Sliding into Summer Traffic with the ABCs of Bridge Replacement By CHRISTINA R. GARRETT, P.E., Michael Baker International Summer is the travel season: travel by plane, boat or, most commonly, by car. Parents drop their children off at summer camps, teenagers go on long road trips, couples drive to the airport to catch flights and families visit relatives. But summer is also construction season, so all these travelers often see orange- and yellow-vested crews working on the road. Road work means delays from lane changes, reduced speeds and detours; the traffic delays and changes that come from road construction are the bane of summer months and often delay commutes as early as spring thaw and well into fall. Nothing causes more delays than bridge replacements with limited widths for construction and swiftly moving traffic. The replacement of more than 43,500 deficient bridges in the United States,1 with only 63 in Utah,2 is complicated by the limited room for construction and traffic during the bridge replacement. The replacement of a simple, 120-foot span bridge also includes repaving the approach slabs. The work takes an average of six to seven months with active traffic. That’s six to seven months of construction delays and changed traffic patterns. Imagine condensing six or seven months of daily construction delays into a single weekend. Accelerated Bridge Construction makes that possible. ACCELERATED BRIDGE CONSTRUCTION Accelerated Bridge Construction (ABC) is an umbrella term for advanced bridge construction technologies. They “reduce the onsite construction time that occurs when building new bridges or replacing and rehabilitating existing bridges.”3 Many ABC methods allow bridge replacement or construction to occur in days or hours, including using precast bridge elements, sliding completed bridges into place, moving bridge girders and decks with self-propelled modular transporters (SPMTs), and performing bridge launches. The methods mentioned above have been used successfully in Utah over the past two decades. One of the most frequently used ABC technologies is Prefabricated Bridge Elements and Systems (PBES). They are “structural components of a bridge that are built offsite, or near-site of a bridge, and include features that reduce the onsite construction time and mobility impact time that occur from conventional construction methods.”3 PBES can easily be divided into prefabricated elements and prefabricated systems. The Federal Highway Administration defines a prefabricated element as a “single structural component of a bridge”3 that reduces the onsite construction time required if the component had been built onsite using conventional construction methods. These elements are usually repetitive members designed for multiple loads and locations to offset the fabrication cost. Prestressed concrete girders are one of the most common prefabricated elements used in Utah. They can be cast and prestressed at precast concrete plants local to Utah before being shipped to the bridge site for placement. Engineers also often use precast deck panels for bridges over active railroads or highways to reduce the construction workers’ time over traffic or trains. The concrete prefabricated 33
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