Instructions
Run out of the mall into Leisure Park. You should see a red car parked nearby.
Hop into the red car and head down the ramp into the parking garage. Take your first right once you reach the tunnels, then the next left. Turn right at the next turn and drive until you hit a dead end.
Enter the room at the end of this path to find the Maintenance Key. This key unlocks the path to the maintenance tunnels that run below the mall.
Head into the maintenance tunnels and take the first right. Drive over a few zombies in the red car, then turn around and drive all the way to the most northwestern point on the map. Here you will find a delivery van.
Take the delivery van and drive south until you have to go left. Run over as many zombies as possible on the way. Take the forced left, and then turn right at the intersection. Follow this path, running over zombies as you go.
Turn right at the next intersection and you will find the white car. You can also run upstairs to save your game.
Hop into the white car and drive back out of the maintenance tunnels, hitting zombies all the way. You will reset the vehicles when you exit the tunnels.
Hop in the red car again and repeat the process until you have amassed the necessary 53,594 kills.
Run into the security office in the mall once you have the right number of kills and wait for the game to end. You will not earn the achievement if the main character dies or if you do not wait for the game to end naturally.