Impact of Climate Change on Pavement Structural Performance in the United States

Transportation Part D, 57, pp. 172-184, doi: 10.1016/j.trd.2017.09.022

This study uses climate projections from multiple models and for different climate regions to investigate how climate change may impact the transportation infrastructure in the United States. Climate data from both an ensemble of 19 different climate models at both RCP8.5 and RCP4.5 as well as three individual prediction models at the same Representative Concentration Pathways (RCP) levels is used. These models are integrated into the AASHTOWare Pavement ME software to predict the pavement performance. Comparisons are made between the predicted performance with respect to typical pavement distresses using both historical climate data as well as climate projection data. Though there is substantial variation for different prediction models in terms of the magnitude of the impact, the consistency in results suggest that projected climate changes are highly likely to result in greater distresses and/or earlier failure of the pavement. This finding is consistent across all the climate zones studied, but varies in magnitude of 2–9% for fatigue cracking and 9–40% for AC rutting at the end of 20 years depending on the climate region of the pavement section and prediction model used. This study also compares the impacts incorporating temperature only projections with temperature and precipitation projections. In this respect, the sections considered in this study do not show any substantial difference in the pavement performance when the precipitation data from the climate predictions are also considered in the climate inputs into AASHTOWare Pavement ME software.

Progress and Challenges in Incorporating Climate Change Information into Transportation Research and Design

Journal of Infrastructure Systems, 23(4), doi: 10.1061/(ASCE)IS.1943-555X.0000377

The vulnerability of the nation’s transportation infrastructure to climate change and extreme weather is now well documented and the transportation community has identified numerous strategies to potentially mitigate these vulnerabilities. The challenges to the infrastructure sector presented by climate change can only be met through collaboration between the climate science community, who evaluate what the future will likely look like, and the engineering community, who implement our societal response. To facilitate this process, the authors asked: what progress has been made and what needs to be done now in order to allow for the graceful convergence of these two disciplines? In late 2012, the Infrastructure and Climate Network (ICNet), a National Science Foundation–supported research collaboration network, was established to answer that question. This article presents examples of how the ICNet experience has shown the way toward a new generation of innovation and cross-disciplinary research, challenges that can be address by such collaboration, and specific guidance for partnerships and methods to effectively address complex questions requiring a cogeneration of knowledge.

Increased Costs to US Pavement Infrastructure from Future Temperature Rise

Nature Climate Change, 7, pp. 704-707, doi: 10.1038/nclimate3390

Roadway design aims to maximize functionality, safety, and longevity. The materials used for construction, however, are often selected on the assumption of a stationary climate. Anthropogenic climate change may therefore result in rapid infrastructure failure and, consequently, increased maintenance costs, particularly for paved roads where temperature is a key determinant for material selection. Here, we examine the economic costs of projected temperature changes on asphalt roads across the contiguous United States using an ensemble of 19 global climate models forced with RCP 4.5 and 8.5 scenarios. Over the past 20 years, stationary assumptions have resulted in incorrect material selection for 35% of 799 observed locations. With warming temperatures, maintaining the standard practice for material selection is estimated to add approximately US$13.6, US$19.0 and US$21.8 billion to pavement costs by 2010, 2040 and 2070 under RCP4.5, respectively, increasing to US$14.5, US$26.3 and US$35.8 for RCP8.5. These costs will disproportionately affect local municipalities that have fewer resources to mitigate impacts. Failing to update engineering standards of practice in light of climate change therefore significantly threatens pavement infrastructure in the United States.

