OLYMPIA — The cost of traveling on a state ferry may go up again this fall.

The keel is being laid for fare hikes in October and again next year to help keep the nation’s largest passenger ferry system afloat.

But the amount of the increase won’t be known until after lawmakers enact a new two-year transportation budget that includes money for the day-to-day operations of Washington State Ferries.

The state House and Senate have been negotiating for weeks. A deal is near on this budget — which is separate from the government operating budget on which the two legislative chambers are bitterly divided —and votes could be taken before the special session ends May 28.

“We think negotiators are close,” House Speaker Frank Chopp, D-Seattle, said Thursday.

In April, during the regular session, the House approved a transportation spending plan that counted on money from a 2.5 percent fare hike on vehicles and passengers this year and next. But the Senate did not act on the House bill, pushing the issue into the extra session.

Rep. Judy Clibborn, chairwoman of the House Transportation Committee, said regular and predictable fare increases are needed to cover annual increases in operating costs due to inflation.

Fares have gone up nearly every year since 2007 for the cash-strapped system. The last across-the-board increase took effect May 1, 2014, and boosted passenger fares by 2 percent and vehicle fares by 2.5 percent.

For drivers of a standard length car — between 14 and 22 feet — it turned out to be a 20-cent increase in the regular one-way fare for the Mukilteo-Clinton route and 45 cents on the Edmonds-Kingston route.

While lawmakers budget in extra money from higher fares, they don’t actually set the fares. That responsibility lies with the state Transportation Commission. That panel will draft a fare increase proposal and hold public hearings on it before making a final decision.

Ray Deardorf, state ferries planning director, told commissioners this week that an advisory commission has been discussing potential elements of a fare hike for months. He assured them that if the process begins in June, it can be completed in time for an increase to take effect Oct. 1.

Rep. Norma Smith, R-Clinton, who serves on the House Transportation Committee, said she understood the reasons for charging ferry riders more but hopes the final amount isn’t as much as the original House budget demanded.

“None of us want to see fares increase,” she said. “I think they can be held down more.”

Jerry Cornfield: 360-352-8623; jcornfield@heraldnet.com.