GPS Based Road Pricing Systems – is the GPS Technology yet Reliable?

Martina Zabic

Department of Transport, Technical University of Denmark

Kgs. Lyngby, Denmark mz@transport.dtu.dk

Abstract

New initiatives and policies in Europe show that road pricing will be a reality in the future as an

efficient mechanism for equitable taxation and congestion control both in urban areas and roads.

Today, the existing Road Pricing systems are all based on toll stations where the vehicles either are

charged by RFID tags or license plate recognition by cameras. The systems are useful, but inflexible

and demands huge set-up costs for the toll stations. The use of GPS for road pricing has often been

suggested as the way of creating more efficient charging strategies than existing systems based on

cordon lines or time use.

In 2001-2004, Copenhagen participated with the AKTA experiment as a part of the Progress Program

sponsored by EU (Nielsen, 2004). Centre for Traffic and Transport1 participated in the AKTA

experiment, both with designing the experiment and analyzing the data and the results. The experiment

tested 3 different charging schemes based on GPS-data from 500 cars (Nielsen & Jørgensen, 2004).

Based on the AKTA experiment, a study of GPS quality in relation to road pricing was carried out. The

collected data from 500 cars over a two-year period (2001-2003) in the Copenhagen region was

analyzed in order to determine whether the GPS quality and reliability was adequate for

implementation of an operational road pricing system in a dense urban area. Both the satellite visibility

and the horizontal dilution of precision (HDOP) were analyzed in relation to the density of the built-up

areas by use of different digital maps in a Geographic Information System (Zabic & Nielsen, 2005).

The results from the analysis showed that the satellite availability at that point in Copenhagen was not

sufficient to form the basis for a reliable operational road pricing system (refer to figure 1). The narrow

street canyons in downtown Copenhagen prevented a sufficient amount of satellite signals to reach

street level, which caused too many gaps in the position logs.

1 Technical University of Denmark.

Figure 1:

A: Average GPS satellite visibility in CPH B: Missing positions per street. Red color: > 80%

With the modernization of both satellites and receivers, it is interesting to evaluate the current GPS

quality in relation to the upcoming road pricing systems in Europe. Therefore, this study continues with

a new trial in Copenhagen this year. Based on latest receiver technology, GPS data from 50 vehicles is

being collected for a period of 3-4 months, providing the input for new comparable analyses of today’s

GPS quality in dense urban areas.

References Nielsen, O. A. Behavioural responses to pricing schemes: Description of the Danish AKTA

experiment. Journal of Intelligent Transportation Systems. Vol. 8(4). Pp. 233-251. Taylor & Francis.

2004.

Nielsen, O. A. and Jørgensen, R. M. Map-matching algorithms for GPS data – Methodology and test on

data from the AKTA road pricing experiment in Copenhagen. World Conference on Transport

Research Society (WCTRS), Proceedings, Paper 1435, D05 July 7th, Istanbul, July 4-8, 2004.

Zabic, M., and Nielsen, O.A. A Geographic Information Analysis of Global Positioning System

Quality for Road Pricing. (Submitted to Transportation Research Part C), 2005.