Standoff distance is also intended to deter terrorists from using car bombs by making it more difficult for them to cause catastrophic damage . In the wake of the Oklahoma City bombing , 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 - because blast falloff is thus often more exponential than linear ( indeed radial - any given explosive must cover a circular-shaped area but blast power generally only increases linearly with explosive strength ) , any standoff distance helps increases survival chances for passersby and minimizes danger , though shrapnel mitigates this effect if present . Hydraulic roadblocks ( 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 barriers and concrete planters filled with dirt 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
Oklahoma City bombing
Oklahoma City bombing
Standoff distance