Climate Change

Bus and Rail Network Design and Exposure to Extreme Heat

We have developed a framework for assessing exposure to environmental conditions (e.g., extreme heat, precipitation, or cold) based on network analyses of parcels, transit networks, and transit schedules. We simulate for every residential parcel in a city how long they are exposed based on their walking times to and from transit and their waiting times at transit. Our results show that, in the case of Southwest U.S. cities, that when temperature is highest (midday), exposure is greatest due to lower headways at offpeak times. We overlay social vulnerability indices to show which neighborhoods are at greatest risk. With this information we are able to direct transit agencies towards strategic investments in schedule changes, public outreach, and communication of transit schedules to reduce these vulnerabilities.

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.

Heat Exposure and Transit Use: Travel Behavior and Infrastructure

ASU Report No. ASU-SSEBE-CESEM-2017-CPR-001

Public transit necessitates environmental exposure and there is increasing recognition that in a future with hotter temperatures new strategies are needed to protect passengers. Arizona State University’s Spring 2017 Urban Infrastructure Anatomy course assessed travel behavior, public transit stop design, and heat exposure to develop recommendations for mitigating heat exposure. Travel surveys, analysis of infrastructure characteristics, and thermal imaging were used to assess exposure. A suite of mitigation strategies was developed from a literature review, conversations with experts, and review of other transit systems. Focusing on neighborhoods in Tempe, Arizona, strategies are developed for protecting future riders from negative health outcomes.

Transit System Design and Vulnerability of Riders to Heat

Journal of Transportation and Health, 2017, 4, pp. 216-225, doi: 10.1016/j.jth.2016.07.005

In the United States public transit utilization has increased significantly in the last decade and is considered a critical component in reducing energy use and greenhouse gas emissions in urban areas. Despite public transit׳s climate change mitigation potential, the use of transit necessitates environmental exposure which may be a health hazard during periods of extreme heat. Transit system design, which includes stop location and schedules, is shown to contribute to environmental exposure resulting from access and waiting. Using Los Angeles Metro (Los Angeles County, CA) and Valley Metro (Maricopa County, AZ) as case studies of systems operating in extreme heat conditions, the research demonstrates how system design contributes to heat exposure times that vary significantly between neighborhoods. Household level access (walking) time estimates are developed using a shortest path algorithm to nearby transit stops. Waiting time estimates for individual transit stops are derived from published transit schedules and on-board survey responses. The results show that transit users from areas with low residential density, limited high capacity roadways and irregular street networks, and not located along direct paths between major activity centers are likely to experience prolonged access and/or waiting times. Public transit may help mitigate climate change impacts but transit proponents, agencies and planners should be cognizant of the impact an uncertain climate future may have on a growing base of transit riders. These insights can allow us to proactively govern and adapt transit systems to protect people from a growing health concern.

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.

Frameworks for Assessing the Vulnerability of U.S. Rail Systems to Flooding and Extreme Heat

Arizona State University Report No. ASU-SSEBE-CESEM-2015-RPR-001

Recent climatic trends show more flooding and extreme heat events and in the future transportation infrastructure may be susceptible to more frequent and intense environmental perturbations. Our transportation systems have largely been designed to withstand historical weather events, for example, floods that occur at an intensity that is experience once every 100 years, and there is evidence that these events are expected become more frequent. There are increasing efforts to better understand the impacts of climate change on transportation infrastructure. An abundance of new research is emerging to study various aspects of climate change on transportation systems. Much of this research is focused on roadway networks and reliable automobile travel. We explore how flooding and extreme heat might impact passenger rail systems in the Northeast and Southwest U.S..