alert announcement be-careful beware black boom boomgate care careful caution communicating communication danger drivers information informing lookout observant observe road road-users safety security sign vehicles warning watch watch-out white access-limited advice advising allocated allocation approved authorised authorized automobiles behave boom-gate communicate denied directive emergency emergency-vehicles entry-denied entry-prohibited limited limited-access no-access no-entry not-allowed not-permitted permission-denied prohibited prohibition red restricted restriction restrictions unauthorised unauthorized