Gadag-Holealur is very easy as no any major bridge coming in this section.
Holealur Badami have only one bridge after holealur that also almost ready except Steel Giders installation.
For Badami - Bagalkot their required two Bridges which can be done easily too. So Gadag to Bagalkot they can take doubling in two or three parts then they can easily finish them soon.
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Bagalkot wandal it is a main delay occurring stretch due to Two major and many small bridges and culverts which can take time to complete them.

These below are some Technical Points i understood for using Steel Girders over Concrete one..
1.steel girders are much easier to design due the fact that the material properties of steel are very well known and understood.
2.Steel girders can generally be used for larger spans without a large increase in girder depth – this allows for a large savings in earth fill
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capable of being used in unique bridges including bridges with high skews (cross the under passing road at an angle), curved bridges, or long single span bridges.
Credit : Chris Koop at Reginabypass.ca/ Structures.
But Exactly i also dont know why they going with steel girders not only in this section but in new rail lines like Ginigera -Raichur , Bagalkot-Kudachi.
Installation of steel girders will be easy due to less bulky with same mechanical strength what concrete girder gives i think.