US20100213321A1

US20100213321A1 - Method and systems for end of train force reporting

Info

Publication number: US20100213321A1
Application number: US12/391,442
Authority: US
Inventors: Mark Edward Kane; James Brady
Original assignee: Quantum Engineering Inc
Current assignee: Siemens Industry Inc
Priority date: 2009-02-24
Filing date: 2009-02-24
Publication date: 2010-08-26
Also published as: WO2010099116A2; CA2752686C; MX2011008863A; CA2752686A1; WO2010099116A3; MX341909B

Abstract

An EOT unit detects an excessive end of train force using an accelerometer and reports the excessive force. The report may be made to a device located off the train, to an event recorder in the EOT unit, and/or to another device located on the train such as a head of train unit and/or an event recorder located outside the EOT unit. The accelerometer may be a singe, dual, or tri-axial accelerometer. The message may be sent in response to the detection of the excessive acceleration or may be part of a periodically transmitted message from the EOT unit to a HOT unit. A HOT unit is configured to receive a message indicating an excessive EOT acceleration and display an indication of the excessive acceleration to the operator and/or record the message in an event recorder and/or report the excessive acceleration to a device located off the train.

Description

FIELD

The invention relates generally to railroad end of train telemetry, and more particularly to the reporting of end of train forces.

BACKGROUND

Within the railroad industry, end of train (EOT) units (sometimes also referred to as end of train devices) are typically attached at the rear of the last car on a train, often to the unused coupling on the end of the last car opposite the head of the train. These EOT devices were originally designed to perform some of the functions previously performed by train personnel located in the caboose, thereby allowing trains to operate without a caboose and with a reduced number of human operators.
Modern EOT units can perform a number of functions, some required by FRA (Federal Railroad Administration) regulations and some not. EOT units monitor air pressure in the air brake pipe and transmit this information to a head of the train (HOT) device located near the front of the train. EOT units also often include an end-of-train marker light to alert trailing trains on the same track of the presence of the end of the train. Two-way EOT units (now required by FRA regulation in the U.S.) can accept a command from the HOT to open a valve to release pressure in the air brake pipe so that the train's air brakes activate to stop the train in an emergency situation. Some EOT units include GPS receivers that are used to transmit location information pertaining to the end of the train to HOT equipment as discussed in U.S. Pat. No. 6,081,769. EOT units typically communicate with the HOT using radio-based communications. This is because there is no hard-wired electrical connection between the head of the train and the end of the train on some trains, especially freight trains.
Some EOT units include motion detectors that are used to inform the HOT as to whether, and in some cases in which direction, a train is moving. In some EOT units, an accelerometer is used as the motion detector. Motion detection is reported by only a single bit (i.e., the single bit indicates only motion or lack thereof without any indication of speed or direction) under AAR Standard S-5701 for “End-of-Train Communications.” The indication of train movement or lack thereof from the motion detector, together with an indication of the head of train movement, may be used by train personnel and/or computerized on-board train control systems to determine whether or not a train separation has occurred. However, such a determination is not very reliable given the single bit used to report motion pursuant to AAR Standard S-5701 because movement in opposite directions, and movement at significantly different speeds in the same direction, cannot be determined.
A somewhat more capable device is described in U.S. Pat. No. 6,087,950, which describes a motion detector that can be attached to an end of train unit. The motion detector includes a single axis accelerometer. The motion detector is configured to report a motion state that can be moving or non-moving and a motion direction that can be forward or reverse.
More recently, EOT units that can communicate their positions to devices located off of the train, such as those described in U.S. Pat. No. 7,096,096 and in U.S. Pat. Pub. No. 2007/0170314 (the entire contents of both hereby being incorporated by reference herein), have become known in the art. These communications allow personnel responsible for such EOT units to locate them. Such communications can occur both when the EOT units are mounted on a train and when they are not mounted on any train.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendant features and advantages thereof will be readily obtained as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a system for reporting excessive EOT force according to one embodiment of the invention.

