8)
which topic would be the best main idea for a new paragraph, that
would be inserted between the current paragraphs 2 and 3?
a)
the cost of those roads
b)
the accessibility of certain roads
the speed limit on interstate roads
d)
the safety measures provided for those roads

the safety measures provided for those roads

Explanation: The second paragraph deals with the high cost of the mobility we value as Americans. There is a cost involved with making sure the roads we drive are safe: (e.g. snow plows, salt in icy conditions, road signs, speed bumps, traffic lights, etc.), and the idea of safety is introduced but not developed in paragraph 2. Therefore, the safety measures provided for those roads would be an appropriate topic for a new paragraph to follow paragraph 2.

where is the graph?

i only can answer with a graph!