US20130200223A1

US20130200223A1 - Crossing safety system

Info

Publication number: US20130200223A1
Application number: US13/639,106
Authority: US
Inventors: Paul Dean Alexander; David Victor Lawrie Haley
Original assignee: Cohda Wireless Pty Ltd
Current assignee: Cohda Wireless Pty Ltd
Priority date: 2010-04-05
Filing date: 2011-04-05
Publication date: 2013-08-08
Also published as: AU2011238414A1; EP2555960A1; WO2011123885A1

Abstract

A system is described that provides redundant communication at a railway crossing. The system comprises a first communication unit for transmitting information associated with a railway vehicle approaching or near the railway crossing on a railway track. A first active warning sign located at or near the railway crossing receives and transmits information associated with the railway crossing. The system includes an onboard equipment unit located on a roadway vehicle approaching or near the railway crossing, the onboard equipment unit comprising a second communication unit for receiving information from the first communication unit and the active warning sign; a processor for processing the received information to determine a first threat indicator indicative of a potential collision, and a user interface for communicating the threat indicator to a user. The system may include sensors to detect and communicate the presence of a train.

Description

FIELD OF THE INVENTION

The invention relates to wireless communications systems to improve safety at railway crossings.

BACKGROUND OF THE INVENTION

Collisions can occur at railway crossings between trains and other vehicles such as cars or trucks. Even if booms, signposts or lights are used, these may be seen too late by drivers resulting in a collision. These collisions can sometimes cause fatalities.
Dedicated Short-Range Communication (DSRC) is the globally coordinated standard for Cooperative Intelligent Transportation Systems (ITS). DSRC combines GPS and wireless communication in a dedicated spectrum at 5.9 GHz. Safety-of-life applications, such as cooperative collision avoidance are the key feature of DSRC, and the 5.9 GHz spectrum includes a communications channel dedicated to cooperative safety applications.
Vehicles use DSRC to share information by continually broadcasting their location, speed, direction, vehicle type and size, and additional status information. The DSRC system also includes a processor that uses local position information, and information received from other vehicles, to accurately detect potential collisions and activate driver warnings. DSRC Roadside Equipment (RSE) allows communications between vehicles and infrastructure, e.g. railway warning systems including active warning signs.
It is desirable to have a communication system that improves collision avoidance at railway crossings.
Reference to any prior art in the specification is not, and should not be taken as an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.

SUMMARY OF THE INVENTION

In one aspect the invention provides a communication System for redundant communication at a railway crossing, the system comprising: a first communication unit for transmitting information associated with a railway vehicle approaching or near the railway crossing on a railway track; a first fixed communication unit located at or near the railway crossing for receiving and transmitting information associated with the railway crossing; and an onboard equipment unit located on a roadway vehicle approaching or near the railway crossing, the onboard equipment unit comprising: a second communication unit for receiving information from the first communication unit and the fixed Communication unit; a processor for processing the received information to determine a first threat indicator indicative of a potential collision, and a user interface for communicating the threat indicator to a user.
The first communication unit may further comprise a sensor system located at or near the railway crossing for sensing information associated with the railway vehicle and a second fixed communication unit adapted to transmit the information sensed by the sensor system, wherein in use the information is received by the first fixed communication unit and the onboard equipment unit.
The first communication unit may be located on the railway vehicle and transmits information about the railway vehicle that in use is received by the first fixed communication unit and the onboard equipment unit.
In another aspect the invention provides an active warning sign for a railway crossing, the sign comprising: a first communication link operable to receive sensor information from a sensor system located at or near the railway crossing for sensing the approach or presence of a railway vehicle; a second communication link operable to receive a crossing-close request (CCR) from onboard equipment located on the railway vehicle; a warning-sign processor programmed to monitor the first and second communication links and to generate a crossing-closed indicator (CCI) based on received sensor information and/or a received crossing-close request; and a transmitter to transmit the crossing-closed indicator.
In another aspect the invention provides an on-board communication system for redundant communication at a railway crossing, the system comprising: an onboard equipment unit for use by a roadway vehicle approaching or near the railway crossing, the onboard equipment unit comprising: a communication unit for receiving information from a plurality of sources, said sources comprising (a) an active warning sign that transmits a crossing-closed indication (CCI) if the crossing is closed and (b) a railway communication unit that transmits information indicative of the presence or approach of a railway vehicle at the railway crossing; a processor for processing the received information to determine a threat indicator indicative of a potential collision, and a user interface for communicating the threat indicator to a user.
Further aspects of the invention will be apparent from the following description, including methods of operating the described system and machine-executable instructions effective to implement the methods in the described system.
As used herein, except where the context requires otherwise, the term “comprise” and variations of the term, such as “comprising”, “comprises” and “comprised”, are not intended to exclude further additives, components, integers or steps.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings.

