Mostly, there are primarily three reasons for this arrangement-
(i) Permanent structure is statically indeterminate structure. all through construction by using span-by-span construction, if first stage of construction contains of first span length L only, then a sagging moment in mid span of partially completed bridge is big than that of completed two-span permanent structure.
To pass up such occurrence, 0.25L of bridge segment is extended further from second pier which offers a counteracting moment, thereby reducing mid-span moment of partially completed bridge.
(ii) The place of 1.25 L countering from first pier is approximate location of point of contra flexure, imagine that two-span Bridge is uniformly loaded in which bridge moment about zero in an event of future is loaded bridge.
Therefore, designing of construction joint in this particular location has least adverse effect on structural performance of a bridge.
(iii) In case of a pre stressed bridge, pre stressing work has to be carried out after construction of first segment of bridge. If pre stressing work is performed at first pier which is heavily reinforced with reinforcement, it is adverse when compared with pre stressing location at 1.25L from first pier everywhere there is relatively new space to accommodate pre stressing works.