Pune - Satara Section of the National Highway NO.4 passes through Katraj Spur of the Western Mountain Range between Pune and Shirwal. Existing highway is a two-lane road with quite a few sharp bends and steep sections. Existing highway also passes through a 275 m long two-lane tunnel located in the Katraj Spur. In view of the space limitations it was considered that straightening out existing sharp curves was almost an impossible task. Further, it was considered that any work on the existing highway would cause hindrance to the present day heavy traffic. To cater to the present day traffic and the traffic that is likely to increase in the next decade or so, provision of independent duel carriageways each with three lanes has been found to be necessary. It was therefore decided to carry out detailed study on a totally separate alignment for the highway with a provision of two independent carriageways each with three lanes. After initial surveys it was decided to carry out a detailed study on the proposed new highway taking off from the Westerly Bypass at Katraj Village and negotiating the Western Mountain Range through the Zorali Mountains and rejoining the existing National Highway NO.4 at the southern end of the Mountain Road. This Chapter brings out the Necessity of Provision & Economics of Construction of the Tunnels required to be provided in the Katraj Ghat and details of studies carried out for Detailed Engineering. The Studies were as follows : -Need for Provision of Tunnels -Requirement of Functional Parameters and Considerations Parameters Proposed to be Adopted -Study of Alternative Alignments of the Tunnels and Selection of one Alternative for further Studies. -Survey of the Area at and around the Alignment of the Selected Alternative. -Geotechnical Studies through Exploratory Bore Holes and Tests thereon for Assessment of Tunnelling Conditions. -Geometry of the Tunnels. -Approach Methodology for Design of Tunnel Supporting Systems. -Methodology of Construction of the Tunnels. -Estimate of Cost of Construction of the Tunnels.