Railroad Crossing Signalling System

Abstract

Disclosed is a highway-railroad crossing signalling system utilizing microwave telemetry to convey control information from a remote sensing location to a receiver coupled to an active motorist warning device.

Description

ORIGIN OF THE INVENTION

The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION

This invention relates to highway-railway crossing detection signalling systems, and more particularly, to the use of microwave telemetry techniques in crossing signalling systems.

Major concerns of the railroad industry, and the cause of two thirds of the rail associated deaths in the United States, are highway-railway crossing accidents. Each year approximately 1,500 people die and 3,000 are injured in train-motor vehicle collisions. The death to injury ratio clearly illustrates the severity of these accidents. One important factor in the quest to eliminate crossing accidents is the installation of automatic warning devices such as flashing lights and movable gates. However, only 20 percent of the 225,000 crossings in the United States have active protection, the remainder being marked only by passive signs. The relatively slow rate at which active devices are being installed (1,000-2,000 per year) is primarily due to high costs, which range from $15,000 to $100,000 for each crossing. Still further costs are associated with maintenance. The high costs are due in large measure to the difficult environments in which the systems must operate and the high reliability required since human life is involved.

A major portion of signalling system costs stem from the required coupling between a warning device and a remote sensor. Many conventional warning systems utilize a source connected across the rails of an electrically isolated section of track. This isolated section must extend far enough from the highway-railway intersection to provide adequate warning time. Typically, the length is one half mile or less, one half mile providing a 30-second warning time with a 60 mph train. A detector, perhaps only a relay, is wired across the tracks at the crossing so that when a train enters the isolated section the tracks are short circuited and the detector receives no signal. This condition, zero received signal, is the operational definition of train presence, and the active signal devices are enabled in response thereto. This system illustrates the fail safe attribute necessary in railroad crossing detectors. That is, should power across the tracks be removed the signal devices are activated falsely, rather than possibly ignoring the presence of a train. Due to the great weight that railroad tracks must bear, provision of an electrically insulated section in a mechanically continuous track is costly and a source of recurrent maintenance problems. For example, water, particularly in the presence of salt spread on the road in the winter, can bridge the insulation that defines the isolated section, or even cause a false actuation. In addition, rust on seldom used tracks sometimes prevents a train from properly short circuiting the tracks. Other systems developed to alleviate these problems include connecting the warning device to a remote sensor by a cable. However, to insure against damage from weather or vandals, the cable must be buried which entails a substantial increase in cost of installation.

The object of this invention therefore is to provide a railraod crossing detection system that is low in cost, can be easily installed, is highly reliable in the difficult railroad environment and possesses the essential fail safe characteristic. A particular object is to provide reliable, low cost coupling between a train sensor and a warning device.

SUMMARY OF THE INVENTION

The invention is characterized by a signalling system including a microwave transmitter for producing a beam of microwave energy that conveys information concerning the presence or absence of a train from a remote location on a railroad track to a receiver located adjacent a highway-railroad crossing. In response to a predetermined modulation characteristic of the microwave beam that signifies the presence of a train, the receiver enables an active motorist warning device. According to one preferred embodiment of the invention, the transmitter is located at a position substantially displaced from the crossing and includes a modulator with a sensor to detect rail traffic on the track section immediately adjacent to the transmitter. The microwave beam is directed toward the receiver and the modulator imposes upon the beam the predetermined modulation characteristic signifying the presence of railroad traffic in response to appropriate signals from the sensor. Considerations such as visibility and the average speeds of the rail and road traffic traversing a particular crossing determine the spacing between the transmitter and the receiver. Typically the spacing is one-fourth to one-half mile. Many prior detection systems utilize the tracks themselves to convey the intrusion information to the receiver, but the tracks are subject to malicious or accidental short circuiting. Other systems utilize cables to make the connections, but it has been found that the cables must be buried to be immune from vandals and weather. Inasmuch as the present system requires no connecting apparatus between the remote transmitter location and the crossing these problems are eliminated. Also, costs are lower than those incurred with the previously known systems since, for example, the expensive burial step is not needed. In addition, microwaves are well suited for these detectors because they are unaffected by inclement weather and can be range limited so as to prevent cross-coupling to other devices.

