Metadata--information about data sets--allow clear understanding of exactly what the elements and structure of a given data set entail. Metadata in conjunction with XML-based specifications, schemas, and tools allow a high level of automated and validated interworking between different types and sources of data. This is an issue of emerging importance to transportation, traffic, and planning, and the communities they serve, as these areas are all data intensive but with very different views of the world. The potential of this linkage is outlined, and a progression is made through a simple example metadata specification for nonmotorized transport, the agreements developed by the geospatial community for geographic data and the transport layers within them, and the formal XML document. The XML specification and validation approach now makes possible and practical a more effective and more accessible use of the information in the multiple fields linked through their involvement in transportation. The key outcome required is a vocabulary (or integrated vocabularies) of globally agreed-upon metadata element definitions for the various fields in and overlapping transportation. The advent of formal document specifications of which XML is a widely used example would then allow a significant expansion of the accessibility, use, and reuse of such data to the great benefit of the user, policy, and analysis user communities.