Take another look at the original sentence:
You wanted to fix it this way:
To delete the comma between ahead and he would cause an equally bad problem, a fused sentence. A fused sentence occurs when you have two main clauses joined with no punctuation whatsoever. Many road signs warned Tommy of the construction work ahead ... begins the first main clause. He didn't realize is the second main clause. The spot between ahead and he needs a stronger break than blank space.
You might want to consult the rules for fixing comma splices and fused sentences.