After six years of promises, Brookfield Office Properties has finally started to build a deck over the exposed Amtrak rail yard for its planned Manhattan West development project. The platform is a long-awaited breakthrough in Mayor Bloomberg’s dream to create a vast new Hudson Yards District in the once-forlorn far West 30s that will be home to major companies, residents and a wealth of public amenities.

It’s also crucial to publicly traded Brookfield’s plan for a $4.5 billion, five million-square-foot project on five acres anchored by two tall office towers and an apartment building.