Why take weak-kneed measures?
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Get private vehicles off King, and Queen, between Parliament and Bathurst.  Make them into transit, cycling, and pedestrian only rights-of-way, and have done with it.   All of the businesses along those streets will benefit enormously.  Transit will move far more people, and will move them more rapidly.  Let deliveries occur between 9:00 p.m. and 7:00 a.m., or by special permit, only.
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It is a very low-cost solution that will benefit everybody, without having to bore a single foot of tunnel.
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Effectively, it would be like having LRT lines on King and Queen, at almost zero cost, until the DRL can be built 20 (maybe 30?) years from now .  (Longer if Patrick Brown & the Oil Party get elected next year.)
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The city would be s much better off.