observation posts may also be positioned further out if desired. When large geographical areas need to be monitored, some types of checkpoint may be quickly airlifted by helicopter from one location to another. Flying roadblocks and checkpoints are usually established for no more than a few hours, in order to decrease the possibility of insurgent attacks on them, as well as to maintain their effectiveness as a surprising, unexpected obstacle. Random checkpoints are a common tactic used by many military forces, and have been recently used by UN forces in Kosovo, the Israeli army in the West Bank and US forces in Iraqi Kurdistan, and Iraq in search of insurgents, fugitives, and other law breakers. In some war zones, soldiers working at these checkpoints can be severely injured or killed if one of the vehicles they are searching contains a suicide bomber who detonates his or her bomb or if one of the occupants fires upon soldiers. Sobriety checkpoints Sobriety checkpoints or roadblocks involve law enforcement officials stopping every vehicle (or more typically, every nth vehicle) on a public roadway and investigating the possibility that the driver might be too impaired to drive due to alcohol or drug consumption. They are often set up late at night or in the very early morning hours and on weekends, and on holidays associated with parties (e.g., New Year's Eve) at which time the proportion of impaired drivers tends to be the highest. Checkpoints are also often set near the exit points of public events where people have been drinking to prevent large numbers of drunk drivers from being released into traffic simultaneously from the event. A roadblock stop is quick action spot for police as well as security personnel. With a portable and quick Breathalyzer test, the police can test all drivers (if the law permits) for their breath alcohol content (BrAC), and process the cars one by one as if in a conveyor belt. If a police force does not have these testing devices, a more complicated routine is necessary. Upon suspicion that the driver has consumed alcohol, due to the officer noting the smell of alcohol, slurred speech, or other signs, the stopped driver is required to exit the vehicle and asked to take a series of roadside field sobriety tests (FSTs or SFSTs). These tests help the officer to determine whether the person's physical and/or mental skills are impaired.