Partnering to Pilot Curb Extensions for Trees: Portland Models a Way Forward

The novel project PBOT and Urban Forestry are collaborating on to bring trees-in-the curb to two stretches of road in East Portland is only a pilot. But City staff say lessons learned will inform scaling up of the model. Expansion will only occur if the new City Council moves to financially support the concept in other tree-needy areas. Public enthusiasm will be critical. If you like this idea, let your district City Council reps know!

By Kyna Rubin

The half mile of newly constructed curb bump-outs scattered along both sides of SE Duke Street between 82nd and 94th Avenues so far look unassuming. But they are a bright spot born from an encouraging inter-bureau endeavor to create more space for the increased canopy we need for climate resilience.

When both of two phases are completed in 2025, more than 40 in-the-curb trees of various hardy, drought-tolerant species will appear in two different clusters of East Portland that, without curb extensions, are unable to accommodate street trees. The first project phase also includes two more locations, adjacent to Duke Street—one on SE 89th Avenue between Duke and Claybourne, and one on SE 90th between Claybourne and Cooper.

No tiny tree wells here, like those we see thwarting tree growth in many parts of town. These curb-zone trees will be housed in single, double, and at least one triple curb planter carefully designed to hold the space, soil volume, and soil mix they need to reach their full canopy potential. Size matters. The greater their canopy, the greater the level of benefits trees give people and the environment.

The City of Portland’s Trees in the Curb Zone project, funded by a $500,000 Bureau of Environmental Services Percent for Green grant, comes at a good time. Portland is in the process of drafting a long overdue update of its Urban Forest Plan, which, responding to climate crisis, will revise city canopy targets and call for ways to make more space for planting large street trees.

Why do we need curb-extended planters, and well beyond the pilot area? Alone, current right-of-way space for trees isn’t enough to meet Portland’s canopy goals. Plenty of that space is either curb-tight—meaning it lacks planting strips—or its strips are too small for trees, says Brian Landoe, strategy & planning manager at Parks & Recreation’s Urban Forestry division. Expanding right-of-way design through curb bump-outs, he says, is a really important means of helping to reach new citywide goals.

This pilot is creating proof-of-concept design and engineering standards needed before the City will consider applying the idea citywide.   

A crucial feature of the pilot is that Urban Forestry will assume responsibility, in perpetuity, for maintaining the trees going into the curb planters. For this pilot, says Portland Bureau of Transportation (PBOT) project manager Gena Gastaldi, the bureau changed its standard operating procedure by making these trees a City asset.

This move responds to ongoing public pressure for the City to relieve homeowners of the cost of watering, pruning, and taking out dead trees in their properties’ rights-of way street frontage. In fact, Urban Forestry has received five years of support from the Portland Clean Energy Fund to plan for planting, maintaining, and removing dead, dying, or dangerous street trees. But Trees for Life Oregon (TFLO) and other advocates are pushing City leaders to find long-term funding to do this, which other cities have managed to do. The pilot is already yielding an indication of homeowners’ response to having the City take over street tree planting and maintenance (hint: they like it).

The pilot’s trees will be treated as park trees are, says Urban Forestry’s Landoe. Their care will be permanently handled and funded by Parks/Urban Forestry.

Why Now?

A fortunate alignment of favorable factors drove this experimental effort, says Gastaldi of PBOT, which is leading the project in partnership with Urban Forestry.

While managing the 2023 update of the City’s Pedestrian Design Guide, she heard Urban Forestry staff and community members, including TFLO, pushing hard for innovative treatments for street tree space. At the same time came the 2021 heat dome, when staff realized, she says, “that no matter our jobs or expertise, we all needed to be acting on climate issues even more than we were.”

According to Gastaldi, the City Commissioner in charge of PBOT at the time, Jo Ann Hardesty, told staff to “move this [concept] forward.”  In the end, the updated Pedestrian Design Guide (B.5.3) permitted “extending the furnishing zone into the curb zone,” and gave PBOT, says Gastaldi, some initial criteria for designing for trees in the curb. Further, PedPDX, the City’s pedestrian plan (see action 8.6), gave PBOT policy support for the curb extensions for trees.

Gastaldi then started analyzing the feasibility of introducing curb bump-outs for trees. With the information gathered, she applied successfully for the Bureau of Environment Services (BES) grant. At that point, she had a few one-off precedents to learn from—the bump-out at SE 46th and Hawthorne, a PBOT-BES project never intended to be replicated; and a similar design on streets around downtown’s Director Park. She also spoke to staff and engineers in other cities and reviewed their designs for trees in the curb. These cities, too, had done occasional one-offs, but nothing citywide or systematic.

