Lub bollard nres tsheb uas muab tais tau yog ib yam khoom siv ruaj ntseg uas tsim los tswj kev nkag mus rau hauv qhov chaw nres tsheb ntiag tug. Cov bollards no tuaj yeem tsa lossis txo tau yooj yim, ua rau muaj kev nkag mus rau hauv lub tsheb ib ntus lossis mus tas li. Thaum tsa, lawv ua haujlwm ua ib qho kev thaiv, tiv thaiv kev nres tsheb tsis raug cai; thaum txo qis, lawv tso cai rau cov tsheb hla mus tau yooj yim.
