Impact of environmental assessment and budgetary restrictions in pavement maintenance decisions: Application to an urban network

Road agencies are facing the challenges of aging pavements, deteriorating networks, and insufficient maintenance budgets. This study addresses two limitations in the current state of practice in pavement management. First, because the evaluation of maintenance strategies has traditionally focused on economic and technical aspects, it neglects the environmental impact of maintenance decisions. Second, current management systems often provide a unique, optimised pavement maintenance strategy based on a specific objective(s) and constraint(s). The main objective of the study is to analyse the effect of including environmental aspects and funding availability in the design of maintenance strategies. To achieve this objective, the study followed a three-step methodology. First, this study reviews existing practices on pavement maintenance and the criteria considered to trigger the application of maintenance treatments and their effects on pavement condition. Then, maintenance strategies are optimised considering three levels of budgetary capacity and a sustainable evaluation which incorporates technical, economic, and environmental aspects over the pavement lifecycle. Finally, a case study dealing with an urban pavement network in Chile is analysed. Results obtained from this case study show that an increment of 2% in maintenance budget allows to account for more sustainable maintenance decisions, such as cold in-place recycling and full-depth slab repair, whose greenhouse gas emissions are lower than other alternatives. Results also show that functional asphalt overlay and microsurfacing are more recommended in flexible pavements when budgetary restrictions are low, whereas recommended treatments for rigid pavements exhibit small variability with budgetary restrictions.     

A joint bottom-up solution methodology for system-level pavement rehabilitation and reconstruction

We present a methodology for the joint optimization of rehabilitation and reconstruction activities for heterogeneous pavement systems under multiple budget constraints. The proposed bottom-up approach adopts an augmented condition state to account for the history-dependent properties of pavement deterioration, and solves for steady-state policies for an infinite horizon. Genetic algorithms (GAs) are implemented in the system-level optimization based on segment-specific optimization results. The complexity of the proposed algorithm is polynomial in the size of the system and the policy-related parameters. We provide graphical presentations of the optimal solutions for various budget situations. As a case study, a subset of California’s highway system is analyzed. The case study results demonstrate the economic benefit of a combined rehabilitation and reconstruction budget compared to separate budgets.     

Incorporating socio-political criteria into the maintenance prioritization of Chilean urban pavement networks

Managing urban pavement networks presents additional challenges when compared to the management of interurban pavements. In particular, the prioritization of maintenance activities – which is critical when resources are limited – requires special considerations. Within these considerations, there are socio-political criteria that are not formally considered in current UPMS (Urban Pavement Management Systems). In practice, decision makers consider these socio-political factors but without a formal procedure and proper information, leading to decisions based on subjective information, which lack traceability and reliability.The objective of this study is the identification and formal definition – including the quantification method – of socio-political criteria relevant for the sustainable management of urban pavement networks. The research method included the application of interviews and a survey of experts and practitioners in various agencies involved in the pavement maintenance decision-making process in Chile. As a result of the study, five primary socio-political criteria were identified: neighbors’ perception, proximity to critical infrastructure, benefited population, presence of alternative routes, and strategic selection based on public policy. These criteria were formalized – including how they should be quantified – through an expert panel. A regression analysis applied to various scenarios considered in the survey resulted in the quantification of the relative importance of the formalized socio-political factors to be considered in the decision process, complementing technical and economic criteria. Future research will explore the use of Geographic Information Systems (GIS) to quantify the recommended socio-political factors and implement them in an UPMS.     

Design of an expert system for aircraft gate assignment

The task of assigning arriving flights at an airport to the available gates is a key activity in airline station operations. With the development of large connecting hub operations, and the resulting volumes of passengers and baggage transferring between flights, the complexity of the task and the number of factors to be considered have increased significantly. Traditional approaches utilizing classical operations research techniques have difficulty with uncertain information and multiple performance criteria, and do not adapt well to the needs of real-time operations support. As a result, several airlines have been exploring the use of expert systems for operational control of ramp activity.This paper discusses the factors that arise in deciding how to allocate flights to gates, and describes the knowledge base structure, data requirements and inference process of an expert system that would recommend gate allocation decisions to ramp control personnel, taking into account the constraints imposed by the available facilities and personnel to handle the aircraft, and the consequences on downstream operations of particular assignment decisions. The paper describes how these concepts have been implemented in a prototype expert system that has been designed to address a restricted set of gate assignment issues within a framework that could be extended to consider a broader range of factors. The operation of the expert system is illustrated through a case study application to a typical flight schedule at a major hub airport.     

