Which 1987 market reform introduced coordinated trading halts after the Black Monday crash?

Circuit breakers were the 1987 market reform introduced as coordinated trading halts after the Black Monday crash.

The October 19, 1987 crash exposed how rapidly selling could spread through international markets and computerized trading systems. In the United States, the Dow Jones Industrial Average fell 22.6 percent in its largest one-day percentage decline.

Regulators and exchanges responded by creating circuit breakers, also called trading curbs. These rules pause trading when a broad market index moves by specified amounts. The pause is intended to give investors time to assess information, reduce panic, and allow orders to be processed in a more orderly way.

Circuit breakers do not prevent prices from falling and are not the same as ordinary exchange closures. Their thresholds and operation have changed over time. U.S. equity-market rules now use percentage movements in the S&P 500 for market-wide halts, while individual securities can also trigger separate limit-up and limit-down protections.