By David Shepardson

Greyhound Lines, the largest U.S. bus company, agreed to pay a $125,000 (102,183 pounds) penalty to the District of Columbia and will bar idling by buses when parked nationwide, according to a court filing on Thursday.

Greyhound, a unit of FirstGroup PLC, agreed to settle the District's 2019 lawsuit, District of Columbia Attorney General Karl Racine said in a statement. Buses must now be immediately turned off while parked and drivers will get training on the new policy and can face discipline if they do not comply.

Greyhound, which transports about 16 million passengers a year in North America, said it was pleased to reach a settlement and "is committed to following the District's environmental regulations. Bus transportation is known as one of the most ecofriendly forms of travel and we are eager to improve upon our anti-idling policy."

Vehicle exhaust is the largest source of air pollution in the U.S. capital, Racine said.

Greyhound will also send regular text messages to all drivers and install stickers in all buses to remind drivers that engine idling is not allowed.

(Reporting by David Shepardson; Editing by Chizu Nomiyama and Peter Cooney)