Contribution to the design of the Athletes Bus Network during the Athens 2004 Olympic Games

This paper describes important aspects of the design of the Athletes transportation system for the Athens 2004 Olympic Games. The unique characteristics of this network include the close dependence of the vehicle schedules on the competition and training program, the requirement for 100% service reliability, as well as the requirement for full system monitoring and control. In this paper we present methods for the development of service specifications, estimation of the bus fleet size, the design of the network’s organization and management system, and corresponding critical implementation issues. All these issues are relevant to the design and management of bus transport systems for large events.     

On the dependence of acoustic performance on pavement characteristics

Acoustic-based mix design is still far from achieving a clear and accepted rationale. The three main dominions (generation, absorption, propagation) which affect pavement acoustic performance involve a number of acoustic parameters. Their relationship with pavement properties is scarcely or insufficiently known. In more detail, the parameters that define the acoustic coupling between the two phases that comprise a porous material are: porosity, resistivity, tortuosity, and viscous and thermal factors. Consequently, the spectrum of a pavement absorption coefficient depends, in particular, on tortuosity, whose relationship with HMA (hot mix asphalt) bulk properties is still an issue.Given that, the study described in this paper aimed at: (i) assessing the effect of the tortuosity on the absorption coefficient of a pavement layer; (ii) assessing the dependence of tortuosity on mix design parameters and/or mix properties; (iii) deriving a straightforward algorithm to estimate the effect of tortuosity-related properties on the absorption coefficient.Based on the above issues, an experimental plan was designed and carried out in order to study these relationships and set out a tentative theoretical and practical framework. The relationships between acoustic and traditional bulk properties of pavement mixtures were analysed. Acoustic models and hydraulic analogies were considered and, based on them, relationships were formalised and submitted to experimental validations. A simple relationship to derive tortuosity from nominal maximum aggregate size and thickness was derived. This relationship was used to derive the frequency of the first peak of the absorption spectrum, based on HMA properties. Nominal maximum aggregate size and lift thickness emerged as key factors in patterning peak frequency.Future research will address a number of issues among which the following can be listed: synergetic assessment of the influence of HMA properties on the absorption coefficient over the entire spectrum, synergetic consideration of generation and absorption factors. Practical benefits and outcomes are expected for both practitioners and researchers.     

Joint optimization of freight facility location and pavement infrastructure rehabilitation under network traffic equilibrium

Establishment of industry facilities often induces heavy vehicle traffic that exacerbates congestion and pavement deterioration in the neighboring highway network. While planning facility locations and land use developments, it is important to take into account the routing of freight vehicles, the impact on public traffic, as well as the planning of pavement rehabilitation. This paper presents an integrated facility location model that simultaneously considers traffic routing under congestion and pavement rehabilitation under deterioration. The objective is to minimize the total cost due to facility investment, transportation cost including traffic delay, and pavement life-cycle costs. Building upon analytical results on optimal pavement rehabilitation, the problem is formulated into a bi-level mixed-integer non-linear program (MINLP), with facility location, freight shipment routing and pavement rehabilitation decisions in the upper level and traffic equilibrium in the lower level. This problem is then reformulated into an equivalent single-level MINLP based on Karush–Kuhn–Tucker (KKT) conditions and approximation by piece-wise linear functions. Numerical experiments on hypothetical and empirical network examples are conducted to show performance of the proposed algorithm and to draw managerial insights.     

沥青路面抗滑性能影响因素识别研究进展

沥青路面作为公路建设的重要内容,其抗滑性能是道路安全问题的核心,探究其影响因素可以为提高路面抗滑性能提供依据。国内外学者对此做了大量研究,也取得了相应的进展。本文对国内外的研究成果进行了系统的归纳总结,将公路沥青路面抗滑性能影响因素分为了沥青混合料的材料特性、环境因素、车辆特性3个主要方面,其中在沥青混合料的材料特性方面,研究认为集料的结构特性与混合料配合比对抗滑性的影响较大;环境因素方面,研究认为温度对于抗滑性的影响较大;车辆特性对抗滑性的影响方面,研究认为主要体现在轮胎特性与荷载方面。此外随着行车速度的增加,路面的抗滑性能呈现降低趋势。     

Incorporating inspection decisions in pavement management

Pavement management systems need to address not only maintenance and rehabilitation (M&R) decisions, but also facility inspection decisions. The state of the art in pavement management is lacking of any consistent methodology for making such decisions on a cost-effectiveness basis. Such a methodology must recognize the presence of interactions between M&R and inspection decisions. These interactions argue for a joint decision-making approach, where the sum of inspection and M&R costs is minimized. This paper reviews different possible mathematical formulations to such a joint decision-making model, having various levels of restriction and computational complexity. These formulations are then compared and the effect of the forecast uncertainty on the minimum expected costs produced by each of them is investigated empirically. It is concluded that optimizing inspection decisions jointly with M&R decisions can lead to substantial cost savings, especially for high precisions of forecasting.     

