A new state report aimed at considering ways to reduce student transportation costs estimates eliminating free school bus service for about 20,000 low-income students would save up to $18 million a year, while cutting service to most Oahu general-education students would save about $15 million.

But officials warn the cost of cutting bus service cannot be conveyed in dollars alone.

Randy Moore, the DOE’s assistant superintendent for facilities and support services, said the report illustrates that "reducing costs … has much greater implications than ‘What are we paying to run the bus system?’ They’re not really student transportation issues. There’s a lot of public policy here."

He said in the coming legislative session, the department will be "looking for guidance" on what cost-saving measures would be acceptable to lawmakers, as they determine whether student transportation funding should be reduced — and by how much.

The report to the Legislature, released Tuesday, is aimed at giving legislators an idea of the wide range of potential measures for bringing down skyrocketing student transportation costs, from rethinking how contracts are structured and awarded to cutting service to certain students or areas.

Lawmakers requested the study after watching the price tag for school bus service triple over the last decade, to $75.6 million in fiscal year 2012.

Sen. Jill Tokuda, chairwoman of the Senate Education Committee, said the study "definitely provides us with some data and some options to consider."

But she added the report falls short in helping legislators get a handle on the "deeper discussion of some of the issues and challenges that are getting some of those large percentage increases (in costs) that we’re seeing."

She said one glaring omission is details on the lack of competition in school bus bidding and what can be done to attract more bidders.

"I would have wanted so much more in that area," she said. The report is "a start, but in no means are we even near the finish line with this. I think we’re going to expect more going forward."

Discussions about cutting transportation expenses come amid growing questions from legislators and parents about why costs have risen so much, so fast.

The FBI has questioned Hawaii school bus contractors and requested documents, apparently as part of an investigation of whether businesses colluded to push up the cost of services. Contractors deny the allegation.

The report notes that the department has taken steps in recent years to reduce student transportation expenses — by consolidating routes, cutting some high school routes and increasing the "minimum qualifying distance" to 1.5 miles from one mile for grade 6 to grade 12 students in an effort to curb costs.

It has also increased fares — by 350 percent in the last two years. The most recent increase, in July, increased the cost of a quarterly pass to $72 from $60.

Moore said the DOE is also looking at other ways to cut costs, including taking another look at how bus contracts are bid. It’s unclear, though, how much those measures will save.

The report’s findings include:

» Eliminating all bus service on Oahu, except on the Leeward Coast, would save about $14.6 million. But a one-time termination cost would eat away at those savings in the first year, to the tune of $7.3 million.

Meanwhile, eliminating all high school and middle school bus service on Oahu would save $6.6 million in the first year and $13 million in subsequent years.

» Cutting service to all free riders would save up to $18 million a year, assuming that 25 percent of those students were to continue to ride the bus but pay a fare. Paradoxically, if half of free riders paid, the state would save about $4 million less, because the student bus fare does not cover the full cost of a ride.

» Eliminating all nonmandated student bus transportation would affect about 39,000 general-education students statewide and save about $40 million per year.

Mandated curb-to-curb bus service would still be provided to 4,000 special-education students at a cost of about $32 million per year.

The study concluded, "Such an action would place a substantial burden on families," and noted the DOE "does not recommend this as a cost-saving measure."

The report notes other possible cost-saving measures include considering a single state bus contract, further increasing the school bus fare, staggering school hours or reducing more routes.