Abstract:
A traffic light control system includes at least one parameter and a signal decoding circuit. The parameter or parameters are useful for assisting in differentiating between multiple communication modes. The signal decoding circuit has a front-end circuit and a back-end circuit. The front-end circuit is adapted to receive respective signals transmitted in multiple communication modes. The front-end circuit is adapted to produce data representative of at least a portion of the respective signals. The back-end circuit is adapted to interpret and process the produced data according to at least one of multiple traffic light control protocols respectively associated with the multiple communication modes. The signal decoding circuit is adapted to access said at least one parameter and associate the produced data with one of the multiple communication modes.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is generally directed to systems and methods that allow traffic light systems to be remotely controlled using data communication, for example, involving optical pulse transmission from an optical emitter to an optical detector that is communicatively-coupled to a traffic light controller at an intersection.  
       BACKGROUND OF THE INVENTION  
       [0002]     Traffic signals have long been used to regulate the flow of traffic at intersections. Generally, traffic signals have relied on timers or vehicle sensors to determine when to change the phase of traffic signal lights, thereby signaling alternating directions of traffic to stop, and others to proceed.  
         [0003]     Emergency vehicles, such as police cars, fire trucks and ambulances, are generally permitted to cross an intersection against a traffic signal. Emergency vehicles have typically depended on horns, sirens and flashing lights to alert other drivers approaching the intersection that an emergency vehicle intends to cross the intersection. However, due to hearing impairment, air conditioning, audio systems and other distractions, often the driver of a vehicle approaching an intersection will not be aware of a warning being emitted by an approaching emergency vehicle.  
         [0004]     There are presently a number of optical traffic priority systems that permit emergency vehicles to preempt the normal operation of the traffic signals at an intersection in the path of the vehicle to permit expedited passage of the vehicle through the intersection. These optical traffic priority systems permit a code to be embedded into an optical communication to identify each vehicle and provide security. Such a code can be compared to a list of authorized codes at the intersection to restrict access by unauthorized users. However, the various optical traffic priority systems are incompatible because the vehicle identification code for each of the various optical traffic priority systems is embedded in the optical communication using incompatible modulation schemes.  
         [0005]     Generally, an optical traffic priority system using a particular modulation scheme is independently purchased and implemented in each jurisdiction, such as a city. Thus, the traffic lights and the emergency vehicles for the jurisdiction are equipped to use the particular modulation scheme. However, a neighboring jurisdiction may use equipment that embeds the vehicle identification code using an incompatible modulation scheme. Frequently, a pursuit by a police car or the route of an ambulance may cross several jurisdictions each using an incompatible modulation scheme to embed the vehicle identification information. It may be burdensome and expensive to allow a vehicle from a neighboring jurisdiction to preempt traffic lights while maintaining appropriate security to prevent unauthorized preemption of traffic lights.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention is directed to overcoming the above-mentioned challenges and others that are related to the types of approaches and implementations discussed above and in other applications. The present invention is exemplified in a number of implementations and applications, some of which are summarized below.  
         [0007]     In connection with one embodiment, the present invention is directed to implementations that allow traffic light systems to be remotely controlled using multiple communication modes.  
         [0008]     In a more particular embodiment, a traffic light control system includes at least one parameter and a signal decoding circuit. The parameter or parameters are useful for assisting in differentiating between multiple communication modes. The signal decoding circuit has a front-end circuit and a back-end circuit. The front-end circuit is adapted to receive respective signals transmitted in multiple communication modes. The front-end circuit is adapted to produce data representative of at least a portion of the respective signals. The back-end circuit is adapted to interpret and process the produced data according to at least one of multiple traffic light control protocols respectively associated with the multiple communication modes. The signal decoding circuit is adapted to access the at least one parameter and associate the produced data with one of the multiple communication modes.  
         [0009]     The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and detailed description that follow more particularly exemplify these embodiments. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The invention may be more completely understood in consideration of the detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:  
         [0011]      FIG. 1  is a perspective view of a bus and an ambulance approaching a typical traffic intersection, with emitters mounted to the bus and the ambulance each transmitting an optical signal using respective incompatible communication modes in accordance with the present invention;  
         [0012]      FIGS. 2A, 2B  and  2 C illustrate optical pulses transmitted between a vehicle and equipment at an intersection for various example communication modes in accordance with the present invention;  
         [0013]      FIG. 3  is a block diagram of the components of an optical traffic preemption system for an embodiment in accordance with the present invention; and  
         [0014]      FIG. 4  is a block diagram of the components of an optical traffic preemption system for another embodiment in accordance with the present invention. 
