BOSTON — About 70 school bus drivers took sick or personal days yesterday, leaving hundreds of students to find other ways to get to school.

Dr. Carol Johnson, superintendent of Boston Public Schools, said in a statement that as many as 12 bus routes were canceled Monday morning, affecting an estimated 680 students.

The district used an automated phone-call system to notify families with children on the canceled routes. Students who couldn’t make it to school because of the cancelations were excused.

"We apologize to families for this disruption and inconvenience," Johnson said Monday. "When school is open, we rely on our bus drivers to get more than 30,000 students safely to and from school. More than 600 drivers arrived at bus yards early this morning ready to work, but it is very problematic that 70 other individuals stayed home."

The number of absent drivers outweighed the number of backup drivers — about 60. But district officials said they expected to secure enough additional bus drivers during the day to adequately cover afternoon routes, although delays were likely due to icy roads.

First Student Inc. provides bus service for the district. According to The Boston Globe, the company said in a statement that the high absentee rate was due to the weekend storm and ensuing icy conditions, but many of the drivers who had been absent Monday morning reported to work that afternoon.