For flyovers in highways and for light rail transport elevated structures, box girder bridges are typically used.
During the design of the concrete box girder bridge, one basic requirement is to determine the number of cells. The following rules can be followed for determining the number of cells for concrete box girder bridges.
If the depth of a concrete box girder bridge exceeds 1/6 or 1/5 of the total bridge width then the single-cell box girder bridge is recommended. But if the depth of the bridge is lower than 1/6 of the total bridge width then it is preferable to choose a twin-cell or in some cases multiple cells.
Please note that even in the cases of wider bridges with comparatively low depths, the number of cells could be minimized as there is no noticeable improvement in the transverse load distribution when the number of cells of the box girder is higher than three or more.
Source: https://specialties.bayt.com/en/specialties/q/335448/in-case-if-concrete-box-girder-bridges-how-is-the-number-of-cells-determined/