If you got trapped in the city or decided to wait it out as the mass of people tried to flee at some point you will have to leave the city’s and large towns for somewhere more remote.
You might have a pretty secure base with a good group of survivors with you but as time goes if you are in a city the number of zombies at or near your base will be too many.
If zombies close in on your base apart from the danger to you as well as your group it also makes it harder and, more dangerous when you enter or leave your base.
The cites are also more likely to have disease or other health risks apart from the chance of a zombie biting you so as soon as you can you should look to pack up and move to a more deserted area.
Hopefully you have picked up a welding set up so you can add strong metal protection to your vehicles and then are able to fit all your group, supplies and enough fuel and weapons.
When you leave your base and the city for a more remote place you convoy will have to stay together for protection and, move quickly to avoid zombies but still not to fast so you can avoid obstacles in the road.