FIGS. 2 a and 2 b are perspective and front views, respectively, of an EOT unit according to one embodiment of the invention.

FIG. 3 is a block diagram of the EOT unit of FIGS. 2 a and 2 b.

FIG. 4 is a flow chart illustrating a location reporting subroutine performed by the end of train unit of FIG. 3.

FIG. 5 is a front view of a head of train device according to one embodiment of the invention.

FIG. 6 is a block diagram of the head of train device of FIG. 5.

FIG. 7 is a flow chart illustrating processing performed by the head of train device of FIG. 5.

DETAILED DESCRIPTION

The present invention will be discussed with reference to preferred embodiments of end of train units. Specific details, such as message formats and various reporting methods, are set forth in order to provide a thorough understanding of the present invention. The preferred embodiments discussed herein should not be understood to limit the invention. Furthermore, for ease of understanding, certain method steps are delineated as separate steps; however, these steps should not be construed as necessarily distinct nor order dependent in their performance.
Excessive forces exerted on trains can damage both equipment (train and track) and cargo being carried on the train. Excessive forces applied to a train tends to become magnified at the end of the train. Such excessive forces can result from various causes. An operator can cause excessive forces at the end of the train by accelerating too rapidly, which will cause a car at the end of the train to jerk in the direction of track once the slack between cars is taken up as the locomotive(s) at the head of the train accelerate. An inexperienced operator, or even an experienced operator who is operating a very long train, may not realize the forces being exerted on an end of the train due to his/her actions. Another potential cause of excessive forces at the end of the train can result from excessively “wavy” tracks that cause cars to sway rapidly from side to side as the cars travel along the tracks. These forces occur mainly along an axis perpendicular to the track. Still another potential cause of excessive forces at an end of a train are poor track joints, which may occur at grade crossings, bridges, or the like but which may also occur anywhere along a track. These forces tend to occur primarily along an axis that is vertically oriented with respect to the track. Excessive forces at the end of the train can also be caused in other ways.
Because of the different possible causes for excessive forces at the end of the train, different actions are performed in different embodiments discussed herein. The first step is to detect the occurrence of an excessive force. This step may be performed using an accelerometer located in an end of train unit (it being understood that an accelerometer measures acceleration, which is proportional to force). In preferred embodiments, the accelerometer is a tri-axial accelerometer with the axes oriented such that a first axis is along a direction of the track, a second axis is along a direction perpendicular to the track and a third axis is along a direction vertical to the track. This arrangement is advantageous in that it provides the ability to determine a direction along with an acceleration has occurred, which may be indicative of the cause of the acceleration (e.g., a sudden vertical acceleration may result from a problem with the track whereas a sudden acceleration in a direction of a track may result from an operator accelerating a train from a stopped position too rapidly). In other embodiments, a single or dual axis accelerometer is used. Such embodiments may employ one or more accelerometers along one of the three axes discussed above, or may orient the accelerometer such that it is sensitive to accelerations in more than one axis as discussed in U.S. Pat. No. 6,087,950. Embodiments utilizing a single accelerometer can be less expensive than embodiments employing multiple accelerometers or multiple axis accelerometers.
The accelerometer(s) may be periodically polled in real time to detect forces greater than a threshold. Alternatively, a triggering circuit such as a one-shot may be used to generate an interrupt when the accelerometer measures a force greater than the threshold. The accelerations reported by the accelerometers are typically “instantaneous” accelerations, and these instantaneous accelerations are used directly in some embodiments. In other embodiments, a plurality of instantaneous accelerations are filtered (e.g., moving window average filtering, Kalman filtering, etc.).
Various embodiments employ different thresholds. In some embodiments, the threshold may be fixed. In such embodiments, the threshold may be set to an acceleration based on a safety factor and maximum force for which a typical car coupling can withstand divided by a maximum car weight. A typical freight car coupling in use in the U.S. can withstand a force of about 350,000 pounds, and a current maximum expected car weight in the U.S. freight railroad industry is 268,000 pounds (this represents the weight of the car plus a maximum cargo). In some embodiments, the acceleration threshold based on these values and a safety factor is chosen as 1 g. The threshold is preferably 0.25 g or greater to ensure that accelerations associated with normal movement of the train are not reported as excessive. In yet other embodiments, the threshold is set dynamically. The threshold may be set dynamically based on a particular cargo being carried on the train, particular equipment (e.g., couplings, types of cars) used on the train, or any other factor which may affect a desirable maximum EOT force.