FIG. 1A shows a DSRC communication system that may be used in a crossing safety system.

FIG. 1B shows a flow diagram of processes run by a Threat Detection Unit.

FIG. 2 shows a sensor-to-sign communication system:

FIG. 3 shows a schematic representation of the sensor-to-sign communication system of FIG. 2.

FIG. 4 shows a sensor-to-vehicle communication system.

FIG. 5 shows a schematic representation of the sensor-to-vehicle communication system of FIG. 4.

FIG. 6 shows a train-to-sign communication system.

FIG. 7 shows a schematic representation of the train-to-sign communication system of FIG. 6.

FIG. 8 shows a train-to-vehicle communication system.

FIG. 9 shows a schematic representation of the train-to-vehicle communication system of FIG. 8.

FIG. 10 shows a vehicle-to-train communication system in an example in which a vehicle has stopped across the tracks.

FIG. 11 shows a schematic representation of the vehicle-to-train communication system of FIG. 10.

FIG. 12 shows a schematic representation of a compound communication system.

FIG. 13 shows a schematic representation of the messages sent in a collision avoidance communication system.

FIG. 14 shows infrastructure-to-vehicle (I2V) communication actual timing in an example based on a collision that occurred near Kerang in Australia.

FIG. 15 shows train-to-vehicle (T2V) communication warning onset in the example of FIG. 14.

FIG. 16 shows T2V communication warning evolution.

FIG. 17 shows an example of how a truck passes safely behind a train with no warnings issued.

FIG. 18 shows an example of how a truck passes safely ahead of a train with no warnings issued.

FIG. 19 shows T2V communication of a near miss with a warning issued.