Collaboration Matters

TFLO has bemoaned the City’s silo’ed bureaucracy and the lower value traditionally given to trees and Urban Forestry than to bureaus that manage gray infrastructure. This pilot shows what collegial collaboration between bureaus with different agendas and areas of expertise can look like, and how it can move the dial on change, if given City Council backing and encouragement.

PBOT and Urban Forestry signed a memorandum of understanding that clearly spelled out respective roles and responsibilities for the pilot, says Urban Forestry planning and policy analyst Belinda Judelman. PBOT was “very receptive” to Urban Forestry’s recommendations, she notes. As the pilot’s funder and a bureau with plenty of experience building curb stormwater management facilities, BES was also involved. With pipes in the ground, the Water Bureau, too, examined the plan.

“Nothing’s going in that those bureaus haven’t reviewed and signed off on,” explains PBOT’s Gastaldi. PBOT and Urban Forestry’s respective expertise is complementary and, by all accounts, has been critical to the pilot’s build-out. She says that PBOT couldn’t do this pilot without Urban Forestry.  

“I’m not a tree expert and Urban Forestry aren’t traffic experts,” she says. And it doesn’t hurt that Gastaldi and Urban Forestry’s project lead, Belinda Judelman, went to graduate school together.

Planting Trees in the Street Isn’t Easy

In determining where to do the pilot, PBOT and Urban Forestry targeted residential areas of town that face scorching summer heat and that, absent this project, would never get street trees because of curb-tight sidewalks. They studied PBOT’s curb extension policy exemption map, which for one, rules out streets slated for potential bike or bus lanes. They overlaid that map with one created by PSU Professor Vivek Shandas that shows the locations of his highest summer 2021 heat dome temperature measures.

What stood out were areas of East Portland, including stretches of SE Duke Street. But many on-the-ground constraints remained.

“Streets are not a hospitable place for trees,” observes Gastaldi. Underground, the first dealbreaker is competition with water lines. Overhead, high-voltage power lines don’t bar all trees underneath but do prohibit the large-form trees that offer residents the most cooling and other benefits.

Utilities aren’t the only obstacles to curb extension placement. At play in tree planter location are fire hydrants, lane width requirements for fire engine clearance, setbacks from street crossings, and the need for drivers to have clear sightlines.  Parking, too, is an issue. Candidate streets must have room to reallocate lost parking spots for residents.

Candidates for the pilot included sections of SE Holgate, Woodstock, and Flavel, but ultimately staff chose SE Duke Street, east of 82nd. In some places its southside water line crosses the street diagonally, allowing some room on that side for planters in addition to the water-line-free north side of the street. PBOT found that Duke Street’s traffic volume and speed are relatively low, and it is more residential than the other streets. The selected expanse of Duke Street contains short blocks, leaving plenty of corner properties and extra parking spots; a PBOT analysis found that parking demand here is low.

Finally, PBOT had already been engaged with this area’s neighborhood and other local groups through its Lower Southeast Rising project.  The team could build on these ties to get community input into the Trees in the Curb Zone project.

Opt-in Projects Call for City Flexibility

This pilot is a PBOT capital project, not an “opt-in,” or optional choice, for adjacent homeowners. Early on, the bureau sent parking removal notifications to property owners and distributed Urban Forestry materials about the benefits of nearby trees. Gastaldi briefed residents and fielded questions at Lents Neighborhood Livability Association meetings and knocked on doors to talk about the project.

Her approach was to be flexible about responding to any homeowner concerns about bump-out placement. The bureau did not site curb extensions in front of home entrances. Staff expedited ADA parking spaces for the few residents worried about losing nearby spots. They complied with a property owner’s request to slightly tweak the planter design to accommodate the way he used his planting strip. And for neighbors who want them, Urban Forestry has offered to plant yard trees on the side of the street that does not hold new in-curb planters.

Lessons

Pilots are learning opportunities, and Trees in the Curb Zone staff will be applying their knowledge from phase 1 to phase 2, whose exact location, in Lents, has yet to be determined.

The project has “really grown our relationships between bureaus,” says Gastaldi, which she has found rewarding. But consistent communication with Urban Forestry and with bureaus whose infrastructure can conflict with where project staff hope to place curb planters takes time.

A big lesson is that the challenge posed by underground and overhead utilities stifled the project team’s intention to get as many large-canopy trees into the curb planters as they’d wished.

“We put trees in those locations, but not large-form ones,” laments Gastaldi, keenly aware of Urban Forestry’s preference for big trees. In this first project phase, just under half of the trees are large-at-maturity species. For the second phase, however, the team says it will seek locations that will accommodate a higher portion of large-form trees.