Predicting asphalt pavement crack initiation following rehabilitation treatments

Prolongation of the service life of pavements requires efficient prediction of the performance of their structural condition and particularly the occurrence and propagation of cracking of the asphalt layer. Although pavement performance prediction has been extensively investigated in the past, models for predicting the cracking probability and for quantifying impacts of associated explanatory factors following pavement treatment, have not been adequately investigated in the past. In this paper the probability of alligator crack initiation following pavement treatments is modeled with the use of genetically optimized Neural Networks, The proposed methodological approach represents the actual (observed) relationships between of probability of crack initiation and the various design, traffic and weather factors as well as the different rehabilitation strategies. Data from the Long Term Pavement Performance (LTPP) Data Base and the Specific Pavement Study 5 (SPS-5) are used for model development. Results indicate that the proposed approach results in accurately predicting the probability of crack initiation following treatment; furthermore it provided information on the relationship between external factors and cracking probability that can help pavement managers in developing appropriate rehabilitation strategies.     

现代信息技术在桥梁结构无损检测中的应用

桥梁结构无损检测与评估技术的研究是当前国际上土木工程领域的难点和热点。文章结合信息技术发展的特点,探讨和总结了现代信息技术在桥梁结构无损检测与评估上的应用与发展,并对相关问题进行了讨论。     

新老路基结合部处治技术

我国已进入道路改扩建高峰期,路基拓宽、新老路基结合面临诸多技术难题。本项目通过多种技术手段相结合的方法,对路基拓宽工程的技术特征和工程问题、新老路基不协调变形的特点、计算方法及对路面结构的影响、拓宽路基的设计理论和方法、新老路基结合部处治的原理、方法和施工技术进行了深入系统的研究,提出了新老路基不协调变形的计算方法,为公路路基拓宽工程的设计和施工提供了技术基础。     

The road network management system in Slovakia

Traffic on the road network in Slovakia is increasing greatly, as a result of the country's location in central Europe. In recent years, transit truck traffic has exceeded the network's capacity causing many accidents, low vehicle speed and rapid degradation of the pavement. To deal with this situation a Road Network Management System (RNMS) has been developed. This system is based on national standards that evaluate road parameters, characteristics, and traffic levels and on new methods that consider the environmental impact and methods based on international standards (HDM III). Using these, the RNMS was developed as one homogeneous unit, not only in terms of its capacity, traffic level and economic efficiency, but also to evaluate individual sections, to optimize action, and prepare a rehabilitation budget. It took only five years to develop the RNMS because Slovakia has much relevant experience based on high level research in highway design, structural pavement design and material engineering.     

Model uncertainty and the management of a system of infrastructure facilities

The network-level infrastructure management problem involves selecting and scheduling maintenance, repair, and rehabilitation (MR&R) activities on networks of infrastructure facilities so as to maintain the level of service provided by the network in a cost-effective manner. This problem is frequently formulated as a Markov decision problem (MDP) solved via linear programming (LP). The conditions of facilities are represented by elements of discrete condition rating sets, and transition probabilities are employed to describe deterioration processes. Epistemic and parametric uncertainties not considered within the standard MDP/LP framework are associated with the transition probabilities used in infrastructure management optimization routines. This paper contrasts the expected costs incurred when model uncertainty is ignored with those incurred when this uncertainty is explicitly considered using robust optimization. A case study involving a network-level pavement management MDP/LP problem demonstrates how explicitly considering uncertainty may limit worst-case MR&R expenditures. The methods and results can also be used to identify the costs of uncertainty in transition probability matrices used in infrastructure management systems.     

Safety Effects of Winter Weather: The State of Knowledge and Remaining Challenges

Abstract

In recent years, there has been growing recognition of the effects of weather on the surface transportation system. Although considerable work has been done in quantifying the effects of weather on the highway system, there is still much that remains unknown about the relationship between weather and highway system performance. This paper synthesizes the findings from some of the major efforts in this area. The review of existing studies found consistent patterns that adverse weather reduces traffic speed and increases crash frequencies, while fatal crashes are decreased. A table is then presented which estimates the change in crash frequency and vehicle travel speed resulting from various winter weather conditions, based on a synthesis of earlier work. To estimate the safety and speed adjustment factors of compacted snow, a severity index is also developed. Recognizing the lack of comparability between the results of the studies, the paper concludes with a detailed discussion of avenues for future research which could help to address some of the gaps which currently exist. These challenges include, but are no limited to: quantification of the dynamic layer, development of the relationship between pavement friction and the composition of the dynamic layer, evaluation of the effects of pavement friction on vehicle speed, and evaluation of safety effects of weather conditions above the pavement.     

