Table of Contents
Train movement related features and concepts
The track network of the WinterTrain will be formed by:
- Track sections of various length
- Points, diverging trains in one of two directions
- Buffer stops and end of track
- Road level crossings
Within the network one particular driving direction will be defined as direction up. The opposite direction will be called direction down.
In order to simplify implementation of data structures and algorithms in the RBC/IL, the possible track topology will be limited:
- The track network has to be connected, i.e. all tracks must be reachable from any other track. This excludes a track network, having “islands” of tracks.
- Direction has to be unambiguous, that is: direction up has to remain direction up when driving in the network. As a consequence of this, a so-called “turning loop” cannot be realized.
In a future version of the WinterTrain special features will be implemented allowing “loops”, “triangles” etc.
Train position and track vacancy
In order for the interlocking to prevent collisions and for the RBC to provide movement authority to trains, the position of each train has to be established with a certain accuracy.
Track vacancy - i.e. whether a specific section is clear and can be used by a train or is occupied and cannot be used - can be detected in may ways. Traditional interlocking is using track circuits, axle counters and the like. If reliable position reports can be achieved from all trains in an area, this can also be used to determine if a section is occupied or clear. Actual train position is traditionally determined by odometry (measurement of travel distance) based on “mile stones” readable by the train.
In the WinterTrain project track vacancy will be determined solely based on the position of each train. All trains will regularly reporting their position. At appropriate intervals all over the track network so called balises will be installed. A balise is a small passive transponder mounted in the track. When a train passes a balise the balise will transmit a unique ID to the train. Starting at the position of the balise the train will measure - as it moves along the track - the distance between the balise and the train.
At regular intervals each train will transmit a position report consisting of the actual distance between the train and the last read balise, the ID of that balise and an indication of the driving direction - up or down.
The actual driving direction will be derived from the polarity of the DC voltage in the rails - i.e. whether the polarity at the right side wheels is positive or negative. To ensure an unambiguous definition of directions and distances, nominal driving direction up (and hence down) will be defined for the whole track layout. The polarity of the traction voltage of the rails will be arranged so that the right side rail as seen in direction up will be positive.
The distance traveled by a train will be measured by counting wheel turns. In the RBC number of wheel turns can be converted to a distance in cm based on the wheel diameter of each train.
Actual train position will hence be expressed as a relative distance - with sign - from the latest read balise. A positive value will indicate, that the train is located at a position further away in direction up from the latest read balise. A negative value will tell, that the train is located in direction down, compared to the balise in question.
Nominal driving direction up and down is not to be confused with train moving direction forward and backward. The former is statically defined for the track network, while the latter is a dynamic property of a moving train. The train has a defined front end and compared to this, the train is said to be moving either forward or backward. Hence if a train is located with its front end pointing in direction down, it will be moving backwards when driving in direction up.
The RBC will have a data model representing the track network including location of all balises and relative distances between balises and other elements of the network. This model will as well include information of the length of each train and the position of the balise antenna at each train.
Based on this model, train data and received position reports from all trains, the RBC will be able to determine where in the network each train is located and hence which parts of the track network are occupied and which are clear.
The OBU will not keep the current position during power down or OBU reset. After power up or re-start, the OBU will send a position report indicating the lack of valid position information. In this situation, the driver has to run the train manually to the next balise in mode SR or SH.
For reasons that has not been identified yet the OBU has a tendency to reboot spontaniously and hence forget its current position. As a work-around for this the RBC will keep the most recently received train position for a specific time (10 - 30 seconds). If the OBU restarts within this period, the RBC will assume this position as the actual position of this train.
Given a position report and the model of the track network as the only information the location of a train will in most cases be unambiguous. That is, the RBC can determine the location based on the report and the model alone.
One exception exists however. If the track network between the last read balise and the train includes a facing point then the location becomes ambiguous. A point is called facing when the train is passing the point in direction from tip to branch. The problem is that the train has no knowledge of which of the two branches of the point is it moving along. In this situation knowledge of the previous location of the train and the lie of the point will be needed in order to unambiguously determine the location of the train.
If the previous location is unknown (e.g. due to reboot of the RBC) and current location of a train is ambiguous the RBC has to assume that the train is occupying both branches of the point.
Mode authorization and train mission
The operational mode of each train will be managed in the following way depending on the actual operational situation of the (model) railway. For each train the operator will be able to mark which modes the train is allowed to operate in. In addition to this, mode SR can as well be allowed by a dedicated switch in the OBU (mostly for test runs without the RBC).
