This article describes a feature in the first Apocalypse Rising
Military Barricades are the small structures set up on streets of towns and partially surrounding military tents. They were used to block zombies and/or stop any civilians driving away to stem the spread of the infection. They could also have been used by the military to stop riots or armed looters as well as defend at evacuation points against the infected. As evidently, they failed. They spawn civilian grade loot as well as military grade loot depending on where they are. If a barricade is in a small grouping of buildings in the middle of nowhere it normally will spawn Civilian Grade Loot. If the barricade is in a bigger town or outside of a Military Tent it will normally spawn Military Level Loot. Both variations can spawn both military and civilian loot, but the aforementioned rule still stands.
Roadblocks seem to be three wooden planks, or logs, with some metal on each side. These were probably meant to quarantine the infected, but failed. These mainly spawn provisions and ammunition, but can spawn other items as well.
Military barricades can temporarily block zombies from getting to you, as it takes a while for them to jump over them. It can be a good tactic if you are overwhelmed by the undead. Another option is to engage an armed assailant because of the limited ability for your attacker to hit you, along with just enough space for you to shoot back. The only real place that a player could hit you is if they drew a bead on your head. A good way to avoid this is to move back and forth behind the barricade making it difficult for your opponent to get an accurate round off.
This poses a threat when attacking using a melee weapon, because the zombie is unreachable by some melee weapons, but the zombie can reach you. Make sure if you are going to engage a zombie you flank around to the other side of the barricade. Thus the zombie will be able to freely move towards you and no obstructions will stop you from taking it out. Military Zombies or any other type of zombie do not spawn with barricades, they spawn in towns and clumps of buildings which may include barricades.
Overall Barricades can play a key role in a players survival by providing adequate, not great protection from players and zombies. They spawn different loot depending where they are located and what structures they are grouped with. The only danger the barricade poses is an obstacle for vehicles like Roadblocks. For one, barricades can damage any part of a vehicle if hit. Second, you can get trapped in small area allowing attackers to have an advantage when shooting at you and your vehicle.
These and Military Tents are the first places most players should loot when in cities/towns.
These are EXTREMELY annoying when you have a car, and are one of the reasons that some unskilled people do not drive anything but bikes through towns.