Patent Publication Number: US-9834237-B2

Title: Route examining system and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 62/165,007, filed 21 May 2015 (the “&#39;007” application) and claims priority to U.S. Provisional Application No. 61/161,626, filed 14 May 2015 (the “&#39;626 application”). This application is a continuation-in-part of and claims priority to U.S. application Ser. No. 14/527,246, filed 29 Oct. 2014 (the “&#39;246 application”), which is a continuation-in-part of and claims priority to U.S. application Ser. No. 14/016,310, filed 3 Sep. 2013 (the “&#39;310 application,” now U.S. Pat. No. 8,914,171), which claims priority to U.S. Provisional Application No. 61/729,188, filed on 21 Nov. 2012 (the “&#39;188 application”). The entire disclosures of the &#39;007 application, the &#39;626 application, the &#39;246 application, the &#39;188 application, and the &#39;310 application are incorporated by reference. 
    
    
     GOVERNMENT LICENSE RIGHTS 
     This invention was made with Government support under contract number DTFR5314C00021 awarded by the Federal Railroad Administration. The Government has certain rights in this invention. 
    
    
     FIELD 
     Embodiments of the subject matter disclosed herein relate to examining routes traveled by vehicles for damage to the routes and/or to determine information about the routes and/or vehicles. 
     BACKGROUND 
     Routes that are traveled by vehicles may become damaged over time with extended use. For example, tracks on which rail vehicles travel may become damaged and/or broken. A variety of known systems are used to examine rail tracks to identify where the damaged and/or broken portions of the track are located. For example, some systems use cameras, lasers, and the like, to optically detect breaks and damage to the tracks. The cameras and lasers may be mounted on the rail vehicles, but the accuracy of the cameras and lasers may be limited by the speed at which the rail vehicles move during inspection of the route. As a result, the cameras and lasers may not be able to be used during regular operation (e.g., travel) of the rail vehicles in revenue service. 
     Other systems use ultrasonic transducers that are placed at or near the tracks to ultrasonically inspect the tracks. These systems may require very slow movement of the transducers relative to the tracks in order to detect damage to the track. When a suspect location is found by an ultrasonic inspection vehicle, a follow-up manual inspection may be required for confirmation of defects using transducers that are manually positioned and moved along the track and/or are moved along the track by a relatively slower moving inspection vehicle. Inspections of the track can take a considerable amount of time, during which the inspected section of the route may be unusable by regular route traffic. 
     Other systems use human inspectors who move along the track to inspect for broken and/or damaged sections of track. This manual inspection is slow and prone to errors. 
     Other systems use wayside devices that send electric signals through the tracks. If the signals are not received by other wayside devices, then a circuit that includes the track is identified as being open and the track is considered to be broken. These systems are limited at least in that the wayside devices are immobile. As a result, the systems cannot inspect large spans of track and/or a large number of devices must be installed in order to inspect the large spans of track. These systems are also limited at least in that a single circuit could stretch for multiple miles. As a result, if the track is identified as being open and is considered broken, it is difficult and time-consuming to locate the exact location of the break within the long circuit. For example, a maintainer must patrol the length of the circuit to locate the problem. 
     These systems are also limited at least in that other track features, such as highway (e.g., hard wire) crossing shunts, wide band (e.g., capacitors) crossing shunts, narrow band (e.g., tuned) crossing shunts, switches, insulated joints, and turnouts (e.g., track switches) may emulate the signal response expected from a broken rail and provide a false alarm. For example, scrap metal on the track, crossing shunts, etc., may short the rails together, preventing the current from traversing the length of the circuit, indicating that the circuit is open. Additionally, insulated joints and/or turnouts may include intentional conductive breaks that create an open circuit. In response, the system may identify a potentially broken section of track, and a person or machine may be dispatched to patrol the circuit to locate the break, even if the detected break is a false alarm (e.g., not a break in the track). A need remains to reduce the probability of false alarms to make route maintenance more efficient. 
     Another problem with some systems is the occurrence of false alarms and/or missed breaks in the track due to environmental noise along the track that distorts and/or conceals the signal response expected from a broken rail. Noise on the track may be produced by vehicles (e.g., locomotive dynamic motoring and/or braking), wayside control circuits, and/or by conditions on the track (e.g., lubrication or other deposits on the tracks, rusted or contaminated rails, etc.). This noise may bury the signal indicative of a break or produce some amplitude change or temporal shift that may be falsely interpreted as a break. A need remains to reduce the probability of false alarms and missed breaks due to noise along the tracks. 
     Some vehicle location determination systems may be unable to determine locations of the vehicle systems in some circumstances. For example, during initialization of the location determination systems, the vehicle system may be unable to determine the location of the vehicle system. During travel of the vehicle system in certain locations such as tunnels, valleys, urban areas, etc., the location determination systems may be unable to determine the locations of the vehicle systems. An improved manner for determining locations of vehicle systems is needed. 
     BRIEF DESCRIPTION 
     In one embodiment, a method (e.g., for examining a route) includes injecting a first electrical examination signal into a conductive route from onboard a vehicle system traveling along the route, detecting a first electrical characteristic of the route based on the first electrical examination signal, and detecting a break in conductivity of the route responsive to the first electrical characteristic decreasing by more than a designated drop threshold for a time period within a designated drop time period. 
     In another embodiment, a system (e.g., a route examining system) includes a first application unit configured to inject a first electrical examination signal into a conductive route from onboard a vehicle system traveling along the route, a first detection unit configured to detect a first electrical characteristic of the route based on the first electrical examination signal, and one or more processors configured to detect a break in conductivity of the route responsive to the first electrical characteristic decreasing by more than a designated drop threshold for a time period within a designated drop time period. 
     In another embodiment, a system (e.g., a route examining system) includes first and second application units, first and second detection units, and one or more processors. The first application unit is configured to be disposed onboard a vehicle traveling along a route having plural conductive rails. The first application unit is configured to inject a first electrical examination signal having one or more of a first frequency or a first unique identifier into a first rail of the plural conductive rails. The second application unit is configured to be disposed onboard the vehicle and to inject a second electrical examination signal having one or more of a different, second frequency or a different, second unique identifier into a second rail of the plural conductive rails. The first detection unit is configured to be disposed onboard the vehicle and to measure a first electrical characteristic of the first rail based on the first electrical examination signal and to measure a second electrical characteristic of the first rail based on the second electrical examination signal. The second detection unit is configured to be disposed onboard the vehicle and to measure a third electrical characteristic of the second rail based on the first electrical examination signal and to measure a fourth electrical characteristic of the second rail based on the second electrical examination signal. The one or more processors are configured to detect a break in conductivity of one or more of the first rail or the second rail of the route responsive to one or more of the first electrical characteristic, the second electrical characteristic, the third electrical characteristic, or the fourth electrical characteristic decreasing by more than a designated drop threshold for a time period that is within a designated drop time period. 
     In an embodiment, a method (e.g., for examining a route and/or determining information about the route and/or a vehicle system) includes injecting a first electrical examination signal into a conductive route from onboard a vehicle system traveling along the route, detecting a first electrical characteristic of the route based on the first electrical examination signal, and detecting, using a route examining system that also is configured to detect damage to the route based on the first electrical characteristic, a first frequency tuned shunt in the route based on the first electrical characteristic. 
     In an embodiment, a system (e.g., a route examining system) includes a first application unit configured to inject a first electrical examination signal into a conductive route from onboard a vehicle system traveling along the route, a first detection unit configured to measure a first electrical characteristic of the route based on the first electrical examination signal, and an identification unit configured to detect damage to the route based on the first electrical characteristic and to detect a first frequency tuned shunt in the route based on the first electrical characteristic. 
     In an embodiment, a system (e.g., a route examining system) includes a first application unit configured to inject a first electrical signal having a first frequency into a first conductive rail of a route from onboard a vehicle system, a first detection unit configured to monitor a first characteristic of the first conductive rail of the route from onboard the vehicle system based on the first electrical signal, a second application unit configured to inject a second electrical signal having a different, second frequency into a second conductive rail of the route from onboard the vehicle system, a second detection unit configured to monitor a second characteristic of the second conductive rail of the route from onboard the vehicle system based on the second electrical signal, and an identification unit configured to detect damage to the route and to determine one or more of identify the route from several different routes, determine a location of the vehicle system along the route, determine a direction of travel of the vehicle system, determine a speed of the vehicle system, or identify a missing or damaged frequency tuned shunt based on one or more of the first or second characteristic. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is made to the accompanying drawings in which particular embodiments and further benefits of the invention are illustrated as described in more detail in the description below, in which: 
         FIG. 1  is a schematic illustration of a vehicle system that includes an embodiment of a route examining system; 
         FIG. 2  is a schematic illustration of an embodiment of an examining system; 
         FIG. 3  illustrates a schematic diagram of an embodiment of plural vehicle systems traveling along the route; 
         FIG. 4  is a flowchart of an embodiment of a method for examining a route being traveled by a vehicle system from onboard the vehicle system; 
         FIG. 5  is a schematic illustration of an embodiment of an examining system; 
         FIG. 6  is a schematic illustration of an embodiment of an examining system on a vehicle of a vehicle system traveling along a route; 
         FIG. 7  is a schematic illustration of an embodiment of an examining system disposed on multiple vehicles of a vehicle system traveling along a route; 
         FIG. 8  is a schematic diagram of an embodiment of an examining system on a vehicle of a vehicle system on a route; 
         FIG. 9  is a schematic illustration of an embodiment of an examining system on a vehicle as the vehicle travels along a route; 
         FIG. 10  is another schematic illustration of an embodiment of an examining system on a vehicle as the vehicle travels along a route; 
         FIG. 11  is another schematic illustration of an embodiment of an examining system on a vehicle as the vehicle travels along a route; 
         FIG. 12  illustrates electrical signals monitored by an examining system on a vehicle system as the vehicle system travels along a route; 
         FIG. 13  is a flowchart of an embodiment of a method for examining a route being traveled by a vehicle system from onboard the vehicle system; 
         FIG. 14  is a schematic illustration of an embodiment of the examining system on the vehicle as the vehicle travels along the route; 
         FIG. 15  illustrates electrical characteristics that may be monitored by the examining system on a vehicle system as the vehicle system travels along the route according to one example; 
         FIG. 16  illustrates a flowchart of one embodiment of a method for examining a route and/or determining information about the route and/or a vehicle system; 
         FIG. 17  illustrates another example of the examining system shown herein in operation; 
         FIG. 18  illustrates a flowchart of one embodiment of a method for examining a route; 
         FIG. 19  illustrates an example of electrical characteristics measured by the detection units shown in  FIG. 17 ; 
         FIG. 20  illustrates an example of electrical characteristics measured by the detection units shown in  FIG. 17 ; 
         FIG. 21  illustrates an example of electrical characteristics measured by the detection units shown in  FIG. 17 ; 
         FIG. 22  illustrates an example of electrical characteristics measured by the detection units shown in  FIG. 17 ; 
         FIG. 23  illustrates examples of feature vectors included in different patterns representative of different conditions of the route; and 
         FIG. 24  illustrates an example of two waveforms of the electrical characteristics measured by the detection units shown in  FIG. 17 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the inventive subject matter described herein relate to methods and systems for examining a route being traveled upon by a vehicle system in order to identify potential sections of the route that are damaged or broken. In an embodiment, the vehicle system may examine the route by injecting an electrical signal into the route from a first vehicle in the vehicle system as the vehicle system travels along the route and monitoring the route at another, second vehicle that also is in the vehicle system. Detection of the signal at the second vehicle and/or detection of changes in the signal at the second vehicle may indicate a potentially damaged (e.g., broken or partially broken) section of the route between the first and second vehicles. In an embodiment, the route may be a track of a rail vehicle system and the first and second vehicle may be used to identify a broken or partially broken section of one or more rails of the track. The electrical signal that is injected into the route may be powered by an onboard energy storage device, such as one or more batteries, and/or an off-board energy source, such as a catenary and/or electrified rail of the route. When the damaged section of the route is identified, one or more responsive actions may be initiated. For example, the vehicle system may automatically slow down or stop. As another example, a warning signal may be communicated (e.g., transmitted or broadcast) to one or more other vehicle systems to warn the other vehicle systems of the damaged section of the route, to one or more wayside devices disposed at or near the route so that the wayside devices can communicate the warning signals to one or more other vehicle systems. In another example, the warning signal may be communicated to an off-board facility that can arrange for the repair and/or further examination of the damaged section of the route. 
     The term “vehicle” as used herein can be defined as a mobile machine that transports at least one of a person, people, or a cargo. For instance, a vehicle can be, but is not limited to being, a rail car, an intermodal container, a locomotive, a marine vessel, mining equipment, construction equipment, an automobile, and the like. A “vehicle system” includes two or more vehicles that are interconnected with each other to travel along a route. For example, a vehicle system can include two or more vehicles that are directly connected to each other (e.g., by a coupler) or that are indirectly connected with each other (e.g., by one or more other vehicles and couplers). A vehicle system can be referred to as a consist, such as a rail vehicle consist. 
     “Software” or “computer program” as used herein includes, but is not limited to, one or more computer readable and/or executable instructions that cause a computer or other electronic device to perform functions, actions, and/or behave in a desired manner. The instructions may be embodied in various forms such as routines, algorithms, modules or programs including separate applications or code from dynamically linked libraries. Software may also be implemented in various forms such as a stand-alone program, a function call, a servlet, an applet, an application, instructions stored in a memory, part of an operating system or other type of executable instructions. “Computer” or “processing element” or “computer device” as used herein includes, but is not limited to, any programmed or programmable electronic device that can store, retrieve, and process data. “Non-transitory computer-readable media” include, but are not limited to, a CD-ROM, a removable flash memory card, a hard disk drive, a magnetic tape, and a floppy disk. “Computer memory”, as used herein, refers to a storage device configured to store digital data or information which can be retrieved by a computer or processing element. “Controller,” “unit,” and/or “module,” as used herein, can to the logic circuitry and/or processing elements and associated software or program involved in controlling an energy storage system. The terms “signal”, “data”, and “information” may be used interchangeably herein and may refer to digital or analog forms. 
       FIG. 1  is a schematic illustration of a vehicle system  100  that includes an embodiment of a route examining system  102 . The vehicle system  100  includes several vehicles  104 ,  106  that are mechanically connected with each other to travel along a route  108 . The vehicles  104  (e.g., the vehicles  104 A-C) represent propulsion-generating vehicles, such as vehicles that generate tractive effort or power in order to propel the vehicle system  100  along the route  108 . In an embodiment, the vehicles  104  can represent rail vehicles such as locomotives. The vehicles  106  (e.g., the vehicles  106 A-E) represent non-propulsion generating vehicles, such as vehicles that do not generate tractive effort or power. In an embodiment, the vehicles  106  can represent rail cars. Alternatively, the vehicles  104 ,  106  may represent other types of vehicles. In another embodiment, one or more of the individual vehicles  104  and/or  106  represent a group of vehicles, such as a consist of locomotives or other vehicles. 
     The route  108  can be a body, surface, or medium on which the vehicle system  100  travels. In an embodiment, the route  108  can include or represent a body that is capable of conveying a signal between vehicles in the vehicle system  100 , such as a conductive body capable of conveying an electrical signal (e.g., a direct current, alternating current, radio frequency, or other signal). 
     The examining system  102  can be distributed between or among two or more vehicles  104 ,  106  of the vehicle system  100 . For example, the examining system  102  may include two or more components that operate to identify potentially damaged sections of the route  108 , with at least one component disposed on each of two different vehicles  104 ,  106  in the same vehicle system  100 . In the illustrated embodiment, the examining system  102  is distributed between or among two different vehicles  104 . Alternatively, the examining system  102  may be distributed among three or more vehicles  104 ,  106 . Additionally or alternatively, the examining system  102  may be distributed between one or more vehicles  104  and one or more vehicles  106 , and is not limited to being disposed onboard a single type of vehicle  104  or  106 . As described below, in another embodiment, the examining system  102  may be distributed between a vehicle in the vehicle system and an off-board monitoring location, such as a wayside device. 
     In operation, the vehicle system  100  travels along the route  108 . A first vehicle  104  electrically injects an examination signal into the route  108 . For example, the first vehicle  104 A may apply a direct current, alternating current, radio frequency signal, or the like, to the route  108  as an examination signal. The examination signal propagates through or along the route  108 . A second vehicle  104 B or  104 C may monitor one or more electrical characteristics of the route  108  when the examination signal is injected into the route  108 . 
     The examining system  102  can be distributed among two separate vehicles  104  and/or  106 . In the illustrated embodiment, the examining system  102  has components disposed onboard at least two of the propulsion-generating vehicles  104 A,  104 B,  104 C. Additionally or alternatively, the examining system  102  may include components disposed onboard at least one of the non-propulsion generating vehicles  106 . For example, the examining system  102  may be located onboard two or more propulsion-generating vehicles  104 , two or more non-propulsion generating vehicles  106 , or at least one propulsion-generating vehicle  104  and at least one non-propulsion generating vehicle  106 . 
     In operation, during travel of the vehicle system  100  along the route  108 , the examining system  102  electrically injects an examination signal into the route  108  at a first vehicle  104  or  106  (e.g., beneath the footprint of the first vehicle  104  or  106 ). For example, an onboard or off-board power source may be controlled to apply a direct current, alternating current, RF signal, or the like, to a track of the route  108 . The examining system  102  monitors electrical characteristics of the route  108  at a second vehicle  104  or  106  of the same vehicle system  100  (e.g., beneath the footprint of the second vehicle  104  or  106 ) in order to determine if the examination signal is detected in the route  108 . For example, the voltage, current, resistance, impedance, or other electrical characteristic of the route  108  may be monitored at the second vehicle  104 ,  106  in order to determine if the examination signal is detected and/or if the examination signal has been altered. If the portion of the route  108  between the first and second vehicles conducts the examination signal to the second vehicle, then the examination signal may be detected by the examining system  102 . The examining system  102  may determine that the route  108  (e.g., the portion of the route  108  through which the examination signal propagated) is intact and/or not damaged. 
     On the other hand, if the portion of the route  108  between the first and second vehicles does not conduct the examination signal to the second vehicle (e.g., such that the examination signal is not detected in the route  108  at the second vehicle), then the examination signal may not be detected by the examining system  102 . The examining system  102  may determine that the route  108  (e.g., the portion of the route  108  disposed between the first and second vehicles during the time period that the examination signal is expected or calculated to propagate through the route  108 ) is not intact and/or is damaged. For example, the examining system  102  may determine that the portion of a track between the first and second vehicles is broken such that a continuous conductive pathway for propagation of the examination signal does not exist. The examining system  102  can identify this section of the route as being a potentially damaged section of the route  108 . In routes  108  that are segmented (e.g., such as rail tracks that may have gaps), the examining system  102  may transmit and attempt to detect multiple examination signals in order to prevent false detection of a broken portion of the route  108 . 
     Because the examination signal may propagate relatively quickly through the route  108  (e.g., faster than a speed at which the vehicle system  100  moves), the route  108  can be examined using the examination signal when the vehicle system  100  is moving, such as transporting cargo or otherwise operating at or above a non-zero, minimum speed limit of the route  108 . 
     Additionally or alternatively, the examining system  102  may detect one or more changes in the examination signal at the second vehicle. The examination signal may propagate through the route  108  from the first vehicle to the second vehicle. But, due to damaged portions of the route  108  between the first and second vehicles, one or more signal characteristics of the examination signal may have changed. For example, the signal-to-noise ratio, intensity, power, or the like, of the examination signal may be known or designated when injected into the route  108  at the first vehicle. One or more of these signal characteristics may change (e.g., deteriorate or decrease) during propagation through a mechanically damaged or deteriorated portion of the route  108 , even though the examination signal is received (e.g., detected) at the second vehicle. The signal characteristics can be monitored upon receipt of the examination signal at the second vehicle. Based on changes in one or more of the signal characteristics, the examining system  102  may identify the portion of the route  108  that is disposed between the first and second vehicles as being a potentially damaged portion of the route  108 . For example, if the signal-to-noise ratio, intensity, power, or the like, of the examination signal decreases below a designated threshold and/or decreases by more than a designated threshold decrease, then the examining system  102  may identify the section of the route  108  as being potentially damaged. 
     In response to identifying a section of the route  108  as being damaged or damaged, the examining system  102  may initiate one or more responsive actions. For example, the examining system  102  can automatically slow down or stop movement of the vehicle system  100 . The examining system  102  can automatically issue a warning signal to one or more other vehicle systems traveling nearby of the damaged section of the route  108  and where the damaged section of the route  108  is located. The examining system  102  may automatically communicate a warning signal to a stationary wayside device located at or near the route  108  that notifies the device of the potentially damaged section of the route  108  and the location of the potentially damaged section. The stationary wayside device can then communicate a signal to one or more other vehicle systems traveling nearby of the potentially damaged section of the route  108  and where the potentially damaged section of the route  108  is located. The examining system  102  may automatically issue an inspection signal to an off-board facility, such as a repair facility, that notifies the facility of the potentially damaged section of the route  108  and the location of the section. The facility may then send one or more inspectors to check and/or repair the route  108  at the potentially damaged section. Alternatively, the examining system  102  may notify an operator of the potentially damaged section of the route  108  and the operator may then manually initiate one or more responsive actions. 
       FIG. 2  is a schematic illustration of an embodiment of an examining system  200 . The examining system  200  may represent the examining system  102  shown in  FIG. 1 . The examining system  200  is distributed between a first vehicle  202  and a second vehicle  204  in thesame vehicle system. The vehicles  202 ,  204  may represent vehicles  104  and/or  106  of the vehicle system  100  shown in  FIG. 1 . In an embodiment, the vehicles  202 ,  204  represent two of the vehicles  104 , such as the vehicle  104 A and the vehicle  104 B, the vehicle  104 B and the vehicle  104 C, or the vehicle  104 A and the vehicle  104 C. Alternatively, one or more of the vehicles  202 ,  204  may represent at least one of the vehicles  106 . In another embodiment, the examining system  200  may be distributed among three or more of the vehicles  104  and/or  106 . 
     The examining system  200  includes several components described below that are disposed onboard the vehicles  202 ,  204 . For example, the illustrated embodiment of the examining system  200  includes a control unit  208 , an application device  210 , an onboard power source  212  (“Battery” in  FIG. 2 ), one or more conditioning circuits  214 , a communication unit  216 , and one or more switches  224  disposed onboard the first vehicle  202 . The examining system  200  also includes a detection unit  218 , an identification unit  220 , a detection device  230 , and a communication unit  222  disposed onboard the second vehicle  204 . Alternatively, one or more of the control unit  208 , application device  210 , power source  212 , conditioning circuits  214 , communication unit  216 , and/or switch  224  may be disposed onboard the second vehicle  204  and/or another vehicle in the same vehicle system, and/or one or more of the detection unit  218 , identification unit  220 , detection device  230 , and communication unit  222  may be disposed onboard the first vehicle  202  and/or another vehicle in the same vehicle system. 
     The control unit  206  controls supply of electric current to the application device  210 . In an embodiment, the application device  210  includes one or more conductive bodies that engage the route  108  as the vehicle system that includes the vehicle  202  travels along the route  108 . For example, the application device  210  can include a conductive shoe, brush, or other body that slides along an upper and/or side surface of a track such that a conductive pathway is created that extends through the application device  210  and the track. Additionally or alternatively, the application device  210  can include a conductive portion of a wheel of the first vehicle  202 , such as the conductive outer periphery or circumference of the wheel that engages the route  108  as the first vehicle  202  travels along the route  108 . In another embodiment, the application device  210  may be inductively coupled with the route  108  without engaging or touching the route  108  or any component that engages the route  108 . 
     The application device  210  is conductively coupled with the switch  224 , which can represent one or more devices that control the flow of electric current from the onboard power source  212  and/or the conditioning circuits  214 . The switch  224  can be controlled by the control unit  206  so that the control unit  206  can turn on or off the flow of electric current through the application device  210  to the route  108 . In an embodiment, the switch  224  also can be controlled by the control unit  206  to vary one or more waveforms and/or waveform characteristics (e.g., phase, frequency, amplitude, and the like) of the current that is applied to the route  108  by the application device  210 . 
     The onboard power source  212  represents one or more devices capable of storing electric energy, such as one or more batteries, capacitors, flywheels, and the like. Additionally or alternatively, the power source  212  may represent one or more devices capable of generating electric current, such as an alternator, generator, photovoltaic device, gas turbine, or the like. The power source  212  is coupled with the switch  224  so that the control unit  206  can control when the electric energy stored in the power source  212  and/or the electric current generated by the power source  212  is conveyed as electric current (e.g., direct current, alternating current, an RF signal, or the like) to the route  108  via the application device  210 . 
     The conditioning circuit  214  represents one or more circuits and electric components that change characteristics of electric current. For example, the conditioning circuit  214  may include one or more inverters, converters, transformers, batteries, capacitors, resistors, inductors, and the like. In the illustrated embodiment, the conditioning circuit  214  is coupled with a connecting assembly  226  that is configured to receive electric current from an off-board source. For example, the connecting assembly  226  may include a pantograph that engages an electrified conductive pathway  228  (e.g., a catenary) extending along the route  108  such that the electric current from the catenary  228  is conveyed via the connecting assembly  226  to the conditioning circuit  214 . Additionally or alternatively, the electrified conductive pathway  228  may represent an electrified portion of the route  108  (e.g., an electrified rail) and the connecting assembly  226  may include a conductive shoe, brush, portion of a wheel, or other body that engages the electrified portion of the route  108 . Electric current is conveyed from the electrified portion of the route  108  through the connecting assembly  226  and to the conditioning circuit  214 . 
     The electric current that is conveyed to the conditioning circuit  214  from the power source  212  and/or the off-board source (e.g., via the connecting assembly  226 ) can be altered by the conditioning circuit  214 . For example, the conditioning circuit  214  can change the voltage, current, frequency, phase, magnitude, intensity, waveform, and the like, of the current that is received from the power source  212  and/or the connecting assembly  226 . The modified current can be the examination signal that is electrically injected into the route  108  by the application device  210 . Additionally or alternatively, the control unit  206  can form the examination signal by controlling the switch  224 . For example, the examination signal can be formed by turning the switch  224  on to allow current to flow from the conditioning circuit  214  and/or the power source  212  to the application device  210 . 
     In an embodiment, the control unit  206  may control the conditioning circuit  214  to form the examination signal. For example, the control unit  206  may control the conditioning circuit  214  to change the voltage, current, frequency, phase, magnitude, intensity, waveform, and the like, of the current that is received from the power source  212  and/or the connecting assembly  226  to form the examination signal. The examination signal optionally may be a waveform that includes multiple frequencies. The examination signal may include multiple harmonics or overtones. The examination signal may be a square wave or the like. 
     The examination signal is conducted through the application device  210  to the route  108 , and is electrically injected into a conductive portion of the route  108 . For example, the examination signal may be conducted into a conductive track of the route  108 . In another embodiment, the application device  210  may not directly engage (e.g., touch) the route  108 , but may be wirelessly coupled with the route  108  in order to electrically inject the examination signal into the route  108  (e.g., via induction). 
     The conductive portion of the route  108  that extends between the first and second vehicles  202 ,  204  during travel of the vehicle system may form a track circuit through which the examination signal may be conducted. The first vehicle  202  can be coupled (e.g., coupled physically, coupled wirelessly, among others) to the track circuit by the application device  210 . The power source (e.g., the onboard power source  212  and/or the off-board electrified conductive pathway  228 ) can transfer power (e.g., the examination signal) through the track circuit toward the second vehicle  204 . 
     By way of example and not limitation, the first vehicle  202  can be coupled to a track of the route  108 , and the track can be the track circuit that extends and conductively couples one or more components of the examining system  200  on the first vehicle  202  with one or more components of the examining system  200  on the second vehicle  204 . 
     In an embodiment, the control unit  206  includes or represents a manager component. Such a manager component can be configured to activate a transmission of electric current into the route  108  via the application device  210 . In another instance, the manager component can activate or deactivate a transfer of the portion of power from the onboard and/or off-board power source to the application device  210 , such as by controlling the switch and/or conditioning circuit. Moreover, the manager component can adjust parameter(s) associated with the portion of power that is transferred to the route  108 . For instance, the manager component can adjust an amount of power transferred, a frequency at which the power is transferred (e.g., a pulsed power delivery, AC power, among others), a duration of time the portion of power is transferred, among others. Such parameter(s) can be adjusted by the manager component based on at least one of a geographic location of the vehicle or the device or an identification of the device (e.g., type, location, make, model, among others). 
     The manager component can leverage a geographic location of the vehicle or the device in order to adjust a parameter for the portion of power that can be transferred to the device from the power source. For instance, the amount of power transferred can be adjusted by the manager component based on the device power input. By way of example and not limitation, the portion of power transferred can meet or be below the device power input in order to reduce risk of damage to the device. In another example, the geographic location of the vehicle and/or the device can be utilized to identify a particular device and, in turn, a power input for such device. The geographic location of the vehicle and/or the device can be ascertained by a location on a track circuit, identification of the track circuit, Global Positioning Service (GPS), among others. 
     The detection unit  218  disposed onboard the second vehicle  204  as shown in  FIG. 2  monitors the route  108  to attempt to detect the examination signal that is injected into the route  108  by the first vehicle  202 . The detection unit  218  is coupled with the detection device  230 . In an embodiment, the detection device  230  includes one or more conductive bodies that engage the route  108  as the vehicle system that includes the vehicle  204  travels along the route  108 . For example, the detection device  230  can include a conductive shoe, brush, or other body that slides along an upper and/or side surface of a track such that a conductive pathway is created that extends through the detection device  230  and the track. Additionally or alternatively, the detection device  230  can include a conductive portion of a wheel of the second vehicle  204 , such as the conductive outer periphery or circumference of the wheel that engages the route  108  as the second vehicle  204  travels along the route  108 . In another embodiment, the detection device  230  may be inductively coupled with the route  108  without engaging or touching the route  108  or any component that engages the route  108 . 
