Four years ago, a bill that was passed in Tennessee raised the maximum age for school buses from 15 to 17 years.

Now, officials in some counties are advocating another increase in the state’s limit on school bus service life, WBIR reported recently.

Under the current law, the normal retirement age for Type D (or transit style) school buses is 15 years, but waivers can be obtained for an additional two years. For Type C (or conventional) school buses, the normal retirement age is 12 years, but waivers can add five years.

For the extended service life, buses have to be inspected twice annually and meet other conditions. For example, any school bus being operated for a 16th or 17th year must have mileage under 200,000.

Considering the rigorous inspection requirements, some pupil transportation officials say that they could safely run their buses even longer.

"Our goal is to have safe buses. But the way that we [maintain] and keep up with them, there's no reason why the miles and years couldn't be extended," Keith Duncan, transportation director for Morgan County Schools, told WBIR.

In early 2013, bills aimed at raising the school bus service life limit were introduced in the Tennessee General Assembly, but they ended up stalling. With state legislators set to reconvene on Jan. 14, some school district officials are hoping for a successful attempt this time.