Carl Henrik Häll

The Integrated Dial-a-Ride Problem

In this paper we present a formulation of the Integrated Dial-a-Ride (IDARP). This problem is to schedule dial-a-ride requests, where some part of each journey may be carried out by a fixed route service. The IDARP is a generalization of the Dial-a-Ride Problem. An arc-based formulation is proposed, and it is shown how the model can be made easier to solve by arc elimination, variable substitution and the introduction of subtour elimination constraints. Small instances of the IDARP can be solved using an exact solution method, and one such instance is studied. We also describe how input and output data can be created and visualized in a geographic information system.

A modeling system for simulation of dial-a-ride services

We present a modeling system for simulation of dial-a-ride services. It can be used as a tool for understanding and study how different designs, and different ways to operate a dial-a-ride service, affect the performance and efficiency of the service. The system simulates the operation of a dynamic dial-a-ride service that operates with multiple fleets of vehicles with different capacities, schedules and depots. It can be used to investigate how the setting of service and cost parameters and the design of the service affect the total cost for the operator and level of service for the customer. We describe the different modules in the system and the possible uses of the system. A short simulation study is performed to exemplify how it can be used. In this study the effects of including costs for customer discomfort are evaluated.

Evaluating the performance of a dial-a-ride service using simulation

In this paper we study the effects of changes to a paratransit system operated as a dynamic dial-a-ride service. The scheduling of requests is limited by time window constraints and maximum ride time constraints; costs for customer discomfort in form of waiting time and excess ride time are considered in the planning of the service. The parameters defining these constraints and costs are evaluated based on simulations of a real-world scenario. Several different criteria, both regarding customer level of service and operational costs, are used to evaluate the simulation results. By showing which parameters have a large impact on the different evaluation criteria, we can give guidelines to operators of public transport of how to design their dial-a-ride services. Numerical results are presented and from these results conclusions are drawn regarding which parameters are most important in dynamic dial-a-ride services.

Improving paratransit scheduling using ruin and recreate methods

Abstract In this paper we study the effects of using ruin and recreate methods in a replanning phase of a dynamic dial-a-ride problem. Several such methods are proposed, and a modeling system is used to evaluate how they improve the quality of the solutions. We show that simple changes to existing planning methods can increase the efficiency of the service. Two cases, with different forms of costs inflicted on the vehicles, are evaluated and significant improvements are found in both cases. The best results of our study are found with ruin methods based on removal of sequences of requests.

Analysis of vehicular wireless channel communication via queueing theory model

The 4G standard Long Term Evolution (LTE) has been developed for high-bandwidth mobile access for todays data-heavy applications, consequently, a better experience for the end user. Since cellular communication is ready available, LTE communication has been designed to work at high speeds for vehicular communication. The challenge is that the protocols in LTE/LTE-Advanced should not only provide good packet delivery but also adapt to changes in the network topology due to vehicle volume and vehicular mobility. It is a critical requirement to ensure a seamless quality of experience ranging from safety to relieving congestion as deployment of LTE/LTE-Advanced become common. This requires learning how to improve the LTE/LTE-Advanced model to better appeal to a wider base and move toward additional solutions. In this paper we present a feasibility analysis for performing vehicular communication via a queueing theory approach based on a multi-server queue using real LTE traffic. A M/M/m model is employed to evaluate the probability that a vehicle finds all channels busy, as well as to derive the expected waiting times and the expected number of channel switches. Also, when a base station (eNB) becomes overloaded with a single-hop, a multi-hop rerouting optimization approach is presented.

The integrated dial-a-ride problem with timetabled fixed route service

This paper concerns operational planning of door-to-door transportation systems for the elderly and/or disabled, who often need a more flexible transportation system than the rest of the population. Highly flexible, but very costly direct transportation is often offered as a complement to standard fixed route public transport service. In the integrated dial-a-ride problem (IDARP), these modes of transport are combined and certain legs of the passengers journeys may be performed with the fixed route public transport system. We extend the IDARP and include timetables for the fixed route services, forcing the fleet of vehicles to schedule the arrival at transfer locations with care. Two mixed integer linear programming formulations of the integrated dial-a-ride problem with timetables are presented and analyzed. The key modeling challenge is that of the transfers between the fleet of vehicles and the fixed route public transport system. The formulations differ in how the transfers are modeled and the differences are thoroughly discussed. The computational study compares the formulations in terms of network size, computational time and memory usage and conclusions about their performances are drawn.