A car bomb, or truck bomb, also known as a vehicle-borne improvised explosive device (VBIED), is an improvised explosive device placed inside a car or other vehicle and detonated.
Car bombs can be roughly divided into two main categories; some are used primarily to kill the occupants of the vehicle (often as an assassination) and others are used as a means to kill, injure or damage people and buildings outside of the vehicle. The latter type may be either parked up (the vehicle disguising the bomb and allowing the bomber to get away) or the vehicle might be used to deliver the bomb (often as part of a suicide bombing).
It is commonly used as a weapon of terrorism or guerrilla warfare, to kill people near the blast site or to damage buildings or other property. Car bombs act as their own delivery mechanisms and can carry a relatively large amount of explosives without attracting suspicion; in larger vehicles and trucks, weights of at least 7,000 pounds (3,200 kg) have been used, for example, in the Oklahoma City bombing. Car bombs are activated in a variety of ways, including opening the vehicle's doors, starting the engine, depressing the accelerator or brake pedals or simply lighting a fuse or setting a timing device. The gasoline in the vehicle's fuel tank may make the explosion of the bomb more powerful by dispersing and igniting the fuel.
Car bombs are effective weapons as they are an easy way to transport a large amount of explosives to the intended target. A car bomb also produces copious shrapnel, or flying debris, and secondary damage to bystanders and buildings. In recent years, car bombs have become widely used by suicide bombers.
Defending against a car bomb involves keeping vehicles at a distance from vulnerable targets by using roadblocks and checkpoints, Jersey barriers, concrete blocks or bollards, metal barriers, or by hardening buildings to withstand an explosion. Since the height of the Provisional Irish Republican Army (PIRA) campaign in 1991, the entrance to Downing Street has been closed, preventing the general public from getting near Number 10. Where major public roads pass near buildings, road closures may be the only option (thus, for instance, in Washington, D.C. the portion of Pennsylvania Avenue immediately in front of the White House is closed to traffic). Historically these tactics have encouraged potential bombers to target "soft" or unprotected targets, such as markets.