FIG. 20 shows T2V communication in an example based on an event that occurred at Benalla in Australia.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A crossing safety system is described herein that provides immediate safety improvement through the use of active signs and sensors with DSRC/WAVE communications and is directly extensible when vehicles are fitted with units. WAVE refers to wireless access in vehicular environments. An acronym list is provided at the end of the description, When fitted with Onboard Equipment (OBE) the vehicles will become aware of the crossing state and/or the presence of a crossing train or other vehicle: The OBE may then choose to alert the driver to the presence of the crossing vehicle. As the underlying wireless technology is DSRC, the warning can be timely and directional, avoiding unnecessary driver distraction and inconvenience due to extended waiting times at the crossing.
1. System Overview
A crossing safety system employed in vehicles and infrastructure elements using wireless communication is described herein.
One embodiment of a DSRC system 100 is shown in FIG. 1A. Infrastructure at the crossing will transmit messages to OBEs indicating the state of the crossing, A vehicle is fitted with OBE 101 that is used to communicate with other OBEs 102 via vehicle-to-vehicle (V2V) communications, and RSEs 104 via vehicle-to-infrastructure (V2I) communications. The types of vehicles involved in a railway crossing, and which could also include such OBE, include cars, trucks, vans, trains, buses, motorbikes (and variants thereof), and pedal bikes. Pedestrians may also be involved.
The OBE 101 includes a human-machine interface (HMI) 106 for driver interaction. The HMI 106 may be an audio, visual or haptic interface, or any combination of these, Examples of interfaces that may be used include a touch screen, or a display screen and a keyboard. The OBE 101 includes a processor 108 for running applications and providing control, The processor may be a microprocessor, DSP, FPGA or other comparable processing device. The OBE 101 further includes a satellite navigation system such as a GPS 110 for providing the processor 108 with position and time data, and a DSRC radio 112 for providing wireless connectivity to other vehicle OBEs 102 and RSE 104 via antenna 114.
Software running on the processor 108 provides a Threat Detection Engine (TDE). The TDE receives local position information from the GPS 110, and receives position and state information from other vehicles, sensors and signs via the DSRC radio 112. The TDE determines any threat and presents required driver interaction on the HMI 106.
The TDE in the OBE will decide which warnings, if any, will be issued to the driver. The TDE will respond (via the human machine interface) to:
1. Basic Safety Messages (BSMs; broadcast messages containing position information of the host unit e.g. train or car) sent from trains and other vehicles; and
2. Road Side Alert messages (RSAs; broadcast messages that transmit a signal using serial data communication, for example one of the SAE J2540 phrases) sent from the Crossing Infrastructure. The complete set of ITIS codes can be found in Volume Two of the J2540 Standard.
A TDE in a train may also warn the train driver of a potential danger such as a vehicle parked across the crossing.
Referring to the flow diagram in FIG. 1B, the TDE functions as follows. When a new message is received 2101 by the DSRC radio 112 (shown in FIG. 1A), then the received message is queued at step 2102. The message type is checked 2103, and if the received message is a BSM then the remote entity (the entity that the message is received from) is pre-qualified 2104. Pre-qualification is a step to determine whether the remote entity, which can be a train or other vehicle, is threatening, i.e. whether there is a possibility of a collision. The checks that are performed at this step 2104 may be one or more of the following:
i. Is the remote entity getting closer (determined from heading, speed of present vehicle and remote entity)?
ii. Can the distance between the remote entity and the present vehicle be closed within a short time based on the closing velocity and the distance between the two entities? Closing velocity is based on the respective headings and speed. Predicted motion can also be employed. For example motion on a circle may be used where each entity is aware of its radius.
iii. Are the two entities very far apart?
iv. Are the entities' speeds above a threshold (both or any)?
v. Do the trajectories of the two entities cross in the future?
Following the pre-qualification step 2104, if the remote entity is threatening, then the distance to the collision is determined at step 2106. Following this, it is determined at step 2107 whether the present vehicle is able to stop at high deceleration. If not, then a high level HMI collision warning is issued 2108. If yes, then at step 2108 it is determined whether the present vehicle is able to stop at low deceleration. If not, a low level HMI crossing warning is issued 2110. If yes, no warning is issued.
If it is determined at step 2103 that the message is not a BSM, then at step 2111 it is determined whether the message is an RSA containing a CCI or CCR. If so, then the likelihood of the present vehicle entering the crossing is determined at step 2112. This may be done as follows:
using data from the GPS 2114 to determine whether the present vehicle is closing on the crossing, i.e. whether the distance to the crossing is reduced over time; or
using map matching to a map database 2115 to determine the future path of the vehicle.
At step 2118 the following decision is made: if the likelihood of entering the crossing is high, then an HMI crossing warning is played 2122; if the likelihood is low, then the HMI crossing warning is disabled 2120.
The TDE is also used to transmit a BSM 2130 based on the local position handler 2116, The message is transmitted 2132 using the DSRC radio 112.
A crossing safety system consists of three main equipment types: vehicle, sensor and sign. The train and the vehicle are very similar and may be accommodated by the same equipment type in a different mode. The sign 104 also includes a processor and a DSRC radio system in communication with the processor.
Table 1 shows what equipment transmits what messages and what equipment listens to those messages. Referring to Table 1, mobile equipment refers to equipment on trains and other vehicles. Fixed equipment or units refer to roadside sensors and signs. The functionality executed upon receipt is described in the summary of the connectivity table below.

