Police have arrested the driver thought to be behind the wheel of an out-of-service MTA bus that killed a 70-year-old woman on Tuesday morning.

The driver, identified by police as Paul Roper, 48, was charged with leaving the scene of an accident, failure to yield to a pedestrian and failure to exercise due care in the death of Carol Bell less than a block away from her home.

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Advocates for pedestrian rights firmly believe the death was avoidable.

Paul Steely White, executive director of Transportation Alternatives, told Metro that the driver had an obligation to yield to the woman who was crossing Fulton Avenue at Sackman Street at around 6:15 a.m. Tuesday.

White described anyone who would hit a pedestrian and drive away from the scene as an "unyielding and uncaring driver."

"As of right now, we can say absolutely that she had the right of way," he said. "It's very clear that the driver had an absolute responsibly to yield to that woman."

RELATED: Pedestrian deaths drop in first year of Vision Zero

Roper allegedly turned onto Fulton Street as Bell used her wheeled walker to cross the street.

Paramedics said she died at the scene not long after the bus driver drove away after striking her. 

"The bus was not in service at the time," said MTA spokeswoman Amanda Kwan, adding that it had completed its B15 route and was on the way to the agency's East New York depot.

"This is a terrible tragedy, and our hearts and prayers go out to all family and friends," said John Samuelsen, president of the Transit Workers Union Local 100, which represents bus drivers. "We will closely follow the investigation, which is in a very early stage."

RELATED:   Vision Zero aims to eliminate traffic and pedestrian deaths in New York City

Earlier this year, the TWU launched a media campaign targeting Mayor Bill de Blasio and his Vision Zero plan to drive down traffic related deaths across the city.

The union at the time accused the mayor of "criminalizing an entire class of hard working, law abiding unionized workers" after six MTA bus drivers were charged with misdemeanors thanks to a 2014 law that increased penalties for injuring or killing pedestrians with the right-of-way.

In September, the city modified understanding of the law to say charges against drivers must demonstrate that they failed to both yield and exercise due care.

A spokesman for the mayor's office did not respond to requests for comment.

But at an unrelated presser, Mayor de Blasio did say his administration remained resolute in its commitment to Vision Zero. 

"Every time we lose someone, we say, you know, this is something that we need to keep reiterating to people — the care they need to take with driving," de Blasio told reporters. "And I think more and more people are getting it."

In September, the administration reported an overall 12.6 percent drop in traffic fatalities, a decrease of 249 from 285 in the latest fiscal year, with pedestrian deaths decreasing to 143 from 158 in the same period.