A barrier, also called plum or talanquera in some countries,[1]​ is a bar that temporarily prevents the passage of vehicles on a certain road or passage so that identity can be verified, or prevents passage to avoid accidents while another vehicle or train is traveling on that road.

They are mainly installed at level crossings to stop automobile traffic while the train travels through that section of its route. It is also common to find barriers in parking lots, tolls, tunnels and drawbridges.

The barriers can be manual or automatic.

The proper functioning of the barrier, as well as its adequate signage, are extremely important points to avoid accidents. So that it is not necessary to install new barriers or to eliminate existing ones, trains must travel at a different level than vehicles. This can be achieved through tunnels or bridges for vehicular traffic, or by having the train run underground (buried) or above the road level.