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

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.     

A comparative study of the emissions by road maintenance works and the disrupted traffic using life cycle assessment and micro-simulation

Life cycle assessment is being accepted by the road industry to measure such key environmental impacts as the energy consumption and carbon footprint of its materials and laying processes. Previous life cycle studies have indicated that the traffic vehicles account for the majority of fuel consumption and emissions from a road. Contractors and road agencies are looking for road maintenance works that have the least overall environmental impact considering both the roadwork itself and the disrupted traffic. We review life cycle assessment studies and describe the development of a model for pavement construction and maintenance, detailing the methodology and data sources. The model is applied to an asphalt pavement rehabilitation project in the UK, and the micro-simulation program VISSIM is used to model the traffic on that road section. The simulation results are fed into a traffic emissions model and emissions from the roadwork and the traffic are compared. The additional fuel consumption and emissions by the traffic during the roadwork are significant. This indicates that traffic management at road maintenance projects should be included in the life cycle assessment analysis of such work.     

Development of commuter and non-commuter mode choice models for the assessment of new public transport infrastructure projects: A case study

This paper uses state of the art stated choice designs to parameterise modal choice models for commuting and non-commuting travel futures in the presence of new public transport infrastructure (variations of new heavy rail, light rail and dedicated busway systems). D-optimal choice experiments are developed for a set of labelled modal alternatives in which respondents establish a reference benchmark based on the existing service levels (for access, linehaul and egress trip legs) which is used in a computer aided personal interview instrument to generate future scenarios of service levels for current and prospective new modals options. We show that a fully integrated stated choice experiment provides all the information required to obtain behaviourally relevant parameter estimates (within a nested logit framework) for all but the mode-specific constants (MSCs). The MSCs can be calibrated for the current modes within a network model setting, giving the transport planner an appropriate model for predicting the patronage potential for proposed new public transport infrastructure services. A useful by-product is a new set of behavioural values of travel time savings for access, egress, linehaul and wait times.     

Development of real-world driving cycle: Case study of Pune,India

The critical component of all emission models is a driving cycle representing the traffic behaviour. Although Indian driving cycles were developed to test the compliance of Indian vehicles to the relevant emission standards, they neglects higher speed and acceleration and assume all vehicle activities to be similar irrespective of heterogeneity in the traffic mix. Therefore, this study is an attempt to develop an urban driving cycle for estimating vehicular emissions and fuel consumption. The proposed methodology develops the driving cycle using micro-trips extracted from real-world data. The uniqueness of this methodology is that the driving cycle is constructed considering five important parameters of the time–space profile namely, the percentage acceleration, deceleration, idle, cruise, and the average speed. Therefore, this approach is expected to be a better representation of heterogeneous traffic behaviour. The driving cycle for the city of Pune in India is constructed using the proposed methodology and is compared with existing driving cycles.     

Urban transportation and equity: A case study of Beijing and Karachi

Development of mega cities of Pakistan and China has greatly been affected by the growth in urbanization and motorization. The uncontrolled rise in urbanization, motorization, exclusionary planning and disproportionate investment in transportation infrastructure has created a socio-economic imbalance, thereby challenging the issue of equity. This paper focuses on a comparative social equity assessment of urban development, characteristics of supply and demand of transportation and infrastructure systems and the impact of existing strategies over equity in the development of urban and transportation system of Beijing and Karachi. The paper concludes by suggesting some strategies for the development of sustainable and equitable urban transportation systems.     

Possibilistic fuel cycle assessment of retrofit technologies for two stroke powered tricycles

Two stroke powered tricycles are a major source of air pollution in the Philippines. A fuelcycle assessment of the liquefied petroleum gas (LPG) and direct injection retrofit technologies for these vehicles is conducted. The results when compared with carbureted two and four strokes units indicate that retrofitting the units to direct injection provides lower fossil energy depletion, global warming, human toxicity and photochemical ozone formation impact potentials compared to LPG fueled carbureted two stroke tricycles while the latter exhibits lower acidification and nutrification impact values. The direct injection retrofitted units show a lower aggregated impact score and dominance over four stroke units. The conversion to LPG revealed minimal environmental benefits compared to the gasoline run units.     