Once an excessive force has been detected, the detection must be communicated. The communication may occur immediately or soon after the detection has been made, and/or the detection may be recorded and communicated later. In some embodiments, the occurrence of the excessive force is communicated to a head of train device for display to an operator immediately or soon after the detection occurs (such display being different from the manner in which an indication of movement of the train is normally displayed to the operator). The message and/or display may include a simple indication that an acceleration greater than the threshold has been observed, or may include the actual (preferably instantaneous) acceleration (or accelerations in multiple axis accelerometer embodiments) measured by the accelerometer. In such embodiments, the head of train device relays the message to a central office, either in addition to or instead of displaying the message. In other embodiments, the EOT device may transmit the message directly to a central data collection site. For example, EOTs equipped for long range communication with a central site (e.g., via a cellular modem that communicates with a cellular base station) are disclosed in U.S. Pat. Pub. No. 2007/0170314. As disclosed in that publication, the EOT may periodically transmit a message including the EOT location.
In some embodiments, the message further includes information (e.g., an amount of excessive force or an indication that an excessive force has been detected together with a location and/or time at which the excessive force was detected). In yet other embodiments, the EOT device includes an event recorder which records information pertaining to the excessive force. The data from the EOT device is accessed later and appropriate action (e.g., informing the operator of the excessive force if the operator was the cause, repairing the section of track causing the excessive force) is taken. In still other embodiments, an excessive force detection message sent from the EOT to the HOT is recorded in an event recorder included in the HOT device and/or forwarded from the HOT device to the train's main event recorder. Still other methods for communicating the detection of an excessive force are possible.
An exemplary embodiment of an EOT force reporting system will now be discussed. This embodiment will include multiple EOT force reporting methods as discussed above. It should be understood that other embodiments employ less than all of, or alternatives to, the reporting methods discussed in connection with this embodiment.
FIG. 1 is a block diagram of a system 10 for measuring and reporting EOT forces. The system includes an EOT unit 100 configured for wireless communications with an HOT device 300. The HOT device 300 is connected to an event recorder 301. The EOT unit 100, the HOT device 300 and the event recorder 301 are all located onboard a train. The HOT device 300 is configured for wireless communications with a central office 303. The EOT unit 100 is also configured for wireless communications with and EOT Tracking Facility 302.
FIGS. 2 a and 2 b illustrate an embodiment of the EOT unit 100. The EOT unit 100 includes a housing 110 in which the internal components of the EOT unit 100 (discussed in further detail below) are located. A handle 111 is attached to the housing 110 to facilitate the installation and removal of the EOT unit 100 from a train car. Also attached to the housing is a connector 120 for connecting the EOT unit 100 to an air brake hose 10 which is in fluid communication with the train's air brake pipe (not shown in FIG. 2 a or 2 b). Also attached to the housing 110 is a coupler 130 which couples the EOT unit 100 to a train car coupling. The EOT unit 100 also includes a marker light 140 attached to the housing 110. Three antennas are also attached to the housing 110: a first antenna 150 for communicating with the HOT, a second antenna 160 for communicating with a cellular base station network, and a third antenna 170 for receiving messages from GPS satellites.
A block diagram 30 of the EOT unit 100 of FIG. 1 is illustrated in FIG. 3. The EOT unit 100 is controlled by a processor 210. The processor 210 receives power from a power subsystem 220 which includes an air-powered electrical generator 221 connected to the air brake pipe 10, a rectifier 222, a voltage regulator 223 and one or more batteries 224. Details concerning the power subsystem 220 are discussed in greater detail in corresponding U.S. Pat. No. 7,096,096.
The processor 210 is connected to control an EOT marker light 140 (although a direct connection is illustrated in FIG. 2, those of skill in the art will understand that the processor 210 may supply the control of power to the EOT marker light 140 via a relay or similar device) in accordance with applicable FRA regulations. Also connected to the processor 210 is a tilt sensor 230. The processor 210 uses the tilt sensor 230, among other things, to determine when the EOT unit 100 has been placed in a horizontal position so that the processor 210 can take the EOT unit to a low power state to conserve battery power.
Also connected to the processor 210 is an air pressure transducer 240, which is in fluid communication with the air brake pipe 10 and is configured to detect the pressure in the air brake pipe 10. The processor 210 reads the pressure in the air brake pipe 10 reported by the transducer 240 and periodically transmits this and other information to the HOT using the HOT transceiver 250. Under AAR Standard S-5701, the report occurs once every 55-65 seconds in the absence of significant pressure changes. The format of an exemplary report is set forth below:

