Police on Friday continue to investigate how and why a Howard County school bus overturned in Columbia.

The bus crashed Thursday afternoon in the 7300 block of Old Columbia Road, leaving the roadway and landing on its side in a field. No other vehicles were involved in the accident and there were “no indications of driver impairment,” Howard County Police said in a release.

School officials said four students — two boys and two girls between 11 and 14 years old — were taken to the Johns Hopkins Children’s Center for treatment. Police on Friday said the injuries were not considered serious.

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In an email sent Friday, Hammond Middle School administrators said the children who had been injured on the bus are “recovering well” and that police and the school system were investigating the crash.

Police confirmed the bus was being operated by Zum, the Howard County Public School System’s largest bus contractor. The 30-year-old driver wasn’t injured in the accident and was interviewed by police.

In an emailed statement, a spokesperson for Zum said the company is working with the county and other authorities to investigate the incident.

“Getting students to and from school safely is our number one priority,” the email said.

Brian Bassett, a spokesman for the Howard County Public School System, said students weren’t in school today because it’s a workday for staff. When they return on Monday, there will be additional support for students involved in the crash, Bassett said.

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He also reiterated that the driver was not a school system employee, because the bus drivers are through a contractor.

In the message sent from Hammond Middle School on Friday, administrators said students would see a substitute bus beginning on Monday for the affected route, and the principal or assistant principal would be on the bus to provide additional support on Monday.

Baltimore Banner reporters Abby Zimmardi and Jess Nocera contributed to this story.

WJZ is a media partner of The Baltimore Banner.