A Sig Alert is defined by the California Highway Patrol as "any unplanned event that causes the closing of one lane of traffic for 30 minutes or more, as opposed to a planned event like road construction, which is planned separately." Sig Alerts are issued by the CHP and are posted on their Web site, broadcast on radio and television stations throughout California, and signalled to motorists via electronic message signs on the freeways. The term was added in 1993 to the New Shorter Oxford English Dictionary. (In practice, there is no standard spelling; the CHP Web site uses "SIG Alert," "SigAlert," and "Sigalert," all on the same page.)