TABLE 1

FRA Message Guidelines - Standard S-5701

Basic	Bit sync	69	bits
Block	Frame sync	11	bits
	Chaining bits
2	bits
	Device battery condition	2	bits
	Message type identifier	3	bits
	Unit address code	17	bits
	Rear brake pipe status and pressure	7	bits
	Discretionary information	11	bits*
	Motion detection	1	bit
	Marker light battery condition	1	bit
	Marker light status	1	bit
	Basic block BCH code	18	bits
	Trailing bit
1	bit
	Total Length	144	bits
Optional	Bit sync	69	bits
Block(s)	Frame sync	11	bits
	Chaining bits
2	bits
	Block format indicator bit	1	bit
	Optional block data bits	42	bits
	Optional block BCH code	18	bits
	Trailing bit
1	bit
	Total length	144	bits

*For two-way systems, see paragraph 3.0.

In embodiments in which excessive EOT forces are reported to the HOT device 300, the occurrence and/or measurement(s) (e.g., magnitudes) of excessive accelerations can be included in the “optional block data bits” portion of the message described above or may be sent in a separate message.

An emergency solenoid 280 is also connected to the processor 210 and the air brake pipe 10. When the processor 210 receives an emergency braking command from the HOT via the HOT transceiver 250, the processor 210 controls the solenoid 280 to open, causing a loss of pressure in the air brake pipe 10 and activation of the train's brakes. In some embodiments, another solenoid (not shown in FIG. 2) is also connected to the processor 210 and between the air brake pipe 10 and the air powered generator 221. This solenoid is used to perform certain tests required by the FRA.
An accelerometer 290 is also connected to the processor 210. As discussed above, the accelerometer may be a single axis, dual axis or three axis accelerometer in various embodiments. Those of skill in the art will recognize that the signals from some accelerometers may be in analog form and that an analog-to-digital (A/D) converter (not shown in FIG. 3) may be used to convert the analog sensor signal to digital form if the processor 210 does not include an integral A/D converter. The accelerometer 290 preferably measures instantaneous acceleration. The processor 210 is configured to filter the instantaneous acceleration reported from the accelerometer in some embodiments; in other embodiments, no filtering is used. In embodiments in which filtering of the instantaneous accelerations measured by the accelerometer is employed, care must be taken in choosing the filtering parameters such that sensitivity to accelerations of short temporal duration (such as those that may occur when an end of train is first forced into motion from a stopped state by a locomotive) are not missed. Some embodiments employ a moving window average filter with a window size of the three most recent readings, with readings being taken every 10 milliseconds.
Also connected to the processor 210 is an event recorder 295. The event recorder 295 records data pertinent to the EOT unit 100, such as the content and time of transmission of various messages sent and received by the EOT unit 100. As discussed above, the occurrence of excessive acceleration events are also recorded for later retrieval in some embodiments. The data recorded for such events can include the date, time, and location of the train at the time of the event as reported by the positioning system 270 plus other circumstances surrounding the event.
The processor 210 is further connected to a positioning system 270, which is a GPS receiver in preferred embodiments but may also be an INS (intertial navigation system), LORAN device, or any other positioning system. The positioning system 270 supplies the processor 210 with reports on the position of the EOT unit 100.
The processor 210 is also connected to a cellular modem 260. The processor 210 uses the cellular modem to send reports including an identifier of the EOT unit 100 and location (and preferably time) information obtained from the positioning system 270 to an EOT tracking station at periodic intervals. The processor 210 also receives “page” messages (messages requesting the EOT unit to report its current location) and “disable” messages (messages instructing the EOT unit to enter an non-operational state) via the cellular modem 260. In addition to reporting EOT location to the EOT tracking facility 302, the cellular modem 260 may also report excessive accelerations detected by the accelerometer 290. This reporting is in addition to (or, in some embodiments, in lieu of, the reporting accomplished via recording at the EOT event recorder 295, the display at the HOT device 300, and/or the recording at the event recorder 301).
