I always wondered what happened to the four survivors in Left 4 Dead between the No Mercy and Death Toll campaigns. I mean, one minute they are getting to the choppa(!) and the next they are on some backwoods interstate. Thankfully, Valve is answering that question this September with some DLC for the PC and Xbox 360.

The DLC, entitled Crash Course, will bring new single-player, multiplayer, and co-op gameplay to the zombie apocalypse. The standard Survival mode and co-op campaign will get the maps with new locations, new speech banks from the original cast, and an “explosive finale.” Yet the focus of the DLC is to bring a complete Versus mode in under 30 minutes, giving a streamlined version of the existing Versus modes. Valve has added a recharge timer for infected teammates and changed the item spawn behavior to make gameplay more balanced.

“Since the release of Left 4 Dead last November, the design team has been excited about creating new experiences for this world and allowing players to do the same, by releasing much of our internal toolset, like the Survival Pack and Authoring Tools,” said Gabe Newell. “We’re working with the fans toward the ongoing entertainment value of the product.”

Crash Course will be free for PC users and run 560 Microsoft Points for the Xbox 360 version. Anyone thinking about getting this only two months before the sequel hits?