     
    
       [0015]     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not necessarily to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0016]     The present invention is believed to be applicable to a variety of different communication modes in an optical traffic preemption system. While the present invention is not necessarily limited to such approaches, various aspects of the invention may be appreciated through a discussion of various examples using these and other contexts.  
         [0017]     The optical traffic preemption system shown in  FIG. 1  is presented at a general level to show the basic circuitry used to implement example embodiments of the present invention. In this context,  FIG. 1  illustrates a typical intersection  10  having traffic signal lights  12 . A traffic signal controller  14  sequences the traffic signal lights  12  through a sequence of phases that allow traffic to proceed alternately through the intersection  10 . The intersection  10  is equipped with an optical traffic preemption system having certain aspects and features enabled in accordance with the present invention to support multiple communication modes in an efficient, flexible and practicable manner.  
         [0018]     This support for multiple communication modes is provided in the optical traffic preemption system of  FIG. 1  by way of optical emitters  24 A,  24 B and  24 C, detector assemblies  16 A and  16 B, and a phase selector  18 . The detector assemblies  16 A and  16 B are stationed to detect light pulses from optical emitters  24 A,  24 B and  24 C mounted on authorized vehicles approaching the intersection  10 . The detector assemblies  16 A and  16 B communicate with the phase selector  18 , which is typically located in the same cabinet as the traffic controller  14 .  
         [0019]     In  FIG. 1 , an ambulance  20  and a bus  22  are approaching the intersection  10 . The optical emitter  24 A is mounted on the ambulance  20  and the optical emitter  24 B is mounted on the bus  22 . The optical emitters  24 A and  24 B each transmit a stream of light pulses. The stream of light pulses can transport data values that identify a requested operation, such as preemption of the normal operation of the traffic lights  12  to allow expedited passage of the vehicle  20  or  22  through the intersection  10 . The detector assemblies  16 A and  16 B receive these light pulses and send an output signal to the phase selector  18 . The phase selector  18  processes and validates the output signal from the detector assemblies  16 A and  16 B.  
         [0020]     The optical emitters  24 A and  24 B can use incompatible communication modes and modulation schemes to embed the data values in the stream of light pulses. Various embodiments of the invention provide extraction and validation of the data values embedded in the stream of light pulses by the detector assemblies  16 A and  16 B and the phase selector  18 , regardless of the communication mode used by a particular emitter  24 A or  24 B. After extraction and successful validation of a requested operation, the phase selector  18  can issue a phase request to the traffic signal controller  14  to preempt the normal operation of the traffic signal lights  12 .  
         [0021]      FIG. 1  also shows an authorized person  21  operating a portable optical emitter  24 C, which is there shown mounted to a motorcycle  23 . In one embodiment, the emitter  24 C is used to configure parameters of the detector assemblies  16 A and  16 B and/or phase selector  18 , including parameters used to differentiate the various communication modes and to validate data values embedded in the stream of light pulses according to multiple traffic light control protocols respectively associated with the multiple communication modes. In another embodiment, the emitter  24 C is used by the authorized person  21  to affect the traffic signal lights  12  in situations that require manual control of the intersection  10 .  
         [0022]     Typically, the data values for a requested operation include a vehicle identification code. Phase selectors constructed in accordance with the present invention can be configured to use a vehicle identification code in various ways. In one configuration, the phase selector  18  is configured with parameters providing a list of authorized identification codes. In this configuration, the phase selector  18  confirms that the vehicle is indeed authorized to preempt the normal traffic signal sequence. If the received vehicle identification code does not match one of the authorized identification codes on the list, preemption does not occur. In another configuration, the phase selector  18  is configured with parameters specifying limits for a range of values of authorized identification codes, possibly with separate ranges for emergency vehicles  20  and mass transit vehicles  22 . If the received vehicle identification code is not within the appropriate range of values, preemption does not occur.  
         [0023]     In yet another configuration, the phase selector  18  logs all preemption requests by recording the time of preemption, direction of preemption, duration of preemption, identification code, confirmation of passage of a requesting vehicle within a predetermined range of a detector, and denial of a preemption request due to improper authorization. In this configuration, attempted abuse of an optical traffic preemption system can be discovered by examining the logged information.  
         [0024]     In another embodiment of the present invention, an optical traffic preemption system helps run a mass transit system more efficiently. An authorized mass transit vehicle having an optical emitter constructed in accordance with the present invention, such as the bus  22  in  FIG. 1 , spends less time waiting at traffic signals, thereby saving fuel and allowing the mass transit vehicle to serve a larger route. This also encourages people to utilize mass transportation instead of private automobiles because authorized mass transit vehicles move through congested urban areas faster than other vehicles.  