     The detection unit  218  monitors one or more electrical characteristics of the route  108  using the detection device  230 . For example, the voltage of a direct current conducted by the route  108  may be detected by monitoring the voltage conducted along the route  108  to the detection device  230 . In another example, the current (e.g., frequency, amps, phases, or the like) of an alternating current or RF signal being conducted by the route  108  may be detected by monitoring the current conducted along the route  108  to the detection device  230 . As another example, the signal-to-noise ratio of a signal being conducted by the detection device  230  from the route  108  may be detected by the detection unit  218  examining the signal conducted by the detection device  230  (e.g., a received signal) and comparing the received signal to a designated signal. For example, the examination signal that is injected into the route  108  using the application device  210  may include a designated signal or portion of a designated signal. The detection unit  218  may compare the received signal that is conducted from the route  108  into the detection device  230  with this designated signal in order to measure a signal-to-noise ratio of the received signal. 
     The detection unit  218  determines one or more electrical characteristics of the signal that is received (e.g., picked up) by the detection device  230  from the route  108  and reports the characteristics of the received signal to the identification unit  220 . The one or more electrical characteristics may include voltage, current, frequency, phase, phase shift or difference, modulation, intensity, embedded signature, and the like. If no signal is received by the detection device  230 , then the detection unit  218  may report the absence of such a signal to the identification unit  220 . For example, if the detection unit  218  does not detect at least a designated voltage, designated current, or the like, as being received by the detection device  230 , then the detection unit  218  may not detect any received signal. Alternatively or additionally, the detection unit  218  may communicate the detection of a signal that is received by the detection device  230  only upon detection of the signal by the detection device  230 . 
     In an embodiment, the detection unit  218  may determine the characteristics of the signals received by the detection device  230  in response to a notification received from the control unit  206  in the first vehicle  202 . For example, when the control unit  206  is to cause the application device  210  to inject the examination signal into the route  108 , the control unit  206  may direct the communication unit  216  to transmit a notification signal to the detection device  230  via the communication unit  222  of the second vehicle  204 . The communication units  216 ,  222  may include respective antennas  232 ,  234  and associated circuitry for wirelessly communicating signals between the vehicles  202 ,  204 , and/or with off-board locations. The communication unit  216  may wirelessly transmit a notification to the detection unit  218  that instructs the detection unit  218  as to when the examination signal is to be input into the route  108 . Additionally or alternatively, the communication units  216 ,  222  may be connected via one or more wires, cables, and the like, such as a multiple unit (MU) cable, train line, or other conductive pathway(s), to allow communication between the communication units  216 ,  222 . 
     The detection unit  218  may begin monitoring signals received by the detection device  230 . For example, the detection unit  218  may not begin or resume monitoring the received signals of the detection device  230  unless or until the detection unit  218  is instructed that the control unit  206  is causing the injection of the examination signal into the route  108 . Alternatively or additionally, the detection unit  218  may periodically monitor the detection device  230  for received signals and/or may monitor the detection device  230  for received signals upon being manually prompted by an operator of the examining system  200 . 
     The identification unit  220  receives the characteristics of the received signal from the detection unit  218  and determines if the characteristics indicate receipt of all or a portion of the examination signal injected into the route  108  by the first vehicle  202 . Although the detection unit  218  and the identification unit  220  are shown as separate units, the detection unit  218  and the identification unit  220  may refer to the same unit. For example, the detection unit  218  and the identification unit  220  may be a single hardware component disposed onboard the second vehicle  204 . 
     The identification unit  220  examines the characteristics and determines if the characteristics indicate that the section of the route  108  disposed between the first vehicle  202  and the second vehicle  204  is damaged or at least partially damaged. For example, if the application device  210  injected the examination signal into a track of the route  108  and one or more characteristics (e.g., voltage, current, frequency, intensity, signal-to-noise ratio, and the like) of the examination signal are not detected by the detection unit  218 , then, the identification unit  220  may determine that the section of the track that was disposed between the vehicles  202 ,  204  is broken or otherwise damaged such that the track cannot conduct the examination signal. Additionally or alternatively, the identification unit  220  can examine the signal-to-noise ratio of the signal detected by the detection unit  218  and determine if the section of the route  108  between the vehicles  202 ,  204  is potentially broken or damaged. For example, the identification unit  220  may identify this section of the route  108  as being broken or damaged if the signal-to-noise ratio of one or more (or at least a designated amount) of the received signals is less than a designated ratio. 
     The identification unit  220  may include or be communicatively coupled (e.g., by one or more wired and/or wireless connections that allow communication) with a location determining unit that can determine the location of the vehicle  204  and/or vehicle system. For example, the location determining unit may include a GPS unit or other device that can determine where the first vehicle and/or second vehicle are located along the route  108 . The distance between the first vehicle  202  and the second vehicle  204  along the length of the vehicle system may be known to the identification unit  220 , such as by inputting the distance into the identification unit  220  using one or more input devices and/or via the communication unit  222 . 
     The identification unit  220  can identify which section of the route  108  is potentially damaged based on the location of the first vehicle  202  and/or the second vehicle  204  during transmission of the examination signal through the route  108 . For example, the identification unit  220  can identify the section of the route  108  that is within a designated distance of the vehicle system, the first vehicle  202 , and/or the second vehicle  204  as the potentially damaged section when the identification unit  220  determines that the examination signal is not received or at least has a decreased signal-to-noise ratio. 
     Additionally or alternatively, the identification unit  220  can identify which section of the route  108  is potentially damaged based on the locations of the first vehicle  202  and the second vehicle  204  during transmission of the examination signal through the route  108 , the direction of travel of the vehicle system that includes the vehicles  202 ,  204 , the speed of the vehicle system, and/or a speed of propagation of the examination signal through the route  108 . The speed of propagation of the examination signal may be a designated speed that is based on one or more of the material(s) from which the route  108  is formed, the type of examination signal that is injected into the route  108 , and the like. In an embodiment, the identification unit  220  may be notified when the examination signal is injected into the route  108  via the notification provided by the control unit  206 . The identification unit  220  can then determine which portion of the route  108  is disposed between the first vehicle  202  and the second vehicle  204  as the vehicle system moves along the route  108  during the time period that corresponds to when the examination signal is expected to be propagating through the route  108  between the vehicles  202 ,  204  as the vehicles  202 ,  204  move. This portion of the route  108  may be the section of potentially damaged route that is identified. 
     One or more responsive actions may be initiated when the potentially damaged section of the route  108  is identified. For example, in response to identifying the potentially damaged portion of the route  108 , the identification unit  220  may notify the control unit  206  via the communication units  222 ,  216 . The control unit  206  and/or the identification unit  220  can automatically slow down or stop movement of the vehicle system. For example, the control unit  206  and/or identification unit  220  can be communicatively coupled with one or more propulsion systems (e.g., engines, alternators/generators, motors, and the like) of one or more of the propulsion-generating vehicles in the vehicle system. The control unit  206  and/or identification unit  220  may automatically direct the propulsion systems to slow down and/or stop. 
     With continued reference to  FIG. 2 ,  FIG. 3  illustrates a schematic diagram of an embodiment of plural vehicle systems  300 ,  302  traveling along the route  108 . One or more of the vehicle systems  300 ,  302  may represent the vehicle system  100  shown in  FIG. 1  that includes the route examining system  200 . For example, at least a first vehicle system  300  traveling along the route  108  in a first direction  308  may include the examining system  200 . The second vehicle system  302  may be following the first vehicle system  300  on the route  108 , but spaced apart and separated from the first vehicle system  300 . 
     In addition or as an alternate to the responsive actions that may be taken when a potentially damaged section of the route  108  is identified, the examining system  200  onboard the first vehicle system  300  may automatically notify the second vehicle system  302 . The control unit  206  and/or the identification unit  220  may wirelessly communicate (e.g., transmit or broadcast) a warning signal to the second vehicle system  302 . The warning signal may notify the second vehicle system  302  of the location of the potentially damaged section of the route  108  before the second vehicle system  302  arrives at the potentially damaged section. The second vehicle system  302  may be able to slow down, stop, or move to another route to avoid traveling over the potentially damaged section. 
     Additionally or alternatively, the control unit  206  and/or identification unit  220  may communicate a warning signal to a stationary wayside device  304  in response to identifying a section of the route  108  as being potentially damaged. The device  304  can be, for instance, wayside equipment, an electrical device, a client asset, a defect detection device, a device utilized with Positive Train Control (PTC), a signal system component(s), a device utilized with Automated Equipment Identification (AEI), among others. In one example, the device  304  can be a device utilized with AEI. AEI is an automated equipment identification mechanism that can aggregate data related to equipment for the vehicle. By way of example and not limitation, AEI can utilize passive radio frequency technology in which a tag (e.g., passive tag) is associated with the vehicle and a reader/receiver receives data from the tag when in geographic proximity thereto. The AEI device can be a reader or receiver that collects or stores data from a passive tag, a data store that stores data related to passive tag information received from a vehicle, an antenna that facilitates communication between the vehicle and a passive tag, among others. Such an AEI device may store an indication of where the potentially damaged section of the route  108  is located so that the second vehicle system  302  may obtain this indication when the second vehicle system  302  reads information from the AEI device. 
     In another example, the device  304  can be a signaling device for the vehicle. For instance, the device  304  can provide visual and/or audible warnings to provide warning to other entities such as other vehicle systems (e.g., the vehicle system  302 ) of the potentially damaged section of the route  108 . The signaling devices can be, but not limited to, a light, a motorized gate arm (e.g., motorized motion in a vertical plane), an audible warning device, among others. 
     In another example, the device  304  can be utilized with PTC. PTC can refer to communication-based/processor-based vehicle control technology that provides a system capable of reliably and functionally preventing collisions between vehicle systems, over speed derailments, incursions into established work zone limits, and the movement of a vehicle system through a route switch in the improper position. PTC systems can perform other additional specified functions. Such a PTC device  304  can provide warnings to the second vehicle system  204  that cause the second vehicle system  204  to automatically slow and/or stop, among other responsive actions, when the second vehicle system  204  approaches the location of the potentially damaged section of the route  108 . 
     In another example, the wayside device  304  can act as a beacon or other transmitting or broadcasting device other than a PTC device that communicates warnings to other vehicles or vehicle systems traveling on the route  108  of the identified section of the route  108  that is potentially damaged. 
     The control unit  206  and/or identification unit  220  may communicate a repair signal to an off-board facility  306  in response to identifying a section of the route  108  as being potentially damaged. The facility  306  can represent a location, such as a dispatch or repair center, that is located off-board of the vehicle systems  202 ,  204 . The repair signal may include or represent a request for further inspection and/or repair of the route  108  at the potentially damaged section. Upon receipt of the repair signal, the facility  306  may dispatch one or more persons and/or equipment to the location of the potentially damaged section of the route  108  in order to inspect and/or repair the route  108  at the location. 
     Additionally or alternatively, the control unit  206  and/or identification unit  220  may notify an operator of the vehicle system of the potentially damaged section of the route  108  and suggest the operator initiate one or more of the responsive actions described herein. 
     In another embodiment, the examining system  200  may identify the potentially damaged section of the route  108  using the wayside device  304 . For example, the detection device  230 , the detection unit  218 , and the communication unit  222  may be located at or included in the wayside device  304 . The control unit  206  on the vehicle system may determine when the vehicle system is within a designated distance of the wayside device  304  based on an input or known location of the wayside device  304  and the monitored location of the vehicle system (e.g., from data obtained from a location determination unit). Upon traveling within a designated distance of the wayside device  304 , the control unit  206  may cause the examination signal to be injected into the route  108 . The wayside device  304  can monitor one or more electrical characteristics of the route  108  similar to the second vehicle  204  described above. If the electrical characteristics indicate that the section of the route  108  between the vehicle system and the wayside device  304  is damaged or broken, the wayside device  304  can initiate one or more responsive actions, such as by directing the vehicle system to automatically slow down and/or stop, warning other vehicle systems traveling on the route  108 , requesting inspection and/or repair of the potentially damaged section of the route  108 , and the like. 
       FIG. 5  is a schematic illustration of an embodiment of an examining system  500 . The examining system  500  may represent the examining system  102  shown in  FIG. 1 . In contrast to the examining system  200  shown in  FIG. 2 , the examining system  500  is disposed within a single vehicle  502  in a vehicle system that may include one or more additional vehicles mechanically coupled with the vehicle  502 . The vehicle  502  may represent a vehicle  104  and/or  106  of the vehicle system  100  shown in  FIG. 1 . 
     The examining system  500  includes an identification unit  520  and a signal communication system  521 . The identification unit  520  may be similar to or represent the identification unit  220  shown in  FIG. 2 . The signal communication system  521  includes at least one application device and at least one detection device and/or unit. In the illustrated embodiment, the signal communication system  521  includes one application device  510  and one detection device  530 . The application device  510  and the detection device  530  may be similar to or represent the application device  210  and the detection device  230 , respectively (both shown in  FIG. 2 ). The application device  510  and the detection device  530  may be a pair of transmit and receive coils in different, discrete housings that are spaced apart from each other, as shown in  FIG. 5 . Alternatively, the application device  510  and the detection device  530  may be a pair of transmit and receive coils held in a common housing. In another alternative embodiment, the application device  510  and the detection device  530  include a same coil, where the coil is configured to inject at least one examination signal into the route  108  and is also configured to monitor one or more electrical characteristics of the route  108  in response to the injection of the at least one examination signal. 
     In other embodiments shown and described below, the signal communication system  521  may include two or more application devices and/or two or more detection devices or units. Although not indicated in  FIG. 5 , in addition to the application device  510  and the detection device  530 , the signal communication system  521  may further include one or more switches  524  (which may be similar to or represent the switches  224  shown in  FIG. 2 ), a control unit  506  (which may be similar to or represent the control unit  208  shown in  FIG. 2 ), one or more conditioning circuits  514  (which may be similar to or represent the circuits  214  shown in  FIG. 2 ), an onboard power source  512  (“Battery” in  FIG. 5 , which may be similar to or represent the power source  212  shown in  FIG. 2 ), and/or one or more detection units  518  (which may be similar to or represent the detection unit  218  shown in  FIG. 2 ). The illustrated embodiment of the examining system  500  may further include a communication unit  516  (which may be similar to or represent the communication unit  216  shown in  FIG. 2 ). As shown in  FIG. 5 , these components of the examining system  500  are disposed onboard a single vehicle  502  of a vehicle system, although one or more of the components may be disposed onboard a different vehicle of the vehicle system from other components of the examining system  500 . As described above, the control unit  506  controls supply of electric current to the application device  510  that engages or is inductively coupled with the route  108  as the vehicle  502  travels along the route  108 . The application device  510  is conductively coupled with the switch  524  that is controlled by the control unit  506  so that the control unit  506  can turn on or off the flow of electric current through the application device  510  to the route  108 . The power source  512  is coupled with the switch  524  so that the control unit  506  can control when the electric energy stored in the power source  512  and/or the electric current generated by the power source  512  is conveyed as electric current to the route  108  via the application device  510 . 
     The conditioning circuit  514  may be coupled with a connecting assembly  526  that is similar to or represents the connecting assembly  226  shown in  FIG. 2 . The connecting assembly  526  receives electric current from an off-board source, such as the electrified conductive pathway  228 . Electric current can be conveyed from the electrified portion of the route  108  through the connecting assembly  526  and to the conditioning circuit  514 . 
     The electric current that is conveyed to the conditioning circuit  514  from the power source  512  and/or the off-board source can be altered by the conditioning circuit  514 . The modified current can be the examination signal that is electrically injected into the route  108  by the application device  510 . Optionally, the control unit  506  can form the examination signal by controlling the switch  524 , as described above. Optionally, the control unit  506  may control the conditioning circuit  514  to form the examination signal, also as described above. 
     The examination signal is conducted through the application device  510  to the route  108 , and is electrically injected into a conductive portion of the route  108 . The conductive portion of the route  108  that extends between the application device  510  and the detection device  530  of the vehicle  502  during travel may form a track circuit through which the examination signal may be conducted. 
     The control unit  506  may include or represent a manager component. Such a manager component can be configured to activate a transmission of electric current into the route  108  via the application device  510 . In another instance, the manager component can activate or deactivate a transfer of the portion of power from the onboard and/or off-board power source to the application device  510 , such as by controlling the switch and/or conditioning circuit. Moreover, the manager component can adjust parameter(s) associated with the portion of power that is transferred to the route  108 . 
     The detection unit  518  monitors the route  108  to attempt to detect the examination signal that is injected into the route  108  by the application device  510 . In one aspect, the detection unit  518  may follow behind the application device  510  along a direction of travel of the vehicle  502 . The detection unit  518  is coupled with the detection device  530  that engages or is inductively coupled with the route  108 , as described above. 
     The detection unit  518  monitors one or more electrical characteristics of the route  108  using the detection device  530 . The detection unit  518  may compare the received signal that is conducted from the route  108  into the detection device  530  with this designated signal in order to measure a signal-to-noise ratio of the received signal. The detection unit  518  determines one or more electrical characteristics of the signal by the detection device  530  from the route  108  and reports the characteristics of the received signal to the identification unit  520 . If no signal is received by the detection device  530 , then the detection unit  518  may report the absence of such a signal to the identification unit  520 . In an embodiment, the detection unit  518  may determine the characteristics of the signals received by the detection device  530  in response to a notification received from the control unit  506 , as described above. 
     The detection unit  518  may begin monitoring signals received by the detection device  530 . For example, the detection unit  518  may not begin or resume monitoring the received signals of the detection device  530  unless or until the detection unit  518  is instructed that the control unit  506  is causing the injection of the examination signal into the route  108 . Alternatively or additionally, the detection unit  518  may periodically monitor the detection device  530  for received signals and/or may monitor the detection device  530  for received signals upon being manually prompted by an operator of the examining system  500 . 
     In one aspect, the application device  510  includes a first axle  528  and/or a first wheel  530  that is connected to the axle  528  of the vehicle  502 . The axle  528  and wheel  530  may be connected to a first truck  532  of the vehicle  502 . The application device  510  may be conductively coupled with the route  108  (e.g., by directly engaging the route  108 ) to inject the examination signal into the route  108  via the axle  528  and the wheel  530 , or via the wheel  530  alone. The detection device  530  may include a second axle  534  and/or a second wheel  536  that is connected to the axle  534  of the vehicle  502 . The axle  534  and wheel  536  may be connected to a second truck  538  of the vehicle  502 . The detection device  530  may monitor the electrical characteristics of the route  108  via the axle  534  and the wheel  536 , or via the wheel  536  alone. Optionally, the axle  534  and/or wheel  536  may inject the signal while the other axle  528  and/or wheel  530  monitors the electrical characteristics. 
     The identification unit  520  receives the one or more characteristics of the received signal from the detection unit  518  and determines if the characteristics indicate receipt of all or a portion of the examination signal injected into the route  108  by the application device  510 . The identification unit  520  interprets the one or more characteristics monitored by the detection unit  518  to determine a state of the route. The identification unit  520  examines the characteristics and determines if the characteristics indicate that a test section of the route  108  disposed between the application device  510  and the detection device  530  is in a non-damaged state, is in a damaged or at least partially damaged state, or is in a non-damaged state that indicates the presence of an electrical short, as described below. 
     The identification unit  520  may include or be communicatively coupled with a location determining unit that can determine the location of the vehicle  502 . The distance between the application device  510  and the detection device  530  along the length of the vehicle  502  may be known to the identification unit  520 , such as by inputting the distance into the identification unit  520  using one or more input devices and/or via the communication unit  516 . 
     The identification unit  520  can identify which section of the route  108  is potentially damaged based on the location of the vehicle  502  during transmission of the examination signal through the route  108 , the direction of travel of the vehicle  502 , the speed of the vehicle  502 , and/or a speed of propagation of the examination signal through the route  108 , as described above. 
     One or more responsive actions may be initiated when the potentially damaged section of the route  108  is identified. For example, in response to identifying the potentially damaged portion of the route  108 , the identification unit  520  may notify the control unit  506 . The control unit  506  and/or the identification unit  520  can automatically slow down or stop movement of the vehicle  502  and/or the vehicle system that includes the vehicle  502 . For example, the control unit  506  and/or identification unit  520  can be communicatively coupled with one or more propulsion systems (e.g., engines, alternators/generators, motors, and the like) of one or more of the propulsion-generating vehicles in the vehicle system. The control unit  506  and/or identification unit  520  may automatically direct the propulsion systems to slow down and/or stop. 
       FIG. 4  is a flowchart of an embodiment of a method  400  for examining a route being traveled by a vehicle system from onboard the vehicle system. The method  400  may be used in conjunction with one or more embodiments of the vehicle systems and/or examining systems described herein. Alternatively, the method  400  may be implemented with another system. 
     At  402 , an examination signal is injected into the route being traveled by the vehicle system at a first vehicle. For example, a direct current, alternating current, RF signal, or another signal may be conductively and/or inductively injected into a conductive portion of the route  108 , such as a track of the route  108 . 
     At  404 , one or more electrical characteristics of the route are monitored at another, second vehicle in the same vehicle system. For example, the route  108  may be monitored to determine if any voltage or current is being conducted by the route  108 . 
     At  406 , a determination is made as to whether the one or more monitored electrical characteristics indicate receipt of the examination signal. For example, if a direct current, alternating current, or RF signal is detected in the route  108 , then the detected current or signal may indicate that the examination signal is conducted through the route  108  from the first vehicle to the second vehicle in the same vehicle system. As a result, the route  108  may be substantially intact between the first and second vehicles. Optionally, the examination signal may be conducted through the route  108  between components joined to the same vehicle. As a result, the route  108  may be substantially intact between the components of the same vehicle. Flow of the method  400  may proceed to  408 . On the other hand, if no direct current, alternating current, or RF signal is detected in the route  108 , then the absence of the current or signal may indicate that the examination signal is not conducted through the route  108  from the first vehicle to the second vehicle in the same vehicle system or between components of the same vehicle. As a result, the route  108  may be broken between the first and second vehicles, or between the components of the same vehicle. Flow of the method  400  may then proceed to  412 . 
     At  408 , a determination is made as to whether a change in the one or more monitored electrical characteristics indicates damage to the route. For example, a change in the examination signal between when the signal was injected into the route  108  and when the examination signal is detected may be determined. This change may reflect a decrease in voltage, a decrease in current, a change in frequency and/or phase, a decrease in a signal-to-noise ratio, or the like. The change can indicate that the examination signal was conducted through the route  108 , but that damage to the route  108  may have altered the signal. For example, if the change in voltage, current, frequency, phase, signal-to-noise ratio, or the like, of the injected examination signal to the detected examination signal exceeds a designated threshold amount (or if the monitored characteristic decreased below a designated threshold), then the change may indicate damage to the route  108 , but not a complete break in the route  108 . As a result, flow of the method  400  can proceed to  412 . 
     On the other hand, if the change in voltage, amps, frequency, phase, signal-to-noise ratio, or the like, of the injected examination signal to the detected examination signal does not exceed the designated threshold amount (and/or if the monitored characteristic does not decrease below a designated threshold), then the change may not indicate damage to the route  108 . As a result, flow of the method  400  can proceed to  410 . 
     At  410 , the test section of the route that is between the first and second vehicles in the vehicle system or between the components of the same vehicle is not identified as potentially damaged, and the vehicle system may continue to travel along the route. Additionally examination signals may be injected into the route at other locations as the vehicle system moves along the route. 
     At  412 , the section of the route that is or was disposed between the first and second vehicles, or between the components of the same vehicle, is identified as a potentially damaged section of the route. For example, due to the failure of the examination signal to be detected and/or the change in the examination signal that is detected, the route may be broken and/or damaged between the first vehicle and the second vehicle, or between the components of the same vehicle. 
     At  414 , one or more responsive actions may be initiated in response to identifying the potentially damaged section of the route. As described above, these actions can include, but are not limited to, automatically and/or manually slowing or stopping movement of the vehicle system, warning other vehicle systems about the potentially damaged section of the route, notifying wayside devices of the potentially damaged section of the route, requesting inspection and/or repair of the potentially damaged section of the route, and the like. 
     In one or more embodiments, a route examining system and method may be used to identify electrical shorts, or short circuits, on a route. The identification of short circuits may allow for the differentiation of a short circuit on a non-damaged section of the route from a broken or deteriorated track on a damaged section of the route. The differentiation of short circuits from open circuits caused by various types of damage to the route provides identification of false alarms. Detecting a false alarm preserves the time and costs associated with attempting to locate and repair a section of the route that is not actually damaged. For example, referring to the method  400  above at  408 , a change in the monitored electrical characteristics may indicate that the test section of the route includes an electrical short that short circuits the two tracks together. For example, an increase in the amplitude of monitored voltage or current and/or a phase shift may indicate the presence of an electrical short. The electrical short provides a circuit path between the two tracks, which effectively reduces the circuit path of the propagating examination signal between the point of injection and the place of detection, which results in an increased voltage and/or current and/or the phase shift. 
       FIG. 6  is a schematic illustration of an embodiment of an examining system  600  on a vehicle  602  of a vehicle system (not shown) traveling along a route  604 . The examining system  600  may represent the examining system  102  shown in  FIG. 1  and/or the examining system  200  shown in  FIG. 2 . In contrast to the examining system  200 , the examining system  600  is disposed within a single vehicle  602 . The vehicle  602  may represent at least one of the vehicles  104 ,  106  of the vehicle system  100  shown in  FIG. 1 .  FIG. 6  may be a top-down view looking at least partially through the vehicle  602 . The examining system  600  may be utilized to identify short circuits and breaks on a route, such as a railway track, for example. The vehicle  602  may be one of multiple vehicles of the vehicle system, so the vehicle  602  may be referred to herein as a first vehicle  602 . 
     The vehicle  602  includes multiple transmitters or application devices  606  disposed onboard the vehicle  602 . The application devices  606  may be positioned at spaced apart locations along the length of the vehicle  602 . For example, a first application device  606 A may be located closer to a front end  608  of the vehicle  602  relative to a second application device  606 B located closer to a rear end  610  of the vehicle  602 . The designations of “front” and “rear” may be based on the direction of travel  612  of the vehicle  602  along the route  604 . 
     The route  604  includes conductive rails  614  in parallel, and the application devices  606  are configured to be conductively and/or inductively coupled with at least one conductive rail  614  along the route  604 . For example, the conductive rails  614  may be rails in a railway context. In an embodiment, the first application device  606 A is configured to be conductively and/or inductively coupled with a first conductive rail  614 A, and the second application device  606 B is configured to be conductively and/or inductively coupled with a second conductive rail  614 B. As such, the application devices  606  may be disposed on the vehicle  602  diagonally from each other. The application devices  606  are utilized to electrically inject at least one examination signal into the route. For example, the first application device  606 A may be used to inject a first examination signal into the first conductive rail  614 A of the route  604 . Likewise, the second application device  606 B may be used to inject a second examination signal into the second conductive rail  614 B of the route  604 . 
     The vehicle  602  also includes multiple receiver coils or detection units  616  disposed onboard the vehicle  602 . The detection units  616  are positioned at spaced apart locations along the length of the vehicle  602 . For example, a first detection unit  616 A may be located towards the front end  608  of the vehicle  602  relative to a second detection unit  616 B located closer to the rear end  610  of the vehicle  602 . The detection units  616  are configured to monitor one or more electrical characteristics of the route  604  along the conductive rails  614  in response to the examination signals being injected into the route  604 . The electrical characteristics that are monitored may include a current, a phase shift, a modulation, a frequency, a voltage, an impedance, and the like. For example, the first detection unit  616 A may be configured to monitor one or more electrical characteristics of the route  604  along the second rail  614 B, and the second detection unit  616 B may be configured to monitor one or more electrical characteristics of the route  604  along the first rail  614 A. As such, the detection units  616  may be disposed on the vehicle  602  diagonally from each other. In an embodiment, each of the application devices  606 A,  606 B and the detection units  616 A,  616 B may define individual corners of a test section of the vehicle  602 . Optionally, the application devices  606  and/or the detection units  616  may be staggered in location along the length and/or width of the vehicle  602 . Optionally, the application device  606 A and detection unit  616 A and/or the application device  606 B and detection unit  616 B may be disposed along the same rail  614 . The application devices  606  and/or detection units  616  may be disposed on the vehicle  602  at other locations in other embodiments. 
     In an embodiment, two of the conductive rails  614  (e.g., rails  614 A and  614 B) may be conductively and/or inductively coupled to each other through multiple shunts  618  along the length of the vehicle  602 . For example, the vehicle  602  may include two shunts  618 , with one shunt  618 A located closer to the front  608  of the vehicle  602  relative to the other shunt  618 B. In an embodiment, the shunts  618  are conductive and together with the rails  614  define an electrically conductive test loop  620 . The conductive test loop  620  represents a track circuit or circuit path along the conductive rails  614  between the shunts  618 . The test loop  620  moves along the rails  614  as the vehicle  602  travels along the route  604  in the direction  612 . Therefore, the section of the conductive rails  614  defining part of the conductive test loop  620  changes as the vehicle  602  progresses on a trip along the route  604 . 
     In an embodiment, the application devices  606  and the detection units  616  are in electrical contact with the conductive test loop  620 . For example, the application device  606 A may be in electrical contact with rail  614 A and/or shunt  618 A; the application device  606 B may be in electrical contact with rail  614 B and/or shunt  618 B; the detection unit  616 A may be in electrical contact with rail  614 B and/or shunt  618 A; and the detection unit  616 B may be in electrical contact with rail  614 A and/or shunt  618 B. 
