NASHVILLE, Tenn. — A shortage of nearly 150 school bus drivers is expected to impact about a quarter of the bus routes at Metro Nashville Public Schools (MNPS).

The district operates a fleet of more than 600 school buses. Officials said that an unusually high number of driver resignations this year has created close to 150 openings.

"We weren’t expecting to have this many driver vacancies at the beginning of school," the district said in a blog post on Monday. "So we want you, our MNPS families, to know that some of you may experience delays as your students are picked up and dropped off."

MNPS officials estimated that about 25% of bus routes will be affected by delays.

Meanwhile, the district is taking steps to mitigate late buses, including consolidating routes, using all available substitute drivers, and recruiting and training new drivers. Also, some buses will begin running two routes per school — dropping off one load of students and then going back to pick up more.

MNPS isn't the only school bus operation in the area that's working to recruit drivers. One of the challenges in dealing with the driver shortage, according to MNPS officials, is the "intense competition for drivers that has built up in and around Nashville, including from other school districts and private bus companies."

School Bus Fleet's 2015 School District Survey, which will appear in the upcoming November issue of the magazine, found that only 8% of the districts surveyed have no shortage of school bus drivers.

MNPS held a school bus driver job fair on Wednesday. Another one is scheduled for Oct. 29.

Also, MNPS has assembled a multi-departmental group to develop a long-term strategy for school bus driver retention. This week, the district is conducting focus groups with drivers and is analyzing exit interview data from drivers who have left.

"This information will be used as the district evaluates compensation for bus drivers," MNPS said.

The district's current starting pay rate for school bus drivers is $13.09 per hour.