There are numerous aspects that may facilitate the need for highways in, around and between cities. From meeting capacity needs to changing traffic, growth and development patterns, the needs and reasons for new highways is constantly changing. Add to these reasons the degradation of older highway systems and diversionary requirements, and there are even more reasons as to why a city might need new highways.

Capacity and Traffic Patterns

As cities grow and traffic patterns change, new highways must often be developed to meet increasing vehicle use. Many of the existing highways were built to accommodate usage levels of the 1950s and 1960s and are now just too small to handle the rush of vehicles found in the commuter patterns of today’s major urban areas. Modified traffic patterns - heavy traffic patterns moving from downtown out into the suburbs or vice versa - may also dictate the need for the construction of a new roadway.

Growth and Development

As a city grows and expands or redevelops itself or its surrounding areas, travelers might be in need of new routes in order to get where they’re going. Growing suburbs and housing developments, a new stadium, city site expansions, or a convention center can all draw thousands of people or more to an area. In such instances a new roadway might be needed. It could also be that the development of such areas might come without the necessary public transportation routes or systems necessary to handle the movement of people in and around the city itself and to and from these newly developed areas.

Diversion

While highways can be a critical factor in bringing people into and delivering them from various parts of a city, they can also be just as important to diverting them away from certain portions of a city. A new highway system might be constructed in order to move traffic flow away from areas already congested by an urban environment. It can also serve to route existing transient highway traffic that is not destined for that particular city more easily around the urban area, helping motorists avoid heavier traffic congestion, rather than passing them through the city itself.

Degradation

Sometimes it is not traffic flow adjustments, expansion requirements, or capacity or development needs that create the need for a new highway. It may be that an existing highway is aging or in a state of disrepair. The costs to rebuild or expand the current highway may be excessive or such impractical. It might instead be cheaper or easier to build a new highway rather than repair or redevelop an existing one. In this case, a city may decide to build an entirely new route or closely mirror the existing route, complementing the current one with a new highway that can handle additional traffic flow.