The transportation - urban form nexus lies at the heart of urban sustainability. Transportation provides the physical connectivity between people, firms and activities that permits economic and social interactions to occur. It also provides physical definition to urban areas in terms of the street system and our perceptions of how locations "connect" in space and time. And the accessibility to opportunities that it provides influences land development decisions and location choices of households and businesses. In particular, as urban areas continue to expand, automobile-dominated transportation systems both facilitate and promote inefficient "sprawl" that has ramifications for all elements of urban physical and social infrastructure (water, handling of wastes, schools, heath care, etc.) in addition to the transportation system per se. Urban form (i.e., the spatial distribution of people, businesses and other activities), in turn, fundamentally determines both travel demand and the cost-effectiveness of alternative forms of transportation. Most notably, public transit systems (as well as non-motorised modes of travel such as walking and bicycles) can only provide effective alternatives to the automobile if transit- and pedestrian-oriented urban forms are built. Transportation systems are major generators of greenhouse gases, air pollution and noise. They are also almost totally dependent on non-renewable fossil fuels as their source of energy. This paper sketches the broad dimensions of the modern urban transportation design problem, with emphasis on its connections with other elements of urban design, particularly the question of urban form. These dimensions include both physical infrastructure and services (roads, transit services, etc.) and the intelligent operational control of these facilities and services. Elements of a coordinated research program to address pressing short- and long-run urban transportation planning problems are then outlined.