According to another preferred embodiment of the invention the transmitter is positioned at the crossing with the receiver and includes a radiator to direct the beam parallel to the railroad track. A remote reflector apparatus directs the beam across the tracks and thence back toward the crossing. The receiver includes a detector responsive to the returning beam which is interrupted by a train at the remote location. An advantage of this system is that all apparatus requiring power is placed near the highway, thereby simplifying service and routine maintenance, and providing ready access to electrical power lines if utilization of an external power source is desired.

A feature of the invention is the utilization of a pulse modulator with a low duty cycle, for example, a duty cycle of 1 percent. IN this mode of operation the transmitter generates a beam only 1 percent of the time so that power requirements are substantially reduced. A self-contained battery source can be functional for a year with this low duty cycle pulse modulation thereby simplifying routine maintenance tasks by eliminating the need for frequent battery replacement.

Another feature of the invention is the inclusion of an attenuator in the sensor for suppressing the beam of microwave energy when the presence of a train is sensed. The receiver enables the warning device only in the event of a sustained absence of the beam. The response of the receiver is too slow to enable the warning device during the spaces between the pulses, but requires a time equivalent to several pulses. This system provides a fail safe feature in that breakdown of either the transmitter or the receiver results in the zero received signal that actuates the warning device. Therefore, in the event of system failure a false alarm will be delivered rather than permitting a train to cross the intersection without warning.

DESCRIPTION OF THE DRAWINGS

These and other features and objects of the present invention will become more apparent upon a perusal of the following description taken in conjunction with the accompanying drawings wherein:

FIG. 1 shows a diagram of a signalling system in conjunction with a highway-railroad crossing comprising multiple tracks;

FIG. 2 shows a block diagram of a transmitter utilized in the system shown in FIG. 1;

FIG. 3 shows a block diagram of the receiver utilized in the embodiment shown in FIG. 1;

FIG. 4 shows an adaptation of the preferred embodiment shown in FIG. 1 that utilizes a single transmitter to protect a plurality of highway-railroad crossings; and

FIG. 5 shows another preferred embodiment of the invention with the transmitter and receiver together at the crossing and remote reflectors disposed so as to return the beam to the receiver in the absence of a train.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1 there is shown a preferred crossing detection and signalling system 21 at a highway-railroad crossing 22 formed by the intersection of a highway 20 and three tracks 23, 24 and 25. At a location 26 substantially displaced from the crossing 22 is a transmitter 27 that projects a beam of microwave energy 28 toward an antenna 30 of a receiver 29 at the crossing. Modulation characteristics of the beam 28 are detected by the receiver 29, and in response to a predetermined characteristic that signifies the presence of a train at the location 26, the receiver enables a signal control 31 that activates an active motorist warning signal 32. A self-contained battery 33 powers the receiver 29. A plurality of sensors 34, which may, for example, be of the magnetic flange detector type manufactured by the Servo Corporation and which are mounted on the railroad track to generate a signal when the trail wheel passes over the sensor, within the transmitter 27 sense the presence of trains on the tracks 23, 24 and 25 at the location 26 and in response thereto supply a suppression signal to a pulse modulator 35 through line 36. The modulator 35, when not suppressed, modulates a microwave oscillator 37, which may be of the Gunn-diode oscillator type, that feeds a transmitting antenna 38 to form the beam 28. A self-contained transmitting battery 39 powers the modulator 35. The signals on the line 36 indicating train presence do not distinguish between the individual tracks 23, 24 and 25. Such a distinction is not necessary inasmuch as the warning device 32 must be activated in response to the presence of a train on any track 23, 24 or 25.

