Homero Larrain

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.

A dynamic multi-plant lot-sizing and distribution problem

In this paper, we investigate a multi-plant, production planning and distribution problem for the simultaneous optimisation of production, inventory control, demand allocation and distribution decisions. The objective of this rich problem is to satisfy the dynamic demand of customers while minimising the total cost of production, inventory and distribution. By solving the problem, we determine when the production needs to occur, how much has to be produced in each of the plants, how much has to be stored in each of the warehouses and how much needs to be delivered to each customer in each period. On a large real data-set inspired by a case obtained from an industrial partner, we show that the proposed integration is highly effective. Moreover, we study several trade-offs in a detailed sensitivity analysis. Our analyses indicate that the proposed scenarios give the company competitive advantage in terms of reduced total logistics cost, and also highlight more possibilities that become available taking advantage of an integrated approach towards logistics planning. These abundant opportunities are to be synergised and exploited in an interconnected open global logistics system.

A Variable MIP Neighborhood Descent algorithm for managing inventory and distribution of cash in automated teller machines

We introduce a new hybrid algorithm for the solution of mixed-integer programming models, called Variable MIP Neighborhood Descent (VMND).We provide formal notation and pseudo-codes for this algorithm, which combines an exact solution method (branch-and-cut) with a local search algorithm (Variable Neighborhood Descent).Neighborhood searches are performed taking advantage of the MIP formulation of the original problem, formulating and solving them as constrained subproblems.We also introduce the Inventory-Routing Problem with Cassettes and Stockouts (IRPCS), a variant of the Inventory-Routing Problem that arises in the cash management and replenishment of ATMs in Santiago, Chile.The IRPCS is used to test our VMND, showing that our algorithm greatly outperforms the solutions of a benchmark branch-and-cut algorithm. In this paper we propose a new hybrid algorithm to solve mixed-integer programming (MIP) models called Variable MIP Neighborhood Search (VMND). The VMND relies on an existing mathematical formulation of the problem and significantly accelerates its resolution compared to standalone MIP solvers. Using this algorithm, we solve a practical problem arising in the ATM management and replenishment in Santiago, Chile. This rich and challenging problem, which we call the inventory-routing problem with cassettes and stockouts, shares much of its structure with the inventory-routing problem, but some features make it unique. We exploit the structure of the problem to derive neighborhoods implemented in our VMND, be it over routes, locations, periods or quantities delivered. Based on extensive computational experiments, our VMND is shown to significantly outperform benchmark solutions from a branch-and-cut algorithm. A sensitivity analysis is performed to confirm the robustness and effectiveness of our method.

When and where are limited-stop bus services justified?

ABSTRACT Although limited-stop bus services around the world have proven to benefit users and operators alike, there are few published studies on design methodologies for such services and little clarity on when or where they are best applied to a given bus corridor. This article reports on an experiment in which a design algorithm for limited-stop services in a corridor was used to optimise almost 1000 scenarios. A regression model was then calibrated to estimate the benefits of operating limited-stop bus services as a function of various attributes of the corridor. The benefits from limited-stop services increase with higher dwell times, number of trips, concentration of trips in few origin–destination pairs and critical arc load, and with lower wait time values and vehicle capacity. The analytic expression derived from the regression model provides an unprecedented tool to forecast the benefits of implementing limited-stop services.