It’s important to ensure that there is enough area behind a temporary barrier to accommodate the barrier’s deflection and the vehicle roll allowance.  

The Working Width of a barrier system is the Dynamic Deflection + System Width + Roll Allowance. These distances differ for different systems.  

Workers are at risk if they are in this zone, but we also need to think about objects in that zone, like signs, vehicles, lighting and plant. These items may become projectiles or may pose a risk to the safety of the errant driver.