A city street is a. always a public good, whether or not it is congested. b. a public good when it is congested, but it is a common resource when it is not congested. c. a common resource when it is congested, but it is a public good when it is not congested. d. always a common resource, whether or not it is congested.

c. a common resource when it is congested, but it is a public good when it is not congested

Explanation:

we have to look at the definition of public good:

A public good when consumed to not impact nor deprive other from consuming (the light of a lighthouse) Thus are non-rivalrous and available for everyone.

The city-streets have this concept but, their supply is compromised when congested as the sheer amount of vehicles reduced the use of that street for other drivers (they go along and drive for other street)

Thus, we can state city street are quasi-public goods which, behave as common resource when congested.

a common resource when it is congested, but it is a public good when it is not congested.

Explanation:

We live in different areas, across city streets, with roads and they can either be public goods or common resources. Now, when the streets are not congested, it simply means that an individual can freely access the areas without that affecting any other person. In this simple case, the use by one person is not in rival consumption and so the streets are said to be a public good. But when the area is fully congested, people might find it difficult to move around through the areas. The use of the areas could cause negative externalities. Because the place would be overcrowded, people can only move at a slow pace. In this case, the street are said to be a common resource.