During normal operation, the processor 210 controls the EOT marker light 140, communicates air brake pipe pressure information to the HOT, activates the emergency solenoid 280 in response to commands from the HOT, communicates train position to the EOT tracking facility 302 and performs other functions that will not be discussed further herein to avoid obscuring this disclosure.
In addition to the operations discussed above, the processor 210 monitors the accelerometer 290 in order to detect excessive accelerations. A flowchart 400 of the operations performed by the processor 210 is shown in FIG. 4. The processor reads the accelerometer 290 at step 402 and uses the value read (which is an instantaneous acceleration in this embodiment) to calculate a filtered acceleration value at step 404. In some embodiments, the filtering algorithm is a moving window filter with a width of three accelerations values. The processor 210 then compares the filtered acceleration to a threshold at step 406. The threshold may be a fixed value, or may be set by an operator of the train on which the EOT unit 100 is mounted and communicated by messages received from the HOT device, or may be communicated to the EOT unit 100 via a message received on the cellular modem 260 from the EOT Tracking Facility 302. Others ways of setting the threshold are also possible. The comparison of step 210 may be an absolute value comparison (i.e., the absolute value of the acceleration is compared to a threshold) or may be a signed value comparison. An absolute value comparison is preferable in some circumstances (e.g., in connection with an accelerometer measuring vertical acceleration for the purpose of detecting track defects) whereas a signed value comparison is preferable in others (e.g., in connection with an accelerometer measuring acceleration in the direction of the track for the purpose of detecting accelerations caused by an operator incorrectly starting movement of a train).
If the filtered acceleration is below the threshold, no reporting is necessary and the processor 210 delays a period of time (100 ms in some embodiments) at step 408 before repeating step 402. If the filtered acceleration exceeds the threshold at step 406, the processor 210 records the filtered acceleration in the EOT event recorder 295 at step 410. Next, the processor 210 reports the filtered acceleration to the EOT Tracking Facility 302 via the cellular modem 260 at step 412. The processor 210 then reports the filtered acceleration to the HOT device 300 at step 414. The processor then delays for a brief period at step 408 before repeating steps 402 and following.
The HOT device 300 of FIG. 1 is shown in more detail in FIG. 5. As discussed above, the HOT device is typically (but not necessarily) mounted in a locomotive at the head of the train. In North America, the HOT device 300 communicates with the EOT unit 100 using a short range 2-watt digital radio transceiver over certain frequencies assigned by the FCC in the U.S. Additional details concerning HOT device/EOT unit communications can be found in U.S. patent application Ser. No. 11/929,605, the contents of which are hereby incorporated by reference herein. Shown in FIG. 5 is an EOT emergency switch 342 for use by an operator in initiating an emergency braking operation. A display 350 indicates the brake pressure measured by the EOT unit 100, and a second display 351 is used for displaying various messages including a message indicating that an excessive EOT force/acceleration has been detected can be displayed to the operator. A keypad 340 is available to the operator for entering data such as the serial number of the EOT unit 100 with which the HOT device 300 is to communicate. Various indicators 330, some of which are combined with push buttons are available for use by the operator as described further in the above-mentioned application. One of the indicators 330 indicates to the operator when the train is in motion.
A block diagram of the HOT device 300 is shown in FIG. 6. The HOT device includes a processor 320 which is connected to a memory (the memory is shown onboard the processor 320 in FIG. 6, but those of skill in the art will recognize that one or more external memories, such as ROM, RAM, etc. may also be used). The processor 320 is connected (via an interface not shown in FIG. 6) to a train event recorder 301. An EOT transceiver 330 is also connected to the processor 320 for communications with an EOT unit 100. A speed sensor input port 360 connects the processor 320 to a speed sensor 470. A GPS receiver 480 is also connected to the processor 320 in some embodiments (this is particularly useful in the event that the EOT unit 100 does not include its own GPS receiver; in this case, the GPS position from the GPS receiver 480 can be used to determine and report the location of the train upon the receipt of an excessive EOT force message from the EOT unit 100 and an approximate EOT location can be calculated with knowledge of a length of the train).