         [0025]     Unlike an emergency vehicle, a mass transit vehicle equipped with an optical emitter may not require total preemption. In one embodiment, a traffic signal offset is used to give preference to a mass transit vehicle, while still allowing all approaches to the intersection to be serviced. For example, a traffic signal controller that normally allows traffic to flow 50 percent of the time in each direction responds to repeated phase requests from the phase selector to allow traffic flowing in the direction of the mass transit vehicle to proceed 65 percent of the time and traffic flowing in the other direction to flow 35 percent of the time. In this embodiment, the actual offset is fixed to allow the mass transit vehicle to have a predictable advantage. Generally, proper authorization should be validated before executing an offset for a mass transit vehicle.  
         [0026]     In a typical installation, the traffic preemption system does not actually control the lights at a traffic intersection. Rather, the phase selector  18  alternately issues phase requests to and withdraws phase requests from the traffic signal controller  14 , and the traffic signal controller determines whether the phase requests can be granted. The traffic signal controller may also receive phase requests originating from other sources, such as a nearby railroad crossing, in which case the traffic signal controller may determine that the phase request from the other source be granted before the phase request from the phase selector. However, as a practical matter, the preemption system can affect a traffic intersection and create a traffic signal offset by monitoring the traffic signal controller sequence and repeatedly issuing phase requests that will most likely be granted.  
         [0027]     According to a specific example embodiment, the traffic preemption system of  FIG. 1  is implemented using a known implementation that is modified to support multiple communication modes. For example, an Opticom™ Priority Control System (manufactured by 3M Company of Saint Paul, Minn.) can be modified to support one or more communication modes in addition to the communication mode for the Opticom™ Priority Control System. Consistent with features of the Opticom™ Priority Control System, one or more embodiments of U.S. Pat. No. 5,172,113 can be modified in this manner. Also according to the present invention, another specific example embodiment is implemented using another commercially-available traffic preemption system, such as the Strobecom II system (manufactured by TOMAR Electronics, Inc. of Phoenix, Ariz.), modified to support one or more additional communication modes.  
         [0028]      FIG. 2A-2C  illustrate optical pulses transmitted between a vehicle and equipment at an intersection for various example communication modes in accordance with the present invention. A first communication mode as illustrated in  FIG. 2A , can have optical pulse stream  100 . A second communication, as illustrated in  FIG. 2B , mode can have optical pulse stream  120 . A third communication mode, as illustrated in  FIG. 2C , can have optical pulse stream  140  that combines the features of optical pulse streams  100  and  120 .  
         [0029]     Optical pulse stream  100  has major stroboscopic pulses of light  102  occurring at a particular frequency that typically is nominally either 10 Hz or 14 Hz. Between the major pulses, optional data pulses  104 ,  106 , and  108  carry the data values embedded in the optical pulse stream  100 . For example, if pulse  104  is present then a data value has a first bit of one, and if pulse  104  is absent then the data value has a first bit of zero. If pulse  106  is present then the data value has a second bit of one, and if pulse  106  is absent then the data value has a second bit of zero. Similarly, if pulse  108  is present then the data value has a third bit of one, and if pulse  108  is absent then the data value has a third bit of zero. Typically, the optional pulses  104 ,  106 , and  108  are half-way between the major pulses  102 . Optical pulse stream  100  may correspond to the communication mode of an Opticom™ Priority Control System.  
         [0030]     Optical pulse stream  120  has stroboscopic pulses of light that nominally occur at a particular frequency that typically is approximately either 10 Hz or 14 Hz, but the pulses are displaced from the nominal frequency to embed the data values in the optical pulse stream  120 . For example, after an initial pulse  122 , only one or the other of pulses  124  and  126  is present and if an early pulse  124  is present then a data value has a first bit of zero and if late pulse  126  is present then the data value has a first bit of one. Only one or the other of pulses  128  and  130  is present and if early pulse  128  is present then the data value has a second bit of zero and if late pulse  130  is present then the data value has a second bit of one. Similarly, only one or the other of pulses  132  and  134  is present and if early pulse  132  is present then the data value has a third bit of zero and if late pulse  134  is present then the data value has a third bit of one.  
         [0031]     Another optical pulse stream is similar to optical pulse stream  120  in having stroboscopic pulses of light that nominally occur at a particular frequency that typically is approximately either 10 Hz or 14 Hz, with the pulses displaced from the nominal frequency to embed the data values in the optical pulse stream  120 . However, each pulse is separated from the prior pulse with a nominal time period corresponding to the nominal frequency with the actual separation between a pulse and the prior pulse being slightly less or slightly more than the nominal time period. An early pulse with a separation from the prior pulse of slightly less than the nominal time period embeds a data bit of zero and a late pulse with a separation from the prior pulse of slightly more than the nominal time period embeds a data bit of one. Such an optical pulse stream may correspond to the communication mode of a Strobecom II system.  
