Revealing mistake: The parade is supposed to take place around Christmas, but in some scenes looking down from above, we see very short shadows under the floats and people (indicating filmed during summer). At Christmas, shadows are long all day especially in Minneapolis.
Other mistake: When Howard, as TurboMan, is stuck spinning around in the sign at the end, the parade crowd disappears.
Continuity mistake: Howard arrives back at his home in a tow truck. It is obviously late in the day judging by the sun angle. In the next scenes however it is afternoon. The parade takes place in bright midday sunshine.
Answer: The cop never states why he pulled Howard over, what he was charging him with or how many tickets he was issued. Howard just says, "I got a speeding ticket.' and holds up a folded piece of paper, so it's likely the ticket was for driving on the shoulder.