All these natural obstacles had to be overcome by engineering skill and technology Centrifugal  and jet  fan ventilation in the tunnels, along with other safety features, were in themselves massive undertakings
बोगद्यांमधील केंद्रोत्सारी व जेट - पंखांनी संवातन तसेच इतर सुरक्षा उपाय हीच मुळात मोठ्या मुश्‍कीलीची कामे होती.