A knowledge-based decision support architecture for advanced traffic management

Fundamental to the operation of most currently envisioned Intelligent Vehicle-Roadway System (IVRS) projects are advanced systems for surveillance, control and management of integrated freeway and arterial networks. A major concern in the development of such Smart Roads, and the focus of this paper, is the provision of decision support for traffic management center personnel, particularly for addressing nonrecurring congestion in large or complex networks. Decision support for control room staff is necessary to effectively detect, verify and develop response strategies for traffic incidents. The purpose of this paper is to suggest a novel artificial intelligence-based solution approach to the problem of providing operator decision support in integrated freeway and arterial traffic management systems, as part of a more general IVRS. A conceptual design is presented that is based on multiple real-time knowledge-based expert systems (KBES) integrated by a distributed blackboard problem-solving architecture. The paper expands on the notions of artificial intelligence and Smart Roads, and in particular the role, characteristics and requirements of KBES for real-time decision support. The overall concept of a decision support architecture is discussed and the blackboard approach is defined. A conceptual design for the proposed distributed blackboard architecture is presented, and discussed in terms of the component KBES functions at an areawide level, as well as the subnetwork or individual traffic control center level.     

多年冻土区公路路面路基管理系统设计

我国多年冻土地区公路受气温及水分变化等影响,公路病害发生严重。为了使公路养护部门合理利用资金,最大限度避免冻土病害,有必要建立冻土区公路路基路面评价预测系统。文章介绍了冻土区公路路基的评价指标和评价方法。在常规路基路面评价预测的方法上,还使用了马尔可夫等预测方法,以适合冻土区公路路面破坏机理复杂、影响因素多的实际情况。     

A GIS-Based traffic accident information system

This paper describes the process of developing a GIS-based traffic accident information system. A roadway network in Kent County, Delaware, was selected to demonstrate the graphic database. The development of the graphic and attribute databases on a workstation environment is described. Software was developed to graphically represent accident information pertaining to any point on the roadway network, and outputs for typical case scenarios are presented. The software also has the capability of displaying historical accident information pertaining to the site. This aspect would be helpful to the planner or designer in studying the impact of a particular roadway design with respect to safety. Some thoughts for future extensions of this study are also presented. Finally, it is concluded that a carefully designed GIS system can efficiently help transportation professionals with traffic safety studies and that its capabilities can be extended to include other areas such as pavement and inventory management, transit applications, and executive information systems.     

A KBS application for market research advice in transport

This paper presents some results of a knowledge based system (KBS) development applied to market research (MR) issues in transport. This application represents a rule production approach to decisions associated with the definition of appropriate survey procedures for various operation‐management problems in a transport enterprise or agency. The basic idea is to provide an aid for the user (manager, student or practitioner), who is concerned with MR, but is not very familiar with this field or has some concerns over data‐gathering and the use of that information. It focuses on specific applications in the transport environment and gives the user some support in maintaining greater consistency in his (her) decisions.

The objective of this paper is to describe the system structure, to point out some important aspects and problems arising during its development and also to make some comments with respect to the further development of this and similar systems.     

Knowledge-based systems for transport network analysis: A fifth generation perspective on transport network problems

This paper considers the formative steps in the development of an expert system for route selection in transport networks. It discusses the application of knowledge-based system (KBS) technology to the production of an expert system to provide route guidance information for some groups of urban travellers. There is a focus on the possibilities for applying a ‘fifth generation’ programming language, such as PROLOG, to the solution of network path selection problems, and the maintenance of a dynamic network database. There are significant arguments both for and against the use of the fifth generation languages, and the alternatives are discussed in speculative terms, on the basis of trials and experiments with PROLOG. The paper develops the specifications for a route guidance KBS for urban road travel, noting that one particular concern is that of providing the most suitable advice to a given traveller, rather than the system-wide rating of ‘best’ advice. Driver attitudes, behaviour, preferences, and vehicle characteristics differ widely, and the degree of satisfaction with any advice provided would depend largely on how closely the expert system could match the preferences of the individual traveller. Thus the system would need to gauge the characteristics of the user as well as those of the network under consideration. Further, prototype route guidance KBS are probably better directed at some clearly defined groups of urban travellers, such as commercial vehicle operations, rather than as community-wide systems.