Ricardo Giesen

Real-Time Control of Buses in a Transit Corridor Based on Vehicle Holding and Boarding Limits

A real-time mathematical programming model of buses operating on a transit corridor that incorporates vehicle-capacity constraints is proposed. The objective for the model is to minimize the total times experienced by all passengers in the system, from the moment they arrive at a stop to the moment they reach their destination. Two control policies are considered: (a) vehicle holding, which is applicable at any stop, and (b) boarding limits that constrain the number of passengers entering a vehicle even when the vehicle is at less than physical capacity, to increase operating speed. The objective function is quadratic, but not convex with linear constraints. This problem is solved by using MINOS in a reasonable amount of computation time. A case study in a high-demand scenario shows that the proposed control achieves reductions in the objective function of more than 22% and 12% compared with no control and only holding strategies, respectively.

Choosing the Right Express Services for Bus Corridor with Capacity Restrictions

In public transit systems with high demand levels, the use of express bus services that serve only a subset of stops along certain routes appears to be a promising alternative given the benefits that they offer to both users and operators. In practice, express services in systems such as Transmilenio (Bogota, Colombia), Transantiago (Santiago, Chile), and Metro Rapid (Los Angeles, California) have proved highly appealing. To determine what types of express services would be attractive on a bus corridor given the characteristics of its demand, four parameters are defined for identifying corridor demand profiles: the base load profile shape, the scale of demand, the demand imbalance between the outbound and inbound directions, and the average trip length. A series of indicators was also defined to measure the potential benefits of express services in the scenarios studied. The results of the experimental simulations show that a crucial parameter for determining the potential benefits of express services is the average trip length along the corridor. The incorporation of express services is particularly attractive in corridors with demand profiles that increase or decrease monotonically. In addition, the results suggest that in other cases, the complexity of the demand shape could allow for more complex express service patterns.

Bus Control Strategy Application: Case Study of Santiago Transit System☆

Buses have an inherent tendency to bunch due to randomness in passenger demand and congestion. Many sophisticated control strategies have been developed to reduce bus bunching, however, few of them have been implemented in high frequency real services. Building upon a control strategy comprised of a rolling horizon mathematical programming model that yields the optimal holding time that minimizes user-waiting times, the authors have developed real-time software and implemented it on two bus services in Santiago using different technologies to communicate the instructions to bus drivers. The results presented in this paper are encouraging, on the days the system was implemented less bus bunching was observed, which translated in fewer headway-irregularity fines. Moreover lower passenger fare evasion was observed when the bus control strategy was used.

Model for the Optimal Location of Bus Stops and Its Application to a Public Transport Corridor in Santiago, Chile

The location and number of bus stops are key to the operational efficiency of the services that use them; these criteria affect commercial speed, reliability, and passenger access times. In the defining of the number of stops, a trade-off arises between reduced access time, which widens a routes coverage area, and both the operational speed of the route and the users’ in-vehicle travel time. In this study, a model for optimally locating stops was developed, and the model was applied to the Grecia Avenue public transport corridor in the city of Santiago, Chile. The proposed model uses a continuous and multiperiod approximation of corridor demand; this approximation allows for the determination of the density of stops, which minimizes the sum of operator costs and total costs to passengers. The model simultaneously solves for the optimal stop density and the headway between successive buses. The actual stop locations of the Grecia Avenue corridor were compared with the optimal locations suggested by the model, and many similarities were found.

Joint optimization of fleet size and maintenance capacity in a fork-join cyclical transportation system

This article presents an asset management-oriented multi-criteria methodology for the joint estimation of a mobile equipment fleet size, and the maintenance capacity to be allocated in a productive system. Using a business-centred life-cycle perspective, we propose an integrated analytical model and evaluate it using global cost rate, availability and throughput as performance indicators. The global cost components include: (i) opportunity costs associated with lost production, (ii) vehicle idle time costs, and (iii) maintenance resources idle time costs. This multi-criteria approach allows a balanced scorecard to be built that identifies the main trade-offs in the system. The methodology uses an improved closed network queueing model approach to describe the production and maintenance areas. We test the proposed methodology using an underground mining operation case study. The decision variables are the size of a load-haul-dump fleet and specialized maintenance crew levels. Our model achieves savings of 20.6% in global cost terms with respect to a benchmark case. We also optimize the system to achieve desired targets of vehicle availability and system throughput (based on system utilization). The results show increments of 7.1% in vehicle availability and 13.5% in system throughput with respect to baseline case. For the case studied, these criteria also have a maximum, which allows for further improvement if desired. The results also show the importance of using balanced performance measures in the decision process. A multi-criteria optimization was also performed, showing the Pareto front of considered indicators. We discuss the trade-offs among different criteria, and the implications in finding balanced solutions. The proposed analytical approach is easy to implement and requires low computational effort. It also allows for an easy re-evaluation of resources when the business cycle changes and relevant exogenous factors vary.