         [0032]     Optical pulse stream  140  combines the possible pulse positions of optical pulse streams  100  and  120 , providing the benefit that more data values can be embedded in the pulse stream in a given time period. The additional data can be used to provide additional operations, to enhance the security using encryption, and/or enhance robustness by adding error detection or correction without increasing the response time of the optical traffic control system. After the initial pulse  142 , the presence or absence of pulse  144  respectively provides a first bit of one or zero. Only one of pulses  146 ,  150 , and  148  is present in pulse stream  140 . The presence of pulse  146  provides a second bit of zero and the presence of pulse  148  provides a second bit of one. The presence of pulse  150  could indicate that the second bit does not have a value or the second bit has an unknown value. Additional bits including a third bit through the sixth bit are similarly embedded.  
         [0033]     It will be appreciated that an optical pulse stream similar to stream  140  can combine the possible pulse positions of pulse stream  100  and a second optical pulse stream that embeds data values by shifting the time period between each pulse and the prior pulse slightly from the nominal time period. Such a combined pulse stream can position the intermediate pulses  104 ,  106 , and  108  of stream  100  halfway between the slightly shifted pulses that are substituted for pulses  102  of stream  100 .  
         [0034]     A detection circuit arranged to extract the embedded data values for optical pulse stream  140  has the advantage of supporting a higher data communication rate and being compatible with both optical pulse streams  100  and  120 . After receiving an optical pulse stream  140  and extracting the embedded data value, a data value with any of the second, fourth, and sixth bits having an unknown value, as indicated by the presence of a pulse  150 ,  152 , or  154 , corresponds to optical pulse stream  100 . None of the second, fourth, and sixth bits having an unknown value, as indicated by the absence of pulses  150 ,  152 , and  154 , and any of the first, third, and fifth bit having a value of a one, as indicated by the presence of a pulse  144 ,  156 , or  158 , corresponds to pulse stream  140 . None of the second, fourth, and sixth bits having an unknown value and none of the first, third, and fifth bits having a value of a one, as indicated by the absence of pulses  144 ,  156 , and  158 , can correspond to pulse stream  120 . Thus, not only can the embedded data be extracted for either of optical pulse streams  100  and  120  by a detection circuit supporting optical pulse stream  140 , in addition the pulse streams  100 ,  120 , and  140  can be readily distinguished.  
         [0035]     The nominal frequency used to transmit pulses of an optical pulse stream  100 ,  120 , and  140  can determine a priority. For example, a frequency of approximately 10 Hz can correspond to a high priority for an emergency vehicle and a frequency of approximately 14 Hz can correspond to a low priority for a mass transit vehicle.  
         [0036]      FIG. 3  is a block diagram showing the optical traffic preemption system of  FIG. 1 . In  FIG. 3 , light pulses originating from the optical emitters  24 A and  24 B are received by the detector assembly  16 B, which is connected to a channel one and channel two of the phase selector  18 . The main processor  40  of phase selector  18  communicates with the traffic signal controller  14 , which in turn controls the traffic signal lights  12 .  
         [0037]     In one embodiment, detector assembly  16 B is a front-end circuit receiving signals from emitters  24 A and  24 B having respective communication modes. Signal processing circuitry  36 A and  36 B and processors  38 A,  38 B, and  40  are a back-end circuit that interprets and processes data produced by the detector assembly  16 B from the received signals. Channel one signal processing circuitry  36 A and processor  38 A can interpret and process the data according to a traffic light control protocol corresponding to the communication mode of emitter  24 A and channel two signal processing circuitry  36 B and processor  38 B can interpret and process the data according to a traffic light control protocol corresponding to the communication mode of emitter  24 B. It will be appreciated that protocols for multiple communication modes may be interpreted and processed in various embodiments with a single signal processing channel as is discussed in connection with  FIG. 4 . Circuits  16 B,  36 A,  36 B,  38 A,  38 B, and  40  may operate using parameters stored internally to the respective circuit or stored in long term memory  42  and some of these parameters can be useful for differentiating between the communication modes of emitters  24 A and  24 B by the respective channel.  
