The main reasons for not choosing Tunnel boring machines (TBM) for constructing the Rohtang tunnel are given below:  1. High deformations and pressures were expected on the tunnel. Thus, the TBM may have got jammed in such situations.  2. The transportation of heavy machine parts over Himalaya's bridges was risky because the Himalayan roads are not designed to bear heavy loads. Also, poor road conditions and tight hairpin bends make the transportation dangerous.