Logistics in real-time: Inventory-routing operations under stochastic demand

This chapter studies real-time distribution strategies and their associated benefits for a two-level distribution system, from one depot to N retailers, wherein vehicle delivery routes can be updated using real-time information about current inventory levels and vehicle status. Three rolling horizon approaches are proposed in which plans are updated using a mathematical programming formulation. The proposed re-planning strategies are compared against two benchmark policies using a general discrete-event simulation framework. Proposed replanning strategies are shown to systematically outperform the two benchmark policies.

Model for Optimization of Locations of Schools and Student Transportation in Rural Areas

Low population densities make it difficult to design efficient networks of schools in rural areas. The most common solution is to operate small schools with children in multiple grades in each classroom, even though this solution may not be the least expensive. School consolidation proposals are difficult to implement because communities may have emotional bonds with their local schools and the impacts on secondary services, such as student transportation, are difficult to evaluate. In rural areas, particularly in Brazil, reductions in the costs associated with school operations and student transportation could allow boards of education to allocate more resources to improve educational practices and teaching materials. This paper presents a methodology for optimizing the location of schools and student transportation in rural areas. This methodology is based on two mixed-integer programming models, which are used sequentially. The first one deals with the school location and sizing problem, and the second one deals with the school bus routing and shift programming problem. The methodology was applied with data from Barao de Grajaú, which is in the northeast region of Brazil, and provided savings in operating costs of 10% to 17%.

Integrated Real-Time Transit Signal Priority Control for High-Frequency Segregated Transit Services

Bus bunching affects transit operations by increasing passenger waiting time and variability. To tackle this phenomenon, a wide range of control strategies has been proposed. However, none of them have considered station and interstation control together. In this study station and interstation control were tackled to determine the optimal vehicle control strategy for various stops and traffic lights in a single service transit corridor. The strategy minimized the total time that users must devote to making a trip, taking into account delays for transit and general traffic users. Based on a high-frequency, capacity-constrained, and unscheduled service (no timetable) for which real-time information about bus position (GPS) and bus load (automated passenger counter) is available, this study focused on strategies for traffic signal priority in the form of green extension considered together with holding buses at stops and limiting passenger boarding at stops. The decisions on transit signal priority were made according to a rolling horizon scheme in which effects over the whole corridor were considered in every single decision. The proposed strategy was evaluated in a simulated environment under different operational conditions. Results showed that the proposed control strategy achieves reductions in the excess delay for transit users close to 61.4% compared with no control, while general traffic increases only by 1.5%.

Rural School Location and Student Allocation

Optimizing school location can dramatically improve the quality of life of a large number of children, especially of those in rural areas in developing countries. Moreover, when transportation costs are considered, improving the location and assignment of student to schools can save important resources that can be used to provide better teaching supplies to the students. We review selected literature on school location and present an application in Brazil as well as overview some experiences in Chile.

Coping with Disruptions: Performance Comparison of Strategies for Online Inventory Routing Systems Under Demand Surges

In real-time distribution operations, it is generally assumed that demand process parameters can be precisely estimated. However, this is rarely the case, particularly for products with a short life cycle. Experiments were done to investigate the performance of various strategies for online distribution operations under disruptions caused by surges in demand patterns at a particular facility. Two sets of strategies are considered: (a) optimization-based strategies, in which an off-line optimization problem is formulated and used to update routing and inventory allocation plans, and (b) fixed-tour strategies, in which a priori sets of routes to provide retailers with recourse actions depending on different degrees of real-time information capabilities for controlling the system are used. These are compared against two benchmark policies. Simulation results for two scenarios (high and low inventory holding cost products) show that strategies that use real-time information to update delivery plans systematically outperform strategies in which routes are not modified after the vehicle leaves the depot. The differences tend to be higher in scenarios of products with low inventory holding costs. For replanning strategies, the benefits of en route plan updates are significant, in particular the possibility of diverting the vehicle. In the case of fixed-tour strategies, the possibility of updating tour intervals provides potentially great savings. Replanning strategies systematically outperform fixed-tour strategies.