CO2 emissions associated with hubbing activities in air transport: an international comparison

Hubbing is an important operational practice in air transport. Many studies have been conducted to examine the benefits and impacts of hubbing from an economic perspective. However, its impact on CO₂ emissions, especially across different air spaces, is not well understood. This paper explores the impact of hubbing activities in air transport from an environmental perspective. With a detailed methodology and data from the Greek and Hong Kong/Sanya flight information regions (FIRs), three levels of CO₂ emissions are estimated: airport-based, airspace-based and flight-based. After contrasting the CO₂ emission efficiencies of Athens International Airport (AIA) and the Hong Kong International Airport (HKIA), aircraft type and flight distance are examined to explain their emission efficiency differences. It is found that HKIA is associated with poorer CO₂ emission efficiency at the airport and airspace levels because of the larger aircraft and longer flight distance. However, when CO₂ emission efficiency at the flight level is considered, HKIA, with a higher passenger load factor, performs better. Major international hub airports should implement additional environmental measures to minimize the impact of hubbing activities on CO₂ emissions at the airport and airspace levels.     

Investigations on the distribution of air transport traffic and CO2 emissions within the European Union

This study analyses the structure of air traffic and its distribution among the different countries in the European Union, as well as traffic with an origin or destination in non-EU countries. Data sources are Eurostat statistics and actual flight information from EUROCONTROL. Relevant variables such as the number of flights, passengers or cargo tonnes and production indicators (RPKs) are used together with fuel consumption and CO₂ emissions data. The segmentation of air traffic in terms of distance permits an assessment of air transport competition with surface transport modes.The results show a clear concentration of traffic in the five larger countries (France, Germany, Italy, Spain and UK), in terms of RPKs. In terms of distance the segment between 500 and 1000 km in the EU, has more flights, passengers, RTKs and CO₂ emissions than larger distances. On the environmental side, the distribution of CO₂ emissions within the EU Member States is presented, together with fuel efficiency parameters. In general, a direct relationship between RPKs and CO₂ emissions is observed for all countries and all distance bands. Consideration is given to the uptake of alternative fuels. Segmenting CO₂ emissions per distance band and aircraft type reveals which flights contribute the most the overall EU CO₂ emissions. Finally, projections for future CO₂ emissions are estimated, according to three different air traffic growth and biofuel introduction scenarios.     

Uncovering the spatiotemporal patterns of CO2 emissions by taxis based on Individuals' daily travel

Traffic-related carbon dioxide (CO₂) emissions have become a major problem in cities. Especially, the CO₂ emissions induced by taxis account for a high proportion in total CO₂ emissions. The availability of taxi trajectory data presents new opportunities for addressing CO₂ emissions induced by taxis. Few previous studies have analyzed the impact of human trips on CO₂ emissions. This paper investigates trip-related CO₂ emission patterns based on individuals' travel behavior using taxi trajectory data. First, we propose a trip purpose inference method that takes into account the spatiotemporal attractiveness of POIs to divide human trips into different types. Further, we reveal the spatiotemporal patterns of CO₂ emissions from various types of trips, including temporal regularity and periodicity as well as spatial distribution of “black areas”. Finally, comparative analysis of CO₂ emissions for different kinds of trips based on trip behavior is conducted using three variables, namely trip distance, trip duration and trip speed. This study is helpful for us to understand how to make travel and cities more sustainable through modifying people's trip behaviors or taxi trips.     

