A combination of factors render the transportation sector a highly desirable area for data management research. The transportation sector receives substantial investments and is of high societal interest across the globe. Since there is limited room for new roads, smarter use of the existing infrastructure is of essence. The combination of the continued proliferation of sensors and mobile devices with the drive towards open data will result in rapidly increasing volumes of data becoming available. The data management community is well positioned to contribute to building a smarter transportation infrastructure. We believe that efficient management and effective analysis of big transportation data will enable us to extract transportation knowledge, which will bring significant and diverse benefits to society. We describe the data, present key challenges related to the extraction of thorough, timely, and trustworthy traffic knowledge to achieve total traffic awareness, and we outline services that may be enabled. It is thus our hope that the paper will inspire data management researchers to address some of the many challenges in the transportation area.