After the general population realizes about the zombie threat the first thing they will do is grab family members and then try to flee. The problem is most Americans live in big cities where traffic isn’t the greatest and not always easy to get around.
Now imagine everyone that hasn’t turned in to a zombie getting on the road at the same time trying to escape the cities. The traffic in many cities such as Los Angeles will be gridlock and then add to that crashed cars blocking the road because of being stopped by zombies or in accidents as people panic and ignore road rules.
As the police and the military figure out whats going on they may be able to set up road blocks and try to protect their own bases as well as hospitals and start to create small safe zones. The police and government will also be dealing with members of their own ranks that have turned in to zombies which will distract them somewhat.
Looting of stores and businesses would be widespread but as its people getting supplies to survive no one would try to stop them and besides law enforcement would be busy elsewhere.
Most likely television and radio would broadcasting the Emergency Broadcasting System so just general information no localized news which would be tough on people to figure out where is safer.