Assessment of positioning accuracy of vehicle trajectories for different road applications
IET Intelligent Transport Systems
Global Navigation Satellite Systems (GNSS) has become a kind of positioning standard due to the high penetration rate of this technology on mass market ITS applications. However, this positioning technique remains a real challenge for very demanding services. This paper reports on a practical and methodological approach for the evaluation of the GNSS positioning and attitude of vehicles in real life conditions. Test scenarios have been set up with several positioning sensors mounted on a
... for the collection of raw data on different road sections. The measurement of a high quality reference trajectory allowed to estimate position accuracy under different environmental conditions. We will show in detail the results and identify some typical situations where the quality of GNSS-only positioning is reduced and may impact the level of ITS services, e.g. road user charging or safety applications. Positioning Accuracy of Vehicle Trajectories for Road Applications 2 necessitate reliable location information of all elements of a transportation network (Retscher and Kealy, 2006) . Today, GNSS data is broadly used in navigation systems, e.g. provision of real time information systems for buses. Such systems require vehicle positioning, however, data accuracy is not critical. In ITS where data accuracy is critical, other types of technologies are used -usually optical-based sensors embedded in the vehicle. Advanced driver assistance systems (ADAS) that provide support to the driver to prevent a crash is only one example (pre-crash systems). Another example is lane departure warning (LDW), where part of the system operation is as follows: a sensor identifies lane markings on the pavement and warnings are triggered if a lane departure is monitored. System accuracy depends greatly on the quality of lane markings and on specific prevailing conditions including weather, lighting and pavement. In particular frost, snow, low temperatures, oncoming headlights or low sun deteriorate the system performance. In addition, a sensor based systems increases the cost of the product. Another typical category of ITS, where GNSS could allow improved and quicker implementation of ITS systems, is "cooperative ITS" where the system involves vehicle-to-vehicle communication. In such cases high penetration rates are required to be effective. GNSS based systems can fulfil this criteria. Such systems range from simple systems that communicate real time information (e.g. an incident while en-route is identified and this information is transmitted to relevant other vehicles) to more complex ones such as vehicle collision warnings or even fully automated highway systems (AHS). Last, there is another family of systems, which can only operate with continuous positioning such as e-call and road user charging (RUC). The latter can operate with limited payment strategies using a manifold of different infrastructure technologies (cameras/toll stations in allocated locations). To improve stand-alone GNSS performance, various low-cost products have been proposed recently to facilitate the end user's localization needs encountered in the road sector. Such systems rely either on specialized data processing algorithms, external sensor (e.g. accelerometers, gyroscopes, odometer and magnetometer) and cameras or even on communication network-assisted GNSS principles (Groves, 2012). Depending on the specific application needs, low-cost vehicle localization systems operate as external devices or they form part of the vehicle motion control system in modern cars. However, as these systems are still new and mostly at a prototype level, testing of their performance is required, especially at GNSS signal challenged situations such as in the urban environment (Stebler et al, 2011) . ITS services are rapidly growing with an increased number of location-based applications. Due to the requirements of such advanced applications, several initiatives have been initiated for the development of standards and the definition of quality metrics in GNSS based positioning. This activity requires a high level coordination between the GNSS actors, the automotive industry and the ITS service providers. The SaPPART (Satellite Positioning Performance Assessment for Road Applications) COST Action TU1302 (Gilliéron and Peyret, 2014) has been introduced to improve cooperation between the ITS and GNSS communities.