intersection and how long the vehicle remains in the intersection. If during an optimization sequence the maximum wait time (Mλ) is exceeded and there is at least one vehicle in the intersection, anti-grid lock sequence  310  engages until the vehicles clear the intersection and RFID enabled device  104  identities are deleted from all queues. System  100  including a reader  102  deployed on an adjacent intersection is capable of taking advantage of road capacity constraints to avoid grid-lock all together. 
         [0041]    In each sequence, system  100  conducts a continuous loop check. If system  100  bypasses all other sequences, for example, run all other sequences=“No,” then an optimization sequence  312  initiates. Optimization sequence  312  includes a model of the traffic flow in system  100  and the form of the model is described below: 
         [0000]      Maximize Z=ΣWx i ; where 
         [0000]      Wx i =Wx ns +Wx ne +Wx nw +Wx en +WX es +WX ew +WX sn +WX se +Wx sw +Wx wn +Wx we +Wx ws , and the model is subject to the following constraints: 
         [0000]      0 ≦x   n ≦1   (a) 
         [0000]        X   ns   +X   sw ≦1 , X   sn   +X   ne ≦1 , X   ew   +X   wn ≦1 , X   we   +X   es &lt;1   (b) 
         [0000]        X   ns   +X   ws ≦1 , X   sn   +X   en ≦1 , X   ew   +X   nw ≦1 , X   we   +X   se ≦1   (c) 
         [0000]        X   ns   ’ 3  X   ne   +X   sn   , X   sn   ≦X   ns   +X   sw   , X   ew ≦X we   +X   es   , X   we   ≦X   ew   +X   wn    (d) 
         [0000]      X ne   +X   se ≦1 , X   es   +X   ws ≦1 , X   sw   +X   nw ≦1 , X   wn   +X   en ≦1   (e) 
         [0000]        X   ns   +X   ew ≦1 , X   ns   +X   we ≦1 , X   sn   +X   ew ≦1 , X   sn   +X   we ≦1   (f) 
         [0042]    The objective function attempts to identify the queues with the longest summed wait times, W xi  that do not violate the constraints. The associated computer model interprets the identified queues and permits those vehicles to move as necessary. Although system  100  minimizes vehicle wait time, for the purposes of constructing the model, the objective function is written as a maximization and constraints written in the “less than or equal to” (≦) format. 
         [0043]    The purpose of constraints (a) through (f) is to avoid any interfering traffic patterns such as all lights green. Constraint (a) ensures that each vehicle queue is either 0 or 1 meaning it will either be permitted to move vehicles, for example, with a green light or a green arrow or be held for example, with a red light. Constraint (b) ensures that if a left hand turn is permitted to move vehicles the opposing lane of traffic must be held and vice versa, if opposing traffic is permitted to move no left hand turn signal may be given. Constraint (c) ensures that if there is a right hand turn signal it can not be green if interfering traffic is permitted to move. Constraint (d) permits delayed green lights and left hand turns to operate independently depending in optimal conditions. Normally a light with extended green will occur continuously regardless of vehicle traffic. System  100  would permit delayed green while also allowing for the possibility of no delay solely based on maximizing traffic through an intersection. Constraint (e) ensures that if there is a right hand turn light you can not have both a right hand turn and a left hand turn traveling to the same lane. Lastly, constraint (f) ensures that opposite direction traffic traveling straight can not occur simultaneously. 
         [0044]    A common method to solve linear mathematical models is the Simplex Method. The Simplex Method uses an iterative algorithm with the following structure: 
         [0045]    Initialization, 
         [0046]    test for optimality, 
         [0047]    continue until current feasible solution optimal. 
         [0048]    System  100  software also includes statistical properties. For example, it is possible that an intersection has a high volume in one direction and a relatively very low volume in an opposing direction such that despite an optimized traffic flow a vehicle attempting to proceed in the opposing direction could wait for an impractically excessive amount of time for the light to change. System  100  uses a Poisson distribution to model the number of vehicles that arrive over an interval and uses probability to ensure optimal flow while accounting for all possible scenarios. 
         [0049]    In the exemplary embodiment, system  100  assumes that the expected arrivals of vehicles over any time interval in any x i , E(x i ), are equal to k i . This is the basis for calculating minimum and maximum wait times for each x i . When system  100  is running optimize sequence  312 , it first checks for optimality. If the optimal sequence is running, system  100  then checks  314  to see if any T xi  (total sum of vehicles in x i ) exceed the maximum wait time as defined by Mλ i . If so, then a light change would be initiated to permit those vehicles to travel through the intersection. In the exemplary embodiment, Mλ i  is selectable to represent a maximum total wait time or a maximum vehicle wait time. In the case above, where one direction has high volume and the opposing direction has a low volume, vehicles in the low volume direction would not have to wait indefinitely to cross an intersection that carries an infinite number of vehicles. Road capacity may limit the use of this function because the waiting vehicle&#39;s time would continue to increase while the cross road, if filled to capacity with moving vehicles, would have a nearly constant total wait time. Eventually any vehicle would be permitted through any intersection though not in a practical manner. 
         [0050]    Once the intersection is changed to a non-optimal route because of Mλ i  it will not instantaneously change back to the optimal route, again, out of practicality. Instead, as shown at  316 , upon change, there is an associated minimum wait time mλ i . Minimum wait time, mλ i  can be set to any finite number, however, creating a dynamic mλ i  allows for optimal flow. The time it takes for a vehicle to travel through the intersection is determined from its change in location over time and an assumption that the time is normally distributed can be made. Because λ i  is known, mλ i  and Mλ i  can be set to a value equal to a number of practical constants or dynamic equations based on intersection infrastructure. 
         [0051]    Upon calculation of the various λ i  the process flow is complete and cycles back to default sequence  304  to continue operation indefinitely. The above discussion assumes each intersection operates independently. However, any number of intersections may be networked together to form a traffic flow solution over a large network of interconnected roads. 
         [0052]    It is possible that each intersection in a given area permits optimal vehicle flow. However, independent optimality does not insure collective optimality of a plurality of interconnected intersections. The mathematical model defines what is considered optimal, in this case maximum vehicle flow through a single intersection. Any number of intersections may be networked and represented by a model that defines maximum vehicle flow through the entire network. In such a scenario, wait time at any particular intersection is extended so that the wait at the next intersection is further reduced. A networked model also includes additional constraints such as a capacity constraint that does not permit more vehicles to wait or travel through an intersection than the downstream roads can hold. 
         [0053]    The above-described methods and systems for controlling traffic in single or networked intersections using a unique identifier for each vehicle is cost effective and highly reliable. Using RFID enabled devices to locate and identify vehicles entering an intersection permits determining congestion in each queue through the intersection and permits adjusting traffic control signals to facilitate reducing wait times of a vehicle, a queue of vehicles, or all the vehicles approaching the intersection. Signal device control sequences permit a power save option, controlling the signals to permit emergency vehicles to have unimpeded access through the intersection, and a sequence to permit clearing a grid-lock situation in the intersection. Accordingly, the methods and systems facilitate controlling traffic in a cost-effective and reliable manner. 
         [0054]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.