1

Managing Wet Weather with 

Green Infrastructure

Municipal Handbook

Green Streets
Managing Wet Weather with Green Infrastructure 

Municipal Handbook 

Green Streets 

prepared by 

Robb Lukes 

Christopher Kloss 

Low Impact Development Center 

The Municipal Handbook is a series of documents 

to help local officials implement green infrastructure in their communities.

December 2008 

EPA-833-F-08-009 

Front Cover Photos 

Top: rain garden; permeable pavers; rain barrel; 

planter; tree boxes. 

Large photo: green alley in Chicago 
1

Green Streets 

Introduction

By design and function, urban areas are covered with impervious surfaces: roofs, roads, sidewalks, and

parking lots. Although all contribute to stormwater runoff, the effects and necessary mitigation of the 

various types of surfaces can vary significantly. Of these, roads and travel surfaces present perhaps the 

largest urban pollution sources and also one of the greatest opportunities for green infrastructure use. 

The Federal Highway Administration (FHA) estimates that more than 20% of U.S. roads are in urban 

areas.1 Urban roads, along with sidewalks and parking lots, are estimated to constitute almost two-thirds 

of the total impervious cover and contribute a similar ratio of runoff.2

 While a significant source of 

runoff, roads are also a part of the infrastructure system, conveying stormwater along gutters to inlets and 

the buried pipe network. Effective road drainage, translated as moving stormwater into the conveyance 

system quickly, has been a design priority while opportunities for enhanced environmental management 

have been overlooked especially in the urban environment. 

The altered flow regime from traditional roadways, increased runoff volume, more frequent runoff events, 

and high runoff peak flows, are damaging to the environment and a risk to property downstream. These 

erosive flows in receiving streams will cause down cutting and channel shifting in some places and 

excessive sedimentation in others. The unnatural flow regime destroys stream habitat and disrupts aquatic 

systems. 

Compounding the deliberate rapid conveyance of stormwater, roads also are prime collection sites for 

pollutants. Because roads are a component of the stormwater conveyance system, are impacted by 

atmospheric deposition, and exposed to vehicles, they collect a wide suite of pollutants and deliver them 

into the conveyance system and ultimately receiving streams (See Table 1). The metals, combustion byproducts, and automotive fluids from vehicles can present a toxic mix that combines with the ubiquitous 

nutrients, trash, and suspended solids. 

Table 1. Examples of Stormwater Pollutants Typical of Roads.3, 4

Pollutant Source Effects 

Trash 

--- 

Physical damage to aquatic animals and 

fish, release of poisonous substances 

Sediment/solids Construction, unpaved areas Increased turbidity, increased transport of 

soil bound pollutants, negative effects on 

aquatic organisms reproduction and 

function 

Metals 

• Copper 

• Zinc 

• Lead 

• Arsenic 

• Vehicle brake pads 

• Vehicle tires, motor oil 

• Vehicle emissions and engines 

• Vehicle emissions, brake linings, 

automotive fluids 

Toxic to aquatic organisms and can 

accumulate in sediments and fish tissues 

Organics associated 

with petroleum (e.g., 

PAHs) 

Vehicle emissions, automotive fluids, 

gas stations 

Toxic to aquatic organisms 

Nutrients Vehicle emissions, atmospheric 

deposition 

Promotes eutrophication and depleted 

dissolved oxygen concentrations 
2

While other impervious surfaces can be replaced, for 

example using green roofs to decrease the amount of

impervious roof surface, for the most part, impervious 

roads will, for some time to come, constitute a 

significant percentage of urban imperviousness 

because of their current widespread existence. 

Reducing road widths and other strategies to limit the amount of impervious surface are critical, but truly 

addressing road runoff requires mitigating its effects. 

Roads present many opportunities for green infrastructure application. One principle of green 

infrastructure involves reducing and treating stormwater close to its source. Urban transportation right-ofways integrated with green techniques are often called “green streets”. Green streets provide a source

control for a main contributor of stormwater runoff and pollutant load. In addition, green infrastructure 

approaches complement street facility upgrades, street aesthetic improvements, and urban tree canopy 

efforts that also make use of the right-of-way and allow it to achieve multiple goals and benefits. Using 

the right-of-way for treatment also links green with gray infrastructure by making use of the engineered 

conveyance of roads and providing connections to conveyance systems when needed. 

