Correct Answer - Option 1 : Loading gauge
A loading gauge is the maximum height and width for railway vehicles and their loads to ensure that they can pass safely through tunnels and under bridges. According to the Indian Railways, the maximum height and maximum width of rolling stock for Broad Gauge is 4140 mm and 3250 mm respectively and for Meter Gauge, the values are 3455 mm and 2745 mm.
Construction Gauge is the loading gauge plus extra clearance necessary given to the loading gauge so that the train can safely passes without any stoppage. It decides the dimensions such as height and width of structures in bridges and tunnels along the track so that all wagons may pass through them without damage to the structures.
Note that Rolling stock is built in accordance to the Loading Gauge and Bridges and tunnels are built in accordance to the Construction Gauge.