Some benefits of using prefabricated systems over prefabricated elements include the following. They minimize: • Utility relocation • Use or addition of the right of way • Traffic phasing or staging • Traffic detours or delays over an extended period They also preserve the existing roadway alignment with no temporary alignments. DOTs across the nation want to reduce the impact of construction on the traveling public. The short schedules and traffic benefits provided by ABC have driven their use. The decreased construction time and reduced mobility issues have become more important because many bridges are approaching the end of their service life, and the demands on transportation infrastructure are increasing. ABC is known for improving work zone safety and site constructability. They also decrease traffic impacts, total project delivery time, on-site construction time and the work zone road user cost because all these benefits are interrelated. The work zone is defined as a road segment in which maintenance or construction activities impact the number of lanes available to traffic or the characteristics of traffic traveling through the roadway segment. Work zone road user cost is defined as the “additional costs borne by motorists and the community at-large” due to maintenance or construction activities in the work zone. It includes travel delay costs, vehicle operating costs, crash costs, noise, business impacts and inconvenience to the local community.8 Travel delay costs can be quantified by the additional travel time required to pass through the work zone or use a detour and the monetary value of the travel time for a person or business.8 On the other hand, negative business impacts from roadway construction are harder to quantify. They include, but are not limited to, customer access and parking, delivery access, utility outages or disruptions, temporary or permanent loss of customers, decrease in sales and profit, and decrease in property or land values.8 All ABC technology increases work zone safety for construction workers and commuters by reducing on-site construction time and distractions. The reduction in on-site construction time reduces actual construction time and the number and length of road closures. It also removes lengthy detours and prevents construction crews from working adjacent to traffic. Crashes are an ever-present hazard in both road and bridge construction zones due to distractions and road changes, but “[44%] of bridge construction worker injuries involve a vehicle traveling through a work zone and two-thirds of these injuries are fatal.”9 While “the long-term presence of contractor-related equipment, labor and staging areas can present driver distractions,”3 using ABC with SPMTs provides an even higher level of safety. It removes traffic from the equation because construction teams complete bridge construction in staging areas away from live traffic. The reduction in road closures, detours and traffic phasing often helps decrease the bridge planning time and reduce the bridge construction time and total project costs. Bridge construction time can be reduced by years with ABC, which directly decreases construction time and project cost. Total project costs for traditional construction can include a rightof-way acquisition, project administration, utility relocation and maintenance of traffic through lane or road closures and detours. Lane closures, or even road closures and the resultant detours, can quickly consume a project’s budget and cost more than the construction itself by the time the work has been completed. Any traffic detour can become prohibitively expensive when direct and indirect project costs are considered. This drawback is particularly apparent with “full-lane closures in large urban centers or on highways with high traffic volumes [that] can have a significant economic impact” on nearby businesses, industries and private homes.10 ABC methods can be helpful for bridge building in wetlands, near endangered species, or areas with low noise thresholds. Still, ABC may not be the best solution for bridges with multiple spans, bridges in areas where traffic volume is low, or when the bridge owners do not have the financial capability to pay for the additional costs incurred by using ABC. In those instances, conventional construction is often the better choice. The substructures of many bridges in Utah constructed using ABC were built using conventional, sequential construction methods. Bridge supports bear on the foundations, so the foundations were placed before the bridge columns and abutments were constructed. Any reinforced concrete bridge supports would need to cure before any bridge girders could be placed. Then the concrete deck would be placed and require additional time to cure before any parapets could be placed on the deck or people could drive on the bridge deck. One of the largest contributors to the time required for bridge construction using traditional methods is the time required to allow concrete to cure and reach full strength. Reinforced concrete is often used for bridge supports, abutments, girders and decks. A large section of the bridge closure schedule must be dedicated to concrete cure times because most of the cure times cannot occur in parallel with the construction sequence. The abutments and the bridge supports could be constructed and cured in parallel. Still, both those structural elements must be cured and reach the minimum calculated strength before any girders could be placed or constructed for the bridge. Once the girders are in place and (if made from concrete) cured, the concrete bridge deck must be placed and cured before the bridge can be used. Even when the bridge girders are steel instead of concrete, the remaining elements mentioned previously still require significant time to cure. 35
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