Green streets are beneficial for new road construction and retrofits. They can provide substantial 

economic benefits when used in transportation applications. Billions of dollars are spent annually on road 

construction and rehabilitation, with a large percentage focused on rehabilitation especially in urban

areas. Coordinating green infrastructure installation with broader transportation improvements can 

significantly reduce the marginal cost of stormwater management by including it within larger 

infrastructure improvements. Also, and not unimportantly, right-of-way installations allow for easy public 

maintenance. A large municipal concern regarding green infrastructure use is maintenance; using roads 

and right-of-ways as locations for green infrastructure not only addresses a significant pollutant source, 

but also alleviates access and maintenance concerns by using public space. 

In urban areas, roads present many opportunities for coordinated green infrastructure use. Some 

municipalities are capitalizing on the benefits gained by introducing green infrastructure in transportation 

applications. This paper will evaluate programs and policies that have been used to successfully integrate 

green infrastructure into roads and right-of-ways. 

Green Street Designs

Green streets can incorporate a wide variety of design elements including street trees, permeable 

pavements, bioretention, and swales. Although the design and appearance of green streets will vary, the 

functional goals are the same: provide source control of stormwater, limit its transport and pollutant

conveyance to the collection system, restore predevelopment hydrology to the extent possible, and 

provide environmentally enhanced roads. Successful application of green techniques will encourage soil

and vegetation contact and infiltration and retention of stormwater. 

Alternative Street Designs (Street Widths) 

A green street design begins before any BMPs are considered. When building a new street or streets, the 

layout and street network must be planned to respect the existing hydrologic functions of the land 

(preserve wetlands, buffers, high-permeability soils, etc.) and to minimize the impervious area. If 

retrofitting or redeveloping a street, opportunities to eliminate unnecessary impervious area should be 

explored. 

Green Streets achieve multiple benefits, such as 

improved water quality and more livable 

communities, through the integration of stormwater 

treatment techniques which use natural processes 

and landscaping. 
3

Implementation Hurdles 

Many urban and suburban streets, sized to meet 

code requirements for emergency service 

vehicles and provide a free flow of traffic, are 

oversized for their typical everyday functions. 

The Uniform Fire Code requires that streets 

have a minimum 20 feet of unobstructed width;

a street with parking on both sides would 

require a width of at least 34 feet. In addition to

stormwater concerns, wide streets have many 

detrimental implications on neighborhood livability, traffic conditions, and pedestrian safety.5 

The Transportation Growth and Management Program of Oregon, through a Stakeholder Design Team, 

developed a guide for reducing street widths titled the Neighborhood Street Design Guidelines.6

 The 

document provides a helpful framework for cities to conduct an inclusive review of street design profiles 

with the goal of reducing widths. Solutions for accommodating emergency vehicles while minimizing 

street widths are described in the document. They include alternative street parking configurations, 

vehicle pullout space, connected street networks, prohibiting parking near intersections, and smaller block 

lengths. 

In 1997, Oregon, which has adopted the 

Uniform Fire Code, specifically granted 

local government the authority to establish 

alternative street design standards but 

requires them to consult with fire 

departments before standards are adopted. 

Table 2 provides examples of alternative 

street widths allowed in U.S. jurisdictions.7

Swales

Swales are vegetated open channels 

designed to accept sheet flow runoff and 

convey it in broad shallow flow. The intent 

of swales is to reduce stormwater volume 

through infiltration, improve water quality 

through vegetative and soil filtration, and 

reduce flow velocity by increasing channel 

roughness. In the simple roadside grassed 

form, they have been a common historical 

component of road design. Additional benefit can be attained through more complex forms of swales, 

such as those with amended soils, bioretention soils, gravel storage areas, underdrains, weirs, and thick 

diverse vegetation. 