TABLE 1

Unit Connectivity Table

	Tx		Rx
Equipment	BSM	RSA	BSM	RSA

Vehicle OBE	✓		✓	✓
Train OBE	✓		✓	✓
Sensor		✓	✓	✓
Sign		✓	✓	✓

The summary of this connectivity table is as follows:
1.1 Mobile Equipment Transmit BSMs
Mobile onboard equipment (in trains and vehicles) announce the train or vehicle's dynamic position to all via broadcast of BSMs, e.g. periodically with a-rate of a few times per second. Mobile equipment may have a positioning service.
1.2 Fixed Equipment Transmit RSAs
Inbound sensors may announce the presence of the train at the sensor location by transmission of a Crossing Close Request message (CCR). The inbound sensor continues to transmit this message, e.g. periodically with a rate of a few times per second while the train is present.
Signs announce the crossing state by transmission of a Crossing Closed message or a Crossing Open message. Transmission may be periodic, e.g. with rate of a few times per second.
In the case of a track that supports bi-directional traffic it is preferred but not required that the sensor should be capable of sensing direction of travel. RSAs are transmitted upon the occurrence of asynchronous events. The fixed units may be programmed with their position and the co-ordinates of the crossing at installation. Otherwise they may determine their position from other wireless equipment in the vicinity of the crossing.
1.3 All Units Listen for BSMs
Mobile equipment determines if a collision could occur. Fixed equipment can still sense the train if the sensing element fails.
Signs can signal to trains that a vehicle may enter or is stationary in the crossing. This is achieved by the sign first determining the current and likely position of the vehicle and then if necessary transmitting a message that the train can use to determine the state of the vehicle relative to the crossing.
1.4 Mobile Units and Signs Listen for RSAs
Mobile equipment determines that the crossing is closed to vehicles. Receipt of a Crossing Closed Indicate message (CCI) tells the mobile equipment that the crossing is closed. Receipt of a (Crossing Closed Request) CCR tells the Mobile equipment that the crossing is closed.
Signs are told by the sensor via a CCR that the crossing should be closed. Signs then close the intersection by broadcast of CCI. This broadcast continues e.g. at a rate of several messages per second until the crossing is opened.
Other messages may be used to convey the information described. In the preferred embodiment DSRC is used. One benefit for DSRC is that it has a standard way of encapsulating positional information.
All units in the system can keep a health check on the other units. Units may periodically transmit a special message indicating that they are functional. This message may or may not contain status information, and may identify the unit transmitting the message. if this message is not heard by all units then the crossing may enter a fail safe mode, e.g. an active sign may switch into active mode. Normal operational messages (due to a crossing event) may be used instead of, Or in addition to, periodic messages to monitor system health in the same way.
For simplicity one approach direction is described herein, but in general there may be two or more signs and an additional inbound sensor on the other approach direction.
2. Implementation Scenarios
The equipment of the system as described above can be implemented in a number of ways. Five example scenarios are described below.
2.1 Sensor-to-Sign: Train Approaching Warning
Referring to FIG. 2, in the Sensor-to-Sign scenario 200, DSRC RSE is installed at inbound 202 and outbound 204 rail sensors and active warning signs 206. Approaching trains 208, and potentially other rolling stock, trigger the inbound sensor 202. An active warning sign 206 is then started to attract the attention of approaching motorists, e.g. through visual and/or auditory warning. An outbound sensor 204 detects departure of the train 208 and deactivates the sign 206.
Inbound 202 and outbound 204 sensors are installed in each direction of approach by rail (for clarity, only a single direction is shown in FIG. 2). Similarly, an active warning sign 206 is installed in each direction of approach by road.
A system schematic of the technology solution for this scenario 200 is shown in FIG. 3. Both sensors 202, 204 are connected to DSRC RSE. When the inbound sensor 202 is triggered, it broadcasts a DSRC standard Roadside Alert Message 302 announcing the arrival of the train 208. DSRC RSE at the sign 206 receives the broadcast and activates the sign, and it also begins to broadcast a Roadside Alert Message 302 announcing the presence of the train 208. The outbound sensor 204 (which may be co-located with the sign 206) detects the departure of the train 208. Once the train has departed, the sign 206 is deactivated and the RSE broadcasts a standard Roadside Alert Message announcing that the crossing is no longer occupied.
The inbound sensor 202 may also provide information pertaining to the speed and direction of the train 208. The speed may be measured in a variety of ways known to those skilled in the art including pairs of sensors such as loops, Doppler RADAR, etc. This information may be used to adjust the amount of time that the sign 206 is active, and minimise unnecessary delays.
