Availability of GNSS for Road Pricing in Copenhagen

Like most older cities, downtown Copenhagen is a net of narrow streets surrounded by tall old buildings and with no, or very limited, possibilities for changing the traffic corridors. During business hours the traffic congestion is intense, and the workforce in Copenhagen spend hours on the roads every day, stuck in slow moving traffic flows or traffic jam.

Several means for regulating vehicle traffic flow exists, and various analyses and experiments have been carried out in a number of European Cities during the last five years as part of the PRoGRESS programme, sponsored by the EU. In Denmark, Copenhagen participated in PRoGRESS with the AKTA project.

The major part of the AKTA project was to equip 500 cars with GPS receivers. GPS positions were logged along with information on speed, number of satellites, HDOP etc. With this paper we present an analysis of the GPS data collected, with the purpose of evaluating whether stand alone GPS is feasible for operational road pricing in Copenhagen.

The analyses show that the GPS satellite availability in the downtown streets is not sufficient to form the basis for an operational road pricing setup in Copenhagen. The narrow street canyons prevent a sufficient amount of satellite signals from reaching street level, and there are too many gabs in the position logs to implement a fair and reliable taxation scheme.

The need for augmentation is evident, and with the advent of Galileo within a few years, it is relevant to investigate how integrated GPS/Galileo receivers will change the situation. With a 3D city model of Copenhagen, a Galileo simulator, and a raytracing algorithm, an analysis of the GNSS availability in the streets of Copenhagen was carried out.

The analysis is focusing on the number of visible satellites and the HDOP. The results show that the satellite availability, given both by the number of visible satellites and by the HDOP, is slightly better with Galileo than with GPS, and the situation is considerably improved if GPS and Galileo are used in combination.

The results also show, however, that there will still be streets in downtown Copenhagen were the receiver–satellite geometry represented by the HDOP is not sufficient for reliable positioning during the full 24 hours of a day, even when combined GPS-Galileo receivers are introduced. Finally the results of the simulations are compared with the analysis based on GPS data collected in situ during the AKTA project, and the comparison show that the results are basically identical, thus verifying that the simulation scenario is reasonable.