Accelerated Construction of Roadways: Life Cycle Assessment and Environmental Impacts

Abstract

Sustainability refers to a long-term perspective of economic, social, and environmental progress, which not only addresses the present conditions but also includes the needs of future generations. The massive network of roadways in United States has the potential to contribute considerably towards achieving sustainability in the infrastructure sector. The “triple bottom line” of sustainability, if incorporated in roadway development projects, can address issues like climate change, environmental protection, funds optimization, and social equity. This study focuses on the life cycle assessment (LCA) of arterial improvement projects. Preservation treatments help in extending the remaining service life of roads; but at the same time, they may have substantial environmental impacts due to the acquisition of raw materials, transportation of the processed materials from extraction to production site, manufacturing of the final product, and the use of various equipment during the treatment process. These, in most cases, are accompanied by considerable mobility impacts on the adjacent traffic due to work-zones associated with pavement treatment activities. Accelerated construction techniques are known to have several advantages over traditional construction, such as reducing delay and congestion, decreasing safety concerns, and in turn minimizing environmental and socio-economic impacts associated with work zones. In this study, a comprehensive work zone environmental assessment (WEA) framework has been prepared, which will help highway officials to assess the environmental benefits of accelerated construction, and opt for the most suitable transportation management plan favoring the environment. Existing studies have presented LCA for pavement construction activities, mostly, on a case-study basis. This research tries to calculate and summarize the environmental effects of all the MRR activities, which can occur over the life span of a pavement. Traditional and accelerated maintenance, repair, and rehabilitation (MRR) techniques were identified for both flexible and rigid pavements. A life cycle assessment (LCA) approach was used, taking into account the life extension of the pavement for each type of strategy. The scope boundary includes only the construction activities relevant to pavement MRR. On the traffic side, the simulation models currently in use to predict the emission of work-zones are mostly static emission factor models (SEFD). SEFD calculates emissions based on average operation conditions e.g. average speed and type of vehicles. Although these models produce accurate results for large scale planning studies, they are not suitable for analyzing driving conditions at the micro level such as acceleration, deceleration, idling, cruising, and queuing in a work zone. This study addresses this gap by using an integrated traffic micro-simulation emission model, which can capture the effects of instantaneous changes in vehicle operations, and can provide an accurate prediction of traffic impacts and emissions for work zones. Software program, INTEGRATION, was used to model real life work zone traffic scenarios and traffic emissions around the area. This program is capable of computing vehicle emissions, such as hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO2) and nitrogen oxide (NOx), for eleven vehicle categories. Changes in emissions were computed by simulating traffic management plans related to traditional and accelerated pavement rehabilitation. A section of Interstate 66 was selected as a case study to demonstrate the application of this framework. Sustainability calls for reducing the above-mentioned impacts. Environmental impacts of the commonly used traditional and accelerated MRR activities were calculated in amounts of greenhouse gases emitted due to resource usage, energy consumption, and mobility impacts. Accelerated construction were found to have favorable results for both flexible and rigid pavements. In addition, a guidance model was prepared to assist agencies with selecting appropriate procurement methods and contracting strategies that accelerate construction. The research also looks into existing environmental policies, and suggests strategies to incentivize accelerated construction for stakeholders.