In this political cartoon, “the open road,” the people symbolize

wealthy citizens of that era.
improvements brought about by urbanization.
types of people causing social injustices.
urban problems of that time.

Urban problems of that time.

Explanation:

In the political cartoon "The Open Road," we see the Progressive Party moving forward. We also see a group of people who are "walking" towards liberty, justice and equality (the goals that the Progressive Party wants to achieve). These people have labels on them, such as "poverty" and "child labor." These are the urban problems of the time that the Progressive Party wants to eliminate.