An MTA bus driver was arrested after killing an 81-year-old pedestrian on Wednesday night as she crossed Bay Parkway — with the light and in a crosswalk.

Police said B6 driver Audley Smith, 62, turned right from Stillwell Avenue at around 8:07 p.m. and slammed into Yu Qing Chen. When police arrived, they found Chen “unresponsive with head trauma.” She died later at Maimonides Hospital.

Smith was charged with  failure to yield to a pedestrian and failure to exercise due care — both misdemeanors punishable by up to 30 days in jail, according to the Brooklyn District Attorney’s office.

An MTA source said the bus was out of service at the time.

“This is a terrible tragedy and our hearts go out to Ms. Chen’s family,” New York City Transit President Andy Byford said in a statement.

The numbers of such deaths under the wheels of MTA buses has dropped dramatically since the City Council criminalized failure to yield in 2014 via Council Intro 238, which was opposed bitterly by the transit workers’ union. Before the law passed, police were not even investigating crashes that hurt New Yorkers unless officers personally witnessed the collision or the victim was deemed likely to die, Streetsblog reported.

But it is not always meted out uniformly. The MTA bus driver who killed 7-year-old Shevon Bethea on Webster Avenue in the Bronx earlier this year was not charged.

Earlier this year, the Post reported that MTA buses were involved in more than 21,000 crashes or “other mishaps” since 2015 — an average of 23 per day. Those “mishaps” led to the deaths of 14 people, the newspaper reporter, though not all were pedestrians.