Guest Editors
Ethan Coffel Dartmouth College
Irene Dedoussi Delft University of Technology
Steven Barrett Massachusetts Institute of Technology
Paul Williams University of Reading
Scope
Besides their significant socioeconomic benefits, transportation systems have environmental externalities. Through the emissions from combustion of fossil-derived fuels, transportation systems contribute to degraded air quality, as well as a changing climate. Transportation also leads to noise pollution, water pollution, and affects ecosystems through multiple direct and indirect interactions. With the continuous growth in transportation, increasingly shifting to high-speed transportation modes, these externalities are expected to grow.
At the same time, transportation systems will also be impacted by environmental change. The aviation sector may contend with increased atmospheric turbulence and heat-related degradation of aircraft performance. The marine sector may have access to new shipping routes as sea ice melts. Roads may be subjected to more freeze-thaw cycles in some areas, and both road and rail systems could experience direct heat damage in others. More frequent weather extremes may disrupt infrastructure, causing ripple effects throughout transportation networks. In addition, new climate policies around the world may necessitate significant changes to transportation systems in order to reduce their greenhouse gas emissions. These and other impacts of climate and environmental change on transportation infrastructure, emphasise the necessity of incorporating an understanding of our non-stationary climate into future transportation planning and investment decisions.
This focus collection will explore both the effects of transportation on the environment, and vice versa. All aspects of environmental change will be covered, including but not limited to air quality, health impacts, climate, noise, water quality, as well as interactions between them. In addition, all transportation systems will be covered, ranging from existing transportation modes of road, marine, rail, aviation, and integrated transportation systems, to new or promising technologies [e.g. electric vehicles, air mobility, alternative fuels or other technologies, etc.]. Contributions to both the scientific understanding, and mitigation options are welcomed.
The articles listed below are the first accepted contributions to the collection and further additions will appear on an ongoing basis.
Research
Open access
A fuel-based method for updating mobile source emissions during the COVID-19 pandemic
Colin Harkins et al 2021 Environ. Res. Lett. 16 065018
The COVID-19 pandemic and ensuing lockdown of many US States resulted in rapid changes to motor vehicle traffic and their associated emissions. This presents a challenge for air quality modelling and forecasting during this period, in that transportation emission inventories need to be updated in near real-time. Here, we update the previously developed fuel-based inventory of vehicle emissions [FIVE] to account for changes due to COVID-19 lockdowns. We first construct a 2020 business-as-usual [BAU] case inventory and adjust the emissions for a COVID-19 case using monthly fuel sales information. We evaluate cellular phone-based mobility data products [Google COVID-19 Community Mobility, Apple COVID-19 Mobility Trends] in comparison to embedded traffic monitoring sites in four US cities. We find that mobility datasets tend to overestimate traffic reductions in April 2020 [i.e. lockdown period], while fuel sales adjustments are more similar to changes observed by traffic monitors; for example, mobility-based methods for scaling emissions result in an approximately two-times greater estimate of on-road nitrogen oxide [NOx] reductions in April 2020 than we find using a fuel-based method. Overall, FIVE estimates a 20%–25% reduction in mobile source NOx emissions in April 2020 versus BAU, and a smaller 6%–7% drop by July. Reductions in April showed considerable spatial heterogeneity, ranging from 6% to 39% at the state level. Similar decreases are found for carbon monoxide [CO] and volatile organic compounds. Decreases to mobile source NOx emissions are expected to lower total US anthropogenic emissions by 9%–12% and 3%–4% in April and July, respectively, with larger relative impacts in urban areas. Changes to diurnal and day-of-week patterns of light- and heavy-duty vehicular traffic are evaluated and found to be relatively minor. Beyond the applicability to modelling air quality in 2020, this work also represents a methodology for quickly updating US transportation inventories and for calibrating mobility-based estimates of emissions.
