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Railway alignment design is a complicated problem affected by intricate environmental factors. Although numerous alignment optimization methods have been proposed, a general limitation among them is the lack of a spatial environmental suitability analysis to guide the subsequent alignment search. Consequently, many unfavorable regions in the study area are still searched, which significantly degrades optimization efficiency. To solve this problem, a geographic information model is proposed for evaluating the environmental suitability of railways. Initially, the study area is abstracted as a spatial voxel set and the 3-D reachable ranges of railways are determined. Then, a geographic information model is devised which considers topographic influencing factors (including those affecting structural cost and stability) as well as geologic influencing factors (including landslides and seismic impacts) for different railway structures. Afterward, a 3-D environmental suitability map can be generated using a multi-criteria decision-making approach to combine the considered factors. The map is further integrated into the alignment optimization process based on a 3-D distance transform algorithm. The proposed model and method are applied to two complex realistic railway cases. The results demonstrate that they can considerably improve the search efficiency and also find better alignments compared to the best alternatives obtained manually by experienced human designers and produced by a previous distance transform algorithm as well as a genetic algorithm. [ABSTRACT FROM AUTHOR]

For the train timetabling problem (TTP) in a metro system, the operator-oriented and passenger-oriented objectives are both important but partly conflicting. This paper aims to minimize both objectives by considering frequency (in the line planning stage) and train cost (in the vehicle scheduling stage). Time-varying passenger demand and train capacity are considered in a nonsmooth, nonconvex programming model, which is transformed into a mixed integer programming model with a discrete time-space graph (DTSG). A novel dwell time determining process considering congestion at stations is proposed, which turns the dwell times into dependent variables. In the solution approach, we decompose the TTP into a subproblem for optimizing segment travel times (OST) and a subproblem for optimizing departure headways from the shuntingyard (OH). Branch-and-bound and frequency determining algorithms are designed to solve OST. A novel rolling optimization algorithm is designed to solve OH. The numerical experiments include case studies on a short metro line and Beijing Metro Line 4, as well as sensitivity analyses. The results demonstrate the predictive ability of the model, verify the effectiveness and efficiency of the proposed approach, and provide practical insights for different scenarios, which can be used for decision-making support in daily operations., 1. Introduction With increasing concerns about urban congestion and climate change, urban metro rail transportation receives increasing attention due to its high capacity, punctuality and sustainability. Metro timetabling is the [...]

The horizontal alignment of existing railway must be re-created and calibrated periodically to meet the requirements of safety, stability and comfort. Most existing re-creation methods perform local section optimization, in which the whole alignment is divided into several sections, depending on the number and positions of intersection points, and then each section is re-created successively. The final whole re-created horizontal alignment is generated by combining optimized re-created sections. In this process, the re-created result of one section must be adjusted in re-creating the next section. Thus, the optimized re-created result of the previous section cannot be preserved. To overcome this problem, some methods use the result of local section optimization as the initial value, and then further optimize the whole alignment. However, the final re-created alignment is affected easily by the local section optimization, so that the re-created alignment is not optimized. This paper proposes an overall swing iteration based on points-alignment consistency integrated with mesh adaptive direct search (MADS). At each iteration, the adverse effect of re-creating successive sections is avoided by preferentially fitting all shared tangents which link nearby sections and then fitting curved segments simultaneously. To optimize curved segments further, MADS is introduced to optimize the parameters and handle constraints. After each iteration, the attributes of measured points for the whole alignment are adjusted based on points-alignment consistency until they are consistent with the attributes of re-created geometric elements. Applications demonstrated that the proposed approach can re-create an optimized horizontal alignment while satisfying multiple constraints. [ABSTRACT FROM AUTHOR]

Among dispatching control approaches, the holding option has attracted the most attention in bus control. However, holding a vehicle at a transfer station may exacerbate the delays because more passengers [...]

The location of rail transit lines and stations is a challenging problem because the number of possible alternatives is astronomical, the number of requirements and constraints is very large, and the evaluation of each alternative is based on numerous measures of effectiveness. Furthermore, large amounts of geographic information of many types are needed to compute some of the effectiveness measures. For instance, detailed spatial data on household locations and characteristics are needed to estimate accessibility to transit stations and the resulting access times and effects on demand. Detailed information on existing street networks, topography, and geology is needed to estimate construction costs and detailed information on land use and land values are needed to estimate right-of-way costs. In this paper we adapt the genetic algorithm and geographic information system approach to rail line optimization. Two types of costs are formulated and evaluated in the model: (1) operator cost which consists of track-related construction cost, station construction cost, right-of-way cost, earthwork cost, and rail operating cost; and (2) user cost which consists of access cost, riding time cost, and wait cost. The model is applied to a section of Anne Arundel County, Md., to reoptimize between a pair of stations an existing light rail transit line connecting Glen Burnie to the Baltimore Washington International Airport. The prototype model presented here produces very good alignments based on its criteria and can be extended to use far more comprehensive and complex evaluation functions. Additional factors and cost components that should be considered in more advanced models are also discussed. DOI: 10.1061/(ASCE)0733-9488(2007) 133:3(161) CE Database subject headings: Routing; Geographic information systems; Rapid transit systems; Optimization; Algorithms.

