NASHVILLE, Tenn. — Large school buses in Tennessee could stay in service up to 17 years under a new state law, which increased the limit by two years.

Gov. Phil Bredesen signed the bill into law on Tuesday. It initially would have allowed up to 20 years of service for school buses, but that was reduced through an amendment.

Tennessee law previously allowed operators to apply for a waiver to run a school bus beyond the normal retirement age of 12 years, with the limit being 15. A waiver had to be granted each year after 12, and certain conditions had to be met, such as the bus undergoing inspection at least twice each of those additional years.

Under the new law, the normal retirement age for Type D (or transit style) school buses is extended to 15 years. Waivers can be obtained for an additional two years.

For Type C (or conventional) school buses, the normal retirement age remains 12 years, but waivers can be obtained for an additional five years.

The requirements for twice-annual inspections and meeting other conditions still apply for the extended service years.

The new law stipulates that any school bus being operated for a 16th or 17th year must have mileage under 200,000, but the owner will have 90 calendar days to replace the bus from the date that it reaches 200,000 miles.

Also, the new law authorizes the Tennessee Department of Safety to collect a fee for additional inspections conducted for the 16th and 17th years of operation for a conventional school bus.

Regulations for small school buses are not affected by the new law. Those with single rear wheels can be in service up to 10 years; those with dual rear wheels can go up to 12. Neither is eligible for extended use.