CHARLOTTE, N.C. – Plagued by two fires on school buses in the last 30 days, Charlotte-Mecklenburg Schools is trying to make it easier for drivers to determine if the lug nuts on their buses are tight.

A wheel fell off a CMS school bus last August shortly after school opened for the new year.

RELATED: School bus catches fire in southwest Charlotte

The bus was carrying students from Garinger High when the wheel fell off. There were no injuries.

The incident was later blamed on a technician who failed to properly tighten a lug nut. The new solution is the addition of green pointers to each lug nut.

RELATED: Manufacturer joins CMS investigation of bus fire

If the green pointers are all lined up in one direction, the nut is tight. If one is pointing the wrong way, attention is needed.

CMS said drivers will now check the green pointers as a routine part of their visual inspection of the vehicle.

After two fires in the past 30 days and the incident involving the wheel, some city residents say they are concerned about safety.

RELATED: Wheel flies off CMS bus with students on board

Eve White’s son is now in high school and doesn’t ride a school bus, but she says she is still as concerned as any parent of a student that does ride a bus.

“I think that it is a shame that there have been so many incidents recently in school buses that endanger children,” she said.

The state had warned every school district as far back as May of 2011 about the potential for fire on board Freightliner buses with Caterpillar engines, and suggested inspections and repairs if necessary.

NBC Charlotte asked CMS about the inspections and a spokesperson in a statement said, “This was done in 2011 when the memo was received.”