Simple Start, Complex Finish

The Casey Arborway project in Boston started as a simple bridge inspection and possible deck replacement. However, it eventually became one of the most multifaceted and intricate planning and engineering undertakings by the Massachusetts Department of Transportation since the famous “Big Dig,” and one that dramatically transformed the Forest Hills neighborhood in Jamaica Plain.

A crumbling, unnecessary overpass was demolished, and a new at-grade transportation system was created. A busy, multimodal hub was expanded and improved; water and rail tunnels were reconstructed; and pedestrian and bicycle facilities were developed. Now, Frederick Law Olmsted’s Emerald Necklace park system is reconnected, the urban streetscape renewed, and surrounding neighborhoods are seamlessly integrated into the historic greenway.

But it was not easy.

“Hands down, in my 31 years of working at HNTB, this was the most complicated and complex project that I’ve ever been involved in,” said Paul Godfrey, HNTB’s Northern New England office leader and the project’s design project manager.

 

Deadlines drive debate

In 2009, the Massachusetts legislature approved the Accelerated Bridge Program, which would reduce a backlog of structurally deficient bridges, with the stipulation that projects be completed by September 2016 to qualify for funding by the program.

“That stipulation meant designated funding and a designated drop-dead date to build,” said Andrea d’Amato, assistant secretary of MassDOT. “That rule made the project very real for people, because they knew that they were going to see it get done.”

Passionate communities and stakeholders emphatically made their interests known.

“In Massachusetts, people take the right to speak their mind pretty seriously,” said Steve McLaughlin, MassDOT project manager. “HNTB helped us identify those communities, reach out to them, and use collaborative planning and agendas to advance the design process.”

Eventually, that process included a 30-person advisory task force representing neighborhoods, regional advocacy groups, and multiple city and state agencies.

“The community provided input and challenged the team to make balanced design choices that benefited all stakeholders,” Kapust said.

Transforming transit

“We asked the community what they wanted us to focus on most and, almost unanimously, it was transit,” d’Amato said.

Removing the overpass and relocating a surface roadway allowed the subway rail platform for the MBTA’s Orange line to be extended and updated, and a new headhouse to be built. Customers are no longer forced to cross a street to access the platform, and the resulting plaza is now available for other uses.

After an origin destination study (forecasting to 2035), two major intersections were redesigned so that left-turning traffic passes straight through, making a U-turn offset from the cross-street, then turning right onto the destination street. As a result, the intersection can handle more traffic, and signals were coordinated to maximize traffic throughput.

“The new pattern improved connectivity and access for all modes,” Godfrey said. “The area was opened up and better connected with the neighborhoods, as well as with people traveling to and through the space.”

A new network of bicycle and pedestrian facilities — three miles of bike path and more than four miles of pedestrian path — separate from each other and motor vehicles, was created, and development of a roundabout equalized bicycle movement and removed pedestrians. Now, there is an uninterrupted path for riders commuting from the neighborhoods south of Forest Hills to downtown Boston.

Improvements above, and below

A large bus network also traverses the space, so the upper busway was relocated and expanded to consolidate route locations. A 22,000 square-foot bus canopy now aligns with new expansion deck columns and existing Massachusetts Bay Transportation Authority tunnel wall, sheltering buses and customers. Reconfigured school bus pickup and drop-off points improved safety and eliminated traffic backups on surrounding streets.

Underground, the rail tunnel contains the terminus of the MBTA Orange Line, a commuter rail station, as well as pass-through points for Amtrak’s Northeast Corridor, so significant modifications were required to accommodate the new design.

A new drainage system was installed on top of the tunnel. Grates cast into the curb connect to multiple small pipes running to the original outlet points and drainage chases. Geofoam blocks under the new landscape grading limit loading on the tunnel, and the old vent grates (12 open holes totaling 2,000 square feet) were closed from above by using a variable depth integral concrete slab designed to accommodate decreased loading of the new roadway. Finite element analysis with staged construction loadings were used to design the integral slab, and to prevent the composite structure from overstressing the existing components of the tunnel structure.

The plan called for a new emergency ventilation system using six jet fans to be attached to the tunnel ceiling, but there was a hiccup: the new fans would not arrive for 18 months, and demolition of the old ventilation system could not begin until they were in place.

“We worked to reverse the entire project staging and build from the project limits into the center, where the station is located,” Kapust said. “The contractor was able to complete large sections on-time, and the community had finished paths and roadways to get excited about.”