Rolling Resistance Contribution to a Road Pavement Life Cycle Carbon Footprint Analysis

International Journal of Life Cycle Assessment, 2017, 22(6), pp. 972-985, doi: 10.1007/s11367-016-1203-9

Although the impact of road pavement surface condition on rolling resistance has been included in the life cycle assessment (LCA) framework of several studies in the last years, there is still a high level of uncertainty concerning the methodological assumptions and the parameters that can affect the results. In order to adopt pavement carbon footprint/LCA as a decision-making tool, it is necessary to explore the impact of the chosen methods and assumptions on the LCA results. This paper provides a review of the main models describing the impact of the pavement surface properties on vehicle fuel consumption and analyses the influence of the methodological assumptions related to the rolling resistance on the LCA results. It compares the CO2 emissions, calculated with two different rolling resistance models existing in literature, and performs a sensitivity test on some specific input variables (pavement deterioration rate, traffic growth, and emission factors/fuel efficiency improvement). The model used to calculate the impact of the pavement surface condition on fuel consumption significantly affects the LCA results. The pavement deterioration rate influences the calculation in both models, while traffic growth and fuel efficiency improvement have a limited impact on the vehicle CO2 emissions resulting from the pavement condition contribution to rolling resistance. Existing models linking pavement condition to rolling resistance and hence vehicle emissions are not broadly applicable to the use phase of road pavement LCA and further research is necessary before a widely-used methodology can be defined. The methods of modelling and the methodological assumptions need to be transparent in the analysis of the impact of the pavement surface condition on fuel consumption, in order to be interpreted by decision makers and implemented in an LCA framework. This will be necessary before product category rules (PCR) for pavement LCA can be extended to include the use phase.

Climate Change: Potential Impacts on Frost-Thaw Conditions and Seasonal Load Restriction Timing for Low-Volume Roadways

Road Materials and Pavement Design, doi: 10.1080/14680629.2017.1302355

Low-volume roads constitute a major percentage of roadways around the world. Many of these are located in seasonal frost areas where agencies increase and decrease the allowable weight limits based on seasonal fluctuations in the load carrying capacity of the roadway due to freeze–thaw conditions. As temperatures shift due to changing climate, the timing and duration of winter freeze and spring thaw periods are likely to change, potentially causing significant impacts to local industry and economies. In this study, an ensemble of 19 climate models were used to project future temperature changes and the impact of these changes on the frost depth and timing of seasonal load changes across five instrumented pavement sites in New England. The study shows that shifts of up to 2 weeks are projected at the end of the century and that moderate variability was observed across the study region, indicating that local conditions are important for future assessments depending on the desired level of accuracy. From 1970 to 1999, the average freezing season lasted between 9 and 13 weeks in the study region. By 2000–2029, the frozen period shortens by approximately 10 days over baseline duration (10–20% reduction). By the end of the century under RCP 4.5, frozen periods are typically shorter by 4 weeks or a 30–40% reduction. However, RCP 8.5 results indicate that four out of the five sites would have no frozen period during at least six winters from 2060 to 2089.

Uncertainty in Life Cycle Costing for Long-Range Infrastructure. Part I: Leveling the Playing Field to Address Uncertainties

International Journal of Life Cycle Assessment, 2017, 22(2), pp. 277-292, doi: 10.1007/s11367-016-1154-1

Life cycle costing (LCC) is a state-of-the-art method to analyze investment decisions in infrastructure projects. However, uncertainties inherent in long-term planning question the credibility of LCC results. Previous research has not systematically linked sources and methods to address this uncertainty. Part I of this series develops a framework to collect and categorize different sources of uncertainty and addressing methods. This systematization is a prerequisite to further analyze the suitability of methods and levels the playing field for part II. Past reviews have dealt with selected issues of uncertainty in LCC. However, none has systematically collected uncertainties and linked methods to address them. No comprehensive categorization has been published to date. Part I addresses these two research gaps by conducting a systematic literature review. Sources of uncertainties were categorized according to (i) its origin, i.e., parameter, model, and scenario uncertainty and (ii) the nature of uncertainty, i.e., aleatoric or epistemic uncertainty. The methods to address uncertainties were classified into deterministic, probabilistic, possibilistic, and other methods. With regard to sources of uncertainties, lack of data and data quality was analyzed most often. Most uncertainties having been discussed were located in the use stage. With regard to methods, sensitivity analyses were applied most widely, while more complex methods such as Bayesian models were used less frequently. Data availability and the individual expertise of LCC practitioner foremost influence the selection of methods. This article complements existing research by providing a thorough systematization of uncertainties in LCC. However, an unambiguous categorization of uncertainties is difficult and overlapping occurs. Such a systemizing approach is nevertheless necessary for further analyses and levels the playing field for readers not yet familiar with the topic. Part I concludes the following: First, an investigation about which methods are best suited to address a certain type of uncertainty is still outstanding. Second, an analysis of types of uncertainty that have been insufficiently addressed in previous LCC cases is still missing. Part II will focus on these research gaps.

