Before 8 a.m., traffic is light; however, at 5 p.m., Fred always wishes that he drove a bulldozer to push other cars out of his way.
1. light;
2. No change is necessary
Explanation:
In the sentence above, a semicolon is used after the word light, to denote that two contrasting clauses are to be beside each other in the same sentence.
The use of however which is a conjunctive adverb and a comma after it is fine and should not be changed because it is used to link together two independent clauses.