FIG. 7 is a flowchart 600 illustrating operations performed by the HOT device 300 in some embodiments of the invention. Less than all of the reporting steps illustrated in FIG. 6 may be performed in various alternative embodiments. The flowchart of FIG. 7 is suitable for implementation as a subroutine called upon receipt of a message from the EOT unit 100. The EOT message is read at step 402. The processor 320 determines the type of message at step 404. If the EOT message is a message other than an excessive force message, other processing (which shall not be discussed in detail herein to avoid obscuring the invention) is performed at step 406.
If the message from the EOT does indicate that an excessive EOT force has been detected by the EOT unit 100 at step 404, a message is displayed at the HOT display 351 at step 408. In those embodiments in which the excessive force message from the EOT only indicates that an excessive EOT force has been detected, the message in the display 351 may simply indicate “EXCS EOT ACC DET.” In those embodiments in which the detected EOT force is reported in the message from the EOT, the HOT may display a message such as “EOT ACC XXG DET,” where XX represents the EOT acceleration (filtered or unfiltered) reported by the EOT unit 100. In those embodiments utilizing a triaxial accelerometer, the message shown to the operator in display 351 may also include an X, Y, or Z to indicate the axis on which the excessive EOT acceleration occurred. In some embodiments, the processor 320 may take corrective action, such as requiring the operator to acknowledge the excessive acceleration (e.g., by pushing one of the indicator buttons 330 or keys 340) or forcing an emergency braking operation in the event that no acknowledgement from the operator is received. Such corrective action may occur only when the EOT acceleration exceeds a second, higher threshold and/or only after a certain number of excessive accelerations have been detected in some period of time in some embodiments. In yet other embodiments, the processor 320 requires an operator acknowledgement if a first threshold is exceeded and initiates an emergency braking operation if the second threshold is exceeded.
It should be noted that, in some embodiments, the accelerometer may be used to both a) determine whether the train is in motion, and b) detect excessive EOT acceleration. In such embodiments, a first threshold is used for the former and a second, higher threshold is used for the latter. Such embodiment may also employ a still higher third threshold that can be used to include an indication in a message to a head of train device that the train's brakes should be activated (alternatively, the third threshold can be implemented in the HOT device).
Next, the processor 320 records the occurrence of the excessive EOT force at the event recorder 301 at step 410 and transmits a message to a central office (e.g., a dispatcher) at step 412. The next EOT message is then processed at step 402. Alternatively, in embodiments in which the excessive force indication is in a message with the format of Table 1, the rest of the message is processed at step 406.
Those of skill in the art will recognize that various modifications to the EOT unit 100 are possible. For example, it is possible to operate the EOT unit 100 solely with battery power rather than using batteries in conjunction with an air powered generator. Cellular modem 260 may be replaced with any type of wireless communication system. Various other modifications to the components of the EOT unit 100 are also possible.
Furthermore, the purpose of the Abstract is to enable the U.S. Patent and Trademark Office and the public generally, and especially the scientists, engineers and practitioners in the art who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application. The Abstract is not intended to be limiting as to the scope of the present invention in any way.
While the invention has been described with respect to certain specific embodiments, it will be appreciated that many modifications and changes may be made by those skilled in the art without departing from the spirit of the invention. It is intended therefore, by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.