An efficient optimization approach, called feasible gate (FG), is developed to enhance the computation efficiency and solution quality of the previously developed highway alignment optimization (HAO) model. This approach seeks [...]

A three-dimensional highway alignment optimization methodology is developed that automatically determines whether and where bridges or tunnels are preferable to embankments or deep cuts, respectively. This is done by comparing the optimized costs of such alternatives. The data for detailed computations of earthwork, right-of-way, vehicle operation, user time, and other costs are obtained from a geographic information system (GIS) for each alternative alignment considered. The alignment optimization process relies on a genetic algorithm developed for this problem. Two example studies implemented in an artificial study area with a real GIS show that by modeling bridges and tunnels we can improve the reliability and adaptability of highway alignment optimization as well as find more practical solutions than otherwise. DOI: 10.1061/(ASCE)0733-947X(2007)133:2(71) CE Database subject headings: Bridges, highway; Tunnels; Alignment; Geographic information systems; Algorithms.

Highway maintenance, like rehabilitation or resurfacing, on four-lane, two-way highways usually requires closing one or two lanes to set up a work zone. In this paper we evaluate several alternatives defined by the number of closed lanes, fractions of traffic diverted to alternate routes, and crossover of diverted traffic to opposite lanes. A methodology is developed to minimize the total cost, including agency cost, user cost, and accident cost, by optimizing work zone length for each alternative and finding optimal diversion fraction, while considering the characteristics of the detour route bypassing the work zone. Finally, guidelines for selecting the best alternative for different characteristics of traffic flows, roads, and maintenance processes are developed by deriving thresholds among alternatives. CE Database subject headings: Workspace; Highway construction; Optimization; Costs; Pavements; Traffic management.

The timed transfer concept, which seeks to schedule vehicles from various routes to arrive at some transfer stations simultaneously (or nearly so), can significantly improve service quality in transit networks. It has been implemented in some cities but with insufficient efforts to optimize coordination among connecting routes. Our problem is to optimize the headways and slack times jointly for timed transfers to minimize the total costs of operating a multiple-hub transit network. In this paper, a heuristic algorithm is used to optimize the headways and slack times for all coordinated routes. Here, headways are integer multiples of a base cycle to ensure that vehicles on different routes can operate in phase and arrive nearly simultaneously at transfer stations. The results show that as demand decreases, optimized headways increase and the net benefits of coordinated operation also increase. For routes with significantly different demand or route length, coordination with integer-ratio headways is preferable to a single common headway. The sensitivity of the transit service characteristics to various demand and cost parameters is discussed. The results also show that the optimized slack times for routes vary with such variables as headways, vehicle arrival-time variance, transfer volumes, and passenger time values. For routes with high standard deviations of arrivals, it is not worth attempting schedule coordination. CE Database subject headings: Transportation networks; Scheduling; Coordination; Time factors.

The evaluation, selection, sequencing, and scheduling of lock reconstruction and rehabilitation projects is a major concern for inland waterway systems. As traffic increases and existing lock conditions deteriorate, users suffer substantially longer processing times and delays. Lock projects tend to be interdependent as improvements at one lock may shift bottlenecks elsewhere. A generalized waterway simulation model that is independent of network geometry was developed to evaluate the system over a multiyear planning horizon. A genetic algorithm was also developed in order to efficiently explore the solution space of this large investment optimization problem. The proposed combination of two stochastic models can solve selection, sequencing, and scheduling problems for interdependent projects in large waterway networks but requires long computation times. Due to lock interdependency, the benefits of multiple projects are not directly obtainable by adding individual project benefits: they are measured from the marginal increment of total system delays. The results show how interdependent projects should be scheduled and how operational lock control improvements can sometimes improve delays significantly without requiring major construction investments. DOI: 10.1061/(ASCE)0733-950X(2005)131:3(89) CE Database subject headings: Inland waterways; Project evaluation; Optimization models; Transportation models; Scheduling; Locks; Simulation.

This paper presents deterministic models for estimating airspace and airport capacity and delays during equipment outages. The National Airspace System (NAS) is very complex and consists of almost 48,000 reportable facilities and services that support air traffic control with very diverse functions and technologies. To better understand NAS performance and develop a methodology for estimating degraded capacity, previous studies about equipment outages and about airspace and airport performance are first reviewed. A deterministic aircraft separation model is used to estimate degraded capacity. It is useful for quick estimates of the number of aircraft operations per facility under some predefined conditions (i.e., mile-in-trail separation and aircraft mix), but does not estimate delays. A deterministic queuing approach is used for estimating delays due to single outages for a hypothetical airport and terminal airspace area. It can also estimate the number of aircraft experiencing queuing and the queue duration, while considering arrival and service rates that vary over time. CE Database subject headings: Airports; Air traffic; Equipment; Outages; Traffic management.

