| 21. | However, these types did see long service in interlocking plants.
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| 22. | The structure consists of a monumental grid of interlocking concrete forms.
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| 23. | The other are still operated locally, some using electromechanical interlocking.
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| 24. | The semaphores were replaced with colour light signals and electrical interlocking.
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| 25. | Today, trams run to Boudry at rigid push button interlocking.
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| 26. | The switches and signals are controlled from the interlocking at Remscheid.
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| 27. | In September 2011, an electronic interlocking was completed in Euskirchen.
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| 28. | Their locations permitted the bunkers to achieve interlocking fields of fire.
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| 29. | Another common symbol for a current source is two interlocking circles.
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| 30. | The whole station was equipped with a relay interlocking in 1971.
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