     The two shunts  618 A,  618 B may be first and second trucks disposed on a rail vehicle. Each truck  618  includes an axle  622  interconnecting two wheels  624 . Each wheel  624  contacts a respective one of the rails  614 . The wheels  624  and the axle  622  of each of the trucks  618  are configured to electrically connect (e.g., short) the two rails  614 A,  614 B to define respective ends of the conductive test loop  620 . For example, the injected first and second examination signals may circulate the conductive test loop  620  along the length of a section of the first rail  614 A, through the wheels  624  and axle  622  of the shunt  618 A to the second rail  614 B, along a section of the second rail  614 B, and across the shunt  618 B, returning to the first rail  614 A. 
     In an embodiment, alternating current transmitted from the vehicle  602  is injected into the route  604  at two or more points through the rails  614  and received at different locations on the vehicle  602 . For example, the first and second application devices  606 A,  606 B may be used to inject the first and second examination signals into respective first and second rails  614 A,  614 B. One or more electrical characteristics in response to the injected examination signals may be received at the first and second detection units  616 A,  616 B. Each examination signal may have a unique identifier so the signals can be distinguished from each other at the detection units  616 . For example, the unique identifier of the first examination signal may have a base frequency, a phase, a modulation, an embedded signature, and/or the like, that differs from the unique identifier of the second examination signal. 
     In an embodiment, the examining system  600  may be used to more precisely locate faults on track circuits in railway signaling systems, and to differentiate between track features. For example, the system  600  may be used to distinguish broken tracks (e.g., rails) versus crossing shunt devices, non-insulated switches, scrap metal connected across the rails  614 A and  614 B, and other situations or devices that might produce an electrical short (e.g., short circuit) when a current is applied to the conductive rails  614  along the route  604 . In typical track circuits looking for damaged sections of routes, an electrical short may appear as similar to a break, creating a false alarm. The examining system  600  also may be configured to distinguish breaks in the route due to damage from intentional, non-damaged “breaks” in the route, such as insulated joints and turnouts (e.g., track switches), which simulate actual breaks but do not short the conductive test loop  620  when traversed by a vehicle system having the examining system  600 . 
     In an embodiment, when there is no break or short circuit on the route  604  and the rails  614  are electrically contiguous, the injected examination signals circulate the length of the test loop  620  and are received by all detection units  616  present on the test loop  620 . Therefore, both detection units  616 A and  616 B receive both the first and second examination signals when there is no electrical break or electrical short on the route  604  within the section of the route  604  defining the test loop  620 . 
     As discussed further below, when the vehicle  602  passes over an electrical short (e.g., a device or a condition of a section of the route  604  that causes a short circuit when a current is applied along the section of the route  604 ), two additional conductive current loops or conductive short loops are formed. The two additional conductive short loops have electrical characteristics that are unique to a short circuit (e.g., as opposed to electrical characteristics of an open circuit caused by a break in a rail  614 ). For example, the electrical characteristics of the current circulating the first conductive short loop may have an amplitude that is an inverse derivative of the amplitude of the second additional current loop as the electrical short is traversed by the vehicle  602 . In addition, the amplitude of the current along the original conductive test loop  620  spanning the periphery of the test section diminishes considerably while the vehicle  602  traverses the electrical short. All of the one or more electrical characteristics in the original and additional current loops may be received and/or monitored by the detection units  616 . Sensing the two additional short loops may provide a clear differentiator to identify that the loss of current in the original test loop is the result of a short circuit and not an electrical break in the rail  614 . Analysis of the electrical characteristics of the additional short loops relative to the vehicle motion and/or location may provide more precision in locating the short circuit within the span of the test section. 
     In an alternative embodiment, the examining system  600  includes the two spaced-apart detection units  616 A,  616 B defining a test section of the route  604  therebetween, but only includes one of the application devices  606 A,  606 B, such as only the first application device  606 A. The detection units  616 A,  616 B are each configured to monitor one or more electrical characteristics of at least one of the conductive rails  614 A,  614 B proximate to the respective detection unit  616 A,  616 B in response to at least one examination signal being electrically injected into at least one of the conductive rails  614 A,  614 B by the application device  606 A. In another alternative embodiment, the examining system  600  includes the two spaced-apart detection units  616 A,  616 B, but does not include either of the application devices  606 A,  606 B. For example, the examination signal may be derived from an inherent electrical current of a traction motor (not shown) of the vehicle  602  (or another vehicle of the vehicle system). The examination signal may be injected into at least one of the conductive rails  614 A,  614 B via a conductive and/or inductive electrical connection between the traction motor and the one or both conductive rails  614 A,  614 B, such as a conductive connection through the wheels  624 . In other embodiments, the examination signal may be derived from electrical currents of other motors of the vehicle  602  or may be an electrical current injected into the rails  614  from a wayside device. 
     Regardless of whether the examining system  600  includes one application device or no application devices, the identification unit  520  (shown in  FIG. 5 ) is configured to examine the one or more electrical characteristics monitored by each of the first and second detection units  616 A,  616 B in order to determine a status of the test section of the route  604  based on whether the one or more electrical characteristics indicate that the examination signal is received by both the first and second detection units  616 A,  616 B, neither of the first or second detection units  616 A,  616 B, or only one of the first or second detection units  616 A,  616 B. The status of the test section may be potentially damaged, neither damaged nor includes an electrical short, or not damaged and includes an electrical short. The status of the test section is potentially damaged when neither of the first or second detection units  616 A,  616 B receive the examination signal, indicating an open circuit loop  620 . The status of the test section is neither damaged nor includes an electrical short when both of the first and second detection units  616 A,  616 B receive the examination signal, indicating a closed circuit loop  620 . The status of the test section is not damaged and includes an electrical short when only one of the first or second detection units  616 A,  616 B receive the examination signal, indicating one open sub-loop and one closed sub-loop within the loop  620 . 
     In an alternative embodiment, the vehicle  602  includes the two spaced-apart application devices  606 A,  606 B defining a test section of the route  604  therebetween, but only includes one of the detection units  616 A,  616 B, such as only the first detection unit  616 A. The first and second application devices  606 A,  606 B are configured to electrically inject the first and second examination signals, respectively, into the corresponding conductive rails  614 A,  614 B that the application devices  606 A,  606 B are coupled to. The detection unit  616 A is configured to monitor one or more electrical characteristics of at least one of the conductive rails  614 A,  614 B in response to the first and second examination signals being injected into the rails  614 . 
     In this embodiment, the identification unit  520  (shown in  FIG. 5 ) is configured to examine the one or more electrical characteristics monitored by the detection unit  616 A in order to determine a status of the test section of the route  604  based on whether the one or more electrical characteristics indicate receipt by the detection unit  616 A of both of the first and second examination signals, neither of the first or second examination signals, or only one of the first or second examination signals. The status of the test section is potentially damaged when the one or more electrical characteristics indicate receipt by the detection unit  616 A of neither the first nor the second examination signals, indicating an open circuit loop  620 . The status of the test section is neither damaged nor includes an electrical short when the one or more electrical characteristics indicate receipt by the detection unit  616 A of both the first and second examination signals, indicating a closed circuit loop  620 . The status of the test section is not damaged and includes an electrical short when the one or more electrical characteristics indicate receipt by the detection unit  616 A of only one of the first or second examination signals, indicating one open circuit sub-loop and one closed circuit sub-loop within the loop  620 . 
     Additionally, or alternatively, the identification unit  520  may be configured to determine that the test section of the route  604  includes an electrical short by detecting a change in a phase difference between the first and second examination signals. For example, the identification unit  520  may compare a detected phase difference between the first and second examination signals that is detected by the detection unit  616 A to a known phase difference between the first and second examination signals. The known phase difference may be a phase difference between the examination signals upon injecting the signals into the route  604  or may be a detected phase difference between the examination signals along sections of the route that are known to be not damaged and free of electrical shorts. Thus, if the one of more electrical characteristics monitored by the detection unit  616 A indicate that the phase difference between the first and second examination signals is similar to the known phase difference, such that the change in phase difference is negligible or within a threshold value that compensates for variations due to noise, etc., then the status of the test section of route  604  may be non-damaged and free of an electrical short. If the detected phase difference varies from the known phase difference by more than the designated threshold value (such that the change in phase difference exceeds the designated threshold), the status of the test section of route  604  may be non-damaged and includes an electrical short. If the test section of the route  604  is potentially damaged, the one or more monitored electrical characteristics may indicate that the examination signals were not received by the detection unit  616 A, so phase difference between the first and second examination signals is not detected. 
     In another alternative embodiment, the vehicle  602  includes one application device, such as the application device  606 A, and one detection unit, such as the detection unit  616 A. The application device  606 A is disposed proximate to the detection unit  616 A. For example, the application device  606 A and the detection unit  616 A may be located on opposite rails  614 A,  614 B at similar positions along the length of the vehicle  602  between the two shunts  618 , as shown in  FIG. 6 , or may be located on the same rail  614 A or  614 B proximate to each other. The application device  606 A is configured to electrically inject at least one examination signal into the rails  614 , and the detection unit  616 A is configured to monitor one or more electrical characteristics of the rails  614  in response to the at least one examination signal being injected into the conductive test loop  620 . 
     In this embodiment, the identification unit  520  (shown in  FIG. 5 ) is configured to examine the one or more electrical characteristics monitored by the detection unit  616 A to determine a status of a test section of the route  604  that extends between the shunts  618 . The identification unit  520  is configured to determine that the status of the test section is potentially damaged when the one or more electrical characteristics indicate that the at least one examination signal is not received by the detection unit  616 A. The status of the test section is neither damaged nor includes an electrical short when the one or more electrical characteristics indicate that the at least one examination signal is received by the detection unit  616 A. The status of the test section is not damaged and does include an electrical short when the one or more electrical characteristics indicate at least one of a phase shift in the at least one examination signal or an increased amplitude of the at least one examination signal. The amplitude may be increased over a base line amplitude that is detected or measured when the status of the test section is not damaged and does not include an electrical short. The increased amplitude may gradually increase from the base line amplitude, such as when the detection unit  616 A and application device  606 A of the signal communication system  521  (shown in  FIG. 5 ) move towards the electrical short in the route  604 , and may gradually decrease towards the base line amplitude, such as when the detection unit  616 A and application device  606 A of the signal communication system  521  move away from the electrical short. 
       FIG. 7  is a schematic illustration of an embodiment of an examining system  700  disposed on multiple vehicles  702  of a vehicle system  704  traveling along a route  706 . The examining system  700  may represent the examining system  600  shown in  FIG. 6 . In contrast to the examining system  600  shown in  FIG. 6 , the examining system  700  is disposed on multiple vehicles  702  in the vehicle system  704 , where the vehicles  702  are mechanically coupled together. 
     In an embodiment, the examining system  700  includes a first application device  708 A configured to be disposed on a first vehicle  702 A of the vehicle system  702 , and a second application device  708 B configured to be disposed on a second vehicle  702 B of the vehicle system  702 . The application devices  708 A,  708 B may be conductively and/or inductively coupled with different conductive tracks  712 , such that the application devices  708 A,  708 B are disposed diagonally along the vehicle system  704 . The first and second vehicles  702 A and  702 B may be directly coupled, or may be indirectly coupled, having one or more additional vehicles coupled in between the vehicles  702 A,  702 B. Optionally the vehicles  702 A,  702 B may each be either one of the vehicles  104  or  106  shown in  FIG. 1 . Optionally, the second vehicle  702 B may trail the first vehicle  702 A during travel of the vehicle system  704  along the route  706 . 
     The examining system  700  also includes a first detection unit  710 A configured to be disposed on the first vehicle  702 A of the vehicle system  702 , and a second detection unit  710 B configured to be disposed on the second vehicle  702 B of the vehicle system  702 . The first and second detection units  710 A,  710 B may be configured to monitor electrical characteristics of the route  706  along different conductive tracks  712 , such that the detection units  710  are oriented diagonally along the vehicle system  704 . The location of the first application device  708 A and/or first detection unit  710 A along the length of the first vehicle  702 A is optional, as well as the location of the second application device  708 B and/or second detection unit  710 B along the length of the second vehicle  702 B. However, the location of the application devices  708 A,  708 B affects the length of a current loop that defines a test loop  714 . For example, the test loop  714  spans a greater length of the route  706  than the test loop  620  shown in  FIG. 6 . Increasing the length of the test loop  714  may increase the amount of signal loss as the electrical examination signals are diverted along alternative conductive paths, which diminishes the capability of the detection units  710  to receive the electrical characteristics. Optionally, the application devices  708  and detection units  710  may be disposed on adjacent vehicles  702  and proximate to the coupling mechanism that couples the adjacent vehicles, such that the defined conductive test loop  714  may be smaller in length than the conductive test loop  620  disposed on the single vehicle  602  (shown in  FIG. 6 ). 
       FIG. 8  is a schematic diagram of an embodiment of an examining system  800  on a vehicle  802  of a vehicle system (not shown) on a route  804 . The examining system  800  may represent the examining system  102  shown in  FIG. 1  and/or the examining system  200  shown in  FIG. 2 . In contrast to the examining system  200 , the examining system  800  is disposed within a single vehicle  802 . The vehicle  802  may represent at least one of the vehicles  104 ,  106  shown in  FIG. 1 . 
     The vehicle  802  includes a first application device  806 A that is conductively and/or inductively coupled to a first conductive track  808 A of the route  804 , and a second application device  806 B that is conductively and/or inductively coupled to a second conductive track  808 B. A control unit  810  is configured to control supply of electric current from a power source  811  (e.g., battery  812  and/or conditioning circuits  813 ) to the first and second application devices  806 A,  806 B in order to electrically inject examination signals into the conductive tracks  808 . For example, the control unit  810  may control the application of a first examination signal into the first conductive track  808 A via the first application device  806 A and the application of a second examination signal into the second conductive track  808 B via the second application device  806 B. 
     The control unit  810  is configured to control application of at least one of a designated direct current, a designated alternating current, or a designated radio frequency signal of each of the first and second examination signals from the power source  811  to the conductive tracks  808  of the route  804 . For example, the power source  811  may be an onboard energy storage device  812  (e.g., battery) and the control unit  810  may be configured to inject the first and second examination signals into the route  804  by controlling when electric current is conducted from the onboard energy storage device  812  to the first and second application devices  806 A and  806 B. Alternatively or in addition, the power source  811  may be an off-board energy storage device  813  (e.g., catenary and conditioning circuits) and the control unit  810  is configured to inject the first and second examination signals into the conductive tracks  808  by controlling when electric current is conducted from the off-board energy storage device  813  to the first and second application devices  806 A and  806 B. 
     The vehicle  802  also includes a first detection unit  814 A disposed onboard the vehicle  802  that is configured to monitor one or more electrical characteristics of the second conductive track  808 B of the route  804 , and a second detection unit  814 B disposed onboard the vehicle  802  that is configured to monitor one or more electrical characteristics of the first conductive track  808 A. An identification unit  816  is disposed onboard the vehicle  802 . The identification unit  816  is configured to examine the one or more electrical characteristics of the conductive tracks  808  monitored by the detection units  814 A,  814 B in order to determine whether a section of the route  804  traversed by the vehicle  802  is potentially damaged based on the one or more electrical characteristics. As used herein, “potentially damaged” means that the section of the route may be damaged or at least deteriorated. The identification unit  816  may further determine whether the section of the route traversed by the vehicle is damaged by distinguishing between one or more electrical characteristics that indicate damage to the section of the route and one or more electrical characteristics that indicate an electrical short on the section of the route. 
       FIGS. 9 through 11  are schematic illustrations of an embodiment of an examining system  900  on a vehicle  902  as the vehicle  902  travels along a route  904 . The examining system  900  may be the examining system  600  shown in  FIG. 6  and/or the examining system  800  shown in  FIG. 8 . The vehicle  902  may be the vehicle  602  of  FIG. 6  and/or the vehicle  802  of  FIG. 8 .  FIGS. 9 through 11  illustrate various route conditions that the vehicle  902  may encounter while traversing in a travel direction  906  along the route  904 . 
     The vehicle  902  includes two transmitters or application units  908 A and  908 B, and two receivers or detection units  910 A and  910 B all disposed onboard the vehicle  902 . The application units  908  and detection units  910  are positioned along a conductive loop  912  defined by shunts on the vehicle  902  and tracks  914  of the route  904  between the shunts. For example, the vehicle  902  may include six axles, each axle attached to two wheels in electrical contact with the tracks  914  and forming a shunt. Optionally, the conductive loop  912  may be bounded between the inner most axles (e.g., between the third and fourth axles) to reduce the amount of signal loss through the other axles and/or the vehicle frame. As such, the third and fourth axles define the ends of the conductive loop  912 , and the tracks  914  define the segments of the conductive loop  912  that connect the ends. 
     The conductive loop  912  defines a test loop  912  (e.g., test section) for detecting faults in the route  904  and distinguishing damaged tracks  914  from short circuit false alarms. As the vehicle  902  traverses the route  904 , a first examination signal is injected into a first track  914 A of the route  904  from the first application unit  908 A, and a second examination signal is injected into a second track  914 B of the route  904  from the second application unit  908 B. The first and second examination signals may be injected into the route  904  simultaneously or in a staggered sequence. The first and second examination signals can each have a unique identifier to distinguish the first examination signal from the second examination signal as the signals circulate the test loop  912 . The unique identifier of the first examination signal may include a frequency, a modulation, an embedded signature, and/or the like, that differs from the unique identifier of the second examination signal. For example, the first examination signal may have a higher frequency and/or a different embedded signature than the second examination signal. Alternatively, the examination signals may have different frequencies to allow for differentiation of the signals from each other. For example, the first examination signal may be injected into the route at a frequency of 4.6 kilohertz (kHz), or another frequency, while the second examination signal is injected into the route at a frequency of 3.8 kHz (or another frequency). In one embodiment, the signals may have different identifiers and different frequencies. 
     In  FIG. 9 , the vehicle  902  traverses over a section of the route  904  that is intact (e.g., not damaged) and does not have an electrical short. Since there is no electrical short or electrical break on the route  904  within the area of the conductive test loop  912 , which is the area between two designated shunts (e.g., axles) of the vehicle  902 , the first and second examination signals both circulate a full length of the test loop  912 . As such, the first examination signal current transmitted by the first application device  908 A is detected by both the first detection device  910 A and the second detection device  910 B as the first examination signal current flows around the test loop  912 . Although the second examination signal is injected into the route  904  at a different location, the second examination signal current circulates the test loop  912  with the first examination signal current, and is likewise detected by both detection devices  910 A,  910 B. Each of the detection devices  910 A,  910 B may be configured to detect one or more electrical characteristics along the route  904  proximate to the respective detection device  910 . Therefore, when the section of route is free of shorts and breaks, the electrical characteristics received by each of the detection devices  910  includes the unique signatures of each of the first and second examination signals. 
     In  FIG. 10 , the vehicle  902  traverses over a section of the route  904  that includes an electrical short  916 . The electrical short  916  may be a device on the route  904  or condition of the route  904  that conductively and/or inductively couples the first conductive track  914 A to the second conductive track  914 B. The electrical short  916  causes current injected in one track  914  to flow through the short  916  to the other track  914  instead of flowing along the full length of the conductive test loop  912  and crossing between the tracks  914  at the shunts. For example, the short  916  may be a piece of scrap metal or other extraneous conductive device positioned across the tracks  914 , a non-insulated signal crossing or switch, an insulated switch or joint in the tracks  914  that is non-insulated due to wear or damage, and the like. As the vehicle  902  traverses along route  904  over the electrical short  916 , such that the short  916  is at least temporarily located between the shunts within the area defined by the test loop  912 , the test loop  912  may short circuit. 
     As the vehicle  902  traverses over the electrical short  916 , the electrical short  916  diverts the current flow of the first and second examination signals that circulate the test loop  912  to additional loops. For example, the first examination signal may be diverted by the short  916  to circulate primarily along a first conductive short loop  918  that is newly-defined along a section of the route  904  between the first application device  908 A and the electrical short  916 . Similarly, the second examination signal may be diverted to circulate primarily along a second conductive short loop  920  that is newly-defined along a section of the route  904  between the electrical short  916  and the second application device  908 B. Only the first examining signal that was transmitted by the first application device  908 A significantly traverses the first short loop  918 , and only the second examination signal that was transmitted by the second application device  908 B significantly traverses the second short loop  920 . 
     As a result, the one or more electrical characteristics of the route received and/or monitored by first detection unit  910 A may only indicate a presence of the first examination signal. Likewise, the electrical characteristics of the route received and/or monitored by second detection unit  910 B may only indicate a presence of the second examining signal. As used herein, “indicat[ing] a presence of” an examination signal means that the received electrical characteristics include more than a mere threshold signal-to-noise ratio of the unique identifier indicative of the respective examination signal that is more than electrical noise. For example, since the electrical characteristics received by the second detection unit  910 B may only indicate a presence of the second examination signal, the second examination signal exceeds the threshold signal-to-noise ratio of the received electrical characteristics but the first examination signal does not exceed the threshold. The first examination signal may not be significantly received at the second detection unit  908 B because the majority of the first examination signal current originating at the device  908 A may get diverted along the short  916  (e.g., along the first short loop  918 ) before traversing the length of the test loop  912  to the second detection device  908 B. As such, the electrical characteristics with the unique identifiers indicative of the first examination signal received at the second detection device  910 B may be significantly diminished when the vehicle  902  traverses the electrical short  916 . 
     The peripheral size and/or area of the first and second conductive short loops  918  and  920  may have an inverse correlation at the vehicle  902  traverses the electrical short  916 . For example, the first short loop  918  increases in size while the second short loop  920  decreases in size as the test loop  912  of the vehicle  902  overcomes and passes the short  916 . It is noted that the first and second short loops  916  are only formed when the short  916  is located within the boundaries or area covered by the test loop  912 . Therefore, received electrical characteristics that indicate the examination signals are circulating the first and second conductive short  918 ,  920  loops signify that the section includes an electrical short  916  (e.g., as opposed to a section that is damaged or is fully intact without an electrical short). 
     In  FIG. 11 , the vehicle  902  traverses over a section of the route  904  that includes an electrical break  922 . The electrical break  922  may be damage to one or both tracks  914 A,  914 B that cuts off (e.g., or significantly reduces) the electrical conductive path along the tracks  914 . The damage may be a broken track, disconnected lengths of track, and the like. As such, when a section of the route  904  includes an electrical break, the section of the route forms an open circuit, and current generally does not flow along an open circuit. In some breaks, it may be possible for inductive current to traverse slight breaks, but the amount of current would be greatly reduced as opposed to a non-broken conductive section of the route  904 . 
     As the vehicle  902  traverses over the electrical break  922  such that the break  922  is located within the boundaries of the test loop  912  (e.g., between designated shunts of the vehicle  902  that define the ends of the test loop  912 ), the test loop  912  may be broken, forming an open circuit. As such, the injected first and second examination signals do not circulate the test loop  912  nor along any short loops. The first and second detection units  910 A and  910 B do not receive any significant electrical characteristics in response to the first and second examination signals because the signal current do not flow along the broken test loop  912 . Once, the vehicle  902  passes beyond the break, subsequently injected first and second examination signals may circulate the test section  912  as shown in  FIG. 9 . It is noted that the vehicle  902  may traverse an electrical break caused by damage to the route  904  without derailing. Some breaks may support vehicular traffic for an amount of time until the damage increases beyond a threshold, as is known in the art. 
     As shown in  FIG. 9 through 11 , the electrical characteristics along the route  904  that are detected by the detection units  910  may differ whether the vehicle  902  traverses over a section of the route  904  having an electrical short  916  (shown in  FIG. 10 ), an electrical break  922  (shown in  FIG. 11 ), or is electrically contiguous (shown in  FIG. 9 ). The examining system  900  may be configured to distinguish between one or more electrical characteristics that indicate a damaged section of the route  904  and one or more electrical characteristics that indicate a non-damaged section of the route  904  having an electrical short  916 , as discussed further herein. 
       FIG. 12  illustrates electrical signals  1000  monitored by an examining system on a vehicle system as the vehicle system travels along a route. The examining system may be the examining system  900  shown in  FIG. 9 . The vehicle system may include vehicle  902  traveling along the route  904  (both shown in  FIG. 9 ). The electrical signals  1000  are one or more electrical characteristics that are received by a first detection unit  1002  and a second detection unit  1004 . The electrical signals  1000  are received in response to the transmission or injection of a first examination signal and a second examination signal into the route. The first and second examination signals may each include a unique identifier that allows the examining system to distinguish electrical characteristics of a monitored current that are indicative of the first examination signal from electrical characteristics indicative of the second examination signal, even if an electrical current includes both examination signals. 
     In  FIG. 12 , the electrical signals  1000  are graphically displayed on a graph  1010  plotting amplitude (A) of the signals  1000  over time (t). For example, the graph  1010  may graphically illustrate the monitored electrical characteristics in response to the first and second examination signals while the vehicle  902  travels along the route  904  and encounters the various route conditions described with reference to  FIG. 9 . The graph  1010  may be displayed on a display device for an operator onboard the vehicle and/or may be transmitted to an off-board location such as a dispatch or repair facility. The first electrical signal  1012  represents the electrical characteristics in response to (e.g., indicative of the first examination signal that are received by the first detection unit  1002 . The second electrical signal  1014  represents the electrical characteristics in response to (e.g., indicative of the second examination signal that are received by the first detection unit  1002 . The third electrical signal  1016  represents the electrical characteristics in response to (e.g., indicative of the first examination signal that are received by the second detection unit  1004 . The fourth electrical signal  1018  represents the electrical characteristics in response to (e.g., indicative of) the second examination signal that are received by the second detection unit  1004 . 
     Between times t 0  and t 2 , the electrical signals  1000  indicate that both examination signals are being received by both detection units  1002 ,  1004 . Therefore, the signals are circulating the length of the conductive primary test loop  912  (shown in  FIGS. 9 and 10 ). At a time t 1 , the vehicle is traversing over a section of the route that is intact and does not have an electrical short, as shown in  FIG. 9 . The amplitudes of the electrical signals  1012 - 1018  may be relatively constant at a baseline amplitude for each of the signals  1012 - 1018 . The base line amplitudes need not be the same for each of the signals  1012 - 1018 , such that the electrical signal  1012  may have a different base line amplitude than at least one of the other electrical signals  1014 - 1018 . 
     At time t 2 , the vehicle traverses over an electrical short. As shown in  FIG. 12 , immediately after t 2 , the amplitude of the electrical signal  1012  indicative of the first examination signal received by the first detection unit  1002  increases by a significant gain and then gradually decreases towards the base line amplitude. The amplitude of the electrical signal  1014  indicative of the second examination signal received by the first detection unit  1002  drops below the base line amplitude for the electrical signal  1014 . As such, the electrical characteristics received at the first detection unit  1002  indicate a greater significance or proportion of the first examination signal (e.g., due to the first electrical signal circulating newly-defined loop  918  in  FIG. 10 ), while less significance or proportion of the second examination signal than compared to the respective base line levels. At the second detection unit  1004  at time t 2 , the electrical signal  1016  indicative of the first examination signal drops in like manner to the electrical signal  1016  received by the first detection unit  1002 . The electrical signal  1018  indicative of the second examination signal gradually increases in amplitude above the base line amplitude from time t 2  to t 4  as the test loop passes the electrical short. 
     These electrical characteristics from time t 2  to t 4  indicate that the electrical short defines new circuit loops within the primary test loop  912  (shown in  FIGS. 9 and 10 ). The amplitude of the examination signals that were injected proximate to the respective detection units  1002 ,  1004  increase relative to the base line amplitudes, while the amplitude of the examination signals that were injected on the other side of the test loop (and spaced apart) from the respective detection units  1002 ,  1004  decrease (or drop) relative to the base line amplitudes. For example the amplitude of the electrical signal  1012  increases by a step right away due to the first examination signal injected by the first application device  908 A circulating the newly-defined short loop or sub-loop  918  in  FIG. 10  and being received by the first detection unit  910 A that is proximate to the first application device  908 A. The amplitude of the electrical signal  1012  gradually decreases towards the base line amplitude as the examining system moves relative to the electrical short because the electrical short gets further from the first application device  908 A and the first detection unit  910 A and the size of the sub-loop  918  increases. The electrical signal  1018  also increases relative to the base line amplitude due to the second examination signal injected by the second application device  908 B circulating the newly-defined short loop or sub-loop  920  and being received by the second detection unit  910 B that is proximate to the second application device  908 A. The amplitude of the electrical signal  1018  gradually increases away from the base line amplitude (until time t 4 ) as the examining system moves relative to the electrical short because the electrical short gets closer to the second application device  908 B and second detection unit  910 B and the size of the sub-loop  920  decreases. The amplitude of an examination signal may be higher for a smaller circuit loop because less of the signal attenuates along the circuit before reaching the corresponding detection unit than an examination signal in a larger circuit loop. The positive slope of the electrical signal  1018  may be inverse from the negative slope of the electrical signal  1012 . For example, the amplitude of the electrical signal  1012  monitored by the first detection device  1002  may be an inverse derivative of the amplitude of the electrical signal  1018  monitored by the second detection device  1004 . This inverse relationship is due to the movement of the vehicle relative to the stationary electrical short along the route. Referring also to  FIG. 10 , time t 3  may represent the electrical signals  1012 - 1018  when the electrical short  916  bisects the test loop  912 , and the short loops  918 ,  920  have the same size. 
     At time t 4 , the test section (e.g., loop) of the vehicle passes beyond the electrical short. Between times t 4  and t 5 , the electrical signals  1000  on the graph  1010  indicate that both the first and second examination signals once again circulate the primary test loop  912 , as shown in  FIG. 9 . 
     At time t 5 , the vehicle traverses over an electrical break in the route. As shown in  FIG. 12 , immediately after t 5 , the amplitude of each of the electrical signals  1012 - 1018  decrease or drop by a significant step. Throughout the length of time for the test section to pass the electrical break in the route, represented as between times t 5  and t 7 , all four signals  1012 - 1018  are at a low or at least attenuated amplitude, indicating that the first and second examination signals are not circulating the test loop due to the electrical break in the route. Time t 6  may represent the location of the electrical break  922  relative to the route examining system  900  as shown in  FIG. 11 . 
