Valve has just announced today through Steam that the latest DLC for their award-winning game Left4Dead will be available on Sept. 29. Crash Course will add a new singleplayer, multiplayer, and versus mode campaign for the PC and XBox 360.

Crash Course will tie together the end and the beginning of the No Mercy and Death Toll campaigns from the original release. Moreover, it looks like there's an additional 10 new achievements bumping the total to 60 achievements for L4D.