Teamwork, innovation and flexibility combine to tame one of America’s worst bottlenecks

Design and engineering features

This project put to use interesting elements not widely used in Connecticut before.

A bituminous coating was applied to 379 piles totaling nearly 30,000 LF at three bridges. The coating mitigates the down drag forces that arose from the soil’s clay layers having been consolidated. Elsewhere, 13,460 CY of lightweight fill reduced the degree of consolidation from the construction of embankments at three bridges and three retaining walls. And a first in Connecticut, stone piers at two different bridges took the place of piles by auguring holes, filling them with stone, and compacting them.

The design called for widening the first five spans of the Charter Oak Bridge, where some 44,000 northbound vehicles cross daily. The design team at CHA used advanced finite element modeling to capture the complexities of the bridge work and come up with a safe, economical design. Which is not to say this widening to better accommodate traffic flow did not present constructability challenges. The new widths varied between spans—widest at the west abutment and narrowing substantially by the third span—resulting in complex framing geometry and difficult, high-level construction. That significant narrowing required non-parallel splayed girders. The steel framing used very long spans, curved girders, splayed girders, and skewed support, again requiring complex design and construction procedures.

But perhaps the centerpiece of this project, the piece that would have the greatest impact for the motoring public, was the innovative reconstruction of Exit 29. It is at this interchange that I-91 northbound connects with northbound Routes 5 and 15, two busy connectors between I-91 and I-84 and Route 2 in East Hartford.

The original ramp was narrow with a single lane and a steep grade. It caused drivers to weave when traffic merged onto Routes 5/15, creating sudden slowdowns and significant daily backups on I-91. It was also the site of numerous crashes. Fixing this problem was one of CTDOT’s highest priorities.

The reconfigured interchange—with its high-speed, two-lane diverging ramp and flatter grades connecting Routes 5/15 to the left side of I-91 northbound—dramatically reduces congestion, weaving, and safety.

Reconfiguring the Exit 29 interchange took a noteworthy design effort that arrived at an innovative solution.

A five-span, trapezoidal steel box girder bridge was designed to carry two lanes of the new ramp over Routes 5/15 from I-91 northbound to the existing Charter Oak Bridge. The two, grade-separated roadways required a unique steel straddle bent pier (see sidebar). It should be noted that all steel straddle bents have been classified as fracture-critical by the Federal Highway Administration, a designation that mandates substantial, biennial inspections to monitor the integrity of the components. For the new Exit 29 ramp, the engineers at CHA arrived at a novel steel straddle pier cap girder design with a triple I-girder straddle bent that eliminated the fracture-critical designation. Three individual plate girders were linked together to create an internally redundant, non-fracture-critical configuration. The benefits are substantial: there is no need for involved biennial inspections, and compared to common steel box girder straddle bents, the girders are approximately 50% less expensive to supply.

Having been proven on this project, the design is gaining widespread attention, with the Texas and Georgia DOTs adopting it for upcoming interchange projects.

GETTING IT ALL BUILT

For CTDOT, the biggest challenges came in the form of the sheer size and complexity of tying the two large projects together into one larger, contiguous job, and in balancing this massive project with other highway and bridge construction demands in the Greater Hartford area.

Two years ahead of project start, in 2017, CTDOT prepared a Regional Transportation Management Plan. That plan determined which projects could be active simultaneously and provided guidance on coordinating the designs of multiple transportation projects and the preparation of contract language to prevent conflicts. “Like most plans, it’s predicated on ideal outcomes,” said CTDOT District Engineer Donald Ward, who oversees this complex District 1 project. “The challenge throughout construction has been actually implementing that coordination through the capital region.”

It is a virtual certainty in heavy civil projects that as work unfolds, design schedules change, as do active construction stages and durations. “Fortunately, with excellent communication—sometimes on a daily and nightly basis between District staff and contractors—between the contractors themselves, state and local police, and the City of Hartford and adjoining municipalities, any conflicts have been quickly resolved and construction has been continuous.”

