In recent years, there has been a significant increase in the number of vehicles which have been equipped with GPS devices. These devices generate huge volumes of trace data, and information extracted from these traces could significantly help transportation planners with routine tasks and special studies. However, extracting information from trace data is a challenging problem because of the proliferation of GPS devices and the rate at which trace data is generated. One approach for handling this problem is to compress the GPS data in such a way that the amount of information lost due to compression is as small as possible. During the period of this project, our focus was on the design, implementation and evaluation of GPS trajectory compression algorithms that can achieve specified compression rates while minimizing the information loss due to compression. Our work has led to new algorithms for compressing single and multiple GPS traces.