Ms. Procter gained notoriety when she struck a jogger with her metrobus earlier this September and consequently earned media scrutiny. Our favorite hometown paper, the Washington Post uncovered a host of prior incidents and tickets
which tended to put Ms. Procter in an unfavorable light. http://www.washingtonpost.com/wp-dyn/content/article/2009/09/15/AR2009091503546.html?nav=emailpage
The specifics of the firing were alluded to only as "failing to follow standard procedures". This bureaucratese probably means running over law-abiding citizens and exposing Metro to big civil liability.
This of course comes on the heels of the horrendous June 22nd Fort Totten Metro crash and a rash of other deaths and incidents.