Travel Time Advantages by Dynamic Route Guidance (DRG) in Germany: Status Quo and Improvement Potential



Travel Time Advantages by Dynamic Route Guidance (DRG) in Germany: Status Quo and Improvement Potential

Authors

Urte Helling, Daimler Chrysler, DE; Joerg Schoenharting, University of Duisburg-Essen, DE

Description

The study shows that:
1. using today?s traffic message quality, DRG Systems can be classified as useful in terms of travel time savings and that
2. the effect of DRG can be tripled by doubling the quality of traffic messages.

Abstract

Motivation and goal
Dynamic Route Guidance Systems shall primarily serve to reduce travel time. Whether and to what extend this benefit can actually be made is ambiguous for practical applications. Accordingly this article aims at answering two vital questions:
1. Do Dynamic Route Guidance Systems offer travel time reduction in Germany today?
2. Which improvement potential can be realized by improved traffic messages?


Methodical Approach
Three factors which influence the reality of a Dynamic Route Guidance are examined:
- Factor 1: Quality of traffic messages
The quality of traffic messages, which are used to make the route guidane dynamic, influences the result of the guidance considerably. Incorrect messages can lead to false guidance and even to wasteful travel time increases. The quality of traffic messages is investigated by test drives in the Stuttgart region.
- Factor 2: Density of the road network
If the original route is obstructed, an alternative route is necessary to realise travel time reduction. This precondition is estimated by the parameter ?density?.
- Factor 3: Levels of traffic in the network
The levels of traffic of the network have a significant influence on the achievement potential of Dynamic Route Guidance: Only if the original route is obstructed a Dynamic Route Guidance System can realise travel time savings. The levels of traffic are detected by a traffic message archive (TMC-format) for the year 2000. The speed-relevant messages are transferred to average travel time increases, which are referenced to the edges of the network.

Based on these considerations and the associated data, travel times and routes by Static and Dynamic Route Guidance on selected journeys are compared. The estimated travel time as calculated by the vehicle and the actual travel time using the current traffic message quality are generated and stored. Finally the selected journeys are once again investigated under the assumption of optimal traffic message quality. The resulting travel times are compared with the above results and the improvement potential is derived.

In order to obtain valid results, simulations are made for the period of a whole year. The users under consideration are commuters, who have regular journeys to and from their place of work. Because traffic messages are only available area-wide for highways the study is limited to this road network. Also it is assumed that the network contains a low number of cars equipped with Dynamic Route Guidance Systems.


Results
The analysis of traffic message quality in the Stuttgart region offers an actual quality value of 35 percent. This means that only 35 percent of the traffic messages correctly represent an incident situation within the given limitations of this study.

The following simulations carried out for the German road network show inhomogeneous results owing to its differentiated network and levels of traffic:
- Travel time savings are detected for the high density areas of Rhine-Ruhr (?Ruhr Area?) and Rhine-Main, which offer a high network density as well as a high level of traffic in the network. The calculated annual savings are in the order of 5 percent. However on single trips they can be significantly greater.
- In urban agglomerations ? for example Hamburg, Berlin, Munich, Stuttgart ? travel time savings cannot be found but informational gains are demonstrated, for example the dynamically guided commuter, who cannot bypass an incident but the system informs him that his arrival time will be delayed. This can be explained by the high level of traffic in a low density network, having few alternative routes available.
- In the remaining parts of Germany there are few and less serious incidents in combination with a significant absence of alternative routes. Therefore only marginal advantages can be found for commuters in this highway network. For several trip simulations increases in travel time can be found because of incorrect or missing traffic messages (for example increases by rerouting around a reported congestion that does not exist in reality).

Further calculations with variable traffic message quality (varying from 35 to 100 percent) show, that the previous results can be improved by enhancing the message quality. A quality enhancement from today?s 35 to 100 percent (optimal information) can realise a threefold improvement in travel time savings. In the areas of Rhine-Ruhr and Rhine-Main, time savings of up to 15 percent are achievable for dynamically guided commuters.
Because of the declining interrelationship between time saving and message quality, it is sufficient to enhance the message quality from today?s 35 percent to 70 percent in order to achieve 95 percent of the possible maximum saving potential. In the high density areas this change averages up to 15 percent time savings.


Conclusions
The investigations carried out give answers to the initially asked questions:
1. Do Dynamic Route Guidance Systems offer travel time reduction in Germany today?
Using today?s traffic message quality, Dynamic Route Guidance Systems can on an annual average be classified as useful in terms of travel time savings or better information for commuters in the highway network in some regions of Germany. Never the less they can in isolated cases lead to increased travel times.
2. Which improvement potential can be reached by improved traffic messages?
The effect of Dynamic Route Guidance Systems can be significantly enhanced by improving the quality of traffic messages, whereas an improvement from today?s 35 to 70 percent is regarded as efficient.

Starting-points for an improvement of traffic message quality and Dynamic Route Guidance lie with:
- Content Provider: Optimisation of the traffic message generation process
- Manufacturer of system and vehicle: accurate and appropriate interpretation of the traffic messages within the route calculation
- Standards (guidelines, technologies): revision of RDS-TMC, Location Code Lists, Event Lists

Finally it is to be noted that an extension of this study regarding further user groups and network classes should be aimed to gain more differentiated results in these fields and to include the problem of missing traffic messages in most network layers.

Publisher

Association for European Transport