Implementation Hurdles 

There is a common misconception of open channel drainage being at the bottom of a street development 

hierarchy in which curb and gutter are at the top. Seattle’s Street Edge Alternative Project and other

natural drainage swale pilot projects have demonstrated that urban swales not only mitigate stormwater

impacts, but they can also enhance the urban environment.8

Figure 1. The street-side swale and adjacent porous

concrete sidewalk are located in the High Point 

neighborhood of Seattle, WA 

(Source: Abby Hall, US EPA).

Oregon State Code Granting Authority for Street 

Standards to Local Government 

ORS 92.044 - Local governments shall supersede and prevail 

over any specifications and standards for roads and streets 

set forth in a uniform fire code adopted by the State Fire 

Marshal, a municipal fire department or a county firefighting 

agency.... Local governments shall consider the needs of the fire 

department or fire-fighting agency when adopting the final 

specifications and standards. 
4

Table 2. Examples of Alternative Street Widths 

Jurisdiction Street Width Parking Condition 

Phoenix, AZ 28' parking both sides 

Santa Rosa, CA 30' 

26'-28' 

20' 

20' 

parking both sides, <1000ADT 

parking one side 

no parking 

neck downs @ intersection 

Orlando, FL 28' 

22' 

parking both sides, res. Lots<55’ wide 

parking both sides, res. Lots>55’ wide 

Birmingham, MI 26' 

20' 

parking both sides 

parking one side 

Howard County, MD 24' parking unregulated 

Kirkland, WA 12' 

20' 

24' 

28' 

alley 

parking one side 

parking both sides – low density only 

parking both sides 

Madison, WI 27' 

28' 

parking both sides, <3DU/AC 

parking both sides, 3-10 DU/AC 

ADT: Average Daily Traffic DU/AC: dwelling units per acre 

Bioretention Curb Extensions and 

Sidewalk Planters 

Bioretention is a versatile green street strategy. 

Bioretention features can be tree boxes taking 

runoff from the street, indistinguishable from 

conventional tree boxes. Bioretention features can 

also be attractive attention grabbing planter boxes

or curb extensions. Many natural processes occur 

within bioretention cells: infiltration and storage

reduces runoff volumes and attenuates peak flows; 

biological and chemical reactions occur in the 

mulch, soil matrix, and root zone; and stormwater 

is filtered through vegetation and soil. 

Implementation Hurdles 

A few municipal DOT programs have instituted 

green street requirements in roadway projects, but 

as of yet, specifications for street bioretention 

have not yet been incorporated into municipal 

DOT specifications. Many cities do have street bioretention pilot projects; two of the well documented

programs are noted in the table. Several concerns and considerations have prevented standard 

implementation of bioretention by DOTs. 

Table 3. Municipalities with Swale Specifications and Standard Details 

Municipality Document Section Title Section # 

City of Austin9 Standard Specifications and 

Standard Details 

Grass-Lined Swale and GrassLined Swale with Stone Center 627S 

City of Seattle10 2008 Standard Specifications for 

Municipal Construction 

Natural Drainage Systems 7-21 

Figure 2. This bioretention area takes runoff from the 

street through a trench drain in the sidewalk as well as 

runoff from the sidewalk through curb cuts 

(Source: Abby Hall, US EPA). 
5

The diversity of shapes, sizes, and layouts bioretention can take is a significant obstacle to their 

incorporation with DOT specifications and standards. Street configurations, topography, soil conditions, 

and space availability are some of the factors that will influence the design of the bioretention facility. 

These variables make documentation of each new bioretention project all the more important. By building 

a menu of templates from local bioretention projects, future projects with similar conditions will be easier 

to implement and cost less to design. The documentation should include copies of the details and 

specifications for the materials used. A section on construction and operation issues, costs, lessons 

learned, and recommendations for similar designs should also be included in project documentation. 