     In an embodiment, the identification unit may be configured to use the received electrical signals  1000  to determine whether a section of the route traversed by the vehicle is potentially damaged, meaning that the section may be damaged or at least deteriorated. For example, based on the recorded waveforms of the electrical signals  1000  between times t 2 -t 4  and t 5 -t 7 , the identification unit may identify the section of the route traversed between times t 2 -t 4  as being non-damaged but having an electrical short and the section of route traversed between times t 5 -t 7  as being damaged. For example, it is clear in the graph  1010  that the receiver coils or detection units  1002 ,  1004  both lose signal when the vehicle transits the damaged section of the route between times t 5 -t 7 . However, when crossing the short on the route between times t 244 , the first detection unit  1002  loses the second examination signal, as shown on the electrical signal  1014 , and the electrical signal  1018  representing second examination signal received by the second detection unit  1004  increases in amplitude as the short is transited. Thus, there is a noticeable distinction between a break in the track versus features that short the route. Optionally, a vehicle operator may view the graph  1010  on a display and manually identify sections of the route as being damaged or non-damaged but having an electrical short based on the recorded waveforms of the electrical signals  1000 . 
     In an embodiment, the examining system may be further used to distinguish between non-damaged track features by the received electrical signals  1000 . For example, wide band shunts (e.g., capacitors) may behave similar to hard wire highway crossing shunts, except an additional phase shift may be identified depending on the frequencies of the first and second examination signals. Narrow band (e.g., tuned) shunts may impact the electrical signals  1000  by exhibiting larger phase and amplitude differences responsive to the relation of the tuned shunt frequency and the frequencies of the examination signals. 
     The examining system may also distinguish electrical circuit breaks due to damage from electrical breaks (e.g., pseudo-breaks) due to intentional track features, such as insulated joints and turnouts (e.g., track switches). In turnouts, in specific areas, only a single pair of transmit and receive coils (e.g., a single application device and detection unit located along one conductive track) may be able to inject current (e.g., an examination signal). The pair on the opposite track (e.g., rail) may be traversing a “fouling circuit,” where the opposite track is electrically connected at only one end, rather than part of the circulating current loop. 
     With regard to insulated joints, for example, distinguishing insulated joints from broken rails may be accomplished by an extended signal absence in the primary test loop caused by the addition of a dead section loop. As is known in the art, railroad standards typically indicate the required stagger of insulated joints to be 32 in. to 56 in. In addition to the insulated joint providing a pseudo-break with an extended length, detection may be enhanced by identifying location specific signatures of signaling equipment connected to the insulated joints, such as batteries, track relays, electronic track circuitry, and the like. The location specific signatures of the signaling equipment may be received in the monitored electrical characteristics in response to the current circulating the newly-defined short loops  918 ,  920  (shown in  FIG. 9 ) through the connected equipment. For example, signaling equipment that is typically found near an insulated joint may have a specific electrical signature or identifier, such as a frequency, modulation, embedded signature, and the like, that allows the examination system to identify the signaling equipment in the monitored electrical characteristics. Identifying signaling equipment typically found near an insulated joint provides an indication that the vehicle is traversing over an insulated joint in the route, and not a damaged section of the route. 
     In the alternative embodiment described with reference to  FIG. 6  in which the examining system includes at least two detection units that are spaced apart from each other but less than two application devices (such as zero or one) such that only one examination signal is injected into the route, the monitored electrical characteristics along the route by the two detection units may be shown in a graph similar to graph  1010 . For example, the graph may include the plotted electrical signals  1012  and  1016 , where the electrical signal  1012  represents the examination signal detected by or received at the first detection unit  1002 , and the electrical signal  1016  represents the examination signal detected by or received at the second detection unit  1004 . Using only the plotted amplitudes of the electrical signals  1012  and  1016  (instead of also  1014  and  1018 ), the identification unit may determine the status of the route. Between times t 0  and t 2 , both signals  1012  and  1016  are constant (with a slope of zero) at base line values. Thus, the one or more electrical characteristics indicate that both detection units  1002 ,  1004  receive the examination signal, and the identification unit determines that the section of the route is non-damaged and does not include an electrical short. Between times t 2 -and t 4 , the first detection unit  1002  detects an increased amplitude of the examination signal above the base line (although the slope is negative), while the second detection unit  1004  detects a drop in the amplitude of the examination signal. Thus, the one or more electrical characteristics indicate that the first detection unit  1002  receives the examination signal but the second detection unit  1004  does not, and the identification unit determines that the section of the route includes an electrical short. Finally, between times t 5  and t 7 , both the first and second detection units  1002 ,  1004  detect drops in the amplitude of the examination signal. Thus, the one or more electrical characteristics indicate that neither of the detection units  1002 ,  1004  receive the examination signal, and the identification unit determines that the section of the route is potentially damaged. Alternatively, the examination signal may be the second examination signal shown in the graph  1010  such that the electrical signals are the plotted electrical signals  1014  and  1018  instead of  1012  and  1016 . 
     In the alternative embodiment described with reference to  FIG. 6  in which the examining system includes at least two application devices that are spaced apart from each other but only one detection unit, the monitored electrical characteristics along the route by the detection unit may be shown in a graph similar to graph  1010 . For example, the graph may include the plotted electrical signals  1012  and  1014 , where the electrical signal  1012  represents the first examination signal injected by the first application device (such as application device  606 A in  FIG. 6 ) and detected by the detection unit  1002  (such as detection unit  616 A in  FIG. 6 ), and the electrical signal  1014  represents the second examination signal injected by the second application device (such as application device  606 B in  FIG. 6 ) and detected by the same detection unit  1002 . Using only the plotted amplitudes of the electrical signals  1012  and  1014  (instead of also  1016  and  1018 ), the identification unit may determine the status of the route. For example, between times t 0  and t 2 , both signals  1012  and  1014  are constant at the base line values, indicating that the detection unit  1002  receives both the first and second examination signals, so the section of the route is non-damaged. Between times t 2  and t 4 , the one or more electrical characteristics monitored by the detection unit  1002  indicate an increased amplitude of the first examination signal above the base line and a decreased amplitude of the second examination signal below the base line. Thus, during this time period the detection unit  1002  only receives the first examination signal and not the second examination signal (beyond a trace or negligible amount), which indicates that the section of the route may include an electrical short. For example, referring to  FIG. 6 , the first application device  606 A is on the same side of the electrical short as the detection unit  616 A, so the first examination signal is received by the detection unit  616 A and the amplitude of the electrical signals associated with the first examination signal is increased over the base line amplitude due to the sub-loop created by the electrical short. However, the second application device  606 B is on an opposite side of the electrical short from the detection unit  616 A, so the second examination signal circulates a different sub-loop and is not received by the detection unit  616 A, resulting in the amplitude drop in the plotted signal  1014  over this time period. Finally, between times t 5  and t 7 , the one or more electrical characteristics monitored by the detection unit  1002  indicate drops in the amplitudes of the both the first and second examination signals, so neither of the examination signals are received by the detection unit  1002 . Thus, the section of the route is potentially damaged, which causes an open circuit loop and explains the lack of receipt by the detection unit  1002  of either of the examination signals. Alternatively, the detection unit  1002  may be the detection unit  1004  shown in the graph  1010  such that the electrical signals are the plotted electrical signals  1016  and  1018  instead of  1012  and  1014 . 
     In the alternative embodiment described with reference to  FIG. 6  in which the examining system includes only one application device and only one detection unit, the monitored electrical characteristics along the route by the detection unit may be shown in a graph similar to graph  1010 . For example, the graph may include the plotted electrical signal  1012 , where the electrical signal  1012  represents the examination signal injected by the application device (such as application device  606 A shown in  FIG. 6 ) and detected by the detection unit  1002  (such as detection unit  161 A shown in  FIG. 6 ). Using only the plotted amplitudes of the electrical signal  1012  (instead of also  1014 ,  1016 , and  1018 ), the identification unit may determine the status of the route. For example, between times t 0  and t 2 , the signal  1012  is constant at the base line value, indicating that the detection unit  1002  receives the examination signal, so the section of the route is non-damaged. Between times t 2  and t 4 , the one or more electrical characteristics monitored by the detection unit  1002  indicate an increased amplitude of the examination signal above the base line, which further indicates that the section of the route includes an electrical short. Finally, between times t 5  and t 7 , the one or more electrical characteristics monitored by the detection unit  1002  indicate a drop in the amplitude of the examination signal, so the examination signal is not received by the detection unit  1002 . Thus, the section of the route is potentially damaged, which causes an open circuit loop. Alternatively, the detection unit may be the detection unit  1004  shown in the graph  1010  (such as the detection unit  616 B shown in  FIG. 6 ) and the electrical signal is the plotted electrical signal  1018  (injected by the application device  606 B shown in  FIG. 9 ) instead of  1012 . Thus, the detection unit may be proximate to the application device in order to obtain the plotted electrical signals  1012  and  1018 . For example, an application device that is spaced apart from the detection device along a length of the vehicle or vehicle system may result in the plotted electrical signals  1014  or  1016 , which both show drops in amplitude when the examining system traverses both a damaged section of the route and an electrical short. A spaced-apart arrangement between the detection unit and the application unit that provides one of the plotted signals  1014 ,  1016  is not useful in distinguishing between these two states of the route, unless the plotted signal  1014  or  1016  is interpreted in combination with other monitored electrical characteristics, such as phase or modulation, for example. 
       FIG. 13  is a flowchart of an embodiment of a method  1100  for examining a route being traveled by a vehicle system from onboard the vehicle system. The method  1100  may be used in conjunction with one or more embodiments of the vehicle systems and/or examining systems described herein. Alternatively, the method  1100  may be implemented with another system. 
     At  1102 , first and second examination signals are electrically injected into conductive tracks of the route being traveled by the vehicle system. The first examination signal may be injected using a first vehicle of the vehicle system. The second examination signal may be injected using the first vehicle at a rearward or frontward location of the first vehicle relative to where the first examination signal is injected. Optionally, the first examination signal may be injected using the first vehicle, and the second examination signal may be injected using a second vehicle in the vehicle system. Electrically injecting the first and second examination signals into the conductive tracks may include applying a designated direct current, a designated alternating current, and/or a designated radio frequency signal to at least one conductive track of the route. The first and second examination signals may be transmitted into different conductive tracks, such as opposing parallel tracks. 
     At  1104 , one or more electrical characteristics of the route are monitored at first and second monitoring locations. The monitoring locations may be onboard the first vehicle in response to the first and second examination signals being injected into the conductive tracks. The first monitoring location may be positioned closer to the front of the first vehicle relative to the second monitoring location. Detection units may be located at the first and second monitoring locations. Electrical characteristics of the route may be monitored along one conductive track at the first monitoring location; the electrical characteristics of the route may be monitored along a different conductive track at the second monitoring location. Optionally, a notification may be communicated to the first and second monitoring locations when the first and second examination signals are injected into the route. Monitoring the electrical characteristics of the route may be performed responsive to receiving the notification. 
     At  1106 , a determination is made as to whether one or more monitored electrical characteristics indicate receipt of both the first and second examination signals at both monitoring locations. For example, if both examination signals are monitored in the electrical characteristics at both monitoring locations, then both examination signals are circulating the conductive test loop  912  (shown in  FIG. 9 ). As such, the circuit of the test loop is intact. But, if each of the monitoring locations monitors electrical characteristics indicating only one or none of the examination signals, then the circuit of the test loop may be affected by an electrical break or an electrical short. If the electrical characteristics do indicate receipt of both first and second examination signals at both monitoring locations, flow of the method  1100  may proceed to  1108 . 
     At  1108 , the vehicle continues to travel along the route. Flow of the method  1100  then proceeds back to  1102  where the first and second examination signals are once again injected into the conductive tracks, and the method  1100  repeats. The method  1100  may be repeated instantaneously upon proceeding to  1108 , or there may be a wait period, such as 1 second, 2 seconds, or 5 seconds, before re-injecting the examination signals. 
     Referring back to  1106 , if the electrical characteristics indicate that both examination signals are not received at both monitoring locations, then flow of the method  1100  proceeds to  1110 . At  1110 , a determination is made as to whether one or more monitored electrical characteristics indicate a presence of only the first or the second examination signal at the first monitoring location and a presence of only the other examination signal at the second monitoring location. For example, the electrical characteristics received at the first monitoring location may indicate a presence of only the first examination signal, and not the second examination signal. Likewise, the electrical characteristics received at the second monitoring location may indicate a presence of only the second examination signal, and not the first examination signal. As described herein, “indicat[ing] a presence of” an examination signal means that the received electrical characteristics include more than a mere threshold signal-to-noise ratio of the unique identifier indicative of the respective examination signal that is more than electrical noise. 
     This determination may be used to distinguish between electrical characteristics that indicate the section of the route is damaged and electrical characteristics that indicate the section of the route is not damaged but may have an electrical short. For example, since the first and second examination signals are not both received at each of the monitoring locations, the route may be identified as being potentially damaged due to a broken track that is causing an open circuit. However, an electrical short may also cause one or both monitoring locations to not receive both examination signals, potentially resulting in a false alarm. Therefore, this determination is made to distinguish an electrical short from an electrical break. 
     For example, if neither examination signal is received at either of the monitoring locations as the vehicle system traverses over the section of the route, the electrical characteristics may indicate that the section of the route is damaged (e.g., broken). Alternatively, the section may be not damaged but including an electrical short if the one or more electrical characteristics monitored at one of the monitoring locations indicate a presence of only one of the examination signals. This indication may be strengthened if the electrical characteristics monitored at the other monitoring location indicate a presence of only the other examination signal. Additionally, a non-damaged section of the route having an electrical short may also be indicated if an amplitude of the electrical characteristics monitored at the first monitoring location is an inverse derivative of an amplitude of the electrical characteristics monitored at the second monitoring location as the vehicle system traverses over the section of the route. If the monitored electrical characteristics indicate significant receipt of only one examination signal at the first monitoring location and only the other examination signal at the second monitoring location, then flow of the method  1100  proceeds to  1112 . 
     At  1112 , the section of the route is identified as being non-damaged but having an electrical short. In response, the notification of the identified section of the route including an electrical short may be communicated off-board and/or stored in a database onboard the vehicle system. The location of the electrical short may be determined more precisely by comparing a location of the vehicle over time to the inverse derivatives of the monitored amplitudes of the electrical characteristics monitored at the monitoring locations. For example, the electrical short may have been equidistant from the two monitoring locations when the inverse derivatives of the amplitude are monitored as being equal. Location information may be obtained from a location determining unit, such as a GPS device, located on or off-board the vehicle. After identifying the section as having an electrical short, the vehicle system continues to travel along the route at  1108 . 
     Referring now back to  1100 , if the monitored electrical characteristics do not indicate significant receipt of only one examination signal at the first monitoring location and only the other examination signal at the second monitoring location, then flow of the method  1100  proceeds to  1114 . At  1114 , the section of the route is identified as damaged. Since neither monitoring location receives electrical characteristics indicating at least one of the examination signals, it is likely that the vehicle is traversing over an electrical break in the route, which prevents most if not all of the conduction of the examination signals along the test loop. The damaged section of the route may be disposed between the designated axles of the first vehicle that define ends of the test loop based on the one or more electrical characteristics monitored at the first and second monitoring locations. After identifying the section of the route as being damaged, flow proceeds to  1116 . 
     At  1116 , responsive action is initiated in response to identifying that the section of the route is damaged. For example, the vehicle, such as through the control unit and/or identification unit, may be configured to automatically slow movement, automatically notify one or more other vehicle systems of the damaged section of the route, and/or automatically request inspection and/or repair of the damaged section of the route. A warning signal may be communicated to an off-board location that is configured to notify a recipient of the damaged section of the route. A repair signal to request repair of the damaged section of the route may be communicated off-board as well. The warning and/or repair signals may be communicated by at least one of the control unit or the identification unit located onboard the vehicle. Furthermore, the responsive action may include determining a location of the damaged section of the route by obtaining location information of the vehicle from a location determining unit during the time that the first and second examination signals are injected into the route. The calculated location of the electrical break in the route may be communicated to the off-board location as part of the warning and/or repair signal. Optionally, responsive actions, such as sending warning signals, repair signals, and/or changing operational settings of the vehicle, may be at least initiated manually by a vehicle operator onboard the vehicle or a dispatcher located at an off-board facility. 
     In addition or as an alternate to using one or more embodiments of the route examination systems described herein to detect damaged sections of a route, one or more embodiments of the route examination systems may be used to determine location information about the vehicles on which the route examination systems are disposed. The location information can include a determination of which route of several different routes on which the vehicle is currently disposed, a determination of the location of the vehicle on a route, a direction of travel of the vehicle along the route, and/or a speed at which the vehicle is moving along the route. 
       FIG. 14  is a schematic illustration of an embodiment of the examining system  900  on the vehicle  902  as the vehicle  902  travels along the route  904 . While only two axles  1400 ,  1402  (“Axle  3 ” and “Axle  4 ” in  FIG. 14 ) are shown in  FIG. 14 , the vehicle  902  may include a different number of axles and/or axles other than the third and fourth axles of the vehicle  902  may be used. 
     The route  904  can be formed from the conductive rails  614  described above (e.g., the rails  614 A,  614 B). The route  904  can include one or more frequency tuned shunts  1404  that extend between the conductive rails  614 A,  614 B. A frequency tuned shunt  1404  can form a conductive pathway or short between the rails  614 A,  614 B of the route  904  for an electric signal that is conducted in the rails  614 A,  614 B at a frequency to which the shunt  1404  is tuned. For example, the shunt  1404  shown in  FIG. 14  is tuned to a frequency of 3.8 kHz. An electric signal having a frequency of 3.8 kHz that is conducted along the rail  614 A will also be conducted through the shunt  1404  to the rail  614 B (and/or such a signal may be conducted from the rail  614 B to the rail  614 A through the shunt  1404 ). Electric signals having other frequencies (e.g., 4.6 kHz or another frequency), however, will not be conducted by the shunt  1404 . As a result, a signal having a frequency to which the shunt  1404  is tuned (referred to as a tuned frequency) that is injected into the rail  614 A by the application unit  908 B (“Tx 2 ” in  FIG. 14 ) will be conducted along a circuit loop or path that includes the rail  614 A, the axle  1400 , the rail  614 B, and the shunt  1404 . This signal is detected by the detection unit  910 B (“Rx 1 ” in  FIG. 14 ). Similarly, a signal having the tuned frequency that is injected into the rail  614 B by the application unit  908 A (“Tx 1 ” in  FIG. 14 ) will be conducted along a circuit loop or path that includes the rail  614 B, the axle  1402 , the rail  614 A, and the shunt  1404 . In one embodiment, one or more of the detection units may detect signals having different frequencies. 
     A signal that has a frequency other than the tuned frequency and that is injected into the rail  614 A by the application unit  908 B will be conducted along a circuit loop or path that includes the rail  614 A, the axle  1400 , the rail  614 B, and the axle  1402 , but that does not include the shunt  1404 . Similarly, a signal that has a frequency other than the tuned frequency and that is injected into the rail  614 B by the application unit  908 A will be conducted along a circuit loop or path that includes the rail  614 B, the axle  1402 , the rail  614 A, and the axle  1400 , but that does not include the shunt  1404 . A shunt that is tuned to multiple frequencies, such as 3.8 kHz and 4.6 kHz or a range of frequencies that include 3.8 kHz and 4.6 kHz, will conduct the signals. For example, a shunt that is tuned to a range of frequencies that include both 3.8 kHz and 4.6 kHz will conduct signals having frequencies of 3.8 kHz or 4.6 kHz between the rails  614 A,  614 B. 
     One or more frequency tuned shunts can be disposed across routes at designated locations to calibrate the location of vehicles traveling along the routes. The frequency tuned shunts can be read by the examining systems described herein to define a specific location of the vehicle on the route. This can allow for accurate calibration of location of the vehicle when combined with a location determining system of the vehicle (e.g., a global positioning system receiver, wireless transceiver, or the like), and can increase the accuracy of the location of the vehicle when using a dead reckoning technique and/or when another locating method is unavailable. The detection of the frequency tuned shunts also can also be used to determine which route of several different routes on which a vehicle is currently located. 
     The examining system can use multiple different frequencies to test the route beneath the vehicle for damage. By placing an element such as a frequency tuned shunt on the route that responds to one or a combination of the frequencies, and placing such elements at planned differences in spacing along the route, codes can be generated to convey information about the specific location to the vehicle in an economical and reliable manner. 
       FIG. 15  illustrates electrical characteristics  1500  (e.g., electrical characteristics  1500 A,  1500 B) and electrical characteristics  1502  (e.g., electrical characteristics  1502 A,  1502 B) of the route that may be monitored by the examining system on a vehicle system as the vehicle system travels along the route  904  (shown in  FIG. 14 ) according to one example. The electrical characteristics  1500 ,  1502  are shown alongside a horizontal axis  1504  representative of time or distance along the route  904  and vertical axes  1506  representative of magnitudes of the electrical characteristics  1500 ,  1502  (as measured by the detection units  910 A,  910 B shown in  FIG. 14 . The electrical characteristics  1500 ,  1502  represent the magnitudes of first and second signals injected into the rails  614  (shown in  FIG. 14 ) of the route  904  by the application units  908 , as detected by the detection units  910 A,  910 B during travel of the vehicle system over the frequency tuned shunt  1404 . 
     The application unit  908 A can inject a first signal having a frequency that is not the tuned frequency of the shunt  1404  (or that is outside of the range of tuned frequencies of the shunt  1404 ). The application unit  908 B can inject a second signal having the tuned frequency of the shunt  1404  (or that is within the range of tuned frequencies of the shunt  1404 ). The detection unit  910 A can detect magnitudes of the first and second signals as conducted to the detection unit  910 A through the rail  614 A and the detection unit  910 B can detect magnitudes of the first and second signals as conducted to the detection unit  910 B through the rail  614 B. The electrical characteristic  1500 A represents the magnitudes of the first signal (the non-tuned frequency signal) as detected by the detection unit  910 B and the electrical characteristic  1500 B represents the magnitudes of the first signal as detected by the detection unit  910 A. The electrical characteristic  1502 A represents the magnitudes of the second signal (the tuned frequency signal) as detected by the detection unit  910 B and the electrical characteristic  1502 B represents the magnitudes of the second signal as detected by the detection unit  910 A. 
     A time t 1  indicates when the axle  1400  (e.g., a leading axle) passes the shunt  1404  as the vehicle system travels along a direction of travel  1406  shown in  FIG. 14 . A time t 2  indicates when the axle  1402  (e.g., a trailing axle) passes the shunt  1404  as the vehicle system travels along the direction of travel  1406 . The time period including and between the times t 1  and t 2  represents when the shunt  1404  is disposed between the axles  1400 ,  1402 . 
     Prior to the axle  1400  passing over the shunt  1404  (e.g., before the time t 1 ), the first and second signals are conducted through a circuit formed from the axles  1400 ,  1402  and the sections of the rails  614  that extend from and between the axles  1400 ,  1402 . As a result, the magnitudes of the electrical characteristics  1500 ,  1502  do not appreciably change (e.g., the electrical characteristics  1500 ,  1502  may not change in magnitude or the changes in the magnitude may be caused by noise or outside interference). 
     Upon the axle  1400  passing the shunt  1404 , however, different circuits are formed for the different first and second signals, depending on the frequencies of the signals. For example, for the first signal (the non-tuned frequency signal), the circuit through which the first signal is conducted to the detection units  910 A,  910 B does not change. As a result, the magnitudes of the electrical characteristics  1500 A,  1500 B do not appreciably change. For the second signal (the tuned frequency signal), the shunt  1404  conducts the second signal and a smaller, different circuit is formed. The circuit that conducts the second signal includes the axle  1400 , the shunt  1404 , and the sections of the rails  614  extending from the axle  1400  to the shunt  1404 . This circuit for the second signal also can prevent the second signal from being conducted to the detection unit  910 A. The smaller circuit that includes the shunt  1404  can prevent the second signal from reaching and being detected by the detection unit  910 A. 
     The detection unit  910 B detects an increase in the second signal at or near the time t 1 , as indicated by the increase in the electrical characteristic  1502 A shown in  FIG. 15 . This increase may be caused by decreased electrical impedance in the circuit formed from the axle  1400 , the shunt  1404 , and the sections of the rails  614  extending from the axle  1400  to the shunt  1404 . For example, because this circuit is shorter than the circuit that does not include the shunt  1404 , the electrical impedance may be less. 
     The detection unit  910 A may no longer be able to detect the second signal after time t 1  due to the circuit formed with the shunt  1404 . The circuit formed with the shunt  1404  can prevent the second signal from being conducted in the rail  614 A. The detection unit  910 A may detect a decrease or elimination of the second signal, as represented by the decrease in the electrical characteristic  1502 B at time t 1 . 
     As the vehicle moves over the shunt  1404 , the axle  1400  moves farther from the shunt  1404 . This increasing distance from the axle  1400  to the shunt  1404  increases the size of the circuit that includes the axle  1400  and the shunt  1404 . The impedance of the circuit through which the electrical characteristic  1502 A is conducted increases from time t 1  to time t 2 . The increasing impedance can decrease the magnitude of the second signal (as detected by the detection unit  910 B). As a result, the magnitude of the electrical characteristic  1502 A detected by the detection unit  910 B decreases from time t 1  to time t 2 . With respect to the detection unit  910 A, because the shunt  1404  continues to prevent the second signal from being conducted to the detection unit  910 A, the magnitude of the electrical characteristics  1502 B remain reduced, as shown in  FIG. 15 . 
     Once the vehicle system has moved over the shunt  1404  and the shunt  1404  is no longer between the axles  1400 ,  1402  (e.g., after time t 2 ), the second signal is again conducted through the circuit that does not include the shunt  1404  and that is formed from the axles  1400 ,  1402  and the sections of the rails  614  extending between the axles  1400 ,  1402 . The magnitude of the second signal as detected by the detection unit  910 B may return to a level that was measured prior to time t 1 . Because the shunt  1404  is no longer preventing the detection unit  910 A from detecting the second signal after time t 2 , the value of the electrical characteristic  1502 B may increase back to the level that existed prior to the time t 1 . 
     The examining system can analyze two or more of the electrical characteristics  1500 A,  1500 B,  1502 A,  1502 B to differentiate detection of a frequency tuned shunt  1404  from detection of a damaged section of the route  904  and/or the presence of another shunt on the route  904 . A break  922  in a rail  614  in the route  904  may result in two or more signals  1012 ,  1014 ,  1016 ,  1018  as detected by the detection units  910 A,  910 B to decrease during concurrent times, as shown in  FIG. 12  during the time period extending from time t 5  to time t 7 . In contrast, only one of the electrical characteristics  1500 A,  1500 B,  1502 A,  1502 B decreases during passage of the vehicle system over the shunt  1404 . The control unit and/or identification unit can determine how many electrical characteristics  1500 A,  1500 B,  1502 A,  1502 B decrease at a time to determine if the vehicle system is traveling over a damaged section of the route  904  or over a frequency tuned shunt  1404 . A shunt  916  that is not a frequency tuned shunt  1404  causes two or more (or all) of the signals  1012 ,  1014 ,  1016 ,  1018  to increase and/or decrease during passage over the shunt  916 , as shown in  FIG. 12  during the time period from time t 2  to the time t 4 . In contrast, only the signals detected by a single detection unit  910 B change during passage over a frequency tuned shunt  1404 . Therefore, if signals detected by two or more detection units change, then the shunt that is detected may not be a frequency tuned shunt. If signals detected by the same detection unit change, but the signals detected by another detection unit do not change, then the shunt that is detected may be a frequency tuned shunt. 
     The examining systems described herein can examine the electrical characteristics  1500 ,  1502  to determine a variety of information about the vehicle system and/or the route  904 , in addition to or as an alternate to detecting damage to the route  904 . As one example, the control unit  206 ,  506  and/or identification unit  220 ,  520  can identify which route  904  the vehicle system is traveling along. Different routes  904  may have frequency tuned shunts  1404  in different locations and/or sequences. The location of the shunts  1404  and/or sequences of the shunts  1404  may be unique to the routes  904  such that, upon detecting the shunts  1404 , the examining systems can determine which route  904  the vehicle system is traveling along. 
     For example, a first route  904  may have a first shunt  1404  tuned to a first frequency and a second route  904  may have a second shunt  1404  tuned to a second frequency. The examining system can inject signals having one or more of the first or second frequencies to attempt to detect the first and/or second shunt  1404 . Upon detecting one or more of the changes in the electrical characteristics  1502 , the examining system can determine that the vehicle system traveled over the first or second shunt  1404 . If the examining system is injecting an electrical test signal having the first frequency into the route  904  and the examining system detects the changes in the signal that are similar to the changes in the electrical characteristics  1502 A and/or  1502 B, the examining system can determine that the vehicle system passed over the first shunt  1404 . The first route  904  may be associated with the first shunt  1404  in a memory  540  of the examining system (shown in  FIG. 5 , such as a memory of the control unit, identification unit, or the like, and/or as communicated to the examining system) such that, upon detecting the first shunt  1404 , the examining system determines that the vehicle system is on the first route  904 . 
     If the examining system is injecting the electrical test signal having the first frequency into the route  904  and the examining system does not detect the changes in the signal that are similar to the changes in the electrical characteristics  1502 A and/or  1502 B, the examining system can determine that the vehicle system has not passed over the first shunt  1404 . The examining system can then determine that the vehicle system is not on the first route  904 . 
     If the examining system is injecting an electrical test signal having the second frequency into the route  904  and the examining system detects the changes in the signal that are similar to the changes in the electrical characteristics  1502 A and/or  1502 B, the examining system can determine that the vehicle system passed over the second shunt  1404 . The second route  904  may be associated with the second shunt  1404  such that, upon detecting the second shunt  1404 , the examining system determines that the vehicle system is on the second route  904 . If the examining system is injecting the electrical test signal having the second frequency into the route  904  and the examining system does not detect the changes in the signal that are similar to the changes in the electrical characteristics  1502 A and/or  1502 B, the examining system can determine that the vehicle system has not passed over the second shunt  1404 . The examining system can then determine that the vehicle system is not on the second route  904 . 
     Additionally or alternatively, different routes  904  may be associated with different sequences of two or more frequency tuned shunts  1404 . A sequence of shunts  1404  can represent an order in which the shunts  1404  are encountered by a vehicle system traveling over the sequence of shunts  1404 , and optionally may include the frequencies to which the shunts  1404  are tuned and/or distances between the shunts  1404 . For example, Table 1 below represents different sequences of shunts  1404  in different routes  904 : 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Route 
                 Shunt Sequence 
               