On the technical and design end, staff had learned from the earlier curb planters on SE 46th and Hawthorne that insufficient soil volume would inhibit tree health and growth. The Duke Street planters are intentionally capacious. Urban Forestry’s expertise on the soil volume that various tree species need for optimum lifespan informed the use of three different planter sizes. Most of the planters hold one tree (the size of a parking space), two are housing two trees, and one is long enough to contain three trees. The planter widths range from 6.5 feet to 8 feet, and the lengths are 20 feet, 40 feet, and 66 feet, respectively. That’s a whole lot more soil volume than most street trees get on traditional parking strips.

Getting the right soil mix has also brought learning. In early December 2024, a project contractor was adding more dirt to the planters, which at the time did not yet hold trees. “A particular mix likes to compact when it gets rained on a lot,” Gastaldi says they discovered, so they’re trying out a few different mixes.

Will the City Expand the Pilot?

The tools and practices the pilot develops “can be implemented by the private or public sector in a variety of construction contexts,” said PBOT Public Information Officer Dylan Rivera in March 2023. Developers build 26 miles of sidewalks a year that PBOT requires to bring street frontage up to code, according to Rivera. “This could be part of that requirement or an option for developers who are building housing—same goes for PBOT or other bureaus’ capital improvement projects.”

Importantly, he added, and TFLO strongly agrees, “We’d like this to be required, not optional.”

Pilot project funding will end in 2025. Gastaldi hopes to see curb extensions like this continue, and there’s been some internal discussions about what that could look like. PBOT won’t be making any decisions until it conducts a post-project analysis and evaluation. Only then will conversations start about the potential for expansion, says Hannah Schaefer, PBOT’s communications director.

Urban Forestry’s Belinda Judelman sees wider application of the model as a question of political acceptance, interest, and funding. 

A feature in its favor is that the pilot exemplifies cross-bureau goal sharing. PBOT’s pre-pilot traffic count will be followed by a measure of traffic volume and speed along Duke Street after project completion. If, as expected, the team finds traffic-calming impacts from the curb extensions for trees, says Urban Forestry’s Brian Landoe, it will show that these tools can meet goals shared by both Urban Forestry and PBOT.

Another plus is that the project visibility’s—eight other U.S. cities have consulted with Gastaldi to inform their thinking about trees in the curb zone—could help bring this work to the attention of the climate-caring leaders among our new City Commissioners. Portland used to be widely considered a green innovator. This project shows we still can be.

It’s exciting that other cities are watching us,” says Schaefer. “This could be a leadership opportunity for us as a city across the country, so as we look to the future for what this project holds, those are things we’ll be talking about with the City leadership and the public.”

District Reps Will Need to Hear from Constituents Who Want This

The public has a big role to play here: The new district-representation now part of the reconfigured City Council could offer easier channels for residents to express their enthusiasm for promising initiatives like the Trees in the Curb Zone. City staff are excited about its potential but reiterate that it’s the public who needs to convey enthusiasm to their district reps (each district has three). The latter, in turn, would share this message with the deputy city administrator in charge of the Vibrant Communities “service area,” which houses Parks & Recreation/Urban Forestry. With enough interest and momentum, a wider application of the pilot could get to city administrator Michael Jordan and then to City Council for consideration.

So far, feedback about Trees in the Curb Zone from affected Duke Street property owners has been favorable. The property owner living adjacent to the triple-tree curb planter, the longest one installed, is very happy with it, says Lents Neighborhood Livability Association secretary and treasurer Char Pennie. “Her only question is, where are the trees?” (They are coming in January.) Another neighbor lives on a corner that had issues with right-of-way garbage dumping. The planter makes it look like the City cares about the street now, which he hopes will help deter this problem, Gastaldi says he told an on-site PBOT contractor.

The fact that the City is planting and maintaining the trees makes a big difference in homeowners’ reception, observes Landoe.  Urban Forestry’s opt-out rate for its street tree planting program, where the City plants trees in low-canopy areas but doesn’t maintain them, is 30 to 40 percent of property owners, he says. They opt out from concern about maintenance or sidewalk repair issues. In contrast, PBOT has received only one concerned comment about the Trees in the Curb pilot.

Trees in the Curb Zone is a great example of what’s possible when Portlanders push for change and City bureaus partner to respond. Pilots are a terrific way of seeing what works and what doesn’t.

In TFLO’s view, there are even more street, sidewalk, and building design modifications that, with City Council support and inter-bureau partnerships, could be piloted with the endgame of creating more new space for trees, meeting canopy goals, and being better prepared for our climate future. Trees in the Curb Zone is a good start.