Do Market-Wide Circuit Breakers Calm the Markets or Panic Them?

Market-wide circuit breakers (MWCBs), which halt trading for 15 minutes across all U.S. stock exchanges, were triggered four times in March 2020. We provide some of the first evidence on the effectiveness of MWCBs using a difference-in-differences approach with tick history data. Although MWCBs increase stocks’ realized volatility and quoted spread immediately after markets reopen, they boost stocks’ trading volume and especially shore up purchases of the stocks that have been hit hard. When we extract the time stamps of stock trading surrounding trading halts, we find significant differences in market opening and reopening time between different stock exchanges. In sum, our results suggest that the MWCBs help to stabilize the markets despite aggravating the trading environment initially.