Constructing the RUB was a big engineering challenge. The RUB has been constructed under seven running tracks on Delhi-Mumbai rail section without disrupting train movements. To achieve the feat, the railways adopted an advance technique of box pushing, which ensures uninterrupted flow of rail traffic throughout the construction period. “In this technique, the entire length of reinforced concrete box is divided into segments. The segments are precast over a horizontal concrete thrust bed, adjacent to railway embankment. The boxes are then pushed into the embankment one after another using hydraulic force created by jacks,” said a senior official, adding, “This underpass is one of the largest in India using this method.