SEC Proposes Cutting Threshold for Marketwide Trading Halts

The U.S. Securities and Exchange Commission began an overhaul of rules adopted a quarter century ago to shut down the stock market and related futures trading during periods of volatility, proposing that curbs be triggered when the Standard & Poor’s 500 Index falls 7 percent.

The changes would switch the index used for circuit breakers to the S&P 500 from the Dow Jones Industrial Average, according to proposals submitted by U.S. equities exchanges and the Financial Industry Regulatory Authority. Index declines that set off halts in stocks, options and futures would be reduced and their duration shortened, according to a summary of the proposals from the SEC.