Crossing predictor with authorized track speed input

1. A method for controlling a grade crossing warning system comprising:

inputting by a control unit an indication of a time-varying maximum allowable speed of a train in an approach to a grade crossing;

determining by the control unit a delay period using the indication;

detecting the presence of a train in the approach by the control unit using a first track occupancy circuit;

activating by the control unit a grade crossing warning system in response to the train being detected and the delay period expiring.

2. The method of claim 1 , wherein the indication is encoded onto a first track occupancy signal associated with the first track occupancy circuit.

3. The method of claim 1 , wherein the indication comprises a code.

4. The method of claim 3 , wherein the code is associated with a signal aspect from a wayside signal device.

5. The method of claim 3 , wherein the code is associated with a setting of a track switch.

6. The method of claim 3 , wherein the code is encoded onto the first track occupancy signal using a frequency shift key technique.

7. The method of claim 1 , further comprising the steps of detecting the presence of the train in an island using an island circuit and deactivating the grade crossing warning system based at least in part on the presence of the train in the island.

8. The method of claim 1 , further comprising the step of detecting the presence of the train using a second track occupancy circuit on a second side of the island opposite a first side of the island on which the first track occupancy circuit is disposed, wherein the deactivating step is further based at least in part on the presence of the train on the second side of the island.

9. A system for controlling a grade crossing warning device, the system comprising:

a control unit having an input for inputting an indication of a time-varying maximum allowable speed of a train in the approach;

a first track occupancy circuit connected to the control unit, the first track occupancy circuit being configured to detect a presence of a train in an approach to a grade crossing;

wherein the control unit

inputs an indication of a time-varying maximum authorized speed of a train in the approach;

determines a delay period using the indication;

receives a first track occupancy signal from the first track occupancy circuit indicating the presence of a train in the approach: and

activates a grade crossing warning system in response to the first track occupancy signal and an expiration of the delay period.

10. The system of claim 9 , wherein the control unit further comprises a timer, and wherein the control unit is configured to initialize the timer with the delay period and start the timer when the signal from the first track occupancy circuit indicating the presence of a train in the approach is received.

11. The system of claim 9 , wherein the indication comprises a code.

12. The system of claim 11 , wherein the first track occupancy circuit includes a receiver and a transmitter, and wherein the transmitter is configured to encode the code onto the first track occupancy signal.

13. The system of claim 12 further comprising a wayside signal device connected to the transmitter, wherein the transmitter is configured to receive a signal aspect from the wayside signal device and select the code based on the signal aspect.

14. The system of claim 12 , further comprising an indicator device connected to the transmitter and configured to output a signal indicative of a configuration of a track switch, wherein the transmitter is configured to receive the signal from the indicator device and select the code based on the signal indicative of the configuration of the track switch.

15. The system of claim 12 , wherein the transmitter is configured to encode the code onto the first track occupancy signal using a frequency shift key technique.

16. The system of claim 9 , further comprising:

an island circuit connected to the control unit;

wherein the control unit is further configured to perform the steps of

detecting the presence of the train in an island using the island circuit; and

deactivating the grade crossing warning system based at least in part on the presence of the train in the island.

17. The system of claim 9 , further comprising:

a second track occupancy circuit on a second side of the island opposite a first side of the island on which the first track occupancy circuit is disposed, the second track occupancy circuit being connected to the control unit;

wherein the control unit is further configured to perform the step of detecting the presence of the train using the second track occupancy circuit; and

wherein the deactivating step is further based at least in part on the presence of the train on the second side of the island.

18. The system of claim 9 , further comprising a grade crossing warning system connected to the control unit.