Bus is probably the most efficient vehicle to move through the city during the zombie apocalypse. It's high and hard to get, but still you should not stop. Rescue all survivors and get to the safe spot.
Hold the steering wheel of the Hell Bus and find the best spot to hide. Rescue all survivors you will find on the map before reaching the safe spot. Kill zombies on your way, but don't spot or the bus will get damaged. Drive safely, otherwise you lose HP and the trip will be over. Save your health for reaching other territories.