Portland’s Bureau of Environmental Services has proven adept at documenting each of its Green Streets 

projects and making them accessible online.13

 

Utilities are a chief constraint to implementing bioretention as a retrofit in urban areas. The Prince

George’s County, MD Bioretention Design Specifications and Criteria manual recommends applying the 

same clearance criteria recommended for storm drainage pipes.14 Municipal design standards should 

specify the appropriate clearance from 

bioretention or allowable traversing. 

Plants are another common concern of 

municipal staff, whether it is maintenance, 

salt tolerance, or plant height with regard to 

safety and security. Cities actively 

implementing LID practices in public spaces 

maintain lists of plants which fit the 

vegetated stormwater management practice 

niche. These are plants that flourish in the 

regional climate conditions, are adapted to 

periodic flooding, are low maintenance, and, 

if in cold climates, salt tolerant. Most often 

these plants are natives, but sometimes an 

approved non-native will best fit necessary criteria. A municipal plant list should be periodically updated 

based on maintenance experience, and vegetation health surveys. 

Permeable Pavement 

Permeable pavement comes in four forms: permeable concrete, permeable asphalt, permeable interlocking 

concrete pavers, and grid pavers. Permeable concrete and asphalt are similar to their impervious 

counterparts but are open graded or have reduced fines and typically have a special binder added. 

Methods for pouring, setting, and curing these permeable pavements also differ from the impervious 

versions. The concrete and grid pavers are modular systems. Concrete pavers are installed with gaps 

between them that allow water to pass through to the base. Grid pavers are typically a durable plastic

matrix that can be filled with gravel or vegetation. All of the permeable pavement systems have an 

aggregate base in common which provides structural support, runoff storage, and pollutant removal 

through filtering and adsorption. Aside from a rougher unfinished surface, permeable concrete and asphalt 

look very similar to their impervious versions. Permeable concrete and asphalt and certain permeable 

concrete pavers are ADA compliant. 

Table 4. Municipalities with Bioretention Pilot Projects in the Right-of-Way 

Municipality Bioretention Type Document 

Maplewood, MN Rain gardens Implementing Rainwater in Urban Stormwater Management 11

Portland, OR • Curb extensions 

• Planters 

• Rain gardens 

2006 Stormwater Management Facility Monitoring Report 12

Prince George’s County, MD - 2.12.1.16 Utility Clearance

Utility clearances that apply to storm drainage pipe and 

structure placement also apply to bioretention. Standard 

utility clearances for storm drainage pipes have been 

established at 1' vertical and 5' horizontal. However, 

bioretention systems are shallow, non-structural IMP's 

consisting of mostly plant and soil components, (often) with a 

flexible underdrain discharge pipe. For this reason, other 

utilities may traverse a bioretention facility without adverse 

impact. Conduits and other utility lines may cross through 

the facility but construction and maintenance operations 

must include safeguard provisions. In some instances, 

bioretention could be utilized where utility conflicts would 

make structural BMP applications impractical. 
6

Implementation Hurdles 

Of all the green streets practices, 

municipal DOTs have been arguably most 

cautious about implementing permeable 

pavements, though it should be noted that 

some DOTs have, for decades, specified 

open-graded asphalt for low use roadways 

because of lower cost; to minimize vehicle 

hydroplaning; and to reduce road noise. 

The reticence to implement on a largescale, however, is understandable given 

the lack of predictability and experience 

behind impervious pavements. However, 

improved technology, new and ongoing 

research, and a growing number of pilot 

projects are dispelling common myths 

about permeable pavements. 

The greatest concern among DOT staff 

seems to be a perceived lack of longterm performance and maintenance data. Universities and DOTs began experimenting with permeable 

pavements in parking lots, maintenance yards, and pedestrian areas as early as twenty years ago in the

U.S., even earlier in Europe. There is now a wealth of data on permeable pavements successfully used for 

these purposes in nearly every climate region of the country. In recent years, the cities of Portland, OR, 

Seattle, WA, and Waterford, CT and several private developments have constructed permeable pavement 

pilots within the roadway with positive results. 