Open access
The social costs of health- and climate-related on-road vehicle emissions in the continental United States from 2008 to 2017
Sarah E Zelasky and Jonathan J Buonocore 2021 Environ. Res. Lett. 16 065009
Local and state policymakers have become increasingly interested in developing policies that both reduce greenhouse gas [GHG] emissions and improve local air quality, along with public health. Interest in developing transportation-related policies has grown as transportation became the largest contributing sector to GHG emissions in the United States in 2017. Information on current emissions and health impacts, along with trends over time, is helpful to policymakers who are developing strategies to reduce emissions and improve public health, especially in areas with high levels of transportation-related emissions. Here, we provide a comprehensive assessment of the public health and climate social costs of on-road emissions by linking emissions data generated by the U.S. Environmental Protection Agency to reduced complexity models that provide impacts per ton emitted for pollutants which contribute to ambient fine particulate matter, and the social costs of GHG emissions from on-road transportation. For 2017, social costs totaled $184 billion [min: $78 billion; max: $280 billion] for all on-road emissions from the eight health and climate pollutants that we assessed in the continental U.S. [in $2017 USD]. Within this total social cost estimate, health pollutants constituted $93 billion of the social costs [min: $52 billion; max: $146 billion], and climate pollutants constituted $91 billion [min: $26 billion; max: $134 billion]. The majority of these social costs came from CO2 followed by NOx emissions from privately owned individual vehicles in urban counties [CO2 contributed $51 billion and NOx contributed $16 billion in social costs from individual vehicles in urban counties]. However, it is important to note that not all the attention should be placed solely on individual vehicles. Although the climate social costs of individual vehicle emissions are higher than those from commercial vehicles in urban counties [by two to eight times depending on the climate pollutant], the health social costs of individual vehicle emissions are roughly equal to those from commercial vehicles in urban counties. Regardless of each pollutant's contributions to the social costs, the highest social benefits from reducing 1 ton of CO2 and its co-pollutants would occur in urban counties, given their high population density.
Open access
Mortality-based damages per ton due to the on-road mobile sector in the Northeastern and Mid-Atlantic U.S. by region, vehicle class and precursor
Calvin A Arter et al 2021 Environ. Res. Lett. 16 065008
On-road vehicular emissions contribute to the formation of fine particulate matter and ozone which can lead to increased adverse health outcomes near the emission source and downwind. In this study, we present a transportation-specific modeling platform utilizing the community multiscale air quality model [CMAQ] with the decoupled direct method [DDM] to estimate the air quality and health impacts of on-road vehicular emissions from five vehicles classes; light-duty autos, light-duty trucks [LDT], medium-duty trucks, heavy-duty trucks [HDT], and buses [BUS], on PM2.5 and O3 concentrations at a 12 × 12 kilometer scale for 12 states and Washington D.C. as well as four large metropolitan statistical areas in the Northeast and Mid-Atlantic U.S. in 2016. CMAQ-DDM allows for the quantification of sensitivities from individual precursor emissions [NO
Open access
Environmental and economic impact of electric vehicle adoption in the U.S
Zhenhua Chen et al 2021 Environ. Res. Lett. 16 045011
Battery electric vehicles [BEVs] have received increasing attention in recent years as BEV technical capabilities have rapidly developed. While many studies have attempted to investigate the societal impacts of BEV adoption, there is still a limited understanding of the extent to which widespread adoption of BEVs may affect both environmental and economic variables simultaneously. This study intends to address this research gap by conducting a comprehensive impact assessment of BEV adoption. Using demand estimates derived from a discrete choice experiment, the impact of various scenarios is evaluated using a computable general equilibrium model. Three drivers of BEV total cost of ownership are considered, namely, subsidy levels, cash incentives by manufacturers, and fuel costs. Furthermore, in light of current trends, improvements in BEV battery manufacturing productivity are considered. This research shows that changes in fuel price and incentives by manufacturers have relatively low impacts on GDP growth, but that the effect of subsidies on GDP and on BEV adoption is considerable, due to a stimulus effect on both household expenditures and on vehicle-manufacturing-related sectors. Productivity shocks moderately impact GDP but only affect BEV adoption in competitive markets. Conversely, the environmental impact is more nuanced. Although BEV adoption leads to decreases in tailpipe emissions, increased manufacturing activity as a result of productivity increases or subsidies can lead to growth in non-tailpipe emissions that cancels out some or all of the tailpipe emissions savings. This demonstrates that in order to achieve desired emissions reductions, policies to promote BEV adoption with subsidies should be accompanied by green manufacturing and green power generation initiatives.
Open access
Mitigation of CO2 emissions from international shipping through national allocation
Henrik Selin et al 2021 Environ. Res. Lett. 16 045009
Neither international treaties nor domestic policies control carbon dioxide [CO2] emissions from international shipping. To enhance mitigation, a new multilateral mechanism could allocate these emissions to national carbon budgets, where different options could be used based on the location of industry actors and ships. We analyze five allocation options, showing that a clear majority of CO2 emissions would be distributed to ten countries under each option; however, the top ten countries vary across allocation options and the amount of CO2 emissions allotted to individual countries could increase their carbon budgets thousand-fold or more. We further examine how the different objectives, principles for decision-making, and geographical coverage of the United Nations Framework Convention on Climate Change [UNFCCC] and the International Maritime Organization influence the design and implementation of an allocation mechanism under each of these two bodies. We find that the allocation mechanism that best meets criteria related to effectiveness and equity would be one in which emissions are assigned to countries of ship owners, and which operates under the UNFCCC.