               
                   
                   
               
             
            
               
                   
                  1 
                 A, A, A, A 
               
               
                   
                  2 
                 A, A, A, B 
               
               
                   
                  3 
                 A, A, B, A 
               
               
                   
                  4 
                 A, B, A, A 
               
               
                   
                  5 
                 B, A, A, A 
               
               
                   
                  6 
                 A, A, B, B 
               
               
                   
                  7 
                 A, B, B, A 
               
               
                   
                  8 
                 B, B, A, A 
               
               
                   
                  9 
                 A, B, B, B 
               
               
                   
                 10 
                 B, B, B, A 
               
               
                   
                 11 
                 A, B, A, B 
               
               
                   
                 12 
                 B, A, B, A 
               
               
                   
                 13 
                 B, B, B, B 
               
               
                   
                 14 
                 B, B, A, B 
               
               
                   
                 15 
                 B, A, B, B 
               
               
                   
                 16 
                 B, A, A, B 
               
               
                   
                   
               
            
           
         
       
     
     The letters A and B represent different frequencies to which the shunts  1404  are tuned. While each sequence of the shunts  1404  in Table 1 includes four shunts  1404 , alternatively, one or more of the sequences may include a different number of shunts  1404 . While the sequences only include two different frequencies, optionally, one or more sequences may include more frequencies. 
     The examining system can track the order in which different shunts  1404  are detected by the vehicle system to determine which route  904  that the vehicle system is traveling along. For example, if the examining system detects a shunt  1404  tuned to frequency B, followed by another shunt  1404  tuned to frequency B, followed by another shunt  1404  tuned to frequency A, followed by a shunt  1404  tuned to frequency A, then the examining system can determine that the vehicle system is on the eighth route  904  listed above. 
     A shunt sequence optionally may include distances between shunts  1404 . Table 2 below illustrates examples of shunt sequences that also include distances: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Route 
                 Shunt Sequence 
               
               
                   
                   
               
             
            
               
                   
                  9 
                 A, 50 m, A 
               
               
                   
                 10 
                 A, 30 m, B 
               
               
                   
                 11 
                 A, 100 m, A 
               
               
                   
                 12  
                 B, 20 m, A, 30 m, A 
               
               
                   
                   
               
            
           
         
       
