Older cities that have been established for centuries usually have at least one form of mass transportation, and newer urban areas are often in the process of growing theirs. Some cities have given up on expanding their network due to lack of use, and they have begun focusing on roads and parking lots to accommodate citizens. Others are looking for new ways to expand their transport network to entice new users to switch to a more environmentally safe option.

The need to transport people into and out of urban areas can be difficult as the future comes rushing into being. Environmentalists prefer mass transport networks, but people still prefer or are going back to their own individual needs. Finding the right balance for all concerned is what building urban transportation networks is about, and it is a challenge that will continue far into the future as the needs of citizens continue to change.