Emissions,performance, and design of UK passenger vehicles

Consumer, legal, and technological factors influence the design, performance, and emissions of light-duty vehicles (LDVs). This work examines how design choices made by manufacturers for the UK market result in emissions and performance of vehicles throughout the past decade (2001–2011). LDV fuel consumption, CO₂ emissions, and performance are compared across different combinations of air and fuel delivery system using vehicle performance metrics of power density and time to accelerate from rest to 100 km/h (62 mph, t_z-62). Increased adoption of direct injection and turbocharging technologies helped reduce spark ignition (SI, gasoline vehicles) and compression ignition (CI, diesel vehicles) fuel consumption by 22% and 19%, respectively, over the decade. These improvements were largely achieved by increasing compression ratios in SI vehicles (3.6%), turbocharging CI vehicles, and engine downsizing by 5.7–6.5% across all technologies. Simultaneously, vehicle performance improved, through increased engine power density resulting in greater acceleration. Across the decade, t_z-62 fell 9.4% and engine power density increased 17% for SI vehicles. For CI vehicles, t_z-62 fell 18% while engine power density rose 28%. Greater fuel consumption reductions could have been achieved if vehicle acceleration was maintained at 2001 levels, applying drive train improvements to improved fuel economy and reduced CO₂ emissions. Fuel consumption and CO₂ emissions declined at faster rates once the European emissions standards were introduced with SI CO₂ emissions improving by 3.4 g/km/year for 2001–2007 to 7.8 g/km/year thereafter. Similarly, CI LDVs declined by 2.0 g/km/year for 2001–2007 and 6.1 g/km/year after.     

Critical aggressive acceleration values and models for fuel consumption when starting and driving a passenger car running on LPG

The models based on vehicle speed have been used to estimate fuel consumption and CO₂ emissions. However, these models could not properly estimate the change in fuel consumption and CO₂ emissions as the speed changes. As for the alternative method, people try to consider using acceleration instead of speed. Although acceleration has been seriously considered, determining critical aggressive acceleration value in relation to fuel consumption and CO₂ emissions is difficult to find. In this study, evaluation models of fuel consumption were developed using instantaneous acceleration, and we defined the critical aggressive acceleration values for different states of the vehicle from the viewpoints of fuel consumption and emissions. We used a mid-sized Liquefied Petroleum Gas (LPG) passenger car and obtained instantaneous data from a digital tachograph installed in the car while it accelerates. We developed two fuel consumption models and found critical aggressive accelerations, respectively: a model of starting vehicle that measures range of speed required to overcome the inertia during acceleration from stop state, and the other model for the driving state. We used Classification and Regression Tree (CART) analysis to find the critical aggressive accelerations at which the increments of fuel consumption change abruptly. As a result, the critical aggressive accelerations causing abrupt change in the increments of fuel consumption were found to be 2.598 m/s² for the starting of vehicles and 1.4705 m/s² when driving them. We also found that the increments of fuel consumption can be explained through quadratic and exponential functions with instantaneous acceleration.     

Profiling road transport activity: Emissions from 2000 to 2005 in Ireland using national car test data

This work describes a methodology for determining the average vehicle kilometres travelled by the private national car fleet in Ireland and estimating the disaggregated CO₂ and NO_x emissions from private vehicles in the Irish road transport sector for the period 2000–2005 using national car test records. The developed methodology facilitates the calculation of greatly improved estimates for vehicle kilometres under a range of constraint variables and thereby enables the disaggregated analysis of specific vehicle fleet groups and their associated activity patterns to support evidence-based policy development. The results indicate that while older vehicles are contributing significantly to car NO_x emissions; newer cars produce a higher share of CO₂ emissions than older cars in the vehicle fleet.     

Responsive relationship between energy-related carbon dioxide emissions from the transportation sector and economic growth in Beijing—Based on decoupling theory

Decoupling theory is effective to analyze the interdependence between variables and has been applied in environmental economics. However, most of the previous literature focus on “decoupling” and “recoupling” analysis, while rarely consider their driving factors. This study aims to explore the relationship between transportation CO₂ emissions and economic growth in Beijing from 1995 to 2014 by an extended Tapio elastic analysis, considering the contribution from industrial emission reduction, industrial energy saving, industrial operating efficiency, and industrial development. The entire decoupling state between transportation CO₂ emissions and economic growth changed with time. From 1995 to 2005, the decoupling relationship between transportation CO₂ emissions and economic growth exhibits a fluctuation among expansive negative decoupling, weak decoupling, and expansive coupling. Since decoupling elasticity values among industrial energy saving, industrial operating efficiency and industrial development were variably large and neutralized with each other, interaction of these decoupling elasticities may explain the fluctuation of the entire decoupling effect during this period. During the period from 2006 to 2008, the negative impact of industrial energy-saving elasticity overtook the positive one from industrial operating efficiency elasticity, which leads to worsening in the decoupling state between transportation CO₂ emissions and economic growth. The decoupling state was improved from expansive negative decoupling to weak decoupling after 2008, which can be attributed to policy-oriented practices supporting energy conservation.     

