[ElderScroller27]

I found a tactic that worked out well.

#1. Jump into the car in the parking lot just outside the tunnel. drive it underground and take an immediate left turn, Drive up to the top left corner by the meat processing room, *there is a drivable van parked there* You ditch the car in a corner and transfer to the van,

#2. Now that you have the Van you drive it down into the dead end hallway by the storage room where the tunnels key was **the room in the very center of the tunnels* Back up out of that tunnel and drive back up to the meat processing area where you got the van. By now the van is on it's last legs so you want to dismount the vehicle and enter the meat processing door. Immediatly step back out into the tunnels and the van will be respawned in it's parking space ready for another run back down to the Storage room.

You will get between 700 and 1200 kills per trip. The variable seems to be how many propane tanks you run over because their blast radius can often kill 50 to 100 zombies each. If you hit a wall more than 2 times your vehicle will usually stop running in the middle of a tunnel heading back to the meat processing area. if this happens it's usually quickest to run up the ramp outside and grab the red car to get you back to the van. any way you slice it this achievement is going to take 3 to 5 hours of zombie mashing.