Referring next to FIG. 2 there is shown a block diagram of the transmitter 27 including one of the sensors 34 connected by the line 36 to a pulse generator 41. An output of the pulse generator is carried by a line 42 to a power amplifier 43, an output thereof being carried by a line 44 to the oscillator 37. The battery 39 supplies power to the modulator 35 that includes the pulse generator 41 and the power amplifier 43. Power for the oscillator 37 is supplied intermittently on the line 44. The beam 28 is therefore an intermittent or pulsed microwave beam, and when a train is detected by the sensor 34 the pulse generator 41 is suppressed entirely. Consequently, the beam 28 is off during the presence of a train at the location 26. Conventionally, a Gunn-diode oscillator suitable for telemetry requires approximately 5 watts of input power. However, the low duty cycle of the pulse modulator 35, being approximately 1 percent, reduces that power requirement to an average of 50 milliwatts. Consequently, a conventional automobile battery 39 can function for 12 months unattended.

Referring next to FIG. 3 there is shown a block diagram of the receiver 29 and the signal controls 31. An output of the receiving antenna 30 resulting from the beam 28 impinging thereon is detected by a diode 51 and the detected signal is amplified in an amplifier 52. Receiving the amplified detected signal on a line 53 is an RC circuit 54 including a capacitor 55 and a resistor 56 that acts as a "pulse stretcher." A Schmidt trigger 57, followed by a power amplifier 58, receives the stretched signal from the resistor 56. A rectifier 59 passes the output of the power amplifier 58 to a filter capacitor 61 and an enabling relay 62. Contacts 63 of the relay 62 are normally closed and are open, as shown in FIG. 3, only when the relay is energized. When the contacts 63 close, power from the battery 33 is carried by a line 64 to the signal controls 31 causing the resultant activation of the warning device 32. The receiver 29 as shown enclosed within a dashed line in FIG. 3 includes the diode 51, the amplifier 52, the RC circuit 54, the Schmidt trigger 57, the power amplifier 58, the rectifier 59, the filter capacitor 61 and the enabling relay 62.

During operation of the warning system 21 as shown in FIGS. 1, 2 and 3, the absence of a train at the location 26 is accompanied by the absence of a signal on the line 36. Therefore, a pulsating voltage on the line 44 powers the oscillator 37 so as to produce the intermittent microwave beam 28. The presence of the beam 28 with the particular pulsating modulation characteristic signifies the absence of a train to the receiver 29. Each pulse of the beam 28 is detected by the diode 51 and amplified by the amplifier 52 thereby producing a pulse of a substantially higher amplitude on the line 53. The signal supplied to the Schmidt trigger 57 is of longer duration than the pulses on the line 53 as a result of the low-pass RC circuit coupling. Therefore, the Schmidt trigger 57 is in the "on" state for a substantially longer time than the period of the pulses on the line 53. The longer period of the pulses delivered to the power amplifier 58 insures that the output thereof is at a high average energy level as compared to the energy level of the voltage on the line 53. Rectification and filtration of the output of the power amplifier 58 produces a sustained dc voltage across the capacitor 61 while the pulsating beam 28 is received. The voltage across the capacitor 61 holds the enabling relay 62 in the activated state, thereby keeping the contacts 63 open and the warning device 32 inactivated. In the event that a train is sensed at the location 26 the pulse generator 41 becomes inoperable and transmission of the beam 28 ceases. With the beam 28 absent, the voltage across the capacitor 61 quickly decays through the relay 62 to a level that can no longer maintain activation and the contacts 63 close. Activation of the warning signal 32 results from the voltage supplied on the line 64 through the closed contacts 63. After the passing of the train, the transmission of the beam 28 is resumed causing the voltage to again appear across the capacitor 61; therefore, the relay 62 is activated and the signal 32 is stopped.

As noted above, railroad signalling systems should be fail safe. That is, the warning device 32 should be activated in the event of system failure because false alarms are preferable to insensitivity to rail traffic. This fail safe attribute is achieved in the system 21 since obstruction of the beam 28 or transmitter 27 or receiver 29 failure causes the voltage on the capacitor 61 to decay and results in activation of the warning device 32.

