A new, long-range forecast for the state’s rail traffic predicts the Yakima Valley could see 13 daily freight trains within about two decades.

That’s a roughly 50 percent increase from current rail traffic — but a smaller increase than the state as a whole, which is expected to see rail traffic more than double in that time.

The report, released Monday by the state Department of Transportation, didn’t consider the effects if proposed coal terminals are built in Longview and north of Bellingham.

However, if one or both are constructed, it’s unlikely that loaded coal trains would travel through Yakima, but it might cause other freight to be re-routed through Yakima and over Stampede Pass. It could also result in more empty coal cars heading back east to coal country in northern Wyoming and southern Montana.

The state’s largest railroad, Burlington Northern Sante Fe, which operates the line through Yakima, declined to make specific growth predictions. In 2007, it told the city it estimated rail traffic would grow from eight trains a day to 10 or 12 in the near future, with the possibility of even more trains if the Stampede Pass tunnel was upgraded, city engineer Brett Sheffield said.

The city of Yakima then began preparing for rail traffic increases with plans for two new downtown underpasses. One, on Lincoln Avenue, opened in 2012. A second underpass on Martin Luther King Jr. Boulevard is expected to be completed sometime next year. The pair carry a total price tag of $41 million.

Still, average train traffic through Yakima has held pretty steady since 2007.

“Traffic volumes reflect customer demand,” said BNSF regional spokesman Gus Melonas, adding that statewide, BNSF has seen strong growth recently.

Washington’s three busiest rail routes are through Stevens Pass to the north, the Columbia Gorge to the south, and the line from Seattle to Portland. The Stampede Pass route that heads southeast from Puget Sound through the Yakima Valley has much less traffic, but Melonas said it plays a key role in keeping the state’s freight network efficient.

No passenger trains travel through Yakima.

“We are averaging nine trains a day through Stampede Pass,” Melonas said. “Primarily, it’s empty trains, which allows for more efficient movement on the busiest routes in Washington.”

Chris Herman, DOT freight rail program manager, said that in 2012, BNSF started using directional running — basically sending the trains in a loop. The climb up and over Stampede Pass is too steep to be an affordable route for heavily loaded cars of grain or oil, so those trains take the path of less resistance to Seattle’s ports along the Columbia. Empty, they head east to make the return trip through Yakima.

The rail capacity through Yakima is the least used in the state, Herman said. The report projects 13 trains a day will pass through the Valley in 2035, but the capacity is much higher than that.

“Because of the directional running, they could conceivably run 39 trains a day over that line,” Herman said.

The report’s projections didn’t calculate what would happen if one or more coal terminals are built.

“What it likely means is that the growth (predicted in the report) will happen sooner if these facilities are developed,” Herman said.

The routes that those controversial coal trains would take across the state have not been officially announced. Tribal leaders across the Northwest, including the Yakama Nation, have joined with environmentalists to speak out against the coal proposals.

Although it’s unlikely that coal would travel through Yakima, the energy industry is already having an impact — empty oil tank cars are now a common sight heading east to resupply in North Dakota. The Tesco oil refinery in Anacortes is now taking rail shipments of oil, and others are poised to follow. That oil is primarily shipped through the Columbia Gorge.

Transporting oil and gas anywhere raises new safety concerns. But Melonas said there hasn’t been a hazardous material fatality on BNSF’s northern network in more than 20 years. He credits track maintenance and safety trainings for local emergency responders.

For now, the freight traffic in Yakima is limited by the Stampede Pass tunnel, which is too small for larger shipping containers or double-stacked cars. Expanding the tunnel would be an expensive investment.

“The (proposed expansion) is always under review, but there are no defined plans at this point,” Melonas said.

Train traffic returned to Yakima in 1996 after BNSF invested $150 million to re-open the pass after it had been dormant for a decade.

This year, BNSF invested $125 million in Washington’s rail infrastructure, following last year’s $100 million. The small share of those funds spent locally went for new rail ties between Yakima and Pasco last year and track re-surfacing this year, Melonas said.

More than 3,500 people in Washington work for BNSF, and Melonas said the company is hiring 300 more this year — including 60 in Pasco and a few at Stampede Pass. Local crews work mainly on train operations, track maintenance and mechanical repairs.