3 Search Results for "Köhler, Ekkehard"


Document
Optimal Bicycle Routes with Few Signal Stops

Authors: Ekkehard Köhler, Markus Rogge, Robert Scheffler, and Martin Strehler

Published in: OASIcs, Volume 115, 23rd Symposium on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS 2023)


Abstract
With the increasing popularity of cycling as a mode of transportation, there is a growing need for efficient routing algorithms that consider the specific requirements of cyclists. This paper studies the optimization of bicycle routes while minimizing the number of stops at traffic signals. In particular, we consider three different types of stopping strategies and three types of routes, namely paths, trails, and walks. We present hardness results as well as a pseudo-polynomial algorithm for the problem of computing an optimal route with respect to a pre-defined stop bound.

Cite as

Ekkehard Köhler, Markus Rogge, Robert Scheffler, and Martin Strehler. Optimal Bicycle Routes with Few Signal Stops. In 23rd Symposium on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS 2023). Open Access Series in Informatics (OASIcs), Volume 115, pp. 1:1-1:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)


Copy BibTex To Clipboard

@InProceedings{kohler_et_al:OASIcs.ATMOS.2023.1,
  author =	{K\"{o}hler, Ekkehard and Rogge, Markus and Scheffler, Robert and Strehler, Martin},
  title =	{{Optimal Bicycle Routes with Few Signal Stops}},
  booktitle =	{23rd Symposium on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS 2023)},
  pages =	{1:1--1:14},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-302-7},
  ISSN =	{2190-6807},
  year =	{2023},
  volume =	{115},
  editor =	{Frigioni, Daniele and Schiewe, Philine},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/OASIcs.ATMOS.2023.1},
  URN =		{urn:nbn:de:0030-drops-187628},
  doi =		{10.4230/OASIcs.ATMOS.2023.1},
  annote =	{Keywords: Constrained shortest path, traffic signals, bicycle routes}
}
Document
Linear Time LexDFS on Chordal Graphs

Authors: Jesse Beisegel, Ekkehard Köhler, Robert Scheffler, and Martin Strehler

Published in: LIPIcs, Volume 173, 28th Annual European Symposium on Algorithms (ESA 2020)


Abstract
Lexicographic Depth First Search (LexDFS) is a special variant of a Depth First Search (DFS), which was introduced by Corneil and Krueger in 2008. While this search has been used in various applications, in contrast to other graph searches, no general linear time implementation is known to date. In 2014, Köhler and Mouatadid achieved linear running time to compute some special LexDFS orderings for cocomparability graphs. In this paper, we present a linear time implementation of LexDFS for chordal graphs. Our algorithm even implements the extended version LexDFS^+ and is, therefore, able to find any LexDFS ordering for this graph class. To the best of our knowledge this is the first unrestricted linear time implementation of LexDFS on a non-trivial graph class. In the algorithm we use a search tree computed by Lexicographic Breadth First Search (LexBFS).

Cite as

Jesse Beisegel, Ekkehard Köhler, Robert Scheffler, and Martin Strehler. Linear Time LexDFS on Chordal Graphs. In 28th Annual European Symposium on Algorithms (ESA 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 173, pp. 13:1-13:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)


Copy BibTex To Clipboard

@InProceedings{beisegel_et_al:LIPIcs.ESA.2020.13,
  author =	{Beisegel, Jesse and K\"{o}hler, Ekkehard and Scheffler, Robert and Strehler, Martin},
  title =	{{Linear Time LexDFS on Chordal Graphs}},
  booktitle =	{28th Annual European Symposium on Algorithms (ESA 2020)},
  pages =	{13:1--13:13},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-162-7},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{173},
  editor =	{Grandoni, Fabrizio and Herman, Grzegorz and Sanders, Peter},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2020.13},
  URN =		{urn:nbn:de:0030-drops-128790},
  doi =		{10.4230/LIPIcs.ESA.2020.13},
  annote =	{Keywords: LexDFS, chordal graphs, linear time implementation, search trees, LexBFS}
}
Document
Traffic Signal Optimization Using Cyclically Expanded Networks

Authors: Ekkehard Köhler and Martin Strehler

Published in: OASIcs, Volume 14, 10th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS'10) (2010)


Abstract
Traditionally, the coordination of multiple traffic signals and the traffic assignment problem in an urban street network are considered as two separate optimization problems. However, it is easy to see that the traffic assignment has an influence on the optimal signal coordination and, vice versa, a change in the signal coordination changes the optimal traffic assignment. In this paper we present a cyclically time-expanded network and a corresponding mixed integer linear programming formulation for simultaneously optimizing both the coordination of traffic signals and the traffic assignment in an urban street network. Although the new cyclically time-expanded network provides a model of both traffic and signals close to reality, it still has the advantage of a linear objective function. Using this model we compute optimized signal coordinations and traffic assignment on real-world street networks. To evaluate the practical relevance of the computed solutions we conduct extensive simulation experiments using two established traffic simulation tools that reveal the advantages of our model.

Cite as

Ekkehard Köhler and Martin Strehler. Traffic Signal Optimization Using Cyclically Expanded Networks. In 10th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS'10). Open Access Series in Informatics (OASIcs), Volume 14, pp. 114-129, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2010)


Copy BibTex To Clipboard

@InProceedings{kohler_et_al:OASIcs.ATMOS.2010.114,
  author =	{K\"{o}hler, Ekkehard and Strehler, Martin},
  title =	{{Traffic Signal Optimization Using Cyclically Expanded Networks}},
  booktitle =	{10th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS'10)},
  pages =	{114--129},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-20-0},
  ISSN =	{2190-6807},
  year =	{2010},
  volume =	{14},
  editor =	{Erlebach, Thomas and L\"{u}bbecke, Marco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/OASIcs.ATMOS.2010.114},
  URN =		{urn:nbn:de:0030-drops-27542},
  doi =		{10.4230/OASIcs.ATMOS.2010.114},
  annote =	{Keywords: dynamic flow, traffic optimization, traffic signals}
}
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