Transportation Tunnels, 2nd Edition provides a comprehensive text on tunneling and tunnel engineering applicable in general to all types of tunnels, with more detailed information on highway and railway tunnels. While the First Edition of the book was confined to deal with railway and highway tunnels, the Second Edition is also extensively considering the latest trends in use of tunnels in different other fields. The book has been revised to provide coverage of water conveyance, navigation and material conveyance tunnels also and deals with these subjects in more detail. It covers all aspects of investigation, design, construction, monitoring and maintenance of tunnels. Special emphasis has been laid on the geotechnical investigations, interpretation of findings and relating the same to the design as well as the construction of tunnels. The book reflects the advancements in the knowledge of ground behaviour and rock mechanics and also in construction technology, including use of TBM in the last two decades. It covers in sufficient detail the basic requirements of tunnel profile, the geometric parameters, clearance requirements, aerodynamics, and cost economics in fixing alignments with different design parameters like curvature, gradient and operational requirements. It discusses in detail alternative forms of the cross section / profile and illustrates design methodology with examples. The different methodologies that have been used in the past using timber or steel supports by stage wise expansion of cross sections and modern methodologies used for boring full profile using new tunneling methods and Tunnel Boring Machines are also comprehensively discussed. Requirements of tunnels in respect of ventilation, lighting and drainage are adequately covered. Separate chapters have been included on 'Instrumentation' and 'Tunnel Inspection and Maintenance'. The expanded text on the use and advantages of methodologies and equipment for dealing with various aspects of construction of tunnels is based on observations through site visits, discussions with, and experiences of people as recorded on large number of tunneling works which have been taken up recently for railways, highways and urban transport subway projects. The book can serve as a textbook for undergraduate and graduate students and as a reference book for practicing engineers.