The two typical maintenance activities are 

periodic sweeping and vacuuming. The City of 

Olympia, WA has experimented with several 

methods of clearing debris from permeable 

concrete sidewalks. Each of the methods was 

evaluated on the ease of use, debris removal, and 

the performance pace. The cost analysis by 

Olympia, WA found that the maintenance cost for pervious pavement was still lower than the traditional

pavement when the cost of stormwater management was considered. 

Freeze/thaw and snow plows are the major concerns for permeable pavements in cold climate 

communities. However, these concerns have proven to be generally unwarranted when appropriate design 

and maintenance practices are employed. A well designed permeable pavement structure will always 

drain and never freeze solid. The air voids in the pavement allow plenty of space for moisture to freeze 

and ice crystals to expand. Also, rapid drainage through the pavement eliminates the occurrence of 

freezing puddles and black ice. Cold climate municipalities will need to make adjustments to snow 

plowing and deicing programs for permeable pavement areas. Snow plow blades must be raised enough to 

prevent scraping the surface of permeable pavements, particularly paver systems. Also, sand should not

be applied. 

Table 5. Municipalities with Permeable Pavement Specifications and Standard Details 

Municipality Document Section Title Section # 

Portland 2007 Standard Construction 

Specifications 

Unit Pavers (includes permeable 

pavers) 

00760 

Olympia WSDOT Specification Pervious Concrete Sidewalks 8-30 

Figure 3. Pervious pavers used in the roadway of a 

neighborhood development in Wilsonville, OR 

(Source: Abby Hall, US EPA). 

Permeable pavement concerns in the roadway often 

raise concerns of safety, maintenance, and durability. 

Municipalities can replace impervious surfaces in other 

non-critical areas such as sidewalks, alleys, and 

municipal parking lots. These types of applications help 

municipalities build experience and a market for the 

technology. 
7

Table 6. A Study in Olympia, WA Comparison of the cost of permeable 

concrete sidewalks to the cost of traditional impervious sidewalks15

Traditional Concrete Sidewalk Permeable Concrete Sidewalk 

Construction Cost Maintenance Cost Construction Cost Maintenance Cost 

$5,003,000* $156,000 $2,615,000* $147,000 

Total = $5,159,000 

$101.16 per square yard 

Total = $2,762,000 

$54.16 per square yard 

*The cost of stormwater management (stormwater pond) for the added impervious surface is 

factored into the significantly higher cost of constructing the traditional concrete sidewalk. 

Maintenance of the stormwater pond is also factored into the traditional concrete sidewalk 

maintenance cost. 

Sidewalk trees and tree boxes 

From reducing the urban heat island effect 

and reducing stormwater runoff to improving 

the urban aesthetic and improving air quality, 

much is expected of street trees. Street trees 

are even good for the economy. Customers 

spend 12% more in shops on streets lined 

with trees than on those without trees.16

However, most often street trees are given 

very little space to grow in often inhospitable 

environments. The soil around street trees 

often becomes compacted during the 

construction of paved surfaces and 

minimized as underground utilities encroach 

on root space. If tree roots are surrounded by 

compacted soils or are deprived of air and 

water by impervious streets and sidewalks, 

their growth will be stunted, their health will 

decline, and their expected life span will be cut short. By providing adequate soil volume and a good soil 

mixture, the benefits obtained from a street tree multiply. To obtain a healthy soil volume, trees can

simply be provided larger tree boxes, or structural soils, root paths, or “silva cells” can be used under 

sidewalks or other paved areas to expand root zones. These allow tree roots the space they need to grow 

to full size. This increases the health of the tree and provides the benefits of a mature sized tree, such as 

shade and air quality benefits, sooner than a tree with confined root space. 

