On June 1, the SEC approved two proposals submitted by the national securities exchanges and FINRA that are designed to address extraordinary volatility in individual securities and the broader U.S. stock market. One initiative establishes a “limit up-limit down” mechanism to prevent trades in individual exchange-listed stocks outside of a specified price band. The second initiative updates existing market-wide circuit breakers which halt trading in all exchange-listed securities throughout the U.S. markets when triggered. The changes lower the percentage-decline threshold for triggering a trading halt and shorten the period of time that trading is halted. Changes will be implemented by February 4, 2013, and have been approved for a one-year pilot period. SEC Release. National Market System Plan Approval Order. Market-Wide Circuit Breaker Approval Order.