Referring next to FIG. 4 there is shown another highway-railway crossing signalling and detector system 71 in conjunction with a single track 72 and a plurality of highways 73a, 74a and 75a forming a plurality of crossings 73, 74 and 75. A single transmitter and antenna combination 76 is connected by a cable 77 to a sensor (not shown) that detects the presence of trains on the track 72 adjacent to the transmitter. The transmitter 76 is similar to the transmitter 27 and produces a pulsating microwave signal that is suppressed in response to the presence of a train. Associated with each crossing 73, 74 and 75 is a receiver and warning device combination 81, 82 and 83 respectively. The receiver combination 81 receives the microwave output from the transmitter 76 and is similar to the receiver 29 and warning device 32 combination. Correspondingly, the receiver combination 82 also receives the microwave output from the transmitter 76 and is similar to the receiver combination 81 with the exception that conventional delay circuits prevent activation of the warning device for a period of time after transmission has stopped. That period of time corresponds to the time required for a train to travel from the crossing 73 to the crossing 74. Likewise, delay circuits in the receiver 83 delay activation of the associated warning device for a period of time equivalent to the time required for a train to travel from the crossing 73 to the crossing 75.

During operation of the system 71 activation of each transmitter receiver pair 76,81; 76,82; and 76,83 is similar to operation of the embodiment 21. The embodiment 71 is useful and economical if a plurality of closely spaced highway-railroad crossings 73, 74 and 75 must be protected. Utilization of a single transmitter 76 results in a substantial cost saving.

Referring now to FIG. 5 there is shown a third preferred railroad crossing signalling and detection system 91 including a transmitter 92 and a receiver 93 both adjacent to a crossing 94 including a single road 95 and a single track 96. At a location 97 substantially displaced from the crossing 94 a reflector 98 at an angle to the track 96 receives a pulsating microwave beam 99 from the transmitter 92 and reflects it across the track to another reflector 101. The beam 99 strikes the reflector 101 perpendicularly thereto and therefore is reflected back along its original path to the reflector 98 and then toward the transmitter 92. DUe to dispersion of the beam 99 a portion of the returning beam from the reflector 98 impinges on an antenna 102 connected to the receiver 93. Also connected to the receiver 93 is an active motorist warning device 103. The transmitter 92 is similar to the transmitter 27 and the receiver 93 is similar to the receiver 29.

During operation of the system 91 the pulsating microwave beam 99 normally is reflected to the antenna 102, and the receiver therefore maintains the warning device 103 in the inactive state. When a train at the location 97 passes between the reflectors 98 and 101, the return beam is interrupted and the receiver 93 responds as did the receiver 29 to the absence of a signal by activating the warning device 103. The system 91 is similarly fail safe, in that the presence of a positive signal prevents the activation of the warning device 103, and the interruption of the signal by a train or system failure causes the activation of the warning signal 103.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example, different and/or more complex modulation can be used so that the system can sense not only train presence, but also train velocity and distinguish which tracks are being used. Also, there are many different types of sensors which can be used by those skilled in the art in many different modes of operation to control the modulation. In addition, each of the described embodiments can be used with any of the crossings shown, and others that may be encountered. It is to be understood, therefore, that the invention can be practiced otherwise than as specifically described.

Claims

What is claimed is:

1. A railroad crossing signalling system comprising:

transmitter means for producing a beam of microwave energy for conveying train presence information;

modulator means for modulating said beam, said modulator means comprising a sensor means having attenuator means for suppressing said beam when a train is sensed to detect the presence of trains at said displaced location and low duty cycle pulse modulator means for modulating said beam in response thereto;

receiver means for receiving said beam of microwave energy and for detecting the presence or absence of trains according to the modulation characteristics of said beam; and

active warning means responsive to said receiver means for warning motorists of the presence of trains detected by said detection means, said receiver means and said warning means are disposed adjacent a highway railroad-track crossing and said transmitter means is disposed at a substantially displaced location therefrom adjacent said railroad track and is coupled to said receiver means by said beam.

2. A railroad crossing signalling system according to claim 1 wherein said receiver means comprises enabling means to enable said warning means in response to a sustained absence of said beam.

3. A railroad crossing signalling system according to claim 1 wherein said transmitter means, said receiver means and said warning means each comprise a separate self-contained power source means.

4. A railroad crossing signalling system according to claim 3 wherein each of said self-contained power source means comprises a battery.