LINCOLN, Neb. (AP) — School districts throughout the U.S. are struggling to find school bus drivers, a challenge that has worsened with low unemployment and a strong economy. The problem has become so severe that some districts are offering sign-up bonuses for new drivers, while others rely on mechanics, custodians and other school employees to fill the gap. For parents and students, the shortage can mean longer waits for a ride to school and more crowded buses.

The shortage stems from a variety of factors, including limited work hours and high barriers to entry. Drivers generally need a commercial driver’s license, which requires training, sometimes without pay, said Mike Martin, executive director of the National Association of Pupil Transportation. “Unless you have something to fill in the gaps (between drives), you can’t make the money you need to support your family,” Martin said. “These days, most people are looking for some kind of regular, full-time hours.”  He said also, many districts require split morning and afternoon shifts for their drivers, which some consider a hassle. Keeping an eye on noisy children while facing away from them can be difficult as well.

In Iowa’s Southeast Polk Community School District, transportation director Daniel Schultz said the persistent shortage has grown worse in the suburban Des Moines district because there aren’t as many retired farmers, a group that commonly took the job for extra income. Now, the district relies on 51 drivers — mostly retirees and stay-at-home parents — to transport roughly 3,400 students to and from school each day. Even with administrators and bus mechanics filling in, the shortage has also resulted in fewer routes, more children waiting at each stop, and crowded buses. The district needs to hire six to eight more drivers, according to Schultz.

Pay starts at $19.10 an hour, followed by a $2-an-hour raise after six months, Schultz said, but the district struggles to fill open jobs. Schultz said he’s now considering a “monthly rodeo” where potential drivers could test-drive a bus in a school parking lot.