Quote:
Originally Posted by queetz@home
If the sole benefit of a TBM is not to disrupt the 850 meter section between the disruptive station construction, then there is simply no justification for it. Disruption will happen because of those stations, and the distance between them is so negligible spending an additional billion or so for the TBM is simply not worth it. Might as well go Cut and Cover all the way since its going to be painful to businesses either way.
Evergreen Line had to use TBM because they had too. I cannot imagine digging a 2 km trench that deep on the mountain side would be economical, so TBM makes sense from a technical and economic point of view.
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I've always thought that
real forward thinking would plan for a transit system in which the tracks dip down after leaving each station and then rise back up again as they reach the next station. That way you get gravity assist during the acceleration and braking phases and reduce the amount of energy and vehicle wear required to run the system. Depending on how deep you want to go with the "valleys" between stations a TBM might be the logical choice to avoid excessively deep cut and cover construction. In fact it seems that if you were forced to use a TBM for other reasons then it would pretty much eliminate the cost difference between a gravity-assisted track profile and conventional "flat" construction.
But that sure has heck isn't going to happen with the Broadway line in Vancouver, despite its adoption in a number of other places.
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