Standoff distance is a security measure that focused on preventing unscreened vehicles from approaching within a certain distance of a building. It is intended to deter truck bombs by making it more difficult for them to cause catastrophic damage. In the wake of the Oklahoma City bombing

Oklahoma City bombing

The Oklahoma City bombing was a terrorist bomb attack on the Alfred P. Murrah Federal Building in downtown Oklahoma City on April 19, 1995. It was the most destructive act of terrorism on American soil until the September 11, 2001 attacks. The Oklahoma blast claimed 168 lives, including 19...

, many high-risk federal buildings began enforcing standoff distances. It is based on the concept that a blast shock load is essentially a high-pressure front that moves out radially and decays very quickly. Hydraulic road blockers (sometimes wedge-shaped), or bollards can be raised to block approaching vehicles; these can be designed to prevent even a heavy, fast-moving truck from getting through. Jersey barrier

Jersey barrier

A Jersey barrier or Jersey wall is a modular concrete barrier employed to separate lanes of traffic. It is designed to both minimize vehicle damage in cases of incidental contact while still preventing crossover in the case of head-on accidents....

s and concrete planters have also been used to maintain separation between screened and unscreened traffic. Certain infrastructure at risk of terrorist attack, such as bridges, may not be well-suited to standoff distances since their purpose is for traffic to travel along them.