Open access
Monthly analyses of convection-related irregular flights and their linear projections for the future climate in China
Yuntao Zhou et al 2021 Environ. Res. Lett. 16 035003
Convective weather such as thunderstorms and rain is one of the main causes of irregular flights including delays, cancelations, turnbacks and diversions. In China, summer [April–September] flights accounted for 94% of irregular flights due to convective weather in 2016–2019. The impact of summer convective weather conditions on irregular flights is however not well understood. In this research, we find that thunderstorms, as indicated by the lifted index [LI], are greatly related to these irregular flights over Southeast China. The global climate model ensemble indicates there will be robust increases in the occurrence of convective weather environments in response to further global warming. We also find that as the LI is decreasing over time, the likelihood of thunderstorm-related irregular flights is increasing. Such an increase indicates there will be a 17% increase in irregular flights by the end of the century.
Open access
Reducing transatlantic flight emissions by fuel-optimised routing
Cathie A Wells et al 2021 Environ. Res. Lett. 16 025002
After decades of limited situational awareness for aircraft flying in the mid-North Atlantic, full satellite coverage will soon be available. This opens up the possibility of altering flight routes to exploit the wind field fully. By considering flights between New York and London, from 1 December, 2019 to 29 February, 2020, it is shown how changes to current practice could significantly reduce fuel use and, hence, greenhouse gas emissions. When airspeed and altitude are constant, the fuel flow rate per unit time is constant and the route with the minimum journey time uses the least fuel. Optimal control theory is used to find these minimum time routes through wind fields from a global atmospheric re-analysis dataset. The total fuel burn and, hence, the emissions [including CO2] are proportional to the 'air distance' [the product of airspeed and flight time]. Minimum-time routes are compared with the actual routes flown through the wind fields. Results show that current flight tracks have air distances that are typically several hundred kilometres longer than the fuel-optimised routes. Potential air distance savings range from 0.7% to 7.8% when flying west and from 0.7% to 16.4% when flying east, depending on airspeed and which of the current daily tracks is used. Thus, substantial reductions in fuel consumption are possible in the short term. This is in contrast to the incremental improvements in fuel-efficiency through technological advances, which are high cost, high risk and take many years to implement.
Open access
Regional sensitivities of air quality and human health impacts to aviation emissions
Flávio D A Quadros et al 2020 Environ. Res. Lett. 15 105013
Emissions from civil aviation degrade air quality, and have been estimated to lead to ∼16 000 premature deaths annually. Previous studies have indicated that aviation emissions in different regions have varying corresponding air quality and human health impacts. Given the global nature of aviation activity and its forecasted regionally heterogeneous growth, this phenomenon poses challenges in aviation air quality decision making. In this study, we quantify the differences in the regional air quality responses to aviation emissions, and analyze their drivers. Specifically, we use the GEOS-Chem atmospheric chemistry-transport model to quantify the regional fine particulate matter [PM2.5] and ozone sensitivity to aviation emissions over Asia, Europe, and North America for 2005. Simulations with perturbed regional aviation emissions are used to isolate health impacts of increases in aviation emissions originating from and occurring in different regions. Health impacts are evaluated as premature mortality attributed to both landing and takeoff and cruise emissions. We find that the sensitivity of PM2.5 global population exposure to full-flight emissions over Europe is 57% and 65% higher than those to emissions over Asia and North America, respectively. Additionally, the sensitivity of ozone global population exposure to aviation emissions over Europe is larger than to emissions over Asia [32%] and North America [36%]. As a result, a unit of fuel burn mass over Europe results in 45% and 50% higher global health impacts than a unit of fuel burn mass over Asia and North America, respectively. Overall, we find that 73% and 88% of health impacts from aviation emissions over Europe and North America, respectively, occur outside the region of emission. These results suggest that inter-regional effects and differences in regional response to emissions should be taken into account when considering policies to mitigate air quality impacts from aviation, given the projected spatially heterogeneous growth in air transportation.