Table 7. Healthy Tree Volume and Permeable Pavement Specifications and Standard Details 

Jurisdictions Minimum Soil Volume Section Title Section # 

Prince William County, VA Large tree 970 cf 

Medium tree 750 cf 

Small tree 500 cf 

Design Construction 

Manual (Sec 800) 

Table 8-8 

Alexandria, VA 300 cf Landscape Guidelines II.B. (2) 

Figure 4. Trees planted at the same time but with different 

soil volumes, Washington DC 

(Source: Casey Trees) 
8

Implementation Hurdles 

Providing an adequate root volume for trees comes down to a trade off between space in the right-of-way 

and added construction costs. The least expensive way to obtain the volume needed for roots to grow to

full size is providing adequate space unhindered by utilities or other encroachments. However, it is often 

hard to reserve space dedicated just to street trees in an urban right-of-way with so many other uses 

competing for the room they need. As a result, some creative solutions, though they cost more to install, 

have become useful alternatives in crowded subsurface space. Structural soils, root paths, and “silva 

cells” leave void space for roots and still allow sidewalks to be constructed near trees. 

Root Paths can be used to increase tree root volume by connecting a small tree root volume with a larger 

subsurface volume nearby. A tunnel-like system extends from the tree underneath a sidewalk and 

connects to an open space on the other side. 

Silva Cells17 are another option for 

supporting sidewalks near trees while still 

providing enough space for roots to grow. 

These plastic milk crate-like frames fit 

together and act as a supporting structure for 

a sidewalk while leaving room for 

uncompacted soil and roots inside the frame. 

Permeable pavement sidewalks are another 

enhancement to the root space. They provide 

moisture and air to roots under sidewalks. 

Soils under permeable pavements can still 

become compacted. Structural soils18 are a 

good companion tree planting practice to 

permeable pavement. When planting a tree in 

structural soils an adequate tree root volume 

is excavated and filled with a mix of stone 

and soil that still provides void space for 

healthy roots and allows for sidewalks, 

plazas or other paved surfaces to be 

constructed over them. 

Case Studies

Portland, OR: Green Street Pilot Projects 

Portland, Oregon is a national leader in developing green infrastructure. Portland’s innovation in 

stormwater management was necessitated by the need to satisfy a Combined Sewer Overflow consent 

decree, Safe Drinking Water Act requirements, impending Total Maximum Daily Load limitations, 

Superfund cleanup measures and basement flooding. Through the 1990s, over 3 billion gallons of 

combined sewer overflow discharged to the Willamette River every year.19 All of these factors plus 

leadership and local desires to create green solutions and industries compelled the city to implement green 

infrastructure as a complement to adding capacity to the sewer system with large pipe overflow 

interceptors. Despite gaps in long-term performance data, Portland took a proactive approach in 

implementing green infrastructure pilot projects. 

Portland’s green infrastructure pilot projects have their roots in the city’s 2001 Sustainable Infrastructure 

Committee. The committee, consisting of representatives from Portland’s three infrastructure 

management Bureaus, documented the city’s ongoing efforts toward sustainable infrastructure, gathered 

research on green infrastructure projects from around the country, and identified opportunities for local 

pilots.20, 21, 22

 

Figure 5. Root Paths direct tree roots under paving and 

into better soil areas for tree root growth 

(Source: Arlington County, VA). 
9

One of the Bureau of Environmental 

Services’ (BES) earliest green 

infrastructure retrofit projects within 

the right-of-way was a set of two 

stormwater curb extensions on NE 

Siskiyou Street. Portland had been 

retrofitting many streets with curb 

extensions for the purpose of 

pedestrian safety, but this was the first 

done for the purpose of treating street 

runoff. In a simulated 25-year storm 

event flow test, the curb extensions 

captured 85% of the runoff volume 

that would be discharged to the 

combined sewer system and reduced 

peak flow by 88%.23

Between 2003 and 2007, Portland 

designed and implemented a variety 

of Green Street pilots. Funding 

sources for these projects have come 

from BES, Portland Department of 

Transportation, U.S. EPA, and an 

Innovative Wet Weather Fund. BES 

combined funds with an EPA grant to 

create the Innovative Wet Weather 

Fund. In 2004, nearly $3 million from 

the Innovative Wet Weather Fund was 

budgeted for a long list of projects 

from city green roofs, public-private 

projects, and a number of pilot 

projects within the right-of-way.24

Several pilots have been cost 

competitive with or less costly than 

conventional upgrades. The Bureau 

recognizes that costs will decrease 

once these projects become more 

routine. Many of the pilot project 

costs included one time costs such as 

the development of outreach materials 

and standard drawings. 

