When it comes to monetary policy, Federal Reserve Chair Janet Yellen is doing all she can to ensure there's little difference between herself and Ben S. Bernanke. The bond market is taking notice.

Measures of volatility based on interest-rate swaps have plunged this year and are now approaching levels not seen since before the Fed first signaled in May its intention to reduce the unprecedented bond buying that's supported the U.S. economy, according to data compiled by Bloomberg.

The relative calm underscores the strides Fed officials have made in reassuring investors that its pullback won't automatically lead to higher interest rates. After yields on 10-year Treasuries reached a 29-month high at the start of the year, they have since retreated as Yellen pledged to maintain her predecessor's tapering policy in "measured steps" and keep borrowing costs low to support the U.S. labor market.