     
     The numbers 50 m, 30 m, and so on, listed between the letters A and/or B represent distances between the shunts  1404  tuned to the A or B frequency. The examining system can detect the shunts  1404  tuned to the different frequencies, the order in which these shunts  1404  are detected, and the distance between the shunts  1404 , in order to determine which route the vehicle system is traveling along. 
     Using the detection of one or more frequency tuned shunts  1404  to determine which route  904  the vehicle system is traveling along can be useful for the control unit  206 ,  506  to differentiate between different routes  904  that are closely spaced together. Some routes  904  may be sufficiently close to each other that the resolution of other location determining systems (e.g., global positioning systems, wireless triangulation, etc.) may not be able to differentiate between which of the different routes  904  that the vehicle system is traveling along. At times, the vehicle system may not be able to rely on such other location determining systems, such as when the vehicle system is traveling in a tunnel, in valleys, urban areas, or the like. The detection of a frequency tuned shunt  1404  associated with a route  904  can allow the examining systems to determine which route  904  the vehicle system is on when the other location determining systems may be unable to determine which route  904  the vehicle system is traveling on. 
     In another example, the control unit  206 ,  506  and/or identification unit  220 ,  520  can determine where the vehicle system is located along a route  904  using detection of one or more shunts  1404 . Different locations along the routes  904  may have frequency tuned shunts  1404  in different locations and/or sequences. The location of the shunts  1404  and/or sequences of the shunts  1404  may be unique to the locations along the routes  904  such that, upon detecting the shunts  1404 , the examining systems can determine where the vehicle system is located along a route  904 . 
     For example, a first location along a route  904  may have a first shunt  1404  tuned to a first frequency and a second location along the route  904  may have a second shunt  1404  tuned to a second frequency. The examining system can inject signals having one or more of the first or second frequencies to attempt to detect the first and/or second shunt  1404 . Upon detecting one or more of the changes in the electrical characteristics  1502 , the examining system can determine that the vehicle system traveled over the first or second shunt  1404 . If the examining system is injecting an electrical test signal having the first frequency into the route  904  and the examining system detects the changes in the signal that are similar to the changes in the electrical characteristics  1502 A and/or  1502 B, the examining system can determine that the vehicle system passed over the first shunt  1404 . The first location along the route  904  may be associated with the first shunt  1404  in the memory  540  of the examining system such that, upon detecting the first shunt  1404 , the examining system determines that the vehicle system is at the location along the first route  904  associated with the first shunt  1404 . 
     If the examining system is injecting the electrical test signal having the first frequency into the route  904  and the examining system does not detect the changes in the signal that are similar to the changes in the electrical characteristics  1502 A and/or  1502 B, the examining system can determine that the vehicle system has not passed over the first shunt  1404 . The examining system can then determine that the vehicle system is not located at the location on the first route  904  that is associated with the first shunt  1404 . 
     If the examining system is injecting an electrical test signal having the second frequency into the route  904  and the examining system detects the changes in the signal that are similar to the changes in the electrical characteristics  1502 A and/or  1502 B, the examining system can determine that the vehicle system passed over the second shunt  1404 . The second location along the route  904  may be associated with the second shunt  1404  such that, upon detecting the second shunt  1404 , the examining system determines that the vehicle system is at the location on the route  904  associated with the second shunt  1404 . If the examining system is injecting the electrical test signal having the second frequency into the route  904  and the examining system does not detect the changes in the signal that are similar to the changes in the electrical characteristics  1502 A and/or  1502 B, the examining system can determine that the vehicle system has not passed over the second shunt  1404 . The examining system can then determine that the vehicle system is not at the location along the route  904  that is associated with the second shunt  1404   
     Additionally or alternatively, different locations along routes  904  may be associated with different sequences of two or more frequency tuned shunts  1404 . Similar to as described above, detection of shunts  1404  in a sequence associated with a designated location along a route  904  can allow for the examining system to determine where the vehicle system is located along the route. 
     Using the detection of one or more frequency tuned shunts  1404  to determine where the vehicle system is located along a route  904  can be useful for the control unit  206 ,  506  to determine where the vehicle system is located. As described above, the vehicle system may not be able to rely on other location determining systems to determine where the vehicle system is located. Additionally, the examining system can determine the location of the vehicle system to assist in calibrating or updating a location that is based on a dead reckoning technique. For example, if the vehicle system is using dead reckoning to determine where the vehicle system is located, determination of the location of the vehicle system using the shunts  1404  can serve as a check or update on the location as determined using dead reckoning. 
     The determined location of the vehicle system may be used to calibrate or update other location determining systems of the vehicle system, such as global positioning system receivers, wireless transceivers, or the like. Some location determining systems may be unable to provide locations of the vehicle system after initialization of the location determining systems. For example, after turning the vehicle system and/or the location determining systems on, the location determining systems may be unable to determine the locations of the vehicle systems for a period of time that the location determining systems are initializing. The detection of frequency tuned shunts during this initialization can allow for the vehicle systems to determine the locations of the vehicle systems during the initialization. 
     Optionally, the failure to detect a frequency tuned shunt  1404  in a designated location can be used by the examining system to determine that the shunt  1404  is damaged or has been removed. Because the locations of the frequency tuned shunts  1404  may be stored in the memory  540  of the vehicle system and/or communicated to the vehicle system, the failure to detect a frequency tuned shunt  1404  at the designated location of the shunt  1404  can serve to notify the examining system that the shunt  1404  is damaged and/or has been removed. The examining system and/or control unit can then notify an operator of the vehicle system of the damaged and/or missing shunt  1404 , can cause the communication unit to automatically send a signal to a scheduling or dispatch facility to schedule inspection, repair, or replacement of the shunt  1404 , or the like. 
     In another example, the control unit  206 ,  506  and/or identification unit  220 ,  520  can determine a direction of travel of the vehicle system responsive to detecting one or more frequency tuned shunts  1404 . Upon detecting the changes in the electrical characteristics  1502  that indicate presence of a frequency tuned shunt  1404 , the identification unit can examine one or more aspects of the electrical characteristics  1502  to determine a direction of travel  1406 . The identification unit can examine the slope of the electrical characteristic  1502  to determine the direction of travel  1406 . If the electrical characteristic  1502  has a negative slope between time t 1  and t 2 , then the slope can indicate that the vehicle system has the direction of travel  1406  shown in  FIG. 14 . But, if the electrical characteristic  1502  has a positive slope between time t 1  and t 2 , the slope can indicate that the vehicle system has an opposite direction of travel. 
     In another example, the control unit  206 ,  506  and/or identification unit  220 ,  520  can determine a moving speed of the vehicle system responsive to detecting one or more frequency tuned shunts  1404 . In one aspect, the examining system can determine the time period elapsed between time t 1  and t 2  based on the changes in the electrical characteristic  1502 A and/or  1502 B that indicate detection of the shunt  1404 . Based on the elapsed time period and a separation distance  1408  (shown in  FIG. 14 ) between the axles  1400 ,  1402 , the control unit and/or identification unit can calculate a moving speed of the vehicle system. For example, if the separation distance  1408  is 397 inches (e.g., ten meters) and the time period between t 1  and t 2  is 1.13 seconds, then the examining system can determine that the vehicle system is traveling at approximately twenty miles per hour (e.g., 32 kilometers per hour). 
     In another example, the control unit  206 ,  506  and/or identification unit  220 ,  520  can determine a moving speed of the vehicle system responsive to detecting one or more frequency tuned shunts  1404 . In one aspect, the examining system can determine the slope of the electrical characteristic  1502 A between the time t 1  and the time t 2 . Larger absolute values of the slopes may be associated with faster speeds of the vehicle system than smaller absolute values of the slopes. Different absolute values of slopes may be associated with different speeds in the memory  540  of the examining system and/or as communicated to the examining system. The control unit and/or identification unit can determine the absolute value of the slope in the electrical characteristic  1502 A and compare the determined slope to absolute values of the slopes associated with different speeds to determine how fast the vehicle system is moving. 
       FIG. 16  illustrates a flowchart of one embodiment of a method  1600  for examining a route and/or determining information about the route and/or a vehicle system. The method  1600  may be performed by one or more embodiments of the examining systems described herein to detect damage to a route, detect a shunt on the route, and/or determine information about the route and/or a vehicle system traveling on the route. 
     At  1602 , an examination signal having a designated frequency is injected into the route. The examination signal may have a frequency associated with one or more frequency tuned shunts. Optionally multiple examination signals may be injected into the route. For example, different signals having different frequencies associated with frequency tuned shunts may be injected into the route. 
     At  1604 , one or more electrical characteristics of the route are monitored. For example, the voltages, currents, resistances, impedances, or the like, of the route may be monitored, as described herein. At  1606 , the one or more electrical characteristics that are monitored may be examined to determine if the one or more electrical characteristics indicate damage to the route, as described above. Optionally, the one or more electrical characteristics may be examined to determine if a shunt (e.g., other than a frequency tuned shunt) is on the route, as described above. If the one or more electrical characteristics indicate damage to the route, flow of the method  1600  may proceed toward  1608 . Otherwise, flow of the method  1600  can proceed toward  1610 . At  1608 , one or more responsive actions may be initiated to detection of the damage to the route, as described above. 
     At  1610 , a determination is made as to whether the one or more electrical characteristics indicate passage of the vehicle system over a frequency tuned shunt. As described above, the characteristic can be examined as one or more of the electrical characteristics  1500 ,  1502  shown in  FIG. 15 . If the characteristic indicates movement over the frequency tuned shunt, then flow of the method  1600  can proceed toward  1616 . Otherwise, flow of the method  1600  can proceed toward  1612 . 
     At  1612 , a determination is made as to whether a frequency tuned shunt previously was at the location of the vehicle. For example, if no frequency tuned shunt was detected at a location, but a frequency tuned shunt is supposed to be at the location, then the failure to detect the shunt can indicate that the shunt is damaged or removed. As a result, flow of the method  1600  can proceed toward  1614 . If a frequency tuned shunt is not known to have previously been at that location, however, then flow of the method  1600  can return toward  1602  or the method  1600  can terminate. 
     At  1614 , one or more responsive actions can be implemented responsive to the failure to detect the shunt. For example, an operator of the vehicle system may be notified, a message may be communicated to an off-board location to automatically schedule inspection, repair, or replacement of the frequency tuned shunt, etc. 
     At  1616 , information about the vehicle system and/or route is determined based on detection of the frequency tuned shunt. As described above, the route on which the vehicle is traveling may be identified, the location of the vehicle system along the route may be determined, the direction of travel of the vehicle system, the speed of the vehicle system, etc., may be determined based on detection of one or more frequency tuned shunts. Flow of the method  1600  may return to  1602  or the method  1600  may terminate. 
     In an embodiment, a system (e.g., a route examining system) includes first and second application devices, a control unit, first and second detection units, and an identification unit. The first and second application devices are configured to be disposed onboard a vehicle of a vehicle system traveling along a route having first and second conductive tracks. The first and second application devices are each configured to be at least one of conductively or inductively coupled with one of the conductive tracks. The control unit is configured to control supply of electric current from a power source to the first and second application devices in order to electrically inject a first examination signal into the conductive tracks via the first application device and to electrically inject a second examination signal into the conductive tracks via the second application device. The first and second detection units are configured to be disposed onboard the vehicle. The detection units are configured to monitor one or more electrical characteristics of the first and second conductive tracks in response to the first and second examination signals being injected into the conductive tracks. The identification unit is configured to be disposed onboard the vehicle. The identification unit is configured to examine the one or more electrical characteristics of the first and second conductive tracks monitored by the first and second detection units in order to determine whether a section of the route traversed by the vehicle and electrically disposed between the opposite ends of the vehicle is potentially damaged based on the one or more electrical characteristics. 
     In an aspect, the first application device is disposed at a spaced apart location along a length of the vehicle relative to the second application device. The first application device is configured to be at least one of conductively or inductively coupled with the first conductive track. The second application device is configured to be at least one of conductively or inductively coupled with the second conductive track. 
     In an aspect, the first detection unit is disposed at a spaced apart location along a length of the vehicle relative to the second detection unit. The first detection unit is configured to monitor the one or more electrical characteristics of the second conductive track. The second detection unit is configured to monitor the one or more electrical characteristics of first conductive track. 
     In an aspect, the first and second examination signals include respective unique identifiers to allow the identification unit to distinguish the first examination signal from the second examination signal in the one or more electrical characteristics of the route. 
     In an aspect, the unique identifier of the first examination signal includes at least one of a frequency, a modulation, or an embedded signature that differs from the unique identifier of the second examination signal. 
     In an aspect, the control unit is configured to control application of at least one of a designated direct current, a designated alternating current, or a designated radio frequency signal of each of the first and second examination signals from the power source to the conductive tracks of the route. 
     In an aspect, the power source is an onboard energy storage device and the control unit is configured to inject the first and second examination signals into the route by controlling conduction of electric current from the onboard energy storage device to the first and second application devices. 
     In an aspect, the power source is an off-board energy storage device and the control unit is configured to inject the first and second examination signals into the route by controlling conduction of electric current from the off-board energy storage device to the first and second application devices. 
     In an aspect, further comprising two shunts disposed at spaced apart locations along a length of the vehicle. The two shunts configured to at least one of conductively or inductively couple the first and second conductive tracks to each other at least part of the time when the vehicle is traveling over the route. The first and second conductive tracks and the two shunts define an electrically conductive test loop when provides a circuit path for the first and second examination signals to circulate. 
     In an aspect, the two shunts are first and second trucks of the vehicle. Each of the first and second trucks includes an axle interconnecting two wheels that contact the first and second conductive tracks. The wheels and the axle of each of the first and second trucks are configured to at least one of conductively or inductively couple the first conductive track to the second conductive track to define respective ends of the conductive test loop. 
     In an aspect, the identification unit is configured to identify at least one of a short circuit in the conductive test loop caused by an electrical short between the first and second conductive tracks or an open circuit in the conductive test loop caused by an electrical break on at least the first conductive track or the second conductive track. 
     In an aspect, when the section of the route has an electrical short positioned between the two shunts, a first conductive short loop defined along the first and second conductive tracks of the second of the route between one of the two shunts and the electrical short. A second conductive short loop is defined along the first and second conductive tracks of the section of the route between the other of the two shunts and the electrical short. The first application device and the first detection unit are disposed along the first conductive short loop. The second application device and the second detection unit are disposed along the second conductive short loop. 
     In an aspect, the identification unit is configured to determine whether the section of the route traversed by the vehicle is potentially damaged by distinguishing between one or more electrical characteristics that indicate the section is damaged and one or more electrical characteristics that indicate the section is not damaged but has an electrical short. 
     In an aspect, the identification unit is configured to determine the section of the route is damaged when the one or more electrical characteristics received by the first detection unit and the second detection unit both fail to indicate conduction of the first or second examination signals through the conductive tracks as the vehicle traverses the section of the route. 
     In an aspect, the identification unit is configured to determine the section of the route is not damaged but has an electrical short when an amplitude of the one or more electrical characteristics indicative of the first examination signal monitored by the first detection unit is an inverse derivative of an amplitude of the one or more electrical characteristics indicative of the second examination signal monitored by the second detection unit as the vehicle traverses the section of the route. 
     In an aspect, the identification unit is configured to determine the section of the route is not damaged but has an electrical short when the one or more electrical monitored by the first detection unit only indicate a presence of the first examination signal and the one or more electrical characteristics monitored by the second detection unit only indicate a presence of the second examination signals as the vehicle traverses over the section of the route. 
     In an aspect, in response to determining that the section of the route is a potentially damaged section of the route, at least one of the control unit or the identification unit is configured to at least one of automatically slow movement of the vehicle system, automatically notify one or more other vehicle systems of the potentially damaged section of the route, or automatically request at least one of inspection or repair of the potentially damaged section of the route. 
     In an aspect, in response to determining that the section of the route is damaged, at least one of the control unit or the identification unit is configured to communicate a repair signal to an off-board location to request repair of the section of the route. 
     In an aspect, the vehicle system further includes a location determining unit configured to determine the location of the vehicle along the route. At least one of the control unit or the identification unit is configured to determine a location of the section of the route by obtaining the location of the vehicle from the location determining unit when the control unit injects the first and second examination signals into the conductive tracks. 
     In an embodiment, a method (e.g., for examining a route being traveled by a vehicle system) includes electrically injecting first and second examination signals into first and second conductive tracks of a route being traveled by a vehicle system having at least one vehicle. The first and second examination signals are injected using the vehicle at spaced apart locations along a length of the vehicle. The method also includes monitoring one or more electrical characteristics of the first and second conductive tracks at first and second monitoring locations that are onboard the vehicle in response to the first and second examination signals being injected into the conductive tracks. The first monitoring location is spaced apart along the length of the vehicle relative to the second monitoring location. The method further includes identifying a section of the route traversed by the vehicle system is potentially damaged based on the one or more electrical characteristics monitored at the first and second monitoring locations. 
     In an aspect, the first examination signal is injected into the first conductive track and the second examination signal is injected into the second conductive track. The electrical characteristics along the second conductive track are monitored at the first monitoring location, and the electrical characteristics along the first conductive track are monitored at the second monitoring location. 
     In an aspect, the first and second examination signals include respective unique identifiers to allow for distinguishing the first examination signal from the second examination signal in the one or more electrical characteristics of the conductive tracks. 
     In an aspect, electrically injecting the first and second examination signals into the conductive tracks includes applying at least one of a designated direct current, a designated alternating current, or a designated radio frequency signal to at least one of the conductive tracks of the route. 
     In an aspect, the method further includes communicating a notification to the first and second monitoring locations when the first and second examination signals are injected into the route. Monitoring the one or more electrical characteristics of the route is performed responsive to receiving the notification. 
     In an aspect, identifying the section of the route is damaged includes determining if one of the conductive tracks of the route is broken when the first and second examination signals are not received at the first and second monitoring locations. 
     In an aspect, the method further includes communicating a warning signal when the section of the route is identified as being damaged. The warning signal is configured to notify a recipient of the damage to the section of the route. 
     In an aspect, the method further includes communicating a repair signal when the section of the route is identified as being damaged. The repair signal is communicated to an off-board location to request repair of the damage to the section of the route. 
     In an aspect, the method further includes distinguishing between one or more electrical characteristics that indicate the section of the route is damaged and one or more electrical characteristics that indicate the section is not damaged but has an electrical short. 
     In an aspect, one or more electrical characteristics indicate the section of the route is damaged when neither the first examination signal nor the second examination signal is received at the first or second monitoring locations as the vehicle system traverses the section of the route. 
     In an aspect, monitoring the one or more electrical characteristics of the first and second conductive tracks includes monitoring the first and second examination signals circulating an electrically conductive test loop that is defined by the first and second conductive tracks between two shunts disposed along the length of the vehicle. If the section of the route includes an electrical short between the two shunts, the first examination signal circulates a first conductive short loop defined between one of the two shunts and the electrical short, and the second examination signal circulates a second conductive short loop defined between the other of the two shunts and the electrical short. 
     In an aspect, the section of the route is identified as non-damaged but has an electrical short when an amplitude of the electrical characteristics indicative of the first examination signal monitored at the first monitoring location is an inverse derivative of an amplitude of the electrical characteristics indicative of the second examination signal monitored at the second monitoring location as the vehicle system traverses the section of the route. 
     In an aspect, the section of the route is identified as non-damaged but has an electrical short when the electrical characteristics monitored at the first monitoring location only indicate a presence of the first examination signal, and the electrical characteristics monitored at the second monitoring location only indicate a presence of the second examination signal as the vehicle system traverses the section of the route. 
     In an aspect, the method further includes determining a location of the section of the route that is damaged by obtaining from a location determining unit a location of the vehicle when the first and second examination signals are injected into the route. 
     In another embodiment, a system (e.g., a route examining system) includes first and second application devices, a control unit, first and second detection units, and an identification unit. The first application device is configured to be disposed on a first vehicle of a vehicle system traveling along a route having first and second conductive tracks. The second application device is configured to be disposed on a second vehicle of the vehicle system trailing the first vehicle along the route. The first and second application devices are each configured to be at least one of conductively or inductively coupled with one of the conductive tracks. The control unit is configured to control supply of electric current from a power source to the first and second application devices in order to electrically inject a first examination signal into the first conductive track via the first application device and a second examination signal into the second conductive track via the second application device. The first detection unit is configured to be disposed onboard the first vehicle. The second detection unit is configured to be disposed onboard the second vehicle. The detection units are configured to monitor one or more electrical characteristics of the conductive tracks in response to the first and second examination signals being injected into the conductive tracks. The identification unit is configured to examine the one or more electrical characteristics of the conductive tracks monitored by the first and second detection units in order to determine whether a section of the route traversed by the vehicle system is potentially damaged based on the one or more electrical characteristics. 
     In an aspect, the first detection unit is configured to monitor one or more electrical characteristics of the second conductive track. The second detection unit is configured to monitor one or more electrical characteristics of the first conductive track. 
     In an aspect, when the section of the route has an electrical short positioned between two shunts of the vehicle system, a first conductive short loop is defined along the first and second conductive tracks between one of the two shunts and the electrical short. A second conductive short loop is defined along the first and second conductive tracks of the section of the route between the other of the two shunts and the electrical short. The first application device and the first detection unit are disposed along the first conductive short loop. The second application device and the second detection unit are disposed along the second conductive short loop. 
     In an embodiment, a method (e.g., for examining a route and/or determining information about the route and/or a vehicle system) includes injecting a first electrical examination signal into a conductive route from onboard a vehicle system traveling along the route, detecting a first electrical characteristic of the route based on the first electrical examination signal, and detecting, using a route examining system that also is configured to detect damage to the route based on the first electrical characteristic, a first frequency tuned shunt in the route based on the first electrical characteristic. 
     In one aspect, detecting the first frequency tuned shunt in the route occurs responsive to a frequency of the first electrical examination signal being one or more of a tuned frequency or within a range of tuned frequencies of the first frequency tuned shunt. 
     In one aspect, the method also includes identifying the route from among several different routes based on detection of the first frequency tuned shunt. 
     In one aspect, the method also includes determining a location of the vehicle system along the route based on detection of the first frequency tuned shunt. 
     In one aspect, the method also includes determining a direction of travel of the vehicle system based on detection of the first frequency tuned shunt. 
     In one aspect, the method also includes determining a speed of the vehicle system based on detection of the first frequency tuned shunt. 
     In one aspect, the method also includes determining that a second frequency tuned shunt is one or more of missing or damaged based on a failure to detect the second frequency tuned shunt at a designated location associated with the second frequency tuned shunt. 
     In one aspect, the method also includes identifying the route from among several different routes based on detection of a sequence of frequency tuned shunts that includes the first frequency tuned shunt and one or more other frequency tuned shunts, wherein the sequence is associated with the route. 
     In one aspect, the method also includes determining a location of the vehicle system along the route based on detection of a sequence of frequency tuned shunts that includes the first frequency tuned shunt and one or more other frequency tuned shunts, wherein the sequence is associated with the location along the route. 
     In one aspect, the first electrical examination signal injected into the route has a first frequency to which the first frequency tuned shunt is tuned. The method also can include injecting a second electrical examination signal having a different, second frequency into the route from onboard the vehicle system, detecting a second electrical characteristic of the route based on the second electrical examination signal, and differentiating between the damage to the route or detection of the first frequency tuned shunt based on the first and second electrical characteristics. 
     In an embodiment, a system (e.g., a route examining system) includes a first application unit configured to inject a first electrical examination signal into a conductive route from onboard a vehicle system traveling along the route, a first detection unit configured to measure a first electrical characteristic of the route based on the first electrical examination signal, and an identification unit configured to detect damage to the route based on the first electrical characteristic and to detect a first frequency tuned shunt in the route based on the first electrical characteristic. 
     In one aspect, the identification unit is configured to detect the first frequency tuned shunt in the route responsive to a frequency of the first electrical examination signal being one or more of a tuned frequency or within a range of tuned frequencies of the first frequency tuned shunt. 
     In one aspect, the identification unit is configured to identify the route from among several different routes based on detection of the first frequency tuned shunt. 
     In one aspect, the identification unit is configured to determine a location of the vehicle system along the route based on detection of the first frequency tuned shunt. 
     In one aspect, the identification unit is configured to determine a direction of travel of the vehicle system based on detection of the first frequency tuned shunt. 
     In one aspect, the identification unit is configured to determine a speed of the vehicle system based on detection of the first frequency tuned shunt. 
     In one aspect, the identification unit is configured to determine that a second frequency tuned shunt is one or more of missing or damaged based on a failure to detect the second frequency tuned shunt at a designated location associated with the second frequency tuned shunt. 
     In one aspect, the identification unit is configured to identify the route from among several different routes based on detection of a sequence of frequency tuned shunts that includes the first frequency tuned shunt and one or more other frequency tuned shunts, wherein the sequence is associated with the route. 