         [0038]     In another embodiment, detector assembly  16 B and signal processing circuitry  36 A and  36 B are a front-end circuit receiving signals from emitters  24 A and  24 B having respective communication modes. Processors  38 A,  38 B, and  40  are a back-end circuit that interprets and process data from the signal processing circuitry  36 A and  36 B. Processor  38 A can interpret and process the data according to a traffic light control protocol corresponding to the communication mode of emitter  24 A and processor  38 B can interpret and process the data according to a traffic light control protocol corresponding to the communication mode of emitter  24 B. Circuits  16 B,  36 A,  36 B,  38 A,  38 B, and  40  may operate using parameters stored internally to the respective circuit or stored in long term memory  42  and some of these parameters can be useful for differentiating between the communication modes of emitters  24 A and  24 B by the processors  38 A,  38 B, and  40 .  
         [0039]     The phase selector  18  includes the two channels, with each channel having signal processing circuitry ( 36 A and  36 B) and a processor ( 38 A and  38 B), a main processor  40 , long term memory  42 , an external data port  43  and a real time clock  44 . With reference to the channel one, the signal processing circuitry  36 A receives an analog signal provided by the detector assembly  16 B. The signal processing circuitry  36 A processes the analog signal and produces digital data that is received by the channel processor  38 A. The channel processor  38 A extracts the embedded data value from the digital data and provides the data value to the main processor  40 . Channel two is similarly configured, with the detector assembly  16 B coupled to the signal processing circuitry  36 B, which in turn is coupled to the channel processor  38 B. Each channel is dedicated to interpreting and processing data according to a respective traffic signal control protocol. It will be appreciated that channel two may process the received signal either in parallel with channel one or after channel one has determined that the received signal is not recognized as corresponding to the communication mode of channel one.  
         [0040]     The long term memory  42  is implemented using electronically erasable programmable read only memory (EEPROM). The long term memory  42  is coupled to the main processor  40  and is used log data and to store configuration parameters and a list of authorized identification codes. The main processor  40  checks for proper authorization by checking that the received vehicle identification code matches an entry in a list authorized identification.  
         [0041]     The external data port  43  is used for coupling the phase selector  18  to a computer. In one embodiment, external data port  43  is an RS232 serial port. Typically, portable computers are used in the field for exchanging data with and configuring a phase selector with parameters. Logged data is removed from the phase selector  18  via the external data port  43  and parameters and a list of authorized identification codes are stored in the phase selector  18  via the external data port  43 . The external data port  43  can also be accessed remotely using a modem, local-area network or other such device.  
         [0042]     The real time clock  44  provides the main processor  40  with the actual time. The real time clock  44  provides time stamps that can be logged to the long term memory  42  and is used for timing other events, such as providing a time tag associated with each light pulse received at detector assembly  16 B.  
         [0043]      FIG. 4  is a block diagram of the components of an optical traffic preemption system for another embodiment in accordance with the present invention. Light pulses originating from the optical emitters  24 A and  24 B are received by the detector assembly  16 B, which is connected to phase selector  18 . Phase selector  18  supports multiple communication modes having corresponding traffic light control protocols. For example, optical emitter  24 A can use one communication mode, optical emitter  24 B can use another communication mode, and phase selector  18  can support both emitters  24 A and  24 B including extracting data values embedded in the optical pulse streams received from emitters  24 A and  24 B. Phase selector  18  includes a decoder  160 , a database  162  and an external port  163 .  
         [0044]     Database  162  includes parameters to configure the operation of the decoder  160  including a single table  164  in one embodiment and multiple tables  164  and  166  in another embodiment. A single table  164  can include information for multiple communication modes. For example, even though different modulation schemes are used to embed a vehicle identification code for two communication modes, a single set of identification codes for both communication modes can be maintained in the table  164 . For another example, table  164  can include identification codes for one communication mode and table  166  can include identification codes for another communication mode.  
         [0045]     Database  162  can also include logs  168  of preemption activity. For example, each successful and unsuccessful preemption request received can be logged in logs  168 , including the vehicle identification code for the preemption request and the communication mode used to make the preemption request. An external port  163  provides access to the database  162  including downloading and erasing the logs  168  and updating the mode tables  164  and  166 .  
         [0046]     Front-end circuit  170  can include a sampling analog to digital converter (ADC) and a digital signal processor (DSP). The ADC may have configurable parameters, such as sampling rate, and the DSP can have configurable parameters, such as filter software routines, that are provided by database  162 . Serially produced data from front-end circuit  170  can be stored in memory  172 . Memory  172  can temporarily store the serial data stream until one or more complete operation requests are available for processing by back-end circuit  174  and until the discriminator  176  determines the communication mode being used using various distinguishing characteristics of the communication modes. Using the communication mode from discriminator  176 , the back-end circuit  174  extracts the data values embedded in the optical pulse stream. The back-end circuit  174  validates the operation request in the data values according to the traffic light control protocol corresponding to the communication mode.