For mode SH the shunting area assigned to the train has to be clear of other trains in order for the RBC to allow mode SH.
When the driver selects a particular mode (and the direction selector is in position Neutral) the OBU will send a Mode request for that mode to the RBC. The RBC will then grant or reject the mode. If the requested mode is granted this is indicated to the driver via the “Mode authority indicator” being off.
If a particular mode is not allowed according to the above, a request from the train driver for this mode will be rejected. This will be indicated to the driver via the “Mode authority indicator” being Red.
Mode N is implicit allowed and requires no authorization form the RBC.
Each train will be authorized by the RBC to move depending on the granted operational mode and the operational situation of the railway. The mechanism for getting a movement authority (or MA for short) is as follows:
Mode SR The authority is implicit given by the mode. The movement of a train i mode SR is not limited by the system. The driver has the responsibility of the train.
Mode SH The OBU will get an MA indicating the maximum allowed speed for shunting. The driver can move the train within a predefined shunting area specified by OBU data.
Mode FS When the driver selects a driving direction, the OBU will send an MA request for that driving direction to the RBC. The RBC can then grant a movement authority indicating how far and how fast the train can move. While running according to the revieved MA the OBU will continue sending MA request. If conditions allows the RBC will then extend the MA.
Mode ATO The RBC can grant movement authorities. The ATO function of the OBU will then drive the train accordingly. While running according to the revieved MA the OBU will continue sending MA request. If conditions allows the RBC will then extend the MA.
Give various conditions are fulfilled the RBC will issue an MA to a particular train.
For a train in mode SH the MA authorizes the train to move with a certain maximum speed. The area in which the train can move is specified by other means. The MA includes:
- Maximum driving speed
- Train ID
For a train in mode FS or ATO the MA authorizes the train to move from its current position to a specific new position called “End of authority” or EoA for short. The MA includes:
- Driving direction (up or down)
- Location of EoA in terms of a signed distance from a specific balise
- Maximum driving speed
- Train ID
The MA will be based on the latest train position known by the RBC. As a moving train may have read another balise since requesting an MA, the OBU has to keep track of the position of the train according to more balises.
An MA received by a train remains valid until:
- The train has reached EoA within a certain margin or
- The driver selects driving direction Neutral or
- The driver selects a different mode
The RBC can withdraw an MA, in which case the train has to stop.
In mode FS the OBU will supervise the traction power and driving direction according to the current Movement Authority given by the RBC. If no MA is available traction will be disabled and the train will stop.
In mode SH the traction will be supervised against a maximum speed provided by the RBC in the MA following the authorization to operate in mode SH. Further both traction and direction will be supervised, in order to prevent the train from leaving a predefined shunting area.
In mode SR traction and direction is not limited; the driver have full responsibility of the train.
Automatic train operation
In mode Automatic Train Operation (ATO) the train will run automatically according to the actual Movement Authority (MA) given by the RBC. The speed will be commanded to maximum whereby the actual speed will be controlled by the supervision system and hence follow the maximum allowed speed in the MA. The driving directions will be as allowed by the MA.
A shunting area is an area in which a train may operate in SH mode. The extent of the shunting area will be statically defined in the OBU. It is defined by a list of shunting area borders, each of which is specified as a signed distance from a balise. This list will be part of the configuration data of each train. In a later version this area specification may be updated dynamically by the RBC.
Each border specification will provide:
- Balise ID
- Distance with sign from balise to shunting area border. A positive distance indicates that the border is located in direction up compared to the balise, while a negative distance indicates that the border is located in direction down.
The balise of a border specification must per definition be located inside the shunting area. Several border specifications (and hence several balises) can point at the same border, increasing the chance that the OBU will observe the border.
When the OBU reads a balise, this balise will be compared against the border list. If the current balise is found in the border list, the train is near a border and must observe this border. The index of the balise in the border list will be stored. When the train moves, the distance from the current balise (equal to the border balise) will be compared with the border distance. When passing the border, the OBU will start braking the train. Braking distance has to be taken into consideration when engineering the borders.
If the current balise is not in the border list, the train can continue without checking the distance.
If a train is located outside the shunting area and current balise is a border balise, mode SH will be rejected by the OBU. If the current balise is not in the border list, mode SH will be accepted, assuming the train is within a shunting area.
In any case, mode SH has to be allowed by the RBC.
The signaler may issue an overall Emergency Stop command whereby the RBC will send an Emergency Stop MA to all trains.
When a train receives an Emergency Stop MA the current MA will be deleted and the train will stop.