Which of the following is an example of an externality in traffic operations?

An externality in traffic operations refers to a consequence of an activity that affects other parties who did not choose to incur that cost or benefit. In this case, noise or air pollution from vehicles is a clear example of a negative externality.

When vehicles operate, they generate emissions and noise that can affect the health and quality of life of nearby residents and commuters, even if those individuals are not directly involved in the decision to use those vehicles. This impact is not reflected in the travel costs incurred by the drivers and can lead to social costs that society must bear. Therefore, the pollution created represents an external cost affecting public welfare, making it an externality in traffic operations.

Traffic congestion during peak hours represents a situation where users experience delays, which doesn't reflect a cost or benefit beyond that interaction; road markings on highways are a necessary infrastructure component and do not produce external effects; increased toll fees, while a financial burden on users, do not create a secondary impact on non-users in the same way as pollution does.