Road Transport Navigation Requirements in Urban Areas: An Assessment of the Performance of GPS and the Design of a LAAS

Washington Yotto Ochieng, Birol E. Turhan, James Fox and Gordon Johnston

Abstract:	In many countries, the road infrastructure is not expected to increase substantially in the coming years. However, car ownership and travel demand continue to increase at an unsustainable rate. This results in long delays in congested urban areas, a high number of accidents and adverse environmental conditions. There are a number of causes of traffic congestion, one of which is due to the sub-optimal use of existing infrastructure. This is compounded by the lack of information required for planning and executing trips. Advanced Transport Telematics Systems (ATTS) employ state-of-the art computer, communications, navigation and control technologies to ensure an efficient and optimal use of existing infrastructure. The navigation function within an ATTS is responsible for providing geometric and physical location information to support various services. For example, a vehicle equipped with an ATTS receiving real-time updates on the state of the road network can use this information in conjunction with location data to compute optimal routing between a trip’s origin and destination. A pre-requisite to this is that the navigation system adopted must satisfy a wide range of requirements including positional accuracy, integrity, continuity and availability. This is particularly important in physically demanding environments such as cities. This paper presents the results of a study carried out in Greater London to assess and characterise the performance of GPS, and to design a local area augmentation system (LAAS) capable of meeting the required navigation performance (RNP) in urban areas. The study has addressed service coverage and the two RNP parameters of accuracy and integrity. The results highlight the shortcomings of GPS and details the temporal and spatial characteristics to be considered in the design of an augmentation system. These characteristics have been used to specify and justify an architecture for local area augmentation to systems such as GPS, GLONASS and Galileo.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	2407 - 2417
Cite this article:	Ochieng, Washington Yotto, Turhan, Birol E., Fox, James, Johnston, Gordon, "Road Transport Navigation Requirements in Urban Areas: An Assessment of the Performance of GPS and the Design of a LAAS," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 2407-2417.
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