2.2 Sensor-to-Vehicle: Train Approaching Warning
Referring to FIG. 4, in the Sensor-to-Vehicle scenario 400 approaching trains 208, and potentially other rolling stock, again trigger an active sign 206, as described in Section 2.1. DSRC OBE is fitted to vehicles 402 approaching the railway crossing on the road 404. Messages broadcast from the infrastructure 202, 204, 206 are also received by approaching vehicles 402, and trigger an in-vehicle warning.
Note that in the case where the crossing has conventional equipment already fitted, new equipment may be fitted to the crossing to transmit messages. This new retrofitted equipment may be sensitive to the state of the crossing as determined by the pre-existing equipment.
A system schematic of the technology solution for this scenario is shown in FIG. 5. The infrastructure system broadcasts Roadside Alert Messages as described in Section 2.1. These messages are also received by an approaching vehicle 402. DSRC OBE in the vehicle processes the message and determines if, and how, the driver should be warned. The nature of the warnings may be based upon the position, speed, acceleration and heading of the vehicle.
2.3 Train-to-Sign: Train Approaching Warning
Referring to FIG. 6, in the Train-to-Sign scenario 600 DSRC OBE is installed in locomotives/trains 208 and RSE 602 is installed in active warning signs 206. Trains 208 broadcast standard DSRC messages that are received by the RSE 602 at the sign 206. The active warning sign is then started to attract the attention of approaching motorists, e.g. through visual and/or auditory warning. The sign 206 is deactivated once the train 208 has departed the crossing.
A system schematic of the technology solution for this scenario 600 is shown in FIG. 7. The locomotive 208 broadcasts DSRC standard Basic Safety Messages 702. These messages contain the position, speed, acceleration, heading, size and type of the locomotive. The DSRC RSE 602 at the sign 206 receives each broadcast, processes the message and determines when to activate and deactivate the sign, based upon the speed. direction and heading of the train.
2.4 Train-to-Vehicle: Train Approaching Warning
Referring to FIG. 8, in the Train-to-Vehicle scenario 800 DSRC OBE is installed in locomotives 208 and vehicles 402. Trains 208 broadcast standard DSRC messages that are received by vehicles 402. An in-vehicle warning is triggered if the potential for collision is detected.
A system schematic of the technology solution for this scenario 800 is shown in FIG. 9. The locomotive 208 broadcasts DSRC standard Basic Safety Messages 702. These messages contain the position, speed, acceleration, heading, size and type of the locomotive. The DSRC OBE in the vehicle 402 receives each broadcast, processes the message and determines if and how the driver should be warned. Warnings may be based upon the status of the train and the speed, direction and heading of the vehicle.
2.5 Vehicle-to-Train: Vehicle Stopped Across Track Warning
Referring to FIG. 10, in the Vehicle-to-Train case scenario DSRC. OBE is installed in locomotives 208 and vehicles 1002. Vehicles broadcast standard DSRC messages that are received by approaching trains 208. If a vehicle 1002 is stopped across the rail line and the potential for collision is detected then an in-train warning is triggered.
A system schematic of the technology solution for this scenario is shown in FIG. 11. The vehicle broadcasts DSRC standard Basic Safety Messages 702. These messages indicate that the vehicle 1002 is stopped, and also contain the position, size and type of the vehicle, The DSRC OBE in the locomotive 208 receives each broadcast, processes the message, and determines if any part of the vehicle 1002 is obscuring the. path of the train 208. If the potential for collision is detected then an audible in-train warning is issued.
3. Complete System Including Redundancy
As described in more detail below, the system described herein includes features that provide redundancy improving the reliability of the overall system. More specifically, redundancy is introduced when two or more of the scenarios as described above are implemented simultaneously.
Referring to FIG. 12, a communication system 1200 is shown that includes the communication equipment as described above in the five scenarios. Dashed connections shown offer redundancy in the system and although the receiver is not the direct target of the message the receiver can increase its confidence that the system is operational through reception and in some cases improve safety even further. For example, the sensor-to-vehicle RSA link allows the approaching car 402 to understand that the crossing is closed even if a message from the sign 206 has not been received.
A preferred embodiment using J2735 BSMs and RSAs is shown in FIG. 13. Standard compliant SAE J2735 and SAE J2540 messages are employed. SAE J2735 is used for over the air communications. OBEs (on any moving vehicle) transmit and receive J2735 BSMs.
A sign upon receipt of a CCR or BSM from a train closes the intersection via transmission of a CCI. This message may be heard by all OBEs (including trains). If an approaching vehicle hears a CCI it knows the crossing ahead is closed (CCIs contain the position of the crossing).