Figure 6. Silva cell structures support the sidewalk while providing 

root space for street trees 

(Source: Deep Root Partners, LP). 

Figure 7. Structural soils provide void space for root growth and 

load-bearing for sidewalk 

(Source: Urban Horticulture Institute, Cornell University). 
10

Table 8. Portland, OR - Green Street Pilot Projects

Location Design 

Year 

Completed Cost 

NE Siskiyou b/w NE 35th Pl. and 

NE 36th Ave 

Stormwater curb extension 2003 $20,000 

3 blocks of the Westmoreland 

Neighborhood 

Permeable Pavers in parking 

lanes and curb to curb 

2004 $412,000 

SE Ankeny b/w SE 56th and SE 

57th Ave. 

Stormwater curb extensions 2004 $11,946 

NE Fremont b/w NE 131st and 

132nd Av 

Stormwater curb extension 2005 $20,400 

SW 12th Ave b/w SW 

Montgomery and Mill 

Stormwater planters 2005 $34,850 

East Holladay Park Pervious paver parking lot 2005 $165,000 

4 blocks of North Gay Avenue b/w 

N Wygant and 

N Sumner 

Porous concrete in curb lanes 

and curb to curb; porous asphalt 

in curb lanes and curb to curb 

2005 -- 

SW Texas Stormwater wetlands and 

swales 

2007 $2.3 

million 

Division St. – New Seasons 

Market 

Stormwater planters and swales -- -- 

SE Tibbetts and SE 21st Ave. Stormwater curb extension and 

planters 

-- -- 

Source: Portland Bureau of Environmental Services, 2008 

http://www.portlandonline.com/bes/index.cfm?c=44463& 

Each of the pilot projects have been well documented by BES. A consistent format has been used to 

describe pilot background, features, engineering design, landscaping, project costs, maintenance, 

monitoring, and, most importantly, lessons learned. These case studies as well as other Green Street 

documentation can be found on BES’s Sustainable Stormwater webpage, 

http://www.portlandonline.com/BES/index.cfm?c=34598. Due to physical factors (drainage, slope, soil, 

existing utilities, multiple uses) and development factors (retrofit, redevelopment, and new construction), 

there will be many variations on Green Streets. As part of the program, a continually updated Green 

Street Profile Notebook will catalog the successful green street projects. Users can use the Notebook for 

permitting guidance, to identify green streets facilities appropriate for various factors, but the document is 

not a technical document with standard details. 

Figure 8: NE Siskiyou Vegetated Curb Extensions

Source: City of Portland – Bureau of Environmental Services 
11

The Green Streets Team 

The City of Portland, OR is widely acknowledged for long term, forward thinking, and comprehensive 

transportation and environmental planning. Portland recognized the fact that 66% of the City’s total 

runoff is collected from streets and the right-of-way.25 The city also saw the potential for transportation

corridors to meet multiple objectives, including: 

• Comprehensively address numerous City goals for neighborhood livability, sustainable development, 

increased green spaces, stormwater management, and groundwater protection; 

• Integrate infrastructure functions by creating “linear parks” along streets that provide both 

pedestrian/bike areas and stormwater management; 

• Avoid the key impacts of unmanaged stormwater whereby surface waterbodies are degraded, and 

water quality suffers; 

• Manage stormwater with investments citizens can support, participate in, and see; 

• Manage stormwater as a resource, rather than a waste; 

• Protect pipe infrastructure investments (extend the life of pipe infrastructure, limit the additional 

demand on the combined sewer system as development occurs); 

• Protect wellhead areas by managing stormwater on the surface; and 

• Provide increased neighborhood amenities and value.

In a two phased process from 2005 to 2007, 

the Green Streets Team, a cross agency and 

interdisciplinary team, developed a 

comprehensive green streets policy and a way 

forward for the green streets agenda. Phase 1 

identified challenges and issues and began a 

process for addressing them. Barriers to the 

public initiation of green street projects 

included a code and standards that would 

disallow or discourage green street strategies, 

long term performance unknowns, and 

maintenance responsibilities. To address 

these barriers, the Green Streets Team 

organized into subgroups focusing on 

outreach, technical guidance, infrastructure, 

maintenance, and resources. 