Conventional,hybrid and electric vehicles for Australian driving conditions. Part 2: Life cycle CO2-e emissions

This paper is the second of a two part study which quantifies the economic and greenhouse performance of conventional, hybrid and fully electric passenger vehicles operating in Australian driving conditions. This second study focuses on the life cycle greenhouse gas emissions. Two vehicle sizes are considered, Class-B and Class-E, which bracket the large majority of passenger vehicles on Australian roads.Using vehicle simulation models developed in the first study, the trade-offs between the ability of increasingly electric powertrains in curtailing the tailpipe emissions and the corresponding rise in the embedded vehicle emissions have been evaluated. The sensitivity of the life cycle emissions to fuel, electricity and the change in the energy mix are all considered. In conjunction with the total cost of ownership calculated in the companion paper, this allows the cost of mitigating life cycle greenhouse gas emissions through electrification of passenger transport to be estimated under different scenarios. For Class-B vehicles, fully electric vehicles were found to have a higher total cost of ownership and higher life cycle emissions than an equivalent vehicle with an internal combustion engine. For Class-E vehicles, hybrids are found to be the most cost effective whilst also having lowest life cycle emissions under current conditions. Further, hybrid vehicles also exhibit little sensitivity in terms of greenhouse emissions and cost with large changes in system inputs.     

Tests of assignment accuracy: An interurban case study

This paper is concerned with methods of testing the accuracy of traffic assignments. It focuses on the fact that whereas assignment models are usually based on a behavioural hypothesis about drivers' route choice (e.g. cost or time minimisation) the test of the accuracy of the assignment is the extent to which observed link loadings are reproduced. This inconsistency opens up the doubt that an apparently “accurate” assignment on this basis may be a result of compensating errors. It is difficult to apply the same test to accuracy of route choices as is applied to accuracy of link loadings (e.g. chi square, correlation coefficient) and hence a new measure is devised here which can be applied both to comparisons between observed and predicted route choices and comparisons between observed and predicted loadings. It is, moreover, possible to devise a test of significance for this measure so that one can test whether a predicted assignment is significantly different from what one, might have observed on the basis of chance observation. A case study is carried out to test the proposed method. Traffic flows between 72 origins and destinations on either side of the Pennine Mountains in Britain are assigned to a network using different assignment techniques with varied parameters. In all, one hundred and ninety assignments are carried out and the degree of correspondence between observed and predicted route choices and link loadings is measured. The results tend to confirm that the link loadings criterion is not a very stable criterion and that the route choice correspondence criteria seems to behave in a sensible way. A simulation exercise is carried out which produces the probability distribution of the “route-fit” index for different assumed sample levels. The paper concludes by suggesting avenues for further research.     

Technical change and productivity growth in airports: A case study

This paper analyses the rate of technical progress at Portuguese airports between 1990 and 2000, using a stochastic cost frontier method. A translog frontier model is used and the maximum likelihood estimation technique is employed to estimate the empirical model. We estimate the efficient scores and disentangle the rate of technical progress into three components: pure technical progress, non-neutral technical progress and scale-augmenting technical progress. The results show that the average score is 88%, denoting a relatively high degree of waste, despite the fact that technical change contributed to a reduction in costs.     

An environmental assessment of air traffic speed constraints in the departure phase of flight: A case study at Gothenburg Landvetter Airport,Sweden

This paper considers the environmental effects of air traffic management speed constraints during the departure phase of flight. We present a CO₂ versus noise trade-off study that compares aircraft departure procedures subject to speed constraints with a free speed scenario. A departure route at Gothenburg Landvetter Airport in Sweden is used as a case study and the analysis is based on airline flight recorded data extracted from the Airbus A321 aircraft. Results suggest that CO₂ emissions could be reduced by 180 kg per flight if all departure speed constraints were removed at a cost of increased noise exposure below 70 dB(A).     

Reliable route guidance: A case study from Chicago

Reliable route guidance can be obtained by solving the reliable a priori shortest path problem, which finds paths that maximize the probability of arriving on time. The goal of this paper is to demonstrate the benefits and applicability of such route guidance using a case study. An adaptive discretization scheme is first proposed to improve the efficiency in computing convolution, a time-consuming step used in the reliable routing algorithm to obtain path travel time distributions. Methods to construct link travel time distributions from real data in the case study are then discussed. Particularly, the travel time distributions on arterial streets are estimated from linear regression models calibrated from expressway data. Numerical experiments demonstrate that optimal paths are substantially affected by the reliability requirement in rush hours, and that reliable route guidance could generate up to 5-15% of travel time savings. The study also verifies that existing algorithms can solve large-scale problems within a reasonable amount of time.     

Railway planning in developing countries: a case study of Colombia

This paper describes a study of possible network changes for the Colombian railway system. A cost model is developed and the variation of costs with traffic density and with gradient is analysed and found to be different from that expected from experience in developed countries. The evaluation of network changes is carried out by a form of systems analysis in which two new lines and many closures are examined. Closures are evaluated by means of social cost benefit analysis incorporating a consumers’ surplus approach. The study recommends fairly radical changes to the present network configuration, these involving the construction of one new line and the closure of several existing ones.     