- If the approaching vehicle is a train it now has confidence that the crossing is closed.
- If the approaching vehicle is a car then the driver may be alerted to the presence of a closed crossing ahead. Also the OBE may assess the dynamics of the vehicle and further advise the driver to stop more rapidly or even activate brakes autonomously, or increase brake pressure beyond that applied by the driver.

Trains can cause trackside equipment to send a Sensor Active message to the sensor element equipment. A sensor clement, upon receipt of a Sensor Active message or a BSM from an approaching train broadcasts a CCR. The train, other approaching vehicles and the signs at the crossing can hear this message.

- It is valuable to the train as it now has confirmation that the crossing has been requested to close.
- It is valuable to an approaching vehicle as it is an early indication that the crossing it about to be closed (like an orange traffic light).
- It is valuable to the signs as they can now signal that the crossing is closed, e.g. by activation of boom gates, warning lights and transmission of CCI RSAs.

The sensor may receive a CCI. This would allow system integrity checking as it makes the CCR issued by the sensor now subject to closed loop verification. The CCR and CCI contain the coordinates of the crossing.
In general equipment is able to improve system performance and reliability by receiving and processing every kind of transmitted message.

4. EXAMPLES

Two fatal collisions between trucks and trains are considered as examples below in order to demonstrate the effectiveness of the proposed system. Two specific features of the system are demonstrated:
1. In the conditions leading up to the collisions the system would have provided significant warning times; and
2. If the timing of the events were different, resulting in a safe scenario, then false alarms would not result.
The latter is demonstrated by advancing or retarding the truck while keeping the train timing fixed.
The timing and position of the train and truck are replayed into a processing unit identical to that inside an OBE. In the field the OBE determines its own position from its local GPS service and obtains the position of remote vehicles or trains from receipt of DSRC messages over the air.
The warning trigger points generated in the examples below are identical to those that would be experienced in the field.
The two scenarios analysed are “Kerang” and “Benalla”:

- Just North of Kerang, Victoria in June 2007 a truck crashed into the side of a commuter train resulting in 11 fatalities. The warning devices at the crossing were active with warning lights operating for 25.4 seconds prior to the collision. The truck was travelling North at about 100 km/hr and started to decelerate too late, at about 50 m out from the crossing. The train was travelling at 91 km/hr in a South-Easterly direction, The truck impacted the train about 50m from the front of the train.

On Oct. 22, 2002 a B-Double truck turned across the path of a steam power locomotive in Benalla, Victoria. The train hit midway between the two trailers of the B-Double. Three fatalities occurred on the locomotive. The truck and train had been travelling South parallel to each other for sometime before the truck turned left across the path of the train on a passive level crossing.
In the results presented, Google Earth™ is used as a replay engine. It works by showing several snapshots of the train and truck with a time-window slider. The various features shown in FIGS. 14-20 are indicated in Table 2.

TABLE 2

Re-Enactment Key

Item	Messaging	Description

Grey Lines	—	Train (1502) and truck (1504) location in space
(1502, 1504)		and time, length of line is length of vehicle
	T2V	A threatening train (Cautionary Collision
		Warning announced in vehicle) (1402, 1508)
	T2V	A threatening train (Imminent Collision Warning
		announced in vehicle) (1404, 1510, 1602)
	—	Lateral G force indication (1406, 1604)
	—	Heading of vehicle (1506, 1512)
Train Sign	I2V	Adjacent vehicle has received a Train Crossing
(1408)		alert and conventional deceleration will be
		sufficient.
Exclamation	I2V	Adjacent Vehicle has received a Train Crossing
Sign (1410)		alert and severe deceleration is required.

4.1 Sensor-to-Vehicle: Train Approaching Warning
The Infrastructure to Vehicle implementation is first considered that applies when either new infrastructure is deployed at a level crossing, or system elements are retrofitted to an existing active crossing and the train does not have an OBE.
In I2V the presence of the train is determined by sensors at inbound and island locations. In this context there are virtual boom gates and therefore the in-vehicle warnings tend to occur earlier and last longer than the case where the train is transmitting directly to the vehicle.
In Table 3 the various timing offsets and the warnings (if any) that are induced are shown.
The vehicle must be much further offset from the crossing in order to avoid all messages. This is because the system is behaving like a virtual boom gate, using track-side sensors only. The Train Crossing Ahead message will last for more than 25 seconds in most cases.