Open access
Impact of climate variabilities on trans-oceanic flight times and emissions during strong NAO and ENSO phases
Jung-Hoon Kim et al 2020 Environ. Res. Lett. 15 105017
This study investigates the impact of the North Atlantic Oscillation [NAO] and El Niño Southern Oscillation [ENSO] on trans-oceanic round-trip flight times and consequent CO2 emissions over the north Atlantic and eastern Pacific regions. For three strongest winter periods of both polarity during 1979–2016, daily mean wind data are used to compute the wind-optimal flight trajectories at cruising altitudes. Results show that intensified upper-level jet streams during the +NAO winters provide stronger headwinds for westbound flights between the eastern US and the western Europe. This causes 4.24 ∼ 9.35 min increase in an averaged total round-trip journey time during the +NAO compared to −NAO winters. In the eastern Pacific region, the jet stream is extended eastward towards the southwestern US during the +ENSO period, which lengthens the travel time for westbound flights between Hawaii and the west coast of the US. The increase in travel time of westbound flights is greater than the corresponding decrease in travel time for eastbound flights, resulting in a 5.92 ∼ 8.73 min increase of the averaged total round-trip time during the +ENSO compared to the −ENSO periods. Extrapolating these results to overall trans-oceanic air traffic suggests that aircraft will take a total of 1908 ∼ 4207 [888 ∼ 1309] extra hours during the +NAO [+ENSO] than the −NAO [–ENSO] winters over the North Atlantic [Eastern Pacific] regions, requiring 6.9 ∼ 15 [3.2 ∼ 4.7] million US gallons of extra fuel burned at a cost of 21 ∼ 45 [9.6 ∼ 14] million US dollars and 66 ∼ 144 [31 ∼ 45] million kg of extra CO2 emissions to all trans-oceanic traffic. In +ENSO and +NAO winters, the chances of a given flight having a slower round-trip flight time with more fuel burn and CO2 emissions are 2–10 times higher than in a −ENSO or −NAO winter. These results have significant implications for the planning of long-term flight routes with climate variability.
Open access
How does weather affect the use of public transport in Berlin?
K M Nissen et al 2020 Environ. Res. Lett. 15 085001
The effect of weather on public transport usage in Berlin is analysed. The number of single and day tickets sold is used as a proxy for the number of occasional public transport users. Analysing more than three years of hourly ticket sale data, it is shown that the most important factor influencing ticket sales is temperature. Temperatures below −5°C lead to an increase in ticket sales by up to 30% on working days, while on hot days [> 28°C] passenger numbers drop by up to 5%. Precipitation increases the number of sales on working days by up to 5%. On weekends, the lowest ticket-sale numbers are associated with wet and either very cold or very hot conditions. Another factor influencing ticket sales is sunshine duration, while wind and snowfall do not seem to play a role for ticket sales in Berlin. It is demonstrated that it is possible to predict ticket sales depending on date, time and weather conditions using a statistical model.
On designated public transport routes the effect of weather on passenger numbers can be much stronger than the district average. This is shown for the example of a bus route to a public beach. With each degree of temperature increase, passenger numbers on this line go up by approximately 30%.
Open access
The recent and future health burden of the U.S. mobile sector apportioned by source
Kenneth Davidson et al 2020 Environ. Res. Lett. 15 075009
Mobile sources emit particulate matter as well as precursors to particulate matter [PM2.5] and ground-level ozone, pollutants known to adversely impact human health. This study uses source-apportionment photochemical air quality modeling to estimate the health burden [expressed as incidence] of an array of PM2.5- and ozone-related adverse health impacts, including premature death, attributable to 17 mobile source sectors in the US in 2011 and 2025. Mobile sector-attributable air pollution contributes a substantial fraction of the overall pollution-related mortality burden in the U.S., accounting for about 20% of the PM2.5 and ozone-attributable deaths in 2011 [between 21 000 and 55 000 deaths, depending on the study used to derive the effect estimate]. This value falls to about 13% [between 13 000 and 37 000 deaths] by 2025 due to regulatory and voluntary programs reducing emissions from mobile sources. Similar trends across all morbidity health impacts can also be observed. Emissions from on-road sources are the largest contributor to premature deaths; this is true for both 2011 [between 12 000 and 31 000 deaths] and 2025 [between 6700 and 18 000 deaths]. Non-road construction engines, C3 marine engines and emissions from rail also contribute to large portions of premature deaths. Across the 17 mobile sectors modeled, the PM2.5-attributable mortality and morbidity burden falls between 2011 and 2025 for 12 sectors and increases for 5. Ozone-attributable mortality and morbidity burden increases between 2011 and 2025 for 10 sectors and falls for 7. These results extend the literature beyond generally aggregated mobile sector health burden toward a representation of highly-resolved source characterization of both current and future health burden. The quantified future mobile source health burden is a novel feature of this analysis and could prove useful for decisionmakers and affected stakeholders.