As a result, there is an increasing pressure on existing natural resources such as water, land and fossil fuels. Additionally, there are growing concerns regarding existing transportation infrastructure, provision of adequate healthcare, access to education and overall safety for the growing population of urban residents. Traditionally, there have been two types of infrastructure: physical (buildings, roads, transportation, power plants) and digital (information technology and communication infrastructure). There is also the concept of a service infrastructure which provides services which run on top of the physical infrastructure (education, healthcare, e-government, mass transit).