Essentialy walls that you can place around on the path, zombies will usually ignore them unless they are blocking the way. Bloaters, Devastators and their skeleton hordes, and a new enemy will always home in on sandbags and attack if they are even near their route. They can be upgraded as well.

The Upgrades

Path 1: Intergrated Barbed Wire ($45 in-game cash, only upgrade on this path.)

Path 2: Jersey Barrier ($35 in-game cash), Titanium Anti Tank Barricade ($1000, must unlock first for 300 SAS dollars.)