Toward regional transportation governance: a case study of Greater Vancouver

This paper discusses the evolving institutional structure and governance of transportation planning, policy development and transit delivery within one major North American city-region, the Greater Vancouver area. Various methods of transportation governance are explored from complete independence to full regional integration. The move away from a direct provincial role in transportation management to a greater regional transit authority is discussed and critiqued. This revised version was published online in June 2006 with corrections to the Cover Date.     

Design and implementation of efficient transit networks: Procedure, case study and validity test

This paper presents and tests a method to design high-performance transit networks. The method produces conceptual plans for geometric idealizations of a particular city that are later adapted to the real conditions. These conceptual plans are generalizations of the hybrid network concept proposed in Daganzo (2010). The best plan for a specific application is chosen via optimization. The objective function is composed of analytic formulae for a concept’s agency cost and user level of service. These formulae include as parameters key demand-side attributes of the city, assumed to be rectangular, and supply-side attributes of the transit technology. They also include as decision variables the system’s line and stop spacings, the degree to which it focuses passenger trips on the city center, and the service headway. These decision variables are sufficient to define an idealized geometric layout of the system and an operating plan. This layout-operating plan is then used as a design target when developing the real, detailed master plan. Ultimately, the latter is simulated to obtain more accurate cost and level of service estimates.This process has been applied to design a high performance bus (HPB) network for Barcelona (Spain). The idealized solution for Barcelona includes 182 km of one-way infrastructure, uses 250 vehicles and costs 42,489 €/h to build and run. These figures only amount to about one third of the agency resources and cost currently used to provide bus service. A detailed design that resembles this target and conforms to the peculiarities of the city is also presented and simulated. The agency cost and user level of service metrics of the simulated system differ from those of the idealized model by less than 10%. Although the designed and simulated HPB systems provide sub-optimal spatial coverage because Barcelona lacks suitable streets, the level of service is good. Simulations suggest that if the proposed system was implemented side-by-side with the current one, it would capture most of the demand.     

Estimating the environmental benefits of ride-sharing: A case study of Dublin

Ride-sharing has often been cited as a successful method to reduce congestion and green house gas emissions. This paper examines the patterns of ride-sharing, in Dublin, and estimates the environmental benefits of ride-sharing both in terms of reductions in emissions and the vehicle kilometres travelled. Data from the 2006 Census of Ireland is used to examine the travel patterns of those that ride-share. The COPERT4 model is used in this paper to estimate the CO₂ emissions saved by ride-sharing.     

Large-scale application of MILATRAS: case study of the Toronto transit network

This paper documents the efforts to operationalize the conceptual framework of MIcrosimulation Learning-based Approach to TRansit Assignment (MILATRAS) and its component models of departure time and path choices. It presents a large-scale real-world application, namely the multi-modal transit network of Toronto which is operated by the Toronto Transit Commission (TTC). This large-scale network is represented by over 500 branches with more than 10,000 stops. About 332,000 passenger-agents are modelled to represent the demand for the TTC in the AM peak period. A learning-based departure time and path choice model was adopted using the concept of mental models for the modelling of the transit assignment problem. The choice model parameters were calibrated such that the entropy of the simulated route loads was optimized with reference to the observed route loads, and validated with individual choices. A Parallel Genetic Algorithm engine was used for the parameter calibration process. The modelled route loads, based on the calibrated parameters, greatly approximate the distribution underlying the observed loads. 75% of the exact sequence of transfer point choices were correctly predicted by the off-stop/on-stop choice mechanism. The model predictability of the exact sequence of route transfers was about 60%. In this application, transit passengers were assumed to plan their transit trip based on their experience with the transportation network; with no prior (or perfect) knowledge of service performance.     

A study on route choice preferences for commuter and non-commuter bicyclists: a case study of Kharagpur and Asansol,India

Transportation - The bicycle is one of the most affordable and flexible means of transportation in a developing country such as India. Despite being an important mode of transportation, a sharp...     

沥青路面病害成因及坑槽修补工艺

随着使用年限的增长,受行车、气候、环境及超载等多方面的影响,沥青路面会出现龟裂、坑槽、车辙等路面病害,介绍了坑槽修补工艺。     

桥面铺装层的室内试验研究及理论分析

以结构层之间的抗剪强度为主要评价指标,对铺装结构层进行系统的试验,运用ANSYS10.0有限元软件,建立典型的水泥混凝土桥面铺装结构的试验试件模型,对试验试件模型进行力学分析,得出层间应力的规律,并和试验研究的结果进行比较,在实践和理论的基础上进行相互验证。