This is an inference question. There are two key findings in the passage: that automated toll rates are higher than manually collected toll rates, and that manually collected tolls do not increase as much during election years as other years. The inference (or conclusion) in the correct choice will likely have something to do with one of those. Consider each one:

(A) This contradicts the claim in the passage, and there is no evidence to support it.
(B) If anything, this is opposite of what we're looking for. The final sentence of the passage suggests that manually collected toll rates may be politically motivated, while automatic tolls are not. This statement claims the opposite.
(C) This is correct. It is the most likely explanation of the election-year distinction, and the distinction in election years between manually collected tolls and automated tolls.
(D) This may or may not be true. We know that manual toll rates increase more in non-election years than in election years, but not how those rates compare to automated tolls in the same years.
(E) This statement may be true, but it goes far beyond the claims made in the passage. Thus it is not a reasonable inference to make.