Claims

1. An end of train unit suitable for use on a train, the end of train unit comprising:

a processor connected to a housing;

a first coupling connected to the housing, the first coupling being configured to engage a train coupling;

an end of train marker light connected to the housing and configured to be controlled by the processor;

a pressure transducer connected to the processor and in fluid communication with a second coupling connectable to an air brake pipe of a train;

an accelerometer connected to the processor; and

a first transmitter connected to the processor;

wherein the processor is configured to perform the steps of

receiving an acceleration from the accelerometer;

performing a comparison of the acceleration to a threshold;

determining that the acceleration exceeds the threshold; and

transmitting a message via the first transmitter in response to the acceleration exceeding the threshold.

2. The end of train unit of claim 1, wherein the message includes an identifier of the end of train unit and wherein the first transmitter is a wireless transmitter configured to transmit the message wirelessly to a head of train device.

3. The end of train unit of claim 1, wherein the message includes an identifier of the end of train unit and an address of a device located off of the train, and the first transmitter is a wireless transmitter configured to transmit the message wirelessly.

4. The end of train unit of claim 1, further comprising:

an event recorder connected to the processor;

wherein the first transmitter transmits the message to the event recorder.

5. The end of train unit of claim 1, wherein the message includes a time corresponding to the acceleration.

6. The end of train unit of claim 1 further comprising:

a positioning system connected to the processor;

wherein the message includes a position corresponding to the acceleration.

7. The end of train unit of claim 1, wherein the threshold is at least 0.25 g.

8. The end of train unit of claim 1, wherein the message includes a magnitude of the acceleration.

9. The end of train unit of claim 1, wherein the message includes an indication that an acceleration in excess of the threshold has been detected.

10. The end of train unit of claim 1, wherein the acceleration is an instantaneous acceleration.

11. The end of train unit of claim 1, wherein the acceleration is a filtered acceleration.

12. The end of train unit of claim 1, wherein the comparison is an absolute value comparison.

13. The end of train unit of claim 1, wherein the accelerometer is a triaxial accelerometer.

14. The end of train unit of claim 13, wherein the message indicates an orientation of the acceleration.

15. The end of train unit of claim 1, wherein the message includes a magnitude for acceleration in each axis of the triaxial accelerometer.

16. An end of train unit comprising:

a processor connected to a housing;

an accelerometer connected to the processor; and

a first transmitter connected to the processor;

wherein the processor is configured to perform the steps of

receiving an acceleration from the accelerometer;

performing a comparison of the acceleration to a threshold;

determining that the acceleration exceeds the threshold; and

transmitting a message including a magnitude of the acceleration via the first transmitter.

17. A head of train device comprising:

a processor;

a wireless receiver connected to the processor; and

a display connected to the processor;

wherein the processor is configured to perform the steps of

receiving a message from an end of train unit, the message indicating that an excessive end of train acceleration has been detected; and

reporting the excessive end of train force.

18. The head of train device of claim 17, wherein the processor is configured to display an indication that the excessive end of train force acceleration has been detected on the display.

19. The head of train device of claim 17, further comprising:

an interface to an event recorder, the interface being connected to the processor;

wherein the processor is further configured to record the message on the event recorder.

20. The head of train device of claim 19, wherein the processor is further configured to perform the step of:

taking a corrective action if an acknowledgment of the display of the excessive end of train acceleration is not received from an operator.

21. The head of train device of claim 20, wherein the corrective action comprises activating the train's brakes.

22. The head of train device of claim 17, wherein the processor is further configured to perform the step of:

comparing the acceleration to a higher threshold; and

taking corrective action if the acceleration exceeds the higher threshold.

23. The end of train device of claim 22, wherein the corrective action comprises activating the train's brakes.