Define externality in the context of traffic operations.

In the context of traffic operations, externality refers to the unintended consequences affecting third parties that are not directly involved in a transportation activity or decision. This can include a variety of impacts, such as increased air pollution, noise pollution, or congestion caused by the transportation system that affects residents or businesses nearby.

When transportation planners or engineers assess the impacts of transportation projects, they need to consider these externalities to develop strategies that minimize negative effects on the community. This recognition of externalities is crucial for sustainable traffic management and urban planning, as it helps to ensure that the benefits of transportation projects are weighed against their social and environmental costs.

The other choices, while pertinent to traffic operations, do not capture the essence of the term "externality." Planned transport projects and intended consequences relate to the direct objectives or goals of those projects, while a type of traffic accident is a specific event that does not encompass the broader, indirect impacts on third parties.