CME was selected to deliver the final design to address safety issues associated with congestion and operational performance of Interchange 29 where I-91NB exits to the Charter Oak Bridge. CME designed the widening of I-91 NB to increase the number of lanes and reconfiguring spans of the Charter Oak Bridge. The widening plan requires significant modifications to seven corridor bridges and construction of a new two-lane, five-span bridge more than 800 feet in length to support a new off-ramp. The new exit ramp bridge will be a continuous trapezoidal box girder bridge with hammerhead piers and a straddle bent pier in order to avoid further highway impacts.
CME also designed significant strengthening measures for the existing Charter Oak Bridge to remain based on CME’s load rating analysis using full finite element modeling of the entire bridge and a strain gauge investigation to verify actual live load stresses. The existing bridge was also widened by approximately 40 feet with curved, splayed girders spanning in excess of 270 feet.
In 1991, the Charter Oak Bridge was opened to traffic, connecting Interstate 91 and Routes 5/15 in Hartford with Interstate 84 on the other side of the Connecticut River in East Hartford. Significant increases in traffic volume paired with a steep on-ramp leading to the bridge has caused persistent bottle-necking and accidents at this interchange. To mitigate traffic safety and congestion issues, a new configuration of ramps and realignment of roadways were approved by the Connecticut Department of Transportation. CME was selected to bring the design to completion.
The project included the widening of I-91 NB for approximately 4,300 feet to provide four lanes between Interchanges 27 and 29. The four lanes on I-91 NB widen to five lanes and bifurcate with the two left-hand lanes diverging as the new Interchange 29 off-ramp. The three remaining lanes continue onward as I-91NB. The new Exit 29 two-lane off-ramp geometry, a major diverge, is anticipated to relieve congestion and address safety concerns along I-91 NB. This major diverge design required a FHWA Change of Access Permit, which was received. The widening plan required significant modifications to seven (7) corridor bridges. A new two-lane, five-span bridge, more than 800 feet in length, will be constructed over 5/15 SB to serve as the new Interchange 29 off-ramp.
Near the existing Charter Oak Bridge approaches, embankment settlement and slope stability were identified as critical concerns requiring in-depth geotechnical analysis and innovative solutions. Laboratory testing was performed on a wide range of soil samples collected from the site. The materials were modeled to determine their ability to support the proposed structures and grading contours. Light weight fill rammed aggregate piers and geogrid reinforcing are detailed in the final design plans to mitigate settlement and stability issues.
There are 45 separate drainage systems and numerous cross culverts which carry streams and drainage ways along the length of the project. CME designed new systems to account for the increased impervious area, provide water quality treatment and eliminate areas of known drainage. The proposed drainage system was modeled three dimensionally with Bentley’s Storm and Sanitary to help identify and eliminate utility conflicts as the project site is located largely in an urban industrial setting. Numerous local state and federal permits were prepared including environmental, stormwater and construction permits for CTDOT, CTDEEP and the USACE.
CME prepared an Environmental Assessment (EA), in accordance with the Federal Highway Administration and the National Environmental Policy Act (NEPA), to evaluate impacts on natural and cultural resources in the project site. The project has required extensive coordination with several state and federal regulatory agencies, and involved impacts to wetlands, floodplains, tidal waters, and potential effects to Threatened and Endangered species (state and federal).
A comprehensive community outreach campaign resulted in broad public support for the project. It also yielded the need for and approval of a proposed 1,000 ft. noise wall to offer sound protection to abutting property owners and provide a visual barrier for privacy from passing motorists.