TABLE 3

I2V Warning Times at Kerang

	Truck	Severe Warning
Warning	Retardation (m)	Range (m)

Cautionary Collision Warning (CCW)	−400	Safe
Imminent Collision Warning (ICW)	−200	250
Actual Incident	−50	250

In FIG. 14 the warnings issued to the driver by the infrastructure elements of the proposed system are shown. The driver is made aware that a train is approaching the crossing several hundred metres out from the crossing. The driver then receives a further warning when his speed has not decreased sufficiently to stop easily prior to the crossing.
4.2 Train-to-Vehicle: Train Approaching Warning
In the Train to Vehicle case the train is equipped with an OBE and infrastructure is required at the crossing. Table 4 shows the various timing offsets and the warnings (if any) that are induced. The truck retardation value is the distance from the crossing of the truck when the front of the train arrives at the crossing. Negative values mean that the train passes through the crossing first.

TABLE 4

T2V Warning Times at Kerang

		Truck	Warning
		Retardation (m)	Range (m)

No warnings (pass behind)	−200	Safe
CCW only	−150	170
CCW then ICW	−120	170
Actual Incident	−50	180
CCW (pass ahead)	+120	160
No warnings (pass ahead)	+220	Safe

FIG. 15 shows that in the Kerang incident the truck driver would have received a warning in his cabin with 170 m distance remaining to the crossing. This is regarded as enough distance for reaction time and stopping distance.
FIG. 16 shows the system evolution at the point of collision. The driver was in receipt of Cautionary Collision Warnings then Imminent Collision warnings. The Imminent Collision Warnings occurred when the driver needed to decelerate at the performance limits of the truck.
False alarm suppression is important. The drivers must trust the system and not be unnecessarily alarmed by the system. FIG. 17 and FIG. 18 show that no alarms are issued if the truck arrives later and earlier to the crossing respectively.
FIG. 19 shows that a Cautionary Collision Warning was issued to the driver if the truck was a little later to the crossing but still too close to pass safely behind the train.
A particularly difficult scenario is that of Benalla. In this case the train and truck are travelling parallel to each other with a separation of about 25 m. Ahead there is a side road that crosses the track. Only in the last few seconds would the train driver be aware that the truck was about to proceed across the track. The scenario is shown in FIG. 20. The proposed system raises an alarm as the truck driver turns the vehicle into the bend crossing the track. With a few seconds warning the driver could stop the truck as speeds are quite low on this corner.
The two examples described above show that the system described herein provides improved communication for collision prevention.
It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

ACRONYMS

BSM Basic safety message
CCI Crossing Closed Indicate message
CCR Crossing Close Request message
DSRC Dedicated Short-Range Communication
GPS Global Positioning System
ITS Intelligent Transportation Systems
OBE Onboard Equipment
RSA Road Side Alert message
RSE Roadside Equipment
TDE Threat Detection Engine
V2I vehicle-to-infrastructure
V2V vehicle-to-vehicle
WAVE wireless access in vehicular environments

Claims

1. A communication system for redundant communication at a railway crossing, the system comprising:

a first communication unit for transmitting information associated with a railway vehicle approaching or near the railway crossing on a railway track;

a first fixed communication unit located at or near the railway crossing for receiving and transmitting information associated with the railway crossing; and

an onboard equipment unit located on a roadway vehicle approaching or near the railway crossing, the onboard equipment unit comprising:

a second communication unit for receiving information from the first communication unit and the fixed communication unit;

a processor for processing the received information to determine a first threat indicator indicative of a potential collision, and

a user interface for communicating the threat indicator to a user.

2. The system of claim 1 wherein the first communication unit comprises:

a sensor system located at or near the railway crossing for sensing information associated with the railway vehicle and

a second fixed communication unit adapted to transmit the information sensed by the sensor system, wherein in use the information is received by the first fixed communication unit and the onboard equipment unit.

