As a human who lives in the city, you must need to park your car in a parking lots where a parking barrier gate was installed. Sometimes you may drive your car and hit the barrier arm by accident, as a result the arm may be broken and your car got damaged too. However if the boom barrier was equipped with swing-off device, both your car and barrier arm will be fine even the car hit the arm. Below you will understand how Dashou barrier gate arm swing off against a hit by car. 

If a swing-out module was installed, the boom arm will swing off 90 degree if it was hit by a vehicle, this will protect both vehicle and boom. It is optional but very useful fundctionf for the safety of both car and arm. You can easily add swing-off module to a barrier which is without swing-off. Check below videos for details.