Timetable Information Systems Research Articles

Connection Scan Algorithm

We introduce the Connection Scan Algorithm (CSA) to efficiently answer queries to timetable information systems. The input consists, in the simplest setting, of a source position and a desired target position. The output consists of a sequence of vehicles such as trains or buses that a traveler should take to get from the source to the target. We study several problem variations such as the earliest arrival and profile problems. We present algorithm variants that only optimize the arrival time or additionally optimize the number of transfers in the Pareto sense. An advantage of CSA is that it can easily adjust to changes in the timetable, allowing the easy incorporation of known vehicle delays. We additionally introduce the Minimum Expected Arrival Time (MEAT) problem to handle possible, uncertain, future vehicle delays. We present a solution to the MEAT problem that is based on CSA. Finally, we extend CSA using the multilevel overlay paradigm to answer complex queries on nationwide integrated timetables with trains and buses.

Engineering graph-based models for dynamic timetable information systems

In the last years we have witnessed remarkable progress in providing efficient algorithmic solutions to the problem of computing best journeys (or routes) in schedule-based public transportation systems. We have now models to represent timetables that allow us to answer queries for optimal journeys in a few milliseconds, also at a very large scale. Such models can be classified into two types: those representing the timetable as an array, and those representing it as a graph. Array-based models have been shown to be very effective in terms of query time, while graph-based ones usually answer queries by computing shortest paths, and hence they are suitable to be combined with the speed-up techniques developed for road networks.In this paper, we study the behavior of graph-based models in the prominent case of dynamic scenarios, i.e., when delays might occur to the original timetable. In particular, we make the following contributions. First, we consider the graph-based reduced time-expanded model and give a simplified and optimized routine for handling delays, and a re-engineered and fine-tuned query algorithm. Second, we propose a new graph-based model, namely the dynamic timetable model, natively tailored to efficiently incorporate dynamic updates, along with a query algorithm and a routine for handling delays. Third, we show how to adapt the ALT algorithm to such graph-based models. We have chosen this speed-up technique since it supports dynamic changes, and a careful implementation of it can significantly boost its performance. Finally, we provide an experimental study to assess the effectiveness of all proposed models and algorithms, and to compare them with the array-based state of the art solution for the dynamic case. We evaluate both new and existing approaches by implementing and testing them on real-world timetables subject to synthetic delays.Our experimental results show that: (i) the dynamic timetable model is the best model for handling delays; (ii) graph-based models are competitive to array-based models with respect to query time in the dynamic case; (iii) the dynamic timetable model compares favorably with both the original and the reduced time-expanded model regarding space; (iv) combining the graph-based models with speed-up techniques designed for road networks, such as ALT, is a very promising approach.

Parallel computation of best connections in public transportation networks

Exploiting parallelism in route planning algorithms is a challenging algorithmic problem with obvious applications in mobile navigation and timetable information systems. In this work, we present a novel algorithm for the one-to-all profile-search problem in public transportation networks. It answers the question for all fastest connections between a given station <it>S</it> and any other station at any time of the day in a single query. This algorithm allows for a very natural parallelization, yielding excellent speed-ups on standard multicore servers. Our approach exploits the facts that, first, time-dependent travel-time functions in such networks can be represented as a special class of piecewise linear functions and, second, only few connections from <it>S</it> are useful to travel far away. Introducing the connection-setting property, we are able to extend Dijkstra's algorithm in a sound manner. Furthermore, we also accelerate station-to-station queries by preprocessing important connections within the public transportation network. As a result, we are able to compute all relevant connections between two random stations in a complete public transportation network of a big city (New York) on a standard multi-core server in real time.

Experimental study of speed up techniques for timetable information systems

AbstractIn recent years, many speed up techniques for DIJKSTRA Algorithm have been developed. Unfortunately, research mainly focused on road networks although fast algorithms are also needed for other applications like timetable information systems. Even worse, the adaption of recently developed techniques to graphs deriving from timetable information problems is often more complicated than expected. In this work, we check whether results from road networks are transferable to timetable information systems. To this end, we present an extensive experimental study of the most prominent speed up techniques on inputs deriving from different applications. It turns out that recently developed techniques are much slower on graphs derived from timetable information problems than on road networks. In addition, we gain interesting insights into the behavior of speed up techniques in general. © 2010 Wiley Periodicals, Inc. NETWORKS, 2011

SHARC

During recent years, impressive speed-up techniques for Dijkstra's have been developed. Unfortunately, the most advanced techniques use bidirectional search, which makes it hard to use them in scenarios where a backward search is prohibited. Even worse, such scenarios are widely spread (e.g., timetable-information systems or time-dependent networks). In this work, we present a unidirectional speed-up technique, which competes with bidirectional approaches. Moreover, we show how to exploit the advantage of unidirectional routing for fast exact queries in timetable information systems and for fast approximative queries in time-dependent scenarios. By running experiments on several inputs other than road networks, we show that our approach is very robust to the input.

Towards Realistic Modeling of Time-Table Information through the Time-Dependent Approach

We consider optimal itinerary problems in time-table information systems supporting a vast number of on-line queries. We exhibit two important extensions of the time-dependent approach to model realistic versions of the Earliest Arrival and Minimum Number of Transfer problems, as well as of a combination of them, that could not be modeled by the original version of the time-dependent approach. We also provide heuristics that speed up implementations and present preliminary experimental results with real-world data.

Scott Induction and Equational Proofs

We consider optimal itinerary problems in time-table information systems supporting a vast number of on-line queries. We exhibit two important extensions of the time-dependent approach to model realistic versions of the Earliest Arrival and Minimum Number of Transfer problems, as well as of a combination of them, that could not be modeled by the original version of the time-dependent approach. We also provide heuristics that speed up implementations and present preliminary experimental results with real-world data.

Web-Based Integrated Timetable Information System for Railways and Airlines

The paper presents a traffic information system called KRJ that covers Polish railways and airlines transportation systems. Basic algorithmic foundations for the system are given. The system was previously designed as a standalone program. Recently, it has been moved to Internet and made available at a commercial Web site as a service called Ekspres. The process of migration into Internet service and problems encountered are described. The paper concludes with experiences gained so far from a one-year exploitation under operational workload.

Context-dependent probability adaptation in speech understanding

By using context-dependent concept language models, we can significantly improve the performance of the speech understanding component of a dialogue system. We use several different modelling methods, such as bigrams, concept set probability estimations using graph theory and combinations of these. The contexts are selected both manually and automatically using mutual information. Using context-dependent bigrams, with contexts selected by the clustering algorithm, we establish a relative increase in performance of 10% on the attribute error rate on data obtained through the currently operational Swiss automatic train timetable information system.

A spoken language inquiry system for automatic train timetable information

This article describes the Philips automatic train timetable information system which enables the user to call up accurate information about train connections between 1200 German cities over the telephone. In contrast to most of the inquiry systems available so far, the caller can talk to our system in unrestricted, natural and fluent speech, very much like talking to a human operator. No instructions are given beforehand. The system consists of four main components: speech recognition, speech understanding, dialogue control, and speech output. They are separated into independent modules and executed sequentially. The speech recogniser creates a word graph from the spoken input. This word graph is then passed to the understanding component which computes the meaning, using an attributed stochastic context-free grammar. A dialogue manager analyses the results and either accesses the database or comes up with another question if necessary. The system has been made available to the general public in an ongoing field test, both to gather speech data and to evaluate its performance.