     In one aspect, the identification unit is configured to determine a location of the vehicle system along the route based on detection of a sequence of frequency tuned shunts that includes the first frequency tuned shunt and one or more other frequency tuned shunts, wherein the sequence is associated with the location along the route. 
     In one aspect, the first application unit is configured to inject the first electrical examination signal with a first frequency to which the first frequency tuned shunt is tuned. The system also can include a second application unit configured to inject a second electrical examination signal having a different, second frequency into the route from onboard the vehicle system and a second detection unit configured to detect a second electrical characteristic of the route based on the second electrical examination signal. The identification unit can be configured to differentiate between the damage to the route or detection of the first frequency tuned shunt based on the first and second electrical characteristics. 
     In an embodiment, a system (e.g., a route examining system) includes a first application unit configured to inject a first electrical signal having a first frequency into a first conductive rail of a route from onboard a vehicle system, a first detection unit configured to monitor a first characteristic of the first conductive rail of the route from onboard the vehicle system based on the first electrical signal, a second application unit configured to inject a second electrical signal having a different, second frequency into a second conductive rail of the route from onboard the vehicle system, a second detection unit configured to monitor a second characteristic of the second conductive rail of the route from onboard the vehicle system based on the second electrical signal, and an identification unit configured to detect damage to the route and to determine one or more of identify the route from several different routes, determine a location of the vehicle system along the route, determine a direction of travel of the vehicle system, determine a speed of the vehicle system, or identify a missing or damaged frequency tuned shunt based on one or more of the first or second characteristic. 
     Another embodiment disclosed herein provides for systems and methods that detect and classify broken rails by filtering and extracting features from electrical characteristics of the rails and classifying these features with pattern recognition, machine learning, and/or signal processing methods. The system and method operate in two or more stages. A first stage includes detecting broken rails based on changes in electrical characteristics in rails responsive to injecting electric examination signals into the rails. To reduce the rate of false-positive detections, a second stage refines the first-pass detection by discriminating broken rails from likely sources of false-positive confusions, such as poor wheel-to-rail shunting and noise, using pattern recognition or machine learning methods. 
       FIG. 17  illustrates another example of the examining system  900  in operation. In the illustrated example, the examining system  900  travels over the route  904  and includes the application unit  908 A (“Tx 1 ” in  FIG. 17 ) that injects an examination signal having a first frequency (e.g., “f 1  current” in  FIG. 17 ) into the rail  614 A (“Rail  1 ” in  FIG. 17 ) and the application unit  908 B (“Tx 2 ” in  FIG. 17 ) that injects an examination signal having a different, second frequency (e.g., “f 2  current” in  FIG. 17 ) into the rail  614 B (“Rail  2 ” in  FIG. 17 ). Optionally, the application units  908  (e.g., application units  908 A,  908 B) may inject signals having the same frequencies but different identifiers included therein into the rails  614 A,  614 B. In contrast to the example shown in  FIG. 14 , the application unit  908 A and the detection unit  910 B may be conductively and/or inductively coupled with the same rail  614 A while the application unit  908 B and the detection unit  910 A are conductively and/or inductively coupled with the other rail  614 B. Alternatively, the application unit  908 A and the detection unit  910 A may be conductively and/or inductively coupled with different rails  614 A,  614 B and/or the application unit  908 B and the detection unit  910 B may be conductively and/or inductively coupled with different rails  614 A,  614 B. 
       FIG. 18  illustrates a flowchart of one embodiment of a method  1800  for examining a route. The method  1800  may be performed by one or more embodiments of the route examining systems described herein to identify damage to the routes, insulated joints in the routes, shunts across the rails of the routes, or the like. For example, the identification unit  220  (shown in  FIG. 2 ) and/or the identification unit  816  (shown in  FIG. 8 ) can perform the analysis of the electrical characteristics and patterns as described herein. 
     At  1802 , a data segment is obtained. The data segment can include the electrical characteristics measured by the detection units  910 A,  910 B. For example, the data segment can include magnitudes of current and/or voltage as measured by the detection units  910 A,  910 B for two or more different frequencies (e.g., frequency  1  and frequency  2 ). The electrical characteristics of the route may also include noise attributable to the vehicle system and/or the surroundings. The noise may have various frequencies that differ from the frequencies of the examination signals injected by the application units  908 A,  908 B. The noise, as used herein, is a summation of unwanted or disturbing energy, and may include electrical interference from sources of electrical energy other than the application units  908 A,  908 B. The noise may be attributable to electric motors on the vehicle system, route-based electrical circuits, or the like. In order to accurately interpret and analyze the electrical characteristics of the route that are based on or attributable to the first and second examination signals, the noise is filtered out of the data segment measured by the detection units  910 A,  910 B. 
     At  1803 , the electrical characteristics measured by the detection units  910 A,  910 B are filtered to extract subsets of the electrical characteristics based on the examination signals injected by the application units  908 A,  908 B from the electrical characteristics based on noise. For example, the examination signals injected by the application units  908 A,  908 B have fixed frequencies, so the relevant electrical characteristics are at these specific frequencies. The electrical characteristics of the route include noise from the vehicle system and/or the surroundings that appears at various frequencies different from the frequencies of the examination signals. In an embodiment, a filter is applied to the electrical characteristics to isolate subsets of the electrical characteristics occurring at frequency ranges of interest (e.g., occurring at the frequencies of the first and second examination signals) and suppress the electrical characteristics at other frequencies that are attributable to noise. 
     Referring now to  FIG. 24 ,  FIG. 24  illustrates two waveforms of electrical characteristics shown alongside a horizontal axis  2402  representative of time and a vertical axis  2404  representative of magnitudes of the waveforms. A first waveform  2406  represents the electrical characteristics of the raw data segment measured by one of the detection units  910 A,  910 B. The first waveform  2406  includes undesirable noise, resulting in a highly fluctuating magnitude of the waveform  2406  over time. Thus, the first waveform  2406  is formed based on un-filtered raw data. A second waveform  2408  represents a subset of filtered electrical characteristics from the electrical characteristics of the raw data. For example, the second waveform  2408  is formed by filtering the electrical characteristics of the raw data segment to isolate a subset of the electrical characteristics occurring at a frequency range of interest. The second waveform  2408  represents electrical characteristics that have frequencies within the frequency range of interest. The frequency range of interest is inclusive of the first frequency of the first examination signal (e.g., frequency  1 ) and/or is inclusive of the second frequency of the second examination signal (e.g., frequency  2 ). The second waveform  2408  does not include as much undesirable noise as the first waveform  2406  since electrical characteristics at frequencies outside of the frequency range of interest are suppressed, eliminated, concealed, or otherwise not depicted in the waveform  2408 . For this reason, the fluctuations of the second waveform  2408  have reduced absolute magnitudes relative to the fluctuations of the first waveform  2406 . 
     Optionally, the first and second waveforms  2406 ,  2408  may represent the electrical characteristics of the rail  614 B (shown in  FIG. 17 ) as measured by the detection unit  910 A based on injection of the first examination signal having the first frequency by the first application unit  908 A. The first waveform  2406  represents the raw electrical characteristics of the rail  614 B detected by the detection unit  910 A without filtering (e.g., inclusive of noise), while the second waveform  2408  represents a filtered subset of the electrical characteristics of the rail  614 B detected by the detection unit  910 A. The filtered subset of electrical characteristics is formed by extracting the electrical characteristics of the data segment at a frequency range of interest and suppressing the electrical characteristics of the data segment at other frequencies outside of the frequency range of interest. In this example, the frequency range of interest includes the frequency of the first examination signal (e.g., frequency  1 ), such that the isolated subset of electrical characteristics represents the magnitude (e.g., current and/or voltage) of the first examination signal within the conductive rail of the route. 
     The electrical characteristics of the data segment may be filtered by applying one or more filtering processes tuned to the specific frequency or frequency range of interest. The filtering may be performed by one or more processors, such as the identification unit  220  (shown in  FIG. 2 ) or the identification unit  816  (shown in  FIG. 8 ). In one embodiment, a band-pass filter may be designed around the first frequency of the first examination signal in order to isolate the subset of electrical characteristics occurring at frequencies within a narrow range of the first frequency from the electrical characteristics occurring at frequencies outside of the frequency range. The one or more processors may isolate the subset of electrical characteristics by extracting the subset of electrical characteristics from the raw data and/or by suppressing, eliminating, or concealing the electrical characteristics occurring outside of the frequency range of interest that are attributable to noise. Assuming, for example, that the first examination signal has a frequency of 4.6 kHz, the band-pass filter may be designed to isolate electrical characteristics in the range of 4.5-4.7 kHz, and to suppress electrical characteristics at frequencies below 4.5 kHz and/or over 4.7 kHz. Furthermore, assuming that the second examination signal has a frequency of 3.8 kHz, the band-pass filter may be designed to isolate a first subset of electrical characteristics in the range of 4.5-4.7 kHz and a second subset of electrical characteristics in the range of 3.7-3.9 kHz, while attenuating or suppressing electrical characteristics between 3.9 and 4.5 kHz, above 4.7 kHz, and below 3.7 kHz to clear out-of-band noise. Optionally, a finite impulse response realization with relatively few coefficients may be used to design the band-pass filter. 
     In another embodiment, a matched filter may be tuned to a frequency range of interest that includes the first frequency of the first examination signal and/or the second frequency of the second examination signal. The matched filter may be used instead of, or in addition to, the band-pass filter. Using the matched filter to isolate a subset of electrical characteristics occurring at the frequency of the first examination signal involves convolving the raw electrical characteristics measured by the respective detection unit  910 A,  910 B (depicted as the first waveform  2406 ) with a sine wave having the same frequency as the first examination signal supplied by the first application unit  908 A. Directly convolving the measured electrical characteristics with the sine wave having the frequency of the first examination signal ensures a match in frequency. Electrical characteristics at frequencies that do not match the frequency of the first examination signal are suppressed or eliminated. Filter coefficients of the matched filter are the impulse response of the finite impulse response filter. The filter coefficients may come from a sine wave, which allows storage of the coefficients to be made relatively compact. For example, it may suffice to store only coefficients corresponding to one quarter of a sine cycle. In an embodiment, between 64 and 128 coefficients are used to achieve a sufficient signal-to-noise ratio for the matched filter. 
     After filtering the raw electrical characteristics, each resulting isolated subset of electrical characteristics has a narrow frequency range that includes the respective frequency of one of the examination signals injected into the route by the application units  908 A,  908 B. Plotting the subset of electrical characteristics yields the second waveform  2408 , which more accurately represents the respective examination signal within the route than the first waveform  2406 . Although a band-pass filter and a matched filter are described, other filtering techniques may be used in other embodiments, such as a low-pass filter, a high-pass filter, Goertzel, a direct demodulation or the like. 
     With continued reference to the flowchart of the method  1800  shown in  FIG. 18 ,  FIGS. 19 through 22  illustrate examples of electrical characteristics  1900 ,  2000 ,  2100 ,  2200  measured by the detection units  910  shown in  FIG. 17 . The electrical characteristics  1900 ,  2000 ,  2100 ,  2200  are shown alongside a horizontal axis  1902  representative of time and vertical axes  1904 ,  2004  representative of magnitudes of the electrical characteristics  1900 ,  2000 ,  2100 ,  2200 . The electrical characteristics  1900 ,  2000 ,  2100 ,  2200  have already been filtered to remove noise. The electrical characteristics  1900  can represent the electrical characteristics of the rail  614 B (shown in  FIG. 17 ) as measured by the detection unit  910 A (shown in  FIG. 17 ) based on injection of the examination signal having the first frequency and injected into the rail  614 A (shown in  FIG. 17 ) by the application unit  908 A (shown in  FIG. 17 ). The electrical characteristics  2000  can represent the electrical characteristics of the rail  614 B as measured by the detection unit  910 A based on injection of the examination signal having the second frequency and injected into the rail  614 B by the application unit  908 B (shown in  FIG. 17 ). The electrical characteristics  2100  can represent the electrical characteristics of the rail  614 A as measured by the detection unit  910 B based on injection of the examination signal having the second frequency and injected into the rail  614 B by the application unit  908 B. The electrical characteristics  2200  can represent the electrical characteristics of the rail  614 A as measured by the detection unit  910 B based on injection of the examination signal having the first frequency and injected into the rail  614 A by the application unit  908 A. 
     One or more indices of the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  measured by the different detection units  910  based on different frequencies (or other different identifiers) can be determined and examined in order to differentiate between noise in the electrical characteristics and electrical characteristics representative of travel over insulated joints, damaged sections of the route  904  (shown in  FIG. 17 ), shunts across the rails  614  of the route  904 , or the like. 
     At  1804  in the flowchart of the method  1800  shown in  FIG. 18 , a determination is made as to whether a change in the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  indicates a break or insulated joint in the route. This determination may be made by determining whether the change in the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  exceeds a designated threshold and/or whether a time period over which the change in the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  occurs is within a designated time period. For example, the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  can be examined to determine if decreases in the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  exceed a designated drop threshold (e.g., 50 dB, 40 dB, 30 dB, 10%, 20%, 30%, or the like). The designated drop threshold may be a relative threshold that is relative to the magnitude of the waveform outside of a respective drop in the waveform instead of being based on a fixed number. For example, the designated drop threshold may be a drop of 40 dB from the magnitude of the waveform before the drop, instead of setting the threshold as a fixed value of 120 dB. In the illustrated examples, all of the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  decrease by more than the designated drop threshold at or near two seconds along the horizontal axis  1902  and then increase at approximately four seconds along the horizontal axis  1902 . 
     The drops in the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  and/or the time periods over which the drops occur may be indices of the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  that are examined in order to determine whether the route includes a break in conductivity (e.g., damage to the route, an insulated joint in the route, or the like). The drops in the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  can be examined to determine drop time periods  1906 ,  2006 ,  2106 ,  2206  over which the drops in the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  occur. For example, the time periods  1906 ,  2006 ,  2106 ,  2206  may be measured from a time when the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  decrease by at least the designated drop threshold to a subsequent time when the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  increase by at least the designated drop threshold. Optionally, a moving average window may be used to locate drops in the electrical characteristics  1900 ,  2000 ,  2100 ,  2200 . For example, the moving average window has a set length of time, such as 150 milliseconds (ms). For each 150 ms block of time, the electrical characteristics within the window are averaged to create a baseline value. A falling or first edge of a respective drop may be identified responsive to a drop between the instantaneous value and the baseline value that exceeds a designated threshold (e.g., a magnitude or percentage). Likewise, a rising or second edge of the drop is identified in response to an increase between the instantaneous value and the baseline value that exceeds another designated threshold. 
     The time periods  1906 ,  2006 ,  2106 ,  2206  of the drops (which may be referred to herein as drop time periods) can be compared to one or more designated time periods  1908 . In the illustrated embodiment, the drop time periods  1906 ,  2006 ,  2106 ,  2206  are compared to the same designated time period  1908  of approximately two seconds, but alternatively, the drop time periods  1906 ,  2006 ,  2106 ,  2206  may be compared to different designated time periods  1908  and/or a designated time period  1908  of other than two seconds. The designated time period  1908  may correspond to the length of the vehicle system between axles  1400 ,  1402  (shown in  FIG. 17 ), such that the designated time period  1908  may be longer for longer distances between the axles  1400 ,  1402  and shorter for shorter distances between the axles  1400 ,  1402 . In one aspect, the designated time period  1908  may change based on the moving speed of the vehicle or vehicles on which the detection units  910  are disposed. For faster moving vehicles, the designated time period  1908  can decrease and for slower moving vehicles, the designated time period  1908  may increase. 
     In one embodiment, if all of the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  decrease by at least the designated drop threshold for time periods  1906 ,  2006 ,  2106 ,  2206  that are no longer or no greater than the designated time period  1908 , then the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  may be indicative of a conductive break in the route, such as damage to the route, an insulated joint in the route, or the like. Optionally, if at least a designated threshold or percentage (e.g., at least 75%, at least 50%, etc.) of the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  decrease by at least the designated drop threshold for time periods  1906 ,  2006 ,  2106 ,  2206  that are no longer or no greater than the designated time period  1908 , then the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  may be indicative of a conductive break in the route, such as damage to the route, an insulated joint in the route, or the like. As a result, flow of the method  1800  can proceed toward  1806  for further examination of the electrical characteristics  1900 ,  2000 ,  2100 ,  2200 . 
     But, if the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  (or at least a designated threshold of the electrical characteristics  1900 ,  2000 ,  2100 ,  2200 ) do not decrease by at least the designated drop threshold and/or within a time period no longer or no greater than the designated time period  1908 , then the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  may not be indicative of a break in the conductivity of the route. As a result, flow of the method  1800  can proceed toward  1808 . 
     At  1808 , a determination is made that the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  are not representative of a break in the electrical conductivity of the route. For example, the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  may not indicate a break in the route, damage to the route, an insulated joint or segment in the route, or the like. Flow of the method  1800  may then terminate or return to  1802  to obtain and examine additional electrical characteristics. 
     At  1806 , the electrical characteristics may be examined to ensure that the detection of the break or insulated joint is not a false-positive detection. The electrical characteristics can be further analyzed to check on whether detection of the break or insulated joint at  1804  is not indicative of another condition, such as oil or other debris on the route, reduced conductivity between the wheels of the vehicle and the route, etc. This additional check on the electrical characteristics can significantly reduce the number of times that a break or insulated joint in a rail is incorrectly identified. 
     In one aspect, one or more feature vectors are determined based on the electrical characteristics  1900 ,  2000 ,  2100 ,  2200 . The feature vectors also may be referred to as indices of the electrical characteristics  1900 ,  2000 ,  2100 ,  2200 . The feature vector for an electrical characteristic  1900 ,  2000 ,  2100 ,  2200  can include multiple measurements or calculations derived from the electrical characteristic  1900 ,  2000 ,  2100 ,  2200 . In one embodiment, several feature vectors are calculated for each electrical characteristic  1900 ,  2000 ,  2100 ,  2200 . 
     The feature vectors calculated for an electrical characteristic  1900 ,  2000 ,  2100 ,  2200  can include one or more statistical measures of the electrical characteristic. A statistical measure can include a mean or median value  1910 ,  2010 ,  2110 ,  2210  of the electrical characteristic  1900 ,  2000 ,  2100 ,  2200  prior to the decrease in the electrical characteristic  1900 ,  2000 ,  2100 ,  2200  by more than the designated drop threshold. The feature vectors also can include a statistical measure, such as a standard deviation  1912 ,  2012 ,  2112 ,  2212  or other measurement representative of how much the electrical characteristic  1900 ,  2000 ,  2100 ,  2200  varies prior to the decrease in the electrical characteristic  1900 ,  2000 ,  2100 ,  2200  by more than the designated drop threshold. 
     The time period over which the mean or median values  1910 ,  2010 ,  2110 ,  2210  are calculated for the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  and/or the standard deviations  1912 ,  2012 ,  2112 ,  2212  can include a time period that is as long as the drop time period  1906 . Alternatively, these values may be calculated over longer or shorter time periods. 
     The feature vectors calculated for an electrical characteristic  1900 ,  2000 ,  2100 ,  2200  can include a statistical measure, such as a mean or median value  1914 ,  2014 ,  2114 ,  2214  of the electrical characteristic  1900 ,  2000 ,  2100 ,  2200 , within the drop time periods  1906 ,  2006 ,  2106 ,  2206 . The feature vectors also can include a statistical measure, such as a standard deviation  1916 ,  2016 ,  2116 ,  2216  or other measurement representative of how much the electrical characteristic  1900 ,  2000 ,  2100 ,  2200  varies during the drop time periods  1906 ,  2006 ,  2106 ,  2206 . 
     The feature vectors calculated for an electrical characteristic  1900 ,  2000 ,  2100 ,  2200  can include statistical measure, such as a mean or median value  1918 ,  2018 ,  2118 ,  2218  of the electrical characteristic  1900 ,  2000 ,  2100 ,  2200  after the drop time periods  1906 ,  2006 ,  2106 ,  2206 . The feature vectors also can include a statistical measure, such as a standard deviation  1920 ,  2020 ,  2120 ,  2220  or other measurement representative of how much the electrical characteristic  1900 ,  2000 ,  2100 ,  2200  varies after the drop time periods  1906 ,  2006 ,  2106 ,  2206 . 
     The time period over which the mean or median values  1918 ,  2018 ,  2118 ,  2218  are calculated for the electrical characteristics  1900 ,  2000 ,  2100 ,  2200  and/or the standard deviations  1920 ,  2020 ,  2120 ,  2220  can include a time period that is as long as the drop time period  1906 . Alternatively, these values may be calculated over longer or shorter time periods. 
     The statistical measures can include means and/or median values, as described herein, but optionally may include other statistical calculations of the electrical characteristics. For example, medians, root mean square values, or the like, may be calculated and included in the feature vectors. The statistical measures that are calculated for the electrical characteristics can be the indices of the electrical characteristics that are examined in order to determine if the electrical characteristics are representative of travel over a break in the conductivity of the route. These indices represent the feature vectors of the electrical characteristics. In one embodiment, a combination of the mean or median value of an electrical characteristic prior to the decrease by more than the drop threshold and the standard deviation of the same electrical characteristic prior to the decrease by more than the drop threshold is a first feature vector of that electrical characteristic. This first feature vector can be referred to as pre-drop feature vector. A combination of the mean or median value of an electrical characteristic during the drop time period and the standard deviation of the same electrical characteristic during the drop time period is a second feature vector of that electrical characteristic. This second feature vector can be referred to as drop feature vector. A combination of the mean or median value of an electrical characteristic after the increase from the drop time period and the standard deviation of the same electrical characteristic after the increase from the drop time period is a third feature vector of that electrical characteristic. This third feature vector can be referred to as post-drop feature vector. If four electrical characteristics are monitored (e.g., voltages associated with injected currents having two different frequencies as sensed by two different detection units), then there can be twelve feature vectors (e.g., three feature vectors per electrical signal). Alternatively, a different number of feature vectors may be determined, or a single feature vector may be determined. The feature vectors for the electrical signals being monitored can be referred to as a set of feature vectors. 
     In one aspect, the values of the feature vectors may be multiplied by a constant value. The constant value may be based on the number of electrical characteristics being monitored. For example, if four electrical characteristics are being monitored, then the values of the feature vectors for all four electrical characteristics may be multiplied by four. Alternatively, the values of the feature vectors may be multiplied by another constant, or may not be multiplied by a constant. 
     At  1810 , the set of feature vectors is compared to one or more patterns of feature vectors. The patterns can represent different conditions of the route. A first feature pattern can include feature vectors representative of travel over a break in a rail of the route. A different, second feature pattern can include feature vectors representative of travel over an insulated joint in the route. A different, third feature pattern can include feature vectors representative of travel over a shunt that conductively couples the rails of the route. A different, fourth feature pattern can include feature vectors representative of travel over a crossing between routes. One or more other patterns may be used. 
     The set of feature vectors can be compared to the patterns of the feature vectors to determine which, if any, of the patterns of the feature vectors that the set of feature vectors matches (or matches more closely than one or more other patterns). In aspect, linear discriminant analysis is used to compare the set of feature vectors with the patterns. The analysis can be used to find a linear combination of feature vectors that matches, or more closely matches, the set of feature vectors, than one or more other linear combination of the feature vectors. Different linear combinations of feature vectors can be the different patterns of the feature vectors. The linear combination that matches or more closely matches the set of feature vectors than one or more other linear combinations may be identified as a matching pattern of feature vectors. 
     In another aspect, a Gaussian mixture model may be used to determine if the set of feature vectors matches a pattern associated with one or more conditions of the route. The Gaussian mixture model can be used to calculate probabilities that at least a subset of the feature vectors in the set match some or all of the feature vectors associated with a pattern. Depending on the probabilities that the subset of the feature vectors in the set match some or all feature vectors of different patterns, a pattern may be selected to identify the condition of the route. 
     In another aspect, one or more support vector machines may be used to determine which pattern is matched by or more closely matched by the set of feature vectors than one or more (or all) other patterns. The support vector machine analysis can involve one or more processors (e.g., of the identification unit  520  shown in  FIG. 5 ) examining feature vectors that are previously associated as being representative or indicative of different conditions of the route. The support vector machine analysis constructs categories of different feature vectors, with the categories associated with the different route conditions. The support vector machine analysis then examines the set of feature vectors to determine which of these categories that the set of feature vectors more closely matches than other categories. The condition of the route may then be identified based on this category. 
     Optionally, another technique may be used to determine if the set of feature vector matches or more closely matches a pattern of feature vectors. 
       FIG. 23  illustrates examples of feature vectors  2300 ,  2302 ,  2304 ,  2306  included in different patterns representative of different conditions of the route. The patterns include different values for the feature vectors  2300 ,  2302 ,  2304 ,  2306  associated with the different electrical characteristics being measured. The feature vectors  2300 ,  2302 ,  2304 ,  2306  (e.g., means and standard deviations) are shown alongside a horizontal axis  2308  and a vertical axis  2310 . The horizontal axis  2308  represents the different electrical characteristics and the vertical axis  2310  represents the values of the feature vectors included in the different patterns  2300 ,  2302 ,  2304 ,  2306 . 
     The feature vectors  2300 ,  2302 ,  2304 ,  2306  are shown in columns associated with different electrical characteristics and different time periods. Along the horizontal axis  2308 , the feature vectors  2300 ,  2302 ,  2304 ,  2306  above “Ch 11  (BRK)” represent the feature vectors  2300 ,  2302 ,  2304 ,  2306  (e.g., the means and standard deviations) calculated during the drop time period for electrical characteristics measured by the first detection unit  910 A based on the signal injected into the rail with the first frequency. The feature vectors  2300 ,  2302 ,  2304 ,  2306  above “Ch 11  (Pre)” represent the feature vectors  2300 ,  2302 ,  2304 ,  2306  (e.g., the means and standard deviations) calculated for the time prior to the drop time period for electrical characteristics measured by the first detection unit  910 A based on the signal injected into the rail with the first frequency. The feature vectors  2300 ,  2302 ,  2304 ,  2306  above “Ch 11  (Post)” represent the feature vectors  2300 ,  2302 ,  2304 ,  2306  (e.g., the means and standard deviations) calculated for the time after the drop time period for electrical characteristics measured by the first detection unit  910 A based on the signal injected into the rail with the first frequency. 
     The feature vectors  2300 ,  2302 ,  2304 ,  2306  above “Ch 22  (BRK)” represent the feature vectors  2300 ,  2302 ,  2304 ,  2306  (e.g., the means and standard deviations) calculated during the drop time period for electrical characteristics measured by the second detection unit  910 B based on the signal injected into the rail with the second frequency. The feature vectors  2300 ,  2302 ,  2304 ,  2306  above “Ch 22  (Pre)” represent the feature vectors  2300 ,  2302 ,  2304 ,  2306  (e.g., the means and standard deviations) calculated for the time prior to the drop time period for electrical characteristics measured by the second detection unit  910 B based on the signal injected into the rail with the second frequency. The feature vectors  2300 ,  2302 ,  2304 ,  2306  above “Ch 22  (Post)” represent the feature vectors  2300 ,  2302 ,  2304 ,  2306  (e.g., the means and standard deviations) calculated for the time after the drop time period for electrical characteristics measured by the second detection unit  910 B based on the signal injected into the rail with the second frequency. 
