This project replaced fourteen structurally deficient bridge superstructures on I-93 in Medford, Massachusetts. The locations of the bridges are shown at right, in green with their dates of replacement. Each green area indicates one bridge carrying I-93 northbound and one bridge carrying I-93 southbound. MassDOT used several innovations, a detailed traffic management plan and a comprehensive communications plan to complete the bridge work safely, efficiently, economically, and in a manner that caused the least possible construction-related impacts and congestion.
The bridges, built roughly sixty years ago, had reached the end of their service lives and were suffering from deterioration. The concrete of the bridge decks was in poor condition. The steel beams under the concrete decks were also in need of repair. MassDOT replaced the steel beams and concrete decks, which together make up the part of the bridge called the superstructure. The bridges' piers and abutments, which make up the bridges' substructures, were in good condition. MassDOT repaired the fourteen bridge substructures and revised them fto fit the replacement superstructures.
USING TECHNOLOGY TO MINIMIZE THE DURATION OF IMPACTS
In order to reduce the duration of construction-related congestion as much as possible, MassDOT used prefabricated replacement superstructures in modular units. Each modular unit was made of a concrete deck with two steel beams underneath it. There was a total of 252 pre-cast pieces used in this project. The modular units were fabricated in a controlled, factory setting, resulting in very high-quality concrete. The modular units were installed by crane, replacing at least one bridge each weekend.
WEEKEND SUPERSTRUCTURE REPLACEMENTS
To install the new superstructures, MassDOT closed each bridge location. To make sure that the project did not impact rush-hour traffic, the bridge replacements were performed on weekends. MassDOT crossed traffic onto one side of the highway, beginning at 8:00 PM on Friday nights. The road beneath the bridge being worked on was closed at 6:00 PM to allow crews to move equipment into place. Once the work zone was secure, the existing superstructures were demolished. The modular units arrived on site, and cranes hoisted the units into place. The steel beams of the modular units were connected and carpenters built formwork for the concrete connection. Once the formwork was complete, crews poured a concrete connection called a closure pour. The concrete set rapidly. Crews then erected temporary barrier systems and applied temporary line striping. I-93 was completely reopened to traffic by 5:00 AM on Monday morning. Other work, such as substructure repairs, barrier installation and paving occurred on weekdays and weeknights, but no work occurred during weekday rush hours.
MassDOT's goal was to reconstruct the bridges while minimizing construction-related congestion on I-93 and area roads. All roads, lanes and ramps that were closed for the weekend work were reopened by 5:00 AM each Monday morning and remained open during peak travel periods on weekdays. During weekends, the crossover directed all I-93 traffic to one side of the existing highway, leaving the work zone side available for construction activities. Traffic from one direction crossed the median onto the opposite side of the highway before the work zone. The two opposing directions of traffic were separated by a moveable "zipper" barrier installed throughout the 4.5-mile construction zone at the beginning of the work each Friday night. Drivers with regional destinations outside of the metropolitan Boston area were strongly encouraged to avoid using the section of I-93 between Route 3 in Braintree and I-95 in Reading and instead use other available high-speed regional highways.
ACCESS ON AND OFF I-93 IN MEDFORD
On the open side of the highway there were two lanes of traffic in each direction, separated by a movable barrier. Where possible, one lane on the work zone side of I-93 remained open to allow people to gain access to and from local destinations using available on and off ramps. Availability of lanes and ramps on the work zone side of the highway was dependent upon which particular bridge(s) were under construction in a given weekend. All ramps were open on the non-work zone side of the highway, for vehicles traveling in the direction that side of the highway usually carries. When the work zone was on the northbound side of I-93, all ramps were open and available to vehicles traveling southbound. When the work zone was on the southbound side of I-93, all ramps on the northbound side of I-93 were open and available to vehicles traveling northbound. Local ramps and local access lanes were available whenever possible to minimize the need to detour local traffic from I-93 and to encourage use, where safe and appropriate, of available sections of the I-93 roadway within the construction that are not impacted by the specific location(s) of bridge construction. Vehicles traveling on I-93 that did not have a Medford destination will remained on I-93 and did not have to be diverted to the local roadway system. Commercial Motor Vehicles without a local origin or destination were be instructed to continue on I-93 or alternate limited access highways.
LOCAL TRAVEL AND DETOUR ROUTES
The 93 Fast 14 weekend work was scheduled so that only one local road was closed each weekend. MassDOT developed a series of local detour routes aimed at keeping the immediate impacts limited to the specific bridge that is under construction each weekend. The local detour routes had modified traffic signal timing and the personnel necessary to provide a means for local traffic to get around the City of Medford and gain access to surrounding communities in a safe manner. Route 28 (Fellsway) and Route 38 (Mystic Avenue) were the primary secondary highway options for travel in the north-southbound directions with local origins/destinations. A series of local detour routes was posted to guide the local traffic around the City of Medford and to facilitate regional access to the surrounding communities.
THROUGH TRAFFIC STRONGLY ENCOURAGED TO USE ALTERNATE ROUTES TO AVOID DELAYS