Factual error: When Sarah's family is fleeing Richmond, the highway sign says "Interstate 66." That highway is about a hundred miles north of Richmond; it starts in Washington DC. Another highway sign says "Virginia Beach 12 miles", which is the wrong way when fleeing Richmond westward.
Suggested correction: The sign says "Virginia Beaches," not Virginia Beach, so it could be anywhere in Virginia that has beaches.
Living in Virginia, there is no sign that says "Virginia Beaches 6 miles." "Virginia Beach" is a large city at the SE corner of Virginia and is more than 10 miles across. Any sign referencing the actual beach says "oceanfront x miles." Virginia Beach also has the tallest building in Virginia, the Westin hotel in downtown.
Plot hole: The government would have no chance of hiding the existence of the comet for a year. Most comets are discovered when they are very faint, literally thousands of times fainter than Wolf-Beiderman when Leo found it. Long before the events in the film take place, probably even before the government itself would be notified, the comet would have been discovered, an orbit calculated, and people panicked. The whole premise of the first half of the movie is thus based on flawed logic.
Suggested correction: Only 3-4% of the visible universe has been discovered. Meaning this comet could have been discovered much later.