     The feature vectors  2300 ,  2302 ,  2304 ,  2306  above “Ch 12  (BRK)” represent the feature vectors  2300 ,  2302 ,  2304 ,  2306  (e.g., the means and standard deviations) calculated during the drop time period for electrical characteristics measured by the first detection unit  910 A based on the signal injected into the rail with the second frequency. The feature vectors  2300 ,  2302 ,  2304 ,  2306  above “Ch 12  (Pre)” represent the feature vectors  2300 ,  2302 ,  2304 ,  2306  (e.g., the means and standard deviations) calculated for the time prior to the drop time period for electrical characteristics measured by the first detection unit  910 A based on the signal injected into the rail with the second frequency. The feature vectors  2300 ,  2302 ,  2304 ,  2306  above “Ch 12  (Post)” represent the feature vectors  2300 ,  2302 ,  2304 ,  2306  (e.g., the means and standard deviations) calculated for the time after the drop time period for electrical characteristics measured by the first detection unit  910 A based on the signal injected into the rail with the second frequency. 
     The feature vectors  2300 ,  2302 ,  2304 ,  2306  above “Ch 21  (BRK)” represent the feature vectors  2300 ,  2302 ,  2304 ,  2306  (e.g., the means and standard deviations) calculated during the drop time period for electrical characteristics measured by the second detection unit  910 B based on the signal injected into the rail with the first frequency. The feature vectors  2300 ,  2302 ,  2304 ,  2306  above “Ch 21  (Pre)” represent the feature vectors  2300 ,  2302 ,  2304 ,  2306  (e.g., the means and standard deviations) calculated for the time prior to the drop time period for electrical characteristics measured by the second detection unit  910 B based on the signal injected into the rail with the first frequency. The feature vectors  2300 ,  2302 ,  2304 ,  2306  above “Ch 21  (Post)” represent the feature vectors  2300 ,  2302 ,  2304 ,  2306  (e.g., the means and standard deviations) calculated for the time after the drop time period for electrical characteristics measured by the second detection unit  910 B based on the signal injected into the rail with the first frequency. 
     The feature vectors  2300  for each of the different time periods and the electrical characteristics represent a first pattern indicative of travel over a break in a rail of the route. For example, the values of the mean and standard deviation for the feature vectors  2300  above Ch 11  (BRK), Ch 11  (Pre), Ch 11  (Post), Ch 22  (BRK), Ch 22  (Pre), Ch 22  (Post), Ch 12  (BRK), Ch 12  (Pre), Ch 12  (Post), Ch 21  (BRK), Ch 21  (Pre), and Ch 22  (Post) are included in the first pattern. 
     The feature vectors  2302  for each of the different time periods and the electrical characteristics represent a second pattern indicative of travel over an insulated joint in a rail of the route. For example, the values of the mean and standard deviation for the feature vectors  2302  above Ch 11  (BRK), Ch 11  (Pre), Ch 11  (Post), Ch 22  (BRK), Ch 22  (Pre), Ch 22  (Post), Ch 12  (BRK), Ch 12  (Pre), Ch 12  (Post), Ch 21  (BRK), Ch 21  (Pre), and Ch 22  (Post) are included in the second pattern. 
     The feature vectors  2304  for each of the different time periods and the electrical characteristics represent a third pattern indicative of travel over a shunt between rails of the route. For example, the values of the mean and standard deviation for the feature vectors  2304  above Chi  1  (BRK), Chi  1  (Pre), Chi  1  (Post), Ch 22  (BRK), Ch 22  (Pre), Ch 22  (Post), Ch 12  (BRK), Ch 12  (Pre), Ch 12  (Post), Ch 21  (BRK), Ch 21  (Pre), and Ch 22  (Post) are included in the third pattern. 
     The feature vectors  2306  for each of the different time periods and the electrical characteristics represent a fourth pattern indicative of travel over a crossing between routes. For example, the values of the mean and standard deviation for the feature vectors  2306  above Ch 11  (BRK), Ch 11  (Pre), Ch 11  (Post), Ch 22  (BRK), Ch 22  (Pre), Ch 22  (Post), Ch 12  (BRK), Ch 12  (Pre), Ch 12  (Post), Ch 21  (BRK), Ch 21  (Pre), and Ch 22  (Post) are included in the fourth pattern. 
     Returning to the description of the flowchart of the method  1800  shown in  FIG. 18 , at  1812 , a determination is made as to whether the set of feature vectors calculated for the electrical characteristics being monitored for a vehicle match the feature vectors of a pattern. If the values of the feature vectors in the set match or are within a designated range of the feature vectors of a pattern, then the set of feature vectors match the pattern. In one embodiment, a degree of match between the set of feature vectors and the feature vectors of a pattern is calculated. The closer that the values of the feature vectors in the set are to the values of the feature vectors in the pattern, the larger of a value of the degree of match. The degree of match may be compared to one or more thresholds, such as 70%, 80%, 90%, or the like. 
     In one embodiment, the patterns to which the feature vectors are compared represent a break in the rail of a route or an insulated joint. If the degree of match exceeds the threshold, then the set of feature vectors may be identified as matching the pattern. As a result, the set of feature vectors may indicate that the route includes a break in a rail or an insulated joint, and flow of the method  1800  can proceed toward  1814 . Otherwise, the set of feature vectors may not indicate a break or insulated joint. As a result, flow of the method  1800  can proceed toward  1816 . 
     At  1814 , a break or insulated joint in the route is identified. The break or insulated joint may be identified based on which pattern was matched or more closely matched by the set of feature vectors. Responsive to the break or insulated joint being identified, one or more responsive actions may be implemented. For example, responsive to a break being detected, the systems and methods described herein may automatically communicate one or more signals to schedule inspection or repair of the route, to slow or stop movement of the vehicle, or the like. Responsive to the insulated joint being identified, the systems and methods described herein may attempt to identify a location of the vehicle along the route, which route is being traveled by the vehicle, or the like. Flow of the method  1800  may then terminate or return to  1802  to obtain and examine additional electrical characteristics. 
     At  1816 , a break or insulated joint in the route is not identified. For example, the set of feature vectors may not match the patterns associated with a break or insulated joint. The set of feature vectors may be representative of noise or another condition in the route other than the break or insulated joint. Flow of the method  1800  may then terminate or return to  1802  to obtain and examine additional electrical characteristics. 
     In one embodiment, a method (e.g., for examining a route) includes injecting a first electrical examination signal into a conductive route from onboard a vehicle system traveling along the route, detecting a first electrical characteristic of the route based on the first electrical examination signal, and detecting a break in conductivity of the route responsive to the first electrical characteristic decreasing by more than a designated drop threshold for a time period within a designated drop time period. 
     In one aspect, the break that is detected includes a break in a conductive rail of the route or an insulated joint in the route. 
     In one aspect, detecting the break includes detecting an opening in a circuit formed by wheels and axles of the vehicle system and segments of conductive rails of the route extending between the wheels of the vehicle system. 
     In one aspect, injecting the first electrical examination signal into the route includes injecting the first electrical examination signal having one or more of a first frequency or a first unique identifier into the route. The method also can include injecting a second electrical examination signal having one or more of a different, second frequency or a different, second unique identifier into the route. 
     In one aspect, the first electrical examination signal is injected into a first conductive rail of the route and the second electrical examination signal is injected into a second conductive rail of the route. 
     In one aspect, the first electrical characteristic of the route includes a first voltage of the first electrical examination signal as measured along the first conductive rail by a first detection unit of a route examining system onboard the vehicle system. The method also can include detecting a second voltage of the first electrical examination signal as measured along the first conductive rail by the first detection unit as a second electrical characteristic of the route, detecting a third voltage of the second electrical examination signal as measured along the second conductive rail by a second detection unit of the route examining system as a third electrical characteristic of the route, detecting a fourth voltage of the second electrical examination signal as measured along the second conductive rail by the second detection unit as a fourth electrical characteristic of the route. 
     In one aspect, the method also includes determining feature vectors representative of different values of each of the first, second, third, and fourth electrical characteristics, and comparing the feature vectors to one or more patterns of feature vectors associated with different conditions of the route, at least one of the patterns of feature vectors associated with the break in the conductivity of the route. The break in the conductivity of the route can be detected responsive to the first electrical characteristic decreasing by more than the designated drop threshold for the time period within the designated drop time period and responsive to the feature vectors more closely matching the at least one pattern of feature vectors associated with the break in the conductivity of the route. 
     In one aspect, the feature vectors are determined for each of the first, second, third, and fourth electrical characteristics. The feature vectors can include, for each of the first, second, third, and fourth electrical characteristic: a first mean and a first standard deviation of values of the respective first, second, third, or fourth electrical characteristic prior to the respective first, second, third, or fourth electrical characteristic decreasing by more than the designated drop threshold for the time period that is within the designated drop time period; a second mean and a second standard deviation of values of the respective first, second, third, or fourth electrical characteristic after the respective first, second, third, or fourth electrical characteristic decreases by more than the designated drop threshold and before the respective first, second, third, or fourth electrical characteristic increases by at least the designated drop threshold; and a third mean and a third standard deviation of values of the respective first, second, third, or fourth electrical characteristic after the respective first, second, third, or fourth electrical characteristic increases by at least the designated drop threshold. 
     In another embodiment, a system (e.g., a route examining system) includes a first application unit configured to inject a first electrical examination signal into a conductive route from onboard a vehicle system traveling along the route, a first detection unit configured to detect a first electrical characteristic of the route based on the first electrical examination signal, and one or more processors configured to detect a break in conductivity of the route responsive to the first electrical characteristic decreasing by more than a designated drop threshold for a time period within a designated drop time period. 
     In one aspect, the break that is detected by the one or more processors includes a break in a conductive rail of the route or an insulated joint in the route. 
     In one aspect, the one or more processors are configured to detect the break by detecting an opening in a circuit formed by wheels and axles of the vehicle system and segments of conductive rails of the route extending between the wheels of the vehicle system. 
     In one aspect, the first application unit is configured to inject the first electrical examination signal into the route by injecting the first electrical examination signal having one or more of a first frequency or a first unique identifier into the route. The system also can include a second application unit configured to inject a second electrical examination signal having one or more of a different, second frequency or a different, second unique identifier into the route. 
     In one aspect, the first application unit is configured to inject the first electrical examination signal into a first conductive rail of the route and the second application unit is configured to inject the second electrical examination signal into a second conductive rail of the route. 
     In one aspect, the first detection unit is configured to measure the first electrical characteristic of the route as a first voltage of the first electrical examination signal measured along the first conductive rail. The first detection unit can be configured to measure a second voltage of the first electrical examination signal along the first conductive rail by the first detection unit as a second electrical characteristic of the route. The system also can include a second detection unit configured to measure a third voltage of the second electrical examination signal along the second conductive rail as a third electrical characteristic of the route. The second detection unit also can be configured to measure a fourth voltage of the second electrical examination signal along the second conductive rail as a fourth electrical characteristic of the route. 
     In one aspect, the one or more processors are configured to determine feature vectors representative of different values of each of the first, second, third, and fourth electrical characteristics, and to compare the feature vectors to one or more patterns of feature vectors associated with different conditions of the route, at least one of the patterns of feature vectors associated with the break in the conductivity of the route. The one or more processors can be configured to detect the break in the conductivity of the route responsive to the first electrical characteristic decreasing by more than the designated drop threshold for the time period within the designated drop time period and responsive to the feature vectors more closely matching the at least one pattern of feature vectors associated with the break in the conductivity of the route. 
     In one aspect, the one or more processors are configured to determine the feature vectors for each of the first, second, third, and fourth electrical characteristics as including: a first mean and a first standard deviation of values of the respective first, second, third, or fourth electrical characteristic prior to the respective first, second, third, or fourth electrical characteristic decreasing by more than the designated drop threshold for the time period that is within the designated drop time period; a second mean and a second standard deviation of values of the respective first, second, third, or fourth electrical characteristic after the respective first, second, third, or fourth electrical characteristic decreases by more than the designated drop threshold and before the respective first, second, third, or fourth electrical characteristic increases by at least the designated drop threshold; and a third mean and a third standard deviation of values of the respective first, second, third, or fourth electrical characteristic after the respective first, second, third, or fourth electrical characteristic increases by at least the designated drop threshold. 
     In another embodiment, a system (e.g., a route examining system) includes first and second application units, first and second detection units, and one or more processors. The first application unit is configured to be disposed onboard a vehicle traveling along a route having plural conductive rails. The first application unit is configured to inject a first electrical examination signal having one or more of a first frequency or a first unique identifier into a first rail of the plural conductive rails. The second application unit is configured to be disposed onboard the vehicle and to inject a second electrical examination signal having one or more of a different, second frequency or a different, second unique identifier into a second rail of the plural conductive rails. The first detection unit is configured to be disposed onboard the vehicle and to measure a first electrical characteristic of the first rail based on the first electrical examination signal and to measure a second electrical characteristic of the first rail based on the second electrical examination signal. The second detection unit is configured to be disposed onboard the vehicle and to measure a third electrical characteristic of the second rail based on the first electrical examination signal and to measure a fourth electrical characteristic of the second rail based on the second electrical examination signal. The one or more processors are configured to detect a break in conductivity of one or more of the first rail or the second rail of the route responsive to one or more of the first electrical characteristic, the second electrical characteristic, the third electrical characteristic, or the fourth electrical characteristic decreasing by more than a designated drop threshold for a time period that is within a designated drop time period. 
     In one aspect, the one or more processors are configured to detect the break by detecting an opening in a circuit formed by wheels and axles of the vehicle system and segments of the first and second rails of the route extending between the wheels of the vehicle system. 
     In one aspect, the one or more processors are configured to determine feature vectors representative of different values of each of the first, second, third, and fourth electrical characteristics and to compare the feature vectors to one or more patterns of feature vectors associated with different conditions of the route, at least one of the patterns of feature vectors associated with the break in the conductivity of the route. The one or more processors can be configured to detect the break in the conductivity of one or more of the first rail or the second rail responsive to the first electrical characteristic decreasing by more than the designated drop threshold for the time period within the designated drop time period and responsive to the feature vectors more closely matching the at least one pattern of feature vectors associated with the break in the conductivity of one or more of the first rail or the second rail. 
     In one aspect, the one or more processors are configured to determine the feature vectors for each of the first, second, third, and fourth electrical characteristics. The feature vectors can include, for each of the first, second, third, and fourth electrical characteristic: a first mean and a first standard deviation of values of the respective first, second, third, or fourth electrical characteristic prior to the respective first, second, third, or fourth electrical characteristic decreasing by more than the designated drop threshold for the time period that is within the designated drop time period; a second mean and a second standard deviation of values of the respective first, second, third, or fourth electrical characteristic after the respective first, second, third, or fourth electrical characteristic decreases by more than the designated drop threshold and before the respective first, second, third, or fourth electrical characteristic increases by at least the designated drop threshold; and a third mean and a third standard deviation of values of the respective first, second, third, or fourth electrical characteristic after the respective first, second, third, or fourth electrical characteristic increases by at least the designated drop threshold. 
     In one embodiment, a method (e.g., for examining a route) includes injecting a first electrical examination signal into a conductive route from onboard a vehicle system traveling along the route, detecting a first electrical characteristic of the route based on the first electrical examination signal, applying a filter to the first electrical characteristic to isolate a subset of the first electrical characteristic occurring at a first frequency range of interest, and detecting a break in conductivity of the route responsive to the subset of the first electrical characteristic decreasing by more than a designated drop threshold for a time period within a designated drop time period. 
     In one aspect, the break that is detected includes a break in a conductive rail of the route or an insulated joint in the route. 
     In one aspect, detecting the break includes detecting an opening in a circuit formed by wheels and axles of the vehicle system and segments of conductive rails of the route extending between the wheels of the vehicle system. 
     In one aspect, the first electrical examination signal that is injected into the conductive route has a first frequency. The filter is tuned to isolate the subset of the first examination characteristic occurring at the first frequency range of interest that includes the first frequency. 
     In one aspect, applying the filter to the first electrical characteristic of the route includes applying at least one of a band-pass filter or a matched filter to the first electrical characteristic. 
     In one aspect, applying the filter to the first electrical characteristic to isolate the subset of the first electrical characteristic occurring at the first frequency range of interest includes suppressing the first electrical characteristic occurring at frequencies outside of the first frequency range of interest attributable to noise along the route. 
     In one aspect, injecting the first electrical examination signal into the route includes injecting the first electrical examination signal having one or more of a first frequency or a first unique identifier into a first conductive rail of the route. The method also includes injecting a second electrical examination signal having a different, second frequency and/or a different, second unique identifier into a second conductive rail of the route. 
     In one aspect, the first electrical characteristic of the route is measured along the first conductive rail by a first detection unit of a route examining system onboard the vehicle system. The method further includes detecting a second electrical characteristic of the route based on the second electrical examination signal as measured along the first conductive rail by the first detection unit and applying a filter to the second electrical characteristic to isolate a subset of the second electrical characteristic occurring at a second frequency range of interest; detecting a third electrical characteristic of the route based on the first electrical examination signal as measured along the second conductive rail by a second detection unit of the route examining system and applying a filter to the third electrical characteristic to isolate a subset of the third electrical characteristic occurring at the first frequency range of interest; and detecting a fourth electrical characteristic of the route based on the second electrical examination signal as measured along the second conductive rail by the second detection unit and applying a filter to the fourth electrical characteristic to isolate a subset of the fourth electrical characteristic occurring at the second frequency range of interest. 
     In one aspect, the method further includes determining feature vectors representative of different values of each of the subsets of the first, second, third, and fourth electrical characteristics, and comparing the feature vectors to one or more patterns of feature vectors associated with different conditions of the route. At least one of the patterns of feature vectors are associated with the break in the conductivity of the route. The break in the conductivity of the route is detected responsive to the subset of the first electrical characteristic decreasing by more than the designated drop threshold for the time period within the designated drop time period and responsive to the feature vectors more closely matching the at least one pattern of feature vectors associated with the break in the conductivity of the route. 
     In one aspect, the feature vectors are determined for each of the subsets of the first, second, third, and fourth electrical characteristics. The feature vectors include, for each subset, a first statistical measure of values of the respective subset prior to the respective subset decreasing by more than the designated drop threshold for the time period that is within the designated drop time period; a second statistical measure of values of the respective subset after the respective subset decreases by more than the designated drop threshold and before the respective subset increases by at least the designated drop threshold; and a third statistical measure of values of the respective subset after the respective subset increases by at least the designated drop threshold. 
     In another embodiment, a system (e.g., a route examining system) includes a first application unit configured to inject a first electrical examination signal into a conductive route from onboard a vehicle system traveling along the route, a first detection unit configured to detect a first electrical characteristic of the route based on the first electrical examination signal, and one or more processors configured to apply a filter to the first electrical characteristic to isolate a subset of the first electrical characteristic occurring at a first frequency range of interest. The one or more processors are further configured to detect a break in conductivity of the route responsive to the subset of the first electrical characteristic decreasing by more than a designated drop threshold for a time period within a designated drop time period. 
     In one aspect, the one or more processors are configured to detect the break by detecting an opening in a circuit formed by wheels and axles of the vehicle system and segments of conductive rails of the route extending between the wheels of the vehicle system. 
     In one aspect, the first electrical examination signal has a first frequency. The one or more processors are configured to apply the filter tuned such that the first frequency range of interest includes the first frequency. 
     In one aspect, the filter applied to the first electrical characteristic by the one or more processors is a band-pass filter and/or a matched filter. 
     In one aspect, the first application unit is configured to inject the first electrical examination signal into the route by injecting the first electrical examination signal having a first frequency into a first conductive rail of the route. The system further includes a second application unit configured to inject a second electrical examination signal having a different, second frequency into a second conductive rail of the route. 
     In one aspect, the first detection unit is configured to measure the first electrical characteristic of the route along the first conductive rail. The first detection unit is configured to measure a second electrical characteristic of the route along the first conductive rail based on the second electrical examination signal injected by the second application unit into the second conductive rail of the route. The system further includes a second detection unit configured to measure a third electrical characteristic of the route along the second conductive rail based on the first electrical examination signal. The second detection unit also is configured to measure a fourth electrical characteristic of the route along the second conductive rail based on the second electrical examination signal. The one or more processors are configured to apply a filter to the second electrical characteristic to isolate a subset of the second electrical characteristic occurring at the second frequency of the second electrical examination signal. The one or more processors are configured to apply a filter to the third electrical characteristic to isolate a subset of the third electrical characteristic occurring at the first frequency of the first electrical examination signal. The one or more processors are configured to apply a filter to the fourth electrical characteristic to isolate a subset of the fourth electrical characteristic occurring at the second frequency of the second electrical examination signal. 
     In one aspect, the one or more processors are configured to determine feature vectors representative of different values of each of the subsets of the first, second, third, and fourth electrical characteristics and to compare the feature vectors to one or more patterns of feature vectors associated with different conditions of the route. At least one of the patterns of feature vectors is associated with the break in the conductivity of the route. The one or more processors are configured to detect the break in the conductivity of the route responsive to the subset of the first electrical characteristic decreasing by more than the designated drop threshold for the time period within the designated drop time period and responsive to the feature vectors more closely matching the at least one pattern of feature vectors associated with the break in the conductivity of the route. 
     In one aspect, the one or more processors are configured to determine the feature vectors for each of the subsets of the first, second, third, and fourth electrical characteristics. The feature vectors include a first statistical measure of values of the respective subset prior to the respective subset decreasing by more than the designated drop threshold for the time period that is within the designated drop time period; a second statistical measure of values of the respective subset after the respective subset decreases by more than the designated drop threshold and before the respective subset increases by at least the designated drop threshold; and a third statistical measure of values of the respective subset after the respective subset increases by at least the designated drop threshold. 
     In another embodiment, a system (e.g., a route examining system) includes a first application unit, a second application unit, a first detection unit, a second detection unit, and one or more processors. The first application unit is configured to be disposed onboard a vehicle traveling along a route having plural conductive rails. The first application unit is configured to inject a first electrical examination signal having a first frequency into a first rail of the plural conductive rails. The second application unit is configured to be disposed onboard the vehicle and to inject a second electrical examination signal having a different, second frequency into a second rail of the plural conductive rails. The first detection unit is configured to be disposed onboard the vehicle and to measure a first electrical characteristic of the first rail based on the first electrical examination signal and to measure a second electrical characteristic of the first rail based on the second electrical examination signal. The second detection unit is configured to be disposed onboard the vehicle and to measure a third electrical characteristic of the second rail based on the first electrical examination signal and to measure a fourth electrical characteristic of the second rail based on the second electrical examination signal. The one or more processors are configured to apply a filter to the first and third electrical characteristics to isolate respective subsets of the first and third electrical characteristics occurring at the first frequency, apply a filter to the second and fourth electrical characteristics to isolate respective subsets of the second and fourth electrical characteristics occurring at the second frequency, and detect a break in conductivity of the first rail and/or the second rail of the route responsive to one or more of the subsets of the first, second, third, or fourth electrical characteristics decreasing by more than a designated drop threshold for a time period that is within a designated drop time period. 
     In one aspect, the one or more processors are configured to determine feature vectors representative of different values of each of the subsets of the first, second, third, and fourth electrical characteristics and to compare the feature vectors to one or more patterns of feature vectors associated with different conditions of the route. At least one of the patterns of feature vectors is associated with the break in the conductivity of the route. The one or more processors are configured to detect the break in the conductivity of the first rail and/or the second rail responsive to the subset of the first electrical characteristic decreasing by more than the designated drop threshold for the time period within the designated drop time period and responsive to the feature vectors more closely matching the at least one pattern of feature vectors associated with the break in the conductivity of one or more of the first rail or the second rail. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the inventive subject matter without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the inventive subject matter, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to one of ordinary skill in the art upon reviewing the above description. The scope of the inventive subject matter should, therefore, be determined with reference to the appended clauses, along with the full scope of equivalents to which such clauses are entitled. In the appended clauses, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following clauses, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following clauses are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such clause limitations expressly use the phrase “means for” followed by a statement of function void of further structure. 
     This written description uses examples to disclose several embodiments of the inventive subject matter and also to enable a person of ordinary skill in the art to practice the embodiments of the inventive subject matter, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the inventive subject matter may include other examples that occur to those of ordinary skill in the art. Such other examples are intended to be within the scope of the clauses if they have structural elements that do not differ from the literal language of the clauses, or if they include equivalent structural elements with insubstantial differences from the literal languages of the clauses. 
     The foregoing description of certain embodiments of the inventive subject matter will be better understood when read in conjunction with the appended drawings. To the extent that the figures illustrate diagrams of the functional blocks of various embodiments, the functional blocks are not necessarily indicative of the division between hardware circuitry. Thus, for example, one or more of the functional blocks (for example, processors or memories) may be implemented in a single piece of hardware (for example, a general purpose signal processor, microcontroller, random access memory, hard disk, and the like). Similarly, the programs may be stand-alone programs, may be incorporated as subroutines in an operating system, may be functions in an installed software package, and the like. The various embodiments are not limited to the arrangements and instrumentality shown in the drawings. 
     As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “an embodiment” or “one embodiment” of the inventive subject matter are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising,” “including,” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property. 
     Since certain changes may be made in the above-described systems and methods without departing from the spirit and scope of the inventive subject matter herein involved, it is intended that all of the subject matter of the above description or shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the inventive subject matter.