Private traffic flows and freight distribution processes are major sources of energy consumption, noxious gas emissions and noise levels in urban areas, causing negative impacts on the environmental quality of cities. Improvements to transport and logistical systems can help to counter this. Public transport services in particular can be more flexible, taking into account changing mobility requirements (e.g. low demand areas/periods, city-peripheral journeys, and commuting). EU transport ministers have called for more flexible public transport services, including specialised Demand Responsive Transport (DRT) systems that complement conventional scheduled passenger transport, and are more responsive to customer needs.