2. The invention according to claim 1, and a speed control means in said electric circuit responsive to train speed and operative to deactivate said trackside mounted door operating device upon approach of the train above a preselected velocity.

3. The invention according to claim 1, and lading depth sensing devices mounted adjacent said lading discharge area to sense lading buildup and signal the trackside mounted door operating means to prevent opening of said discharge doors to prevent discharge of lading in the builtup area.

4. The invention according to claim 1, and: said trackside mounted hopper door operating means including a discharge door opening means positioned at the beginning of the lading discharge area and a discharge door closing means positioned At end of said discharge area; said door operating means having cam track portions vertically movable between said tracks; said discharge door closing means having cam track portions vertically movable between said tracks.

5. The invention according to claim 1, and a link pivotally attached to said hopper discharge door means; a slide member operatively connected to said link member and movable outwardly of the hopper car upon opening movement of said discharge doors to engage the hopper car mounted switch actuating means and move same outwardly of the hopper car for engagement with said second trackside mounted switch means.

6. The invention according to claim 1, and said first, said second, and said third trackside mounted switch means each including a pivoted arm member adjacent the track.

7. The invention according to claim 1, and a door operating mechanism locking member positioned on said hopper car; a ground mounted first cam member engageable with said locking member to thereby unlock the discharge door operating mechanism; a second ground mounted cam member engageable with said locking member to thereby lock the discharge door operating mechanism.

8. The invention according to claim 4, and said caboose mounted switch actuating means comprising a first caboose mounted switch actuating means and a second caboose mounted switch actuating means; said end portion of the lading discharge area including adjacent control switch means operable upon the hopper discharge door closing means to thereby close said discharge doors, said control switch means including: first trackside mounted control switch means including cam track operating switch means engageable by the locomotive mounted switch actuating means to thereby move said discharge door closing cam track portions into operative position to close said discharge doors; second trackside mounted control switch means having means engageable with both said hopper car mounted switch actuating means and with the caboose mounted switch actuating means; said second trackside mounted control switch means including spaced switch members; third trackside mounted control switch means having means engaging said caboose mounted switch actuating means to move the discharge door closing cam track portions from the operative to the inoperative position; said spaced switch members positioned at trackside and simultaneously operable by the hopper car mounted switch actuating means of passing hopper cars; said spaced switch members positioned at trackside and simultaneously operable by the second caboose mounted switch actuating means and the hopper door actuated indicator member of the preceding hopper car; the spaced switch members including means coupled with said hydraulic circuit to move said discharge door closing cam track portions to an operative position and also including means to move the discharge door closing means to an inoperative position; the spaced switch members including normally open and normally closed switching points in parallel to interpret the open and closed condition of the hopper car discharge doors to thereby move the door closing cam track portions to an inoperative position if discharge door means of an approaching hopper car are closed and move the door closing means to an operative position if the discharge door means are open.

9. The invention according to claim 4, and said discharge door closing means including a vertically movable cam track having a first cam portion and a second cam portion.

10. The invention according to claim 5, and the hopper door actuated indicator member including angled and rounded edge portions.

11. The invention according to claim 6, and said pivoted arm member including a roller portion engageable with the associated train mounted switch actuating means.

12. The invention according to claim 7, and said first and said second ground mounted cam memBers including associated hydraulic control means operatively connected thereto.

13. The invention according to claim 7, and said first trackside mounted control switch means including a cam member operating switch means engageable with the locomotive mounted switch actuating means; said first ground mounted cam member positioned at the beginning of the lading discharge area and said second ground mounted cam member positioned at the end of the lading discharge area; hydraulic cylinder means operatively connected with the first and with the second ground mounted cam members and actuated by the cam member operating switch means.

14. The invention according to claim 7, and said first cam member and said second cam member being positioned between said rails and movable vertically to engage the door mechanism locking member.

15. The invention according to claim 8, and said trackside mounted control switch means comprising trackside limit switch members; a solenoid valve means operatively connected with said trackside limit switch members; hydraulic cylinder means operatively connected with the solenoid valve means and with the cam track portions to thereby control raising and lowering of said cam track portions by operation of the limit switch members.

16. The invention according to claim 8, and hydraulic cylinder means operatively connected to the cam track portions; solenoid valve means operatively connected with the hydraulic cylinder means; said spaced switch members including a first circuit portion having a normally closed contact and a normally open contact in parallel and a second circuit portion having a second normally open contact and a third normally open contact and a relay latching contact in parallel; said first circuit portion in series with the second circuit portion.

17. The invention according to claim 16, and an associated electromagnetic relay in series with said normally open relay latching contact to close said latching contact and thereby seize said relay in the operated position.

18. The invention according to claim 16, and each spaced switch member including first and second limit switch operatively connected to and controlling operation of an associated portion of the cam track.

20. The invention according to claim 19, and said control device including speed responsive control means operable by approach of the unit train above a preselected velocity to de-energize the control device.

21. The invention according to claim 19, and said control device including an electric circuit and a hydraulic circuit; said electric circuit operatively connected with said off train mounted actuating means; the hydraulic circuit including solenoid means and valve means operatively connected with electric circuit; said solenoid means activated by the off train switch means to control operation of the off train mounted discharge door actuating means for controlled opening and closing of the discharge doors.

22. The invention according to claim 19, and said safety means including spaced Switch members including a first circuit portion having a normally closed contract means and a first normally open contact means in parallel and including a second circuit portion having a second normally open contact, a third normally open contact and a normally open relay latching contact in parallel; the first circuit portion in series with the second circuit portion.