The Limits of Partial Life Cycle Assessment Studies in Road Construction Practices: A Case Study on the use of Hydrated Lime in Hot Mix Asphalt

Transportation Part D, 2016, 48, pp. 141-160, doi: 10.1016/j.trd.2016.08.005

Extensive published literature shows that hydrated lime improves Hot Mix Asphalt (HMA) durability. Its impact on the environmental impact of HMA has not been investigated. This paper presents a comparative Life Cycle Assessment (LCA) for the use of HMA without hydrated lime (classical HMA) and with hydrated lime (modified HMA) for the lifetime of a highway. System boundaries cover the life cycle from cradle-to-grave, meaning extraction of raw materials to end of life of the road. The main assumptions were: 1. Lifetime of the road 50 years; 2. Classical HMA with a life span of 10 years, maintenance operations every 10 years; 3. Modified HMA with an increase in the life span by 25%, maintenance operations every 12.5 years. For the lifetime of the road, modified HMA has the lowest environmental footprint compared to classical HMA with the following benefits: 43% less primary total energy consumption resulting in 23% lower emissions of greenhouse gases. Partial LCAs focusing only on the construction and/or maintenance phase should be used with caution since they could lead to wrong decisions if the durability and the maintenance scenarios differ. Sustainable construction technologies should not only consider environmental impact as quantified by LCA, but also economic and social impacts as well. Avoiding maintenance steps means less road works, fewer traffic jams and hence less CO2 emissions.

Uncertainty in Life Cycle Costing for Long-Range Infrastructure. Part II: Guidance and Suitability of Applied Methods to Address Uncertainty

International Journal of Life Cycle Assessment, 2016, 21(8), pp. 1170-1184, doi: 10.1007/s11367-016-1154-1

Life cycle costing (LCC) is the state-of-the-art method to economically evaluate long-term projects over their life spans. However, uncertainty in long-range planning raises concerns about LCC results. In Part I of this series, we developed a holistic framework of the different types of uncertainty in infrastructure LCCs. The aim of Part II is to evaluate the suitability of methods to cope with uncertainty in LCC. Part I addressed two research gaps. It presented a systematic collection of uncertainties and methods in LCC and, furthermore, provided a holistic categorization of both. However, Part I also raised new issues. First, a combined analysis of sources and methods is still outstanding. Such an investigation would reveal the suitability of different methods to address a certain type of uncertainty. Second, what has not been assessed so far is what types of uncertainty are insufficiently addressed in LCC. This would be a feature to improve accuracy of LCC results within LCC, by suggesting options to better cope with uncertainty. To address these research gaps in Part II, the suitability of methods to address uncertainties were analyzed. The suitability depends on data availability, type of data (tangible, intangible, random, non-random), screened hotspots, and tested modeling specifications. The methods include probabilistic modeling such as design of experiment or subset simulation and evolutionary algorithm and Bayesian modeling such as the Bayesian latent Markov decision process. Subsequently, the learning potential from other life cycle assessment (LCA) and life cycle sustainability assessment (LCSA) were evaluated. This analysis revealed 28 possible applications that have not yet been used in LCC. Lastly, best practices for LCC practitioners were developed. This systematic review complements prior research on uncertainty in LCC for infrastructure, as laid out in Part I. Part II concludes that all relevant methods to address uncertainty are currently applied in LCC. Yet, the level of application is different. Moreover, not all methods are equally suited to address different categories of uncertainty. This review offers guidance on what to do for each source and type of uncertainty. It illustrates how methods can address both based on current practice in LCC, LCA, and LCSA. The findings of Part II encourage a dialog between practitioners of LCC, LCA, and LCSA to advance research and practice in uncertainty analysis.

