DES MOINES, Iowa (AP) — Data shows the number of Iowa school buses flagged for repeated safety citations has nearly doubled since 2012. The Des Moines Register reports nearly 22,000 bus inspection citations have been issued since June 2012. They include unsafe tires, inoperable warning signals or strobe lights and dysfunctional wheel bearings.

The newspaper says most affected school districts have notified state officials that the buses were repaired before they were returned to service. But the state’s education department has sent letters to three districts this year over safety concerns.

The letters accuse the districts of falsifying some repair records. Representatives for two of the districts say some of the issues weren’t necessarily related to the same problem. One district official said a private company is now conducting its bus service.