The Central Artery/Tunnel project in Boston is the largest and most complex highway project in the heart of a major American city. Part of the $7.7 billion project involves replacing existing six lane elevated Interstate 93 through downtown Boston with a modern 8-10 lane underground expressway. The elevated highway in combination with surface streets splits Boston into two segments and creates lack of pedestrian access at numerous points. The proposed plan improves pedestrian flow by reducing conflicts between pedestrians and vehicular traffic. Extensive and detailed simulation models were developed, taking into consideration massive pedestrian flows. For instance, South Station which is a transportation centre experiences 80,000 people circulating through it having to cross surface streets. Traffic lights were optimised by effective mix of exclusive pedestrian times and modification of signal design to accommodate pedestrians concurrently with vehicles wherever possible. Traffic simulation and optimisation were completed using TRANSYT-7F traffic engineering software. Islands and medians with greenery would be built between surface streets with adequate storage and recreational intent.
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