A Methodology for Robust Comparative Life Cycle Assessments Incorporating Uncertainty

Environmental Science and Technology, 2016, 50, pp. 6397-6405, doi: 10.1021/acs.est.5b04969

A methodology for conducting robust comparative life cycle assessments (LCA) by leveraging uncertainty is proposed. The method evaluates a broad range of the possible scenario space in a probabilistic fashion while simultaneously considering uncertainty in input data. The method is intended to ascertain which scenarios have a definitive environmentally preferable choice among the alternatives being compared and the significance of the differences given uncertainty in the parameters, which parameters have the most influence on this difference, and how to identify the resolvable scenarios (where one alternative in the comparison has a clearly lower environmental impact). This is accomplished via an aggregated probabilistic scenario-aware analysis, followed by an assessment of which scenarios have resolvable alternatives. Decision-tree partitioning algorithms are used to isolate meaningful scenario groups. In instances where the alternatives cannot be resolved for scenarios of interest, influential parameters are identified using sensitivity analysis. If those parameters can be refined, the process can be iterated using the refined parameters. Definitions of uncertainty quantities that have not been applied in the field of LCA and approaches for characterizing uncertainty in those quantities are presented. The methodology is then demonstrated through a case study of pavements.

Pavement Life-Cycle Assessment Framework

Federal Highway Administration Project Report

Awareness of the importance of environmental protection, and the possible impacts associated with the production, use, and retirement of products, has generated considerable interest in the use of assessment methods to better understand and address those impacts. Life-cycle assessment (LCA) is one of the techniques developed for this purpose. LCA is a structured evaluation methodology that quantifies environmental impacts over the full life cycle of a product or system, including impacts that occur throughout the supply chain. LCA provides a comprehensive approach for evaluating the total environmental burden of a product by examining all the inputs and outputs over the life cycle, from raw material production to the end-of-life (EOL). For pavements, this cycle includes the material production, design, construction, use, maintenance and rehabilitation (M&R), and EOL stages. LCA has a commonly accepted standard method (published by the International Organization for Standardization [ISO]), however, specifics within this method vary greatly from one application to another. Additionally, there are no widely accepted standards that focus on pavement-LCA. This pavement LCA framework document is an important first step in the implementation and adoption of LCA principles in the pavement community within the U.S. A framework for performing an LCA specific to pavement systems along with guidance on the overall approach, methodology, system boundaries, and current knowledge gaps are presented in this document.

Life Cycle Assessment of Pavements: Reviewing Research Challenges and Opportunities

Journal of Cleaner Production, 2016, 112(4), pp. 2187-2197, doi: 10.1016/j.jclepro.2015.09.080

An extensive growth in pavement life cycle assessment studies is noticed in recent years. Current literature in pavement life cycle assessment demonstrates a wide range of implications on environmental burdens associated with the pavements. However, immature parts still remain, needing further research, in the next years, in different stages of pavement life cycle assessment. Most of these papers focused on the implementation of new technologies on pavements construction, the use of recycled materials, and the investigation of various phases of the pavement life cycle rather than improving the applicability and the adequacy of life cycle assessment methodology to the pavement problems. These stages are based on ISO 14040 and 14044 frameworks: the goal and scope definition, the inventory analysis, the life cycle impact assessment and interpretation. In this paper, a comprehensive review (i.e. a critical review and research gaps investigation) of life cycle assessment studies on pavements was conducted. The presentation comprises (not an extensive list) inventory analysis such as surface roughness, noise, lighting, albedo, carbonation, and earthwork in addition to locally applicable data collection, consequential and temporal consideration of pavement life cycle, and sensitivity analysis. Addressing these inadequacies will permit enhanced pavement life cycle assessment studies. This will then be useful for policy makers, project managers, construction engineers, and other stakeholders in identifying prospective in sustainable development of the pavement sector.

