Next at South Station: hard hats, detours and lots of headaches

This rendering shows the expanded outdoor concourse under soaring arches that will support a new 51-story tower above South Station in Boston. DBOX

The tens of thousands of commuter rail and bus riders who pour through South Station every day will soon have a more complicated course through the terminal.

Construction zones will go up in and around the station and platforms as work begins this month on a 51-story tower above the railbed area where passengers board trains. Over the coming months, the open area in front of the platforms will slowly be cordoned off, as workers build an extension of the loading zone over a portion of the rails, according to detailed construction plans the Massachusetts Department of Transportation posted on a new website late Friday.

Construction zones will also be set up along the Atlantic Avenue and Summer Street side entrances to the platform areas, and work will begin on an expanded bus terminal.

By July, work will be in full swing, and passing through the station will be a very different experience.

That’s when work crews plan to close a majority of the doors between the waiting area inside the station and the outdoor boarding platform. Much of the platform will become a construction zone, funneling passengers through a narrow area between the concourse and trains. Trains may stop on different tracks than they typically do now. Bike storage, bus stops, and taxi stands will move.

Acknowledging things will be more complicated, MBTA officials are suggesting commuter rail passengers plan an extra five to 10 minutes to make their trips, though they promise there’ll be no disruption of service — and no impact at all on the Red or Silver Lines below ground.

The enormous project is one of the most ambitious in Boston in decades: a skyscraper on top of Boston’s busiest rail hub, along with the expansion of the bus terminal and a new parking garage — all without disrupting operations.

Huge archways will be built atop the platform — tied into a foundation that was installed when South Station was renovated in the 1980s — and gradually a deck will stretch overhead, at the level of a second floor, to support the tower, according to a video the state transportation agency posted on its website.

The complexity of all of this is one big reason why the project — first proposed by the development arm of Tufts University in the 1990s — has taken so long.

Hines, a Houston-based developer that has built skyscrapers all over the world, has spent the last few years plotting the intricate details of construction with MassDOT and lining up financing for an office and condo tower that will take four-plus years to build. For now, the developer has yet to line up tenants for the building, but in December it closed on an $870 million construction loan from a British investment fund.

When it’s done — the bus terminal slated for 2022, and the rest of the project in the summer of 2024 — South Station will be a very different place.

Instead of using the open-air cement platform there today, passengers will board through a larger platform beneath soaring archways that form the base of the tower.

New elevators and escalators will carry people from the main headhouse to an expanded bus terminal along Atlantic Avenue. And likely thousands of people will live and work above, bringing more activity through and around the station much like the recently completed Hub on Causeway project has at North Station.

Then will come the second and third phases of the project — an office building and a hotel atop the bus terminal. No word on what they will mean for commuters.