engleski

Simulation Modelling of Satellite Positioning for Road User Charging

The last few years have seen a rapid growth of applications based on positioning information provided by satellite positioning systems. In transport management and control, satellite positioning has proven to be the most promising means for spatial location data collection. With the GPS modernisation programme well underway, and the recent developments of the Galileo project, even more GNSS-based applications are to be expected in the future. One such GNSS-based application is the use of position and velocity information as the prime input to a road user charging (RUC) scheme. However, positioning in urban environments raises a number of problems. Most important are the difficulties related to signal obstruction by features such as tall buildings, urban canyons, bridges and trees, as well as the effects of multipath caused by signal refl ections from buildings and other vehicles. Given the inevitable limitations of road trials, the use of simulation modelling to assess the present and future satellite positioning systems’ capability to support urban RUC seems indispensable. The main objective of the research undertaken at the University of Nottingham Institute of Engineering Surveying and Space Geodesy (IESSG), and the Nottingham Centre for Infrastructure (NCI), was to develop a tool to simulate GPS for urban Satellite Positioning-based Road User Charging (SPRUC). The tool would help local governments to set up a charging scheme, for which satellite positioning performance would be analysed in advance, using simulation modelling. In this regard, an existing GPS simulator was modifi ed to rectify one of its major weaknesses, namely the inability to address properly the change in non-static GPS measurements with respect to changes in built environment. For this purpose, state-of-the-art Geographic Information Systems (GIS) software was used to complement the simulator, and consequently a seamless interface between the two software has been developed. In order to provide a prime input to the simulator, fi eld tests have been undertaken and signifi cant amounts of GPS data were collected. Statistics were also derived for positioning accuracy and signal availability, enabling the results from the simulation modelling to be validated against those from the road trials that were undertaken. The road trials provide a good indication of the levels of GPS accuracy and achievable availability in urban environments. However, these can only give a snapshot of a few roads on a sample day(s). Hence, the use of simulation modelling is advocated in order to quantify GPS positioning performance over an entire urban area, over a signifi cant period of time. Results suggest that the newly developed simulation tool may be deemed as sound. Nevertheless, it still requires full practical validation. Given the recent RUC developments in the UK and continental Europe, it may not be long before the application’ s potential gets recognised in practice. This research also demonstrated that urban SPRUC, facilitated by low-cost standalone GPS positioning, might be feasible provided the charging points have open locations. Although signal loss can be expected, the total signal loss/travel time ratio is likely to be low. Hence the potential erroneous vehicle positioning may be remedied by lengthening the virtual tollbooths or by introducing low-cost signal blockage modelling.

Road user charging; GPS; simulation modelling

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