| 11. | An interlocking system was installed on 6 October 1924.
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| 12. | Development and successful testing of the first generation of the computer-based interlocking system MPTs-I ).
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| 13. | An interlocking system was installed on 5 April 1968.
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| 14. | An interlocking system became operational from 20 January 1927.
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| 15. | An interlocking system was installed on 18 October 1924.
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| 16. | An interlocking system was installed on 19 February 1934.
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| 17. | Northern Railway is equipped with 40 Route Relay Interlocking systems including the system at Delhi Main.
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| 18. | In 1969, the system was supplemented by a shunting interlocking system ( SPDRs 600 technology ).
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| 19. | These are soldered interlocking systems of metal panels.
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| 20. | From the same date the interlocking system at Sk�yen has been remotely controlled from Oslo Central Station.
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