If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
In a world filled with zombies, you are the only one who has the guts to rescue what's left of human kind. Take your school bus and drive through the city in the search for survivors. Use it to run over zombies in your path, and kill others with the weapons at your disposal. In each safe zone, improve your bus with new weapons, heavy bumpers and hardwire, among other upgrades. In your search for salvation, look for supplies left by the army.