The Importance of the Use Phase on the LCA of Environmentally Friendly Solutions for Asphalt Road Pavements

Transportation Part D, 32, pp. 97-110, doi: 10.1016/j.trd.2014.07.006

In order to assess sustainability of products and processes, different methodologies have been developed and used in the last years. In the road pavement construction area, most methodologies used for Life Cycle Assessment (LCA) are essentially focused in the construction phase. The present paper analyses the importance of the use phase of a road in the LCA of different paving alternatives, namely by evaluating energy consumption and gaseous emissions throughout the road pavement’s life. Therefore, a new LCA methodology for road pavements was developed, and the results of its application to a case study involving the construction of alternative pavement structures are discussed. The study intends to assess the influence of using more sustainable paving construction alternatives (asphalt recycling vs. conventional asphalt mixtures), and/or different surface course materials (which have a higher influence on the rolling resistance and, therefore, affect the performance during the use phase). The LCA results obtained for this case study showed that the reductions in energy consumption and gaseous emissions obtained during the use phase, for pavement alternatives with a lower rolling resistance surface course, are higher than the total amount of energy consumption and gas emissions produced during construction. It is therefore clear that some improvements in the characteristics of the surface course may have an effect over the road use phase that will rapidly balance the initial costs and gas emissions of those interventions. The LCA results obtained also showed that the sustainability of pavement construction may also be improved using recycled asphalt mixtures.

Hybrid Life Cycle Assessment for Asphalt Mixtures with High RAP Content

Resources, Conservation, and Recycling, 83, pp. 77-86, doi: 10.1016/j.resconrec.2013.12.004

With the pavement industry adopting sustainable practices to align itself with the global notion of habitable environments, there has been growing use of life-cycle assessment (LCA). A hybrid LCA was used to analyze the environmental footprint of using a reclaimed asphalt pavement (RAP) content in asphalt binder mixtures. The analysis took into consideration the material, construction, and maintenance and rehabilitation phases of the pavement life cycle. The results showed significant reductions in energy consumption and greenhouse gas (GHG) emissions with an increase in RAP content. The contribution of the construction phase to the GHGs and energy consumption throughout pavement life cycle is minimal. Feedstock energy, though not consequential when comparing asphalt mixtures only, has a significant impact on total energy. Based on LCA analysis performed for various performance scenarios, breakeven performance levels were identified for mixtures with RAP. The study highlighted the importance of achieving equivalent field performance for mixtures with RAP and virgin mixtures.

Life-Cycle Assessments of Pavements. Part I: Critical Review

Resources, Conservation, and Recycling, 55(9-10) pp. 801-809, doi: 10.1016/j.resconrec.2011.03.010

The rapidly expanding set of pavement life-cycle assessments (LCAs) available in the literature represents the growing interest in improving the sustainability of this critical infrastructure system. The existing literature establishes a foundational framework for quantifying environmental impact, but fails to deliver global conclusions regarding materials choices, maintenance strategies, design lives, and other best-practice policies for achieving sustainability goals. In order to comprehensively quantify environmental footprints and effectively guide sustainability efforts, functional units need to be standardized, systems boundaries expanded, data quality and reliability improved, and study scopes broadened. Improving these deficiencies will allow future studies to perform equitable and comparable assessments, thus creating a synergistic set of literature that continuously builds upon itself rather than generates independent and isolated conclusions. These improvements will place the body of pavement LCA research in a better position to confidently lead private industry and government agencies on successful paths towards sustainability goals.