Portland school officials will pay Metro bus service up to $159,750 for the first year of transporting Portland’s high school students, who will no longer be riding traditional yellow school buses, according to a draft contract released Wednesday.

District officials plan to pay the tab out of the transportation budget, with the expectation of saving money because they are not transporting the students with district buses.

The Portland School Board will vote on Sept. 1 on whether to authorize the board chairwoman to sign the contract.

Under the draft contract, the district will pay Metro 75 cents for each student’s ride. There is a minimum cost provision that guarantees the district will pay for Metro’s actual cost to provide the service, or $115,000, whichever is lower. The maximum cost to the district is capped at $159,750 for 213,000 rides. Portland has about 2,100 high school students, but the students have unlimited use of the pass during the school year and transfers count as an additional ride.

If the district has high ridership and pays the maximum cost, the contract will increase 15 percent in each consecutive year of the agreement, up to $211,269 in 2018.

If the district only needs to make the minimum cost guarantee, because of lower ridership numbers, the cost will increase annually by 5.8 percent the first year and 5 percent the second year, up to $127,752 in 2018.

Metro created a new bus route, Route 9, to accommodate the students. It loops around the city, hitting Portland, Deering and Casco Bay high schools, and includes some service into the North Deering neighborhood.

Officials approved the use of Metro buses as part of a plan to add 20 minutes to the school day for all grades and reorganize the yellow school bus system. Moving high school students to Metro buses freed up the district’s yellow bus fleet to make more runs in a shorter amount of time to accommodate changes in start times for elementary and middle school students.