UK supply chain carbon mitigation strategies using alternative ports and multimodal freight transport operations

In the last few decades, the building evidence that CO₂e emissions lead to climate change has pointed to a need to reduce CO₂e emissions. This research uses five scenarios in the context of UK import trade to assess total CO₂e emissions and costs of import re-routing containers. The overall objective is to assess possible carbon mitigation strategies for UK supply chains by using a combination of alternative ports and revised multimodal strategies. The model adopted includes three elements: port expansion, container handling and freight transport. The alternative scenarios explore different settings modal shift and short sea shipping.     

Including aviation emissions in the EU ETS: Much ado about nothing? A review

The European Community, motivated by the rapid growth of the aviation industry and related impacts on climate change, has decided to include aviation in the European Emissions Trading Scheme (EU ETS). Mitigation policies such as the EU ETS are considered to be necessary in order to change travel behaviour and induce operational and technological changes in the aviation industry that will result in lower environmental impacts. This paper reviews the available impact assessments of the proposed emissions trading scheme for airlines published between 2005 and 2009. It analyses the methods used and finds that the models used are often over-simplified, omitting important variables or that the reliability and robustness of the modelling results are reduced by linking models that are based on different assumptions. The paper also summarises the possible environmental (CO₂ emissions) and economic (air fares, demand for airline services, supply of airline services, competitiveness, GDP, carbon price) impacts in the studies reviewed for the year 2020. Overall, the effects are found to be small: for example, CO₂ emissions are expected to decline by a maximum of 3.8% and the maximum impact on GDP in the EU was found to be ?0.002%. The reasons for these insignificant impacts are analysed in this paper; it is also found that there are some positive aspects of including aviation in the EU ETS.     

Urban bus fleet-to-route assignment for pollutant emissions minimization

This study proposes a methodology to optimize the assignment of an urban bus fleet to a set of fixed routes, taking into account the differences among routes and the differences among vehicle types and propulsion technologies in order to reduce pollutant emissions (CO₂, CO, THC, NO_x and PM). A Mixed Integer Linear Programming optimization model is stated and two scenarios are assessed: minimization of CO₂ and NO_x. The results show that it is feasible to obtain a fleet distribution in which emissions for any given pollutant are reduced without increase in emissions of other pollutants.     

Tourism travel under climate change mitigation constraints

The paper first describes an inventory for 2005 giving the tourism related CO₂ emission caused by global tourism, and presents a 30-year projection and a 45-year simulation. The study found that tourists cause 4.4% of global CO₂ emissions. Also these emissions are projected to grow at an average rate of 3.2% per year up to 2035. This increase is problematic as globally a reduction of emissions by 3–6% is required to avoid ‘dangerous’ climate change. Using contemporary scenario techniques it appeared difficult to find a future tourist travel system consistent with CO₂ emission reductions of up to 70% by 2050 with respect to 2005. Based on the model underlying the 30-year projection, 70 scenarios are presented in a ‘landscape’ graph exploring the effect of opportunities to reduce the emissions, but this attempt did not reach the large reductions envisaged. We therefore explored automated scenario generation as a way to define backcasting scenarios that both reach the emission reduction target and retain the highest possible economic value for the sector. The main contributions made by this study are (1) in comparing the value of different ways to approach a (desired) future and (2) giving insight into the kind of structural changes required within tourism and tourism transport in case very strong emission reductions are required. Finally the model showed signs of ‘complex’ behaviour.     