3. The system of claim 1 wherein the first communication unit is located on the railway vehicle and transmits information about the railway vehicle that in use is received by the first fixed communication unit and the onboard equipment unit.

4. The system of claim 3 further comprising:

a sensor system located at or near the railway crossing for sensing information associated with the railway vehicle; and

a second fixed communication unit adapted to transmit the information sensed by the sensor system.

5. The system of claim 3 or 4 wherein the onboard equipment unit communicates information about the roadway vehicle to the first communication unit located on the railway vehicle.

6. The system of any one of claims 3-5 wherein the onboard equipment unit communicates information about the roadway vehicle to the first fixed communication unit.

7. The system of any one of the preceding claims wherein the information comprises one or more of the following: a position of the railway or roadway vehicle, a direction of the railway or roadway vehicle, a speed of the railway or roadway vehicle.

8. The system of any one of claims 3-7 wherein the first communication unit located on the railway vehicle comprises:

a receiver for receiving information;

a railway-vehicle processor programmed to process the received information to determine a second threat indicator indicative of a potential collision; and

a human-to machine interface to alert a human operator if the railway-vehicle processor has determined a second threat indicator.

9. The system of any one of the preceding claims wherein the first fixed communication unit comprises:

a receiver for receiving information;

a railway-sign processor programmed to processing the received information to determine whether to close the railway crossing; and

a transmitter that in use transmits a crossing-closed indicator if the railway-sign processor determines that the crossing should be closed.

10. The system of any one of the preceding claims wherein the onboard equipment unit comprises a first navigation satellite system to monitor a position of the roadway vehicle.

11. The system of any one of claims 3-13 wherein the first communication unit comprises a second navigation satellite system to monitor a position of the railway vehicle.

15. An active warning sign for a railway crossing, the sign comprising:

a first communication link operable to receive sensor information from a sensor system located at or near the railway crossing for sensing the approach or presence of a railway vehicle;

a second communication link operable to receive a crossing-close request (CCR) from onboard equipment located on the railway vehicle;

a warning-sign processor programmed to monitor the first and second communication links and to generate a crossing-closed indicator (CCI) based on received sensor information and/or a received crossing-close request; and

a transmitter to transmit the crossing-closed indicator.

16. The active warning sign of claim 15 further comprising at least one warning light, wherein the warning-sign processor activates the at least one warning light if the crossing is closed.

17. The active warning sign of claim 15 or 16 wherein the railway crossing comprises a physical barrier and the warming-sign processor initiates closure of the physical barrier if the crossing is closed.

18. The active warning sign of any one of claims 15-17 wherein the first communication link is a hard-wired link between the warning sign and the sensor system.

19. An on-board communication system for redundant communication at a railway crossing, the system comprising:

an onboard equipment unit for use by a roadway vehicle approaching or near the railway crossing, the onboard equipment unit comprising:

a communication unit for receiving information from a plurality of sources, said sources comprising (a) an active warning sign that transmits a crossing-closed indication (CCI) if the crossing is closed and (b) a railway communication unit that transmits information indicative of the presence or approach of a railway vehicle at the railway crossing;

a processor for processing the received information to determine a threat indicator indicative of a potential collision, and

a user interface for communicating the threat indicator to a user.

20. The system of claim 19 wherein the communication unit transmits roadway vehicle information indicating at least one of a position, direction and speed of the roadway vehicle,

21. A method of operating an active warning sign for a railway crossing, the method comprising:

monitoring for sensor information from a sensor system located at or near the railway crossing for sensing the approach or presence of a railway vehicle;

monitoring for receipt of a crossing-close request (CCR) from on-board equipment located on the railway vehicle;

generating a crossing-closed indicator (CCI) based on received sensor information and/or a received crossing-close request; and

transmitting the crossing-closed indicator,

22. A method of operating an on-board communication system for a roadway vehicle approaching or near a railway crossing, the method comprising:

monitoring for information from an active warning sign that transmits a crossing-closed indication (CCI) if the railway crossing is closed;

monitoring for information from a railway communication unit that transmits information indicative of the presence or approach of a railway vehicle at the railway crossing;

processing received information to determine a threat indicator indicative of a potential collision, and

communicating the threat indicator to a user.