More Hierarchy in Route Planning Using Edge Hierarchies

TL;DR

This paper introduces a novel edge hierarchy approach for route planning in networks, aiming to reduce search space size by assigning hierarchy levels to edges, thus enriching existing hierarchical routing techniques.

Contribution

It proposes a more fine-grained edge-based hierarchy for route planning, extending beyond vertex-based hierarchies like contraction hierarchies.

Findings

Smaller search spaces in terms of visited edges.

No consistent improvement in query times yet.

Enriches the set of techniques for future route planning improvements.

Abstract

A highly successful approach to route planning in networks (particularly road networks) is to identify a hierarchy in the network that allows faster queries after some preprocessing that basically inserts additional "shortcut"-edges into a graph. In the past there has been a succession of techniques that infer a more and more fine grained hierarchy enabling increasingly more efficient queries. This appeared to culminate in contraction hierarchies that assign one hierarchy level to each vertex. In this paper we show how to identify an even more fine grained hierarchy that assigns one level to each edge of the network. Our findings indicate that this can lead to considerably smaller search spaces in terms of visited edges. Currently, this rarely implies improved query times so that it remains an open question whether edge hierarchies can lead to consistently improved performance. However, we believe that the technique as such is a noteworthy enrichment of the portfolio of available techniques that might prove useful in the future.