Transitions to low carbon transport futures: strategic conversations from London and Delhi

Climate change is a global problem and across the world there are major difficulties being experienced in reducing carbon dioxide (CO₂) emissions. The transport sector in particular is finding it difficult to reduce CO₂ emissions. This paper reports on two studies carried out by the authors in London (UK) and Delhi (India). It considers the common objectives for transport CO₂ reduction, but the very different contexts and baselines, potentials for change, and some possible synergies.Different packages of measures are selected and scenarios developed for each context which are consistent with contraction and convergence objectives. CO₂ reduction potentials are modelled and quantified by package and scenario. London is considering deep reductions on current transport CO₂ emission levels; Delhi is seeking to break the huge projected rise in transport CO₂ emissions.The scale of policy intervention required to achieve these goals is huge and there is certainly little public discussion of the magnitude of the changes required. The paper argues for a ‘strategic conversation’ at the city level, using scenario analysis, to discuss the priorities for intervention in delivering low carbon transport futures. A greater focus is required in developing participatory approaches to decision making, alongside network investments, urban planning, low emission vehicles and wider initiatives. Aspirations towards equitable target emissions may assist in setting sufficiently demanding targets. Only then is a wider awareness and ownership of potential carbon efficient transport futures likely to take place.     

Examining the carbon emission impact of livelihood transitions in pro-poor tourism

This study examines carbon dioxide (CO₂) emission changes from livelihood transitions during tourism development to assess the environmental impact of pro-poor tourism (PPT) in China. The results indicate that livelihood transitions during PPT increased household income but also produced more CO₂ emissions. CO₂ emissions vary depending on factors including livelihood types after transition, income and household sizes, etc. The CO₂ per unit of income from tourism-based livelihoods is higher than from non-tourism-based livelihoods. Different livelihood strategies post transition also affect emissions. Practical suggestions that may mitigate emissions while not compromising residents’ income levels are provided.     

A carbon footprint analysis of renewable energy technology adoption in the modal substitution of high-speed rail for short-haul air travel in Australia

This study presents a carbon footprint analysis of renewable energy technology adoption in the modal substitution of high-speed rail for short-haul air travel in Australia. The carbon footprint analysis of renewable energy technology adoption in such modal substitution establishes the efficacy of various renewable energy technologies in assisting CO₂ emissions reduction on the Sydney–Melbourne city pair. Renewable energy technology efficacy, captured in the presented low-carbon pathways for high-speed transportation, provides an indication as to the CO₂ emissions reduction potential of the technologies under consideration and their impact upon the environmental performance of the air and high-speed rail modes. These low-carbon pathways displayed a reduction in annual CO₂ emissions throughout the longitudinal period ranging from moderate to significant. Furthermore, this study examines the cumulative effects of the considered renewable energy technologies upon the annual CO₂ emissions production of the high-speed transportation system. A reduction of 56%–69% in annual life cycle CO₂ emissions demonstrated the powerful mitigation potential of a combined air and high-speed rail transportation system in conjunction with renewable energy technologies adoption and a modal shift of 60%. Given this significant mitigation potential, the hybridization of the air and high-speed rail transportation systems with associated renewable energy technologies is considered. The effect of such hybridization would result in the formation of an integrated low-carbon, high-speed transportation system underpinned by the concept of “sustainable mobility” at the national level.     

Comparing the impacts of local land use and urban spatial structure on household VMT and GHG emissions

To highlight the role of sustainable urban spatial structure in reducing household vehicle miles traveled (VMT) and CO₂ emissions, this empirical study of the 121 largest urban areas (UAs) in the U.S. compares the effects of local land use and UA scale spatial structure in a multilevel analysis framework. The results show that centralized population and mezzo scale jobs-housing balance as well as higher UA population density can significantly reduce VMT and CO₂ emissions. The combined effects of all UA level variables, including population-weighted density (PWD), are found to be on par with the elasticity of VMT with regard to a census tract level compactness index. Further, we find that urban spatial structure moderates local urban form effects on travel behavior. For example, while 10% more compact census tracts are associated with 5% fewer VMT in UAs with the sample average PWD, such as St. Louis and Pittsburgh, this estimated local effect increases to 7.5% and 10% in UAs where PWD is as high as in Chicago and New York, respectively. The findings of this study strongly support policy programs that aim to boost “articulated densities” in the urban region and call for stronger institutional frameworks for regional planning.     

