In August 2009, there were 66 flights with passengers were stranded in planes for more than 3 hours, the DOT said. In August 2010, there was only one such incident, the department said Tuesday.
U.S. airlines made the improvement without any change in the rate of canceled flights, which could have affected the data.
The lone flight delay that left passengers stranded past the DOT maximum was a United Airlines flight leaving San Juan, Puerto Rico, that was a diverted flight.
The new rule mandating passengers be allowed off the plane if delayed for 3 hours or more on a runway went into effect April 29.
"These numbers who that the tarmac delay rule is protecting passengers from being trapped indefinitely aboard an airplane -- with little or no increase in canceled fights," U.S. Transportation Secretary Ray LaHood said.