Urbanization is one of the major current trends in society. Cities around the world are looking into 'smart' solutions based on information and communication technology to deal with the challenges that result from this development. Mobility is one of the most important areas to address, and system-of-systems solutions where vehicles and infrastructure are connected have a potential to improve urban transportation in many aspects. In this paper, current initiatives related to mobility in smart cities around the world are surveyed, and this is complemented with input from focus groups of transportation stakeholders to identify the important aspects of the problem. Based on this, challenges related to the application of systems-of-systems in urban mobility are identified.