Measuring the potential implications of introducing a cap and share scheme in Ireland to reduce green house gas emissions

This paper examines some of the potential impacts of introducing a cap and share scheme in Ireland. Under such a scheme a cap or limit is placed on national CO₂ emissions and individuals are allocated an annual CO₂ allowance. The research presented in this paper focuses on travel-to-work trips specifically. CO₂ emissions for these annual work trips are calculated and a cap is determined based on these results. Cap levels are set based on average emissions and a 20% reduction in average emissions as per Ireland's reduction targets. A national and Dublin only cap are examined and the results are presented as a means of comparison. Binary logistic models are used to determine the socio-economic characteristics of individuals who fall above and below the cap. The results demonstrate the importance of car ownership, journey distance, mode choice and household composition in determining whether a commuter is above or below the cap. Many commuters who fall above the cap are likely drive to work over long distances, have dependent children in their household and own more than one car.     

Transport and climate change: a review

Transport accounts for 26% of global CO₂ emissions and is one of the few industrial sectors where emissions are still growing. Car use, road freight and aviation are the principal contributors to greenhouse gas emissions from the transport sector and this review focuses on approaches to reduce emissions from these three problem areas. An assessment of new technologies including alternative transport fuels to break the dependence on petroleum is presented, although it appears that technological innovation is unlikely to be the sole answer to the climate change problem. To achieve a stabilisation of greenhouse gas emissions from transport, behavioural change brought about by policy will also be required. Pressure is growing on policy makers to tackle the issue of climate change with a view to providing sustainable transport. Although, there is a tendency to focus on long-term technological solutions, short-term behavioural change is crucial if the benefits of new technology are to be fully realised.     

Key research themes on urban space,scale, and sustainable urban mobility

abstract

Land-use policies are frequently proposed as a means of reducing the negative impacts of transport on the environment, such as emissions of CO₂ and pollutants, and noise nuisance. In this article we discuss whether land-use policies make sense as a strategy for reducing vehicle travel and lessening environmental impacts. We conclude that they do, but that the greatest benefits may come from the enhancement of accessibility. We argue that land-use policies should be evaluated across a much broader range of benefits than is generally done at present.     

Sustainable design of a closed-loop location-routing-inventory supply chain network under mixed uncertainty

Considering economic, environmental and social impacts, this paper presents a new sustainable closed-loop location-routing-inventory model under mixed uncertainty. The environmental impacts of CO₂ emissions, fuel consumption, wasted energy and the social impacts of created job opportunities and economic development are considered in this paper. The uncertain nature of the network is handled using a stochastic-possibilistic programming approach. Furthermore, for large-sized problems, a hybrid meta-heuristic algorithm and lower bounds are developed and discussed. Finally, a real case study is provided to demonstrate the applicability of the model in real-world applications, and several in-depth analyses are conducted to develop managerial implications.     

Modeling different penetration rates of eco-driving in urban areas: Impacts on traffic flow and emissions

Climate change and air quality are two main environmental challenges in metropolitan areas. As road transportation is one of the main contributors, public administrations are facing these problems with a number of complementary policy measures: shift to cleaner modes, new fuels and vehicle technologies, demand management, and the use of information and communication technologies (ICT) applied to transportation. Eco-driving is one of the measures that present large fuel savings at individual level. Although these savings are well documented in the literature, few studies focus on how eco-drivers driving patterns affect the surrounding vehicles and the traffic in general, and more particularly what would be the impact when the number of eco-drivers grows. Using a traffic microsimulation tool, four models in urban context have been built, corresponding to the different types of urban roads. Both the base-case and the parameters setting to simulate eco-driving have been calibrated with real data collected through floating vehicles performing the trips with normal and eco behaviors. In total, 72 scenarios were simulated, varying the type of road, traffic demand, and the percentage of eco-drivers. Then, the CO₂ and NO_x emissions have been estimated through a microscopic emission model. The results show that in scenarios with low or medium demand levels and increasing number of eco-drivers, the effects are positive in terms of emissions. On the other side, with high percentage of eco-drivers and high traffic demand, the emissions rise. Higher headways and smooth acceleration and decelerations increase congestion, producing higher emissions globally.