Portland-area transportation planners are looking underground for a potential big-ticket project: a subway that runs beneath the downtown core and across the Willamette River.

City transportation officials floated the idea Tuesday in a presentation before the Portland Planning and Sustainability Commission. The concept, represented on a map by a meandering line with no clear endpoints, is clearly far from reality.

Though much of the presentation outlined smaller transportation projects over a 20-year timeline, Portland Bureau of Transportation spokesman Dylan Rivera said any subway project would be at least 30 to 40 years away.

But the presentation does indicate the subway is on a track to be included on an update to the Regional Transportation Plan next year, a requirement if the project is to receive future federal funding.

A map of proposed future transit projects in the city of Portland and beyond presented to the city's Planning and Sustainability Commission on Tuesday.

Art Pearce, the transportation bureau's policy, planning and projects group manager, acknowledged that the project is unlikely to move forward in what he called a "constrained environment."

President Donald Trump's budget blueprint zeros out federal programs that have helped fund nearly every MAX light-rail line and the Portland Streetcar's eastside expansion.

"We still think it's important to capture that it's a move we anticipate happening," Pearce told the commission.

He described the plan as one developed in coordination with planners at TriMet and Metro, the regional government.

The idea for a tunnel to get MAX through downtown more quickly isn't new. Rivera said it's been studied as far back as the 1990s.

A tunnel would be an expensive proposition. In Seattle, a 3-mile tunnel from downtown to the University of Washington cost $1.8 billion when it was completed in 2012.

But some transportation planners outside of city government view it as virtually a foregone conclusion, given that the capacity of above-ground MAX trains is constrained through downtown by the city's short block faces. The current above-ground route is also slowed by frequent stops.

When surface transit is at capacity & just too slow, it's time for a subway. Portland's there (1/2): https://t.co/ZGlK0wVQcQ — Jarrett Walker (@humantransit) June 14, 2017

Tuesday's presentation included other, more concrete proposals for speeding up the region's transit system.

Among them were pilots of transit-only lanes, priority traffic signals, bus stop consolidation and other low-cost changes designed to help frequent-service buses move faster in the city's resurgent traffic congestion.

The transportation bureau said it would start with the Line 72 along 82nd Avenue, Line 12 along Northeast Sandy Boulevard and, with sufficient funding, Line 6 along Martin Luther King Boulevard.

It's pitching that "Enhanced Transit Corridors Plan" to the public starting with an open house this month, with an eye toward finalizing the plan in 2018.

The city also plans to seek funding to expand the Portland Streetcar system and improve its current system by buying five new streetcars and using some of the same strategies discussed for buses.

It also includes MAX extensions to Vancouver and Oregon City, imagined in an 11- to 20-year timeframe, as well as some form of high-capacity transit along Powell Boulevard, which was dropped from a rapid-bus project that's now proposed along Southeast Division Street.

Also included is a project addressing the Steel Bridge, a pinch point for the MAX system that also constrains its capacity. TriMet is planning an $11 million project to shore up the bridge, which is owned by the railroad Union Pacific, while also spending $800,000 to assess its long-term future.

TriMet spokeswoman Tia York said the agency is looking at a range of options for a new Willamette River crossing, including building a new bridge or tunnel.

"At this point, planners are in the brainstorming phase, and there are a lot of ideas on the table," she said in an email. "Our hope is to develop concepts that will integrate with transit technology that will be available in 2040 and beyond."

-- Elliot Njus

enjus@oregonian.com

503-294-5034

@enjus