along with their diagonals, known as the diamond quadrilateral, carry about half the freight and nearly half the passenger traffic, although they form only 16 per cent of the length. References 5 ft 6 in gauge railways in India Railway lines opened in 1929 Rail transport in Delhi Rail transport in Haryana Rail transport in Uttar Pradesh Rail transport in Rajasthan Rail transport in Madhya Pradesh Rail transport in Maharashtra Rail transport in Andhra Pradesh Rail transport in Tamil Nadu