It takes most air passengers far more time to reach their destination despite a federal rule that penalizes airlines for stranding them onboard during lengthy tarmac delays, a Dartmouth College-Massachusetts Institute of Technology study finds.

The study, which includes recommendations on how to improve the U.S. Department of Transportation's 2010 Tarmac Delay Rule, appears in the journal Transportation Research Part A: Policy and Practice.

"Overall, the rule is estimated to have significantly increased passenger delays, especially for passengers scheduled to travel on the flights that are at risk of long tarmac delays," says Vikrant Vaze, an assistant professor at Dartmouth's Thayer School of Engineering.

Amid pressure from consumer advocacy groups, the DOT enacted the rule in 2010 in an effort to improve passenger welfare, but faced with potentially large fines, airlines were widely expected to cancel many flights when delays become too long. The rule stipulates that commercial aircraft lift off or allow passengers to deplane no later than three hours after the cabin door closes at the departure airport, and that passengers be allowed to deplane no later than three hours after touchdown at the arrival airport. The rule aims to protect passengers from excessively long delays on the tarmac upon taxi-out or taxi-in, and monetarily penalizes airlines that violate the three-hour tarmac time limit.

The Dartmouth-MIT researchers used actual flight schedule and delay data from 2007 before the rule was enacted, and compared these delays to those estimated for hypothetical scenarios with the rule in effect for that same year. The results show that the rule has been highly effective in decreasing tarmac delays, especially long delays, but each passenger-minute of tarmac time saving is achieved at the cost of an increase of approximately three passenger-minutes in total passenger delays. This is due primarily to increases in flight cancellations, resulting in passengers requiring rebooking and often leading to extensive delays in reaching their final destinations.

"We concluded that a better balance between the conflicting objectives of reducing the frequency of long tarmac times and reducing total passenger delays can be achieved through a modified version of the existing rule," Vaze says. "This modified version involves increasing the tarmac time limit to 3.5 hours and only applying the rule to flights with planned departure times before 5 p.m. Finally, in order to implement the rule more effectively, we suggest the tarmac time limit be defined in terms of when the aircraft begin returning to the gate instead of when passengers are allowed to deplane."

Going forward, the researchers plan to examine the rule's impact on commercial airlines across different years, on commercial airline schedule decision-making and separately on international carriers, regional carriers, legacy carriers and low-cost carriers.