Island County is disputing low projected growth numbers for the Mukilteo-Clinton ferry route that Washington State Ferries recently presented as concepts for its long-range plan.

State Ferries, which is under the Washington State Department of Transportation, projects an increase in ridership of 16 percent between 2017 and 2040, the lowest of all the ferry routes in the system.

Island County Planning Director Hiller West asked the Board of County Commissioners Wednesday to respond to the ferry system, which is requesting comments on the planning process until May 24. The commissioners said they agree that the numbers need to be reevaluated, citing projected growth in the greater Seattle area, Snohomish County and planned improvements to the Mukilteo ferry terminal as reasons to expect higher usage.

Commissioner Jill Johnson pointed out the data also doesn’t account for the people who drive around and use the Deception Pass Bridge instead after being deterred by long wait times at the ferry.

“I agree,” Commissioner Rick Hannold said. “I don’t think they’re looking at all the factors.”

West said his letter will include information he can find about permit activity and vacation homes in the county. He said population projections don’t provide a full picture for the county because of the high number of second homes. Overall, he said, the number of building permits applied for has increased significantly since 2015.

“That is just a way to make a point that the residential levels on the island are actually increasing pretty fast and WSDOT should take that into account,” West said.

The Island Regional Transportation Planning Organization, for which Commissioner Helen Price Johnson serves as chairwoman, drafted a letter to the ferry system as well.

The letter points out that ridership for the Port Townsend-Coupeville route was projected to increase 53 percent, a number which seems to be based on population projections for Jefferson County.

However, the Clinton route’s projected number appeared to use Island County’s expected population growth.

Hadley Rodero, spokesperson for Washington State Ferries, said the numbers were based on regional growth projections. She couldn’t speak to the specific numbers used for different routes. She said as the plan moves forward, a more detailed breakdown of the ridership will be provided to show seasonal changes and different types of riders.

“We’re still really early in the planning process,” she said.

The draft long-range plan is expected to be completed in the summer, and Rodero said the agency will hold another round of workshops in September to present the draft and get feedback.

She said the county and regional planning organization’s feedback will help guide the draft.

“This is exactly the type of questions and feedback we want at this point,” she said.

West said he and staff anticipate presenting the commissioners a draft letter during their May 15 regular meeting.