Ward notes that it is a busy area and a busy project. Every day an estimated 67,000 vehicles travel northbound through the area where I-91 and Routes 5 and 15 converge and connect to I-84 and Route 2, while another 44,000 traveling in the same direction cross the Charter Oak Bridge. General contractor O&G/BHD, JV and its subcontractors have had as many as 225 employees on site. “The general contractor has coordinated the work to keep the project on time without any undue disruptions to the motoring public,” Ward said.

Safety has been a challenge and a priority. Putting out and taking up traffic patterns with multiple truckloads of safety barrels and signs, often over miles of busy highway, and working within those patterns present critical safety windows of time. “O&G/BHD has been doing an excellent job executing both,” Ward said.

The O&G/BHD, JV team on the ground faced some initial challenges, according to Project Manager Michael Daley. “This project meshed what had been two different project designs initially so some of the stagings didn’t match well. But we all worked together to optimize the staging and the schedule to complete enough work to make the high-profile incentive date for opening Exit 29 in May.”

There were issues with field conditions not matching plans, something not unexpected on a project 12 miles long running through a congested area. But with cooperative, creative thinking and flexibility in apportioning manpower, the team keeps moving ahead.

“One of the biggest challenges, in my opinion, is the people,” said veteran Highways Superintendent Larry Doyon. “The union is hard-pressed to provide them to us. And you need the right people for the particular work, or that makes it even harder. Throw in COVID and it’s been a struggle. We’re not alone on this project, that’s just how the construction industry has been here. But we have strong core people and we’re pushing the work through. The teamwork has been very good.”

Despite the challenges, the schedule remains on track. Daley runs through all the work being “buttoned up” as winter approaches and the upcoming work awaiting the team, with the majority of work in Wethersfield and Hartford to be finished by the winter. “Then we have all of East Hartford for next year, some median work on I-91, too,” he said. “If we’re able to push the work as we have to-date, we’ll wrap up on schedule in October of 2022.”

An incentive for a high-profile milestone

It did not take CTDOT long in its up-front analysis to choose the one area of this project whose completion would provide the greatest immediate benefit to the public. The elimination of crashes at right-hand Exit 29 was the priority—there had been 372 of them with 85 injuries between January 2018 and April 2020.

A contract incentive was incorporated to open at least one lane of traffic on the new left-hand Exit 29 by May 26, 2021. It was a success, and the televised ribbon cutting was attended by the Governor, state representatives, mayors, the CTDOT Commissioner, and other distinguished guests.

The downs and ups of COVID-19

Unsurprisingly, the worldwide impacts of the pandemic have made themselves felt on the project. The tight supply of construction materials has affected regional suppliers, fabricators, finishers, and subcontractors who nonetheless found ways to continue working with no major overall delay to the current completion of the project. Flexibility—with changing stages and shifting crews to alternate work areas when, for instance, materials are not available or when an employee is exposed to the virus—has kept work progressing despite the additional complications for field management.

On the flip side, because the pandemic forced many people to work from home, traffic volumes dropped almost in half in 2020. Capitalizing on this road builder’s boon, CTDOT expanded the limits of operations for that window of time and allowed extended lane closures and lane closures during the day, creating more day work with its inherent increases in productivity and safety.

This project, a focal point of the state’s “Let’s Go CT” initiative, was identified as a key corridor objective to reduce traffic congestion in the capital region. More than once this area, and specifically the Exit 29 I-91 northbound ramp, was among the five worst choke points in Connecticut and earned the dubious distinction of being named among the 100 worst bottlenecks in America. Today, one lane of the new ramp is open and already greatly reducing crashes. With effective teamwork, design innovations, and skillful construction and project management, the expansive I-91 Charter Oak Bridge Project—the “congestion buster”—has passed 70% completion and is on point to finish just as scheduled.

For maps, graphics, additional background, and the latest updates on this project, visit www.i-91charteroakbridge.com.

About The Author: Duke is with O&G Industries. Ward is District 1 Engineer with the Connecticut Department of Transportation.