Increasing flight frequency on airline routes tends to reduce user delay costs but increase airline operating costs. Flight frequency should vary as demand intensity changes at various times of day. Models are presented here for optimizing the departure times of flights on single airline routes with time-dependent demand. An analytic model is developed to find the departure times that minimize average schedule delay per passenger for given flight frequencies and to identify the algebraic relations among the variables. Using an analytic approach, the departure times of flights that minimize airline operating cost and users' waiting cost are determined. To minimize the objective function, it is found that the headways should be inversely proportional to the square root of demand intensity near the departure times. Computer models for both cost minimization and profit maximization are developed to solve the problems with relaxed assumptions and verify the numerical results obtained analytically. CE Database subject headings: Airlines; Optimization; Scheduling; Routes; Computer models; Costs.

A method for precisely formulating intersection construction costs including earthwork costs, right-of-way costs, and pavement costs is introduced in this paper. Intersection design characteristics are reviewed and intersection cost components are formulated. A highway alignment is described by parametric representation in space, and vector manipulation is used to find the coordinates of intersections and other points of interest. A simplified typical fill section is studied to obtain actual ground and road elevation coordinates that are crucial for setting the boundaries and computing the costs. Because estimating right-of-way costs requires identifying affected properties and structures in the vicinity of an intersection, two examples based on geographic information system (GIS) databases from Maryland and an artificial study area are presented to show how the developed cost functions can be used in real applications. The developed intersection construction cost functions can be incorporated in previously developed highway alignment optimization models that neglected the characteristics and costs of intersections. CE Database subject headings: Intersections; Construction costs; Earthwork; Pavements; Alignment; Optimization models.

Determinations of alignments and station locations are major tasks in railway design, which jointly and fundamentally influence the construction and operation of the whole project. Currently, although considerable efforts have been invested into the separate optimization of alignments or station locations, the complex interactions between alignments and stations, as well as their concurrent impacts on railways still need further investigations. Therefore, this study focuses on modeling and optimization of passenger railway alignments and station locations simultaneously. A novel optimization model is formulated for maximizing net present value (NPV) considering comprehensive costs and revenue from riders over the railway's design life. Specifically, the comprehensive cost includes construction and operation costs of alignments and stations. The railway ridership is quantified by combining travel time and trip coverage using a logit function. Then, the railway revenue is estimated and combined with costs through an economic growth model to obtain the NPV. To solve this model, two customized and mutually exclusive methods, that is, the station‐alignment‐integration (SAI) and alignment‐station‐integration (ASI) methods, are developed based on a particle swarm algorithm. The SAI primarily searches for possible stations in the landscape and then generates alignments to connect adjacent stations. The ASI directly yields the main alignment, on which potential stations are located by handling specific constraints. The model and methods are applied to an actual high‐speed railway. Results show that both SAI‐ and ASI‐generated railways have higher NPV values compared to the corresponding railway designed by experienced designers. Sensitivity analysis reveals that SAI is more flexible than ASI in solving actual cases. The convergence of the proposed methods is also discussed. With some changes in input parameters based on locally applicable design standards, the proposed methods are generally applicable to other cases or countries. [ABSTRACT FROM AUTHOR]

The design of grade-separated road and railway crossings can be complicated and time-consuming since the intersection point as well as the road and rail alignments should jointly optimize an objective such as minimum construction costs. Moreover, the design of grade-separated road and railway crossings should consider additional crossing constraints and possible revisions of the road alignments. However, research on alignment optimization with variable ends is scarce. In this article, a grade-separated road and railway crossing model is developed, the crossing point of which as well as both connection points with the road, are variable. Subsequently, by searching synchronously for the paths that connect different endpoints, a distance transform algorithm is applied. The effectiveness of the method is verified through a real-world case study. The results show that the proposed method can find various promising solutions that both satisfy multiple constraints and are considerable improvements on the designs produced by experienced human designers. [ABSTRACT FROM AUTHOR]

Highway maintenance is very expensive in terms of not only costs to the responsible agencies but also disruptive delays to users. Construction and maintenance activities on two-lane two-way highways often require the closure of one lane. During certain periods of a day, the user delay associated with lane closure may be quite intolerable to motorists. A numerical method is developed to optimize work-zone scheduling and traffic control on two-lane two-way highways where one lane at a time is closed. The objective is to minimize the total cost, including maintenance, labor/equipment idle, and user-delay costs, considering traffic flows varying over time. The optimized variables (e.g., work-zone lengths and cycle times) and the sensitivity results generated from a numerical example are presented in this study. CE Database keywords: Optimization; Workspace; Highway maintenance; Scheduling; Costs.