Phase 2 of the Green Streets project 

synthesized the opportunities and solutions 

identified in Phase 1 into a citywide Green 

Streets Program. The first priority for this 

phase was the drafting of a binding citywide 

policy. The resolution was adopted by the 

Portland City Council in March 2007. 

Prior to the start of the Portland effort, 90% of implemented 

green street projects were issued by private permits rather 

than city initiated projects. 

Six Approaches to Implementing Green Streets 

Pathway Implementation 

City-initiated street 

improvement projects 

City designs, manages, maintains 

City-initiated stormwater 

retrofits 

City designs, manages, maintains 

Neighborhood-initiated 

LIDs 

Developer-initiated 

subdivisions with public 

streets 

Developer designs and builds via 

City permit and review process, 

then turns over new right of way to 

the City after warranty period 

Developer-initiated 

subdivisions with 

private streets 

Developer designs and builds via 

City permit and review process, and 

turns over to home-owner 

association 

Developer-related 

initiated frontage 

improvements on 

existing public streets 

Developer designs and builds new 

sidewalks and curbs via City permit 

and review process, usually 

because the City required it via a 

building permit or via a land division 

Source: Portland Green Streets, Phase 1 
12

The second priority for Phase 2 was developing communication and planning procedures for 

incorporating multi-bureaus plans into the scheduled Portland DOT Capital Improvement Program (CIP). 

Three timeframes for green street project planning were recommended. In the short term, the CIP 

Planning Group, backed by the citywide policy directive, will shift to a focus on “identifying and 

evaluating opportunities to partner.” For example, coordinating Water Bureau and BES pipe replacement 

Portland City Council Approved Green Streets Policy

Goal: City of Portland will promote and incorporate the use of green street facilities in public and private 

development. 

City elected officials and staff will: 

1. Infrastructure Projects in the Right of Way: 

a. Incorporate green street facilities into all City of Portland funded development, redevelopment or 

enhancement projects as required by the City’s September 2004 (or updated) Stormwater Management 

Manual. Maintain these facilities according to the May 2006 (or updated) Green Streets Maintenance 

Policy. 

If a green street facility (infiltrating or flow through) is not incorporated into the Infrastructure Project, or only 

partial management is achieved, then an off site project or off site management fee will be required. 

b. Any City of Portland funded development, redevelopment or enhancement project, that does not trigger the 

Stormwater Manual but requires a street opening permit or occurs in the right of way, shall pay into a “% for 

Green” Street fund. The amount shall be 1% of the construction costs for the project. 

Exceptions: Emergency maintenance and repair projects, repair and replacement of sidewalks and 

driveways, pedestrian and trail replacement, tree planting, utility pole installation, street light poles, traffic, 

signal poles, traffic control signs, fire hydrants, where this use of funds would violate contracted or legal 

restrictions. 

2. Project Planning and Design: 

a. Foster communication and coordination among City Bureaus to encourage consideration of watershed 

health and improved water quality through use of green street facilities as part of planning and design of 

Bureau projects. 

b. Coordinate Bureau work programs and projects to implement Green Streets as an integrated aspect of City 

infrastructure. 

c. Plan for large-scale use of Green Streets as a means of better connecting neighborhoods, better use of the 

right of way, and enhancing neighborhood livability. 

d. Strive to develop new and innovative means to cost-effectively construct new green street facilities. 

e. Develop standards and incentives (such as financial and technical resources, or facilitated permit review) for 

Green Streets projects that can be permitted and implemented by the private sector. These standards and 

incentives should be designed to encourage incorporation of green street facilities into private 

development, redevelopment and enhancement projects. 

3. Project and Program Funding: 

a. Seek opportunities to leverage the work and associated funding of projects in the same geographic areas 

across Bureaus to create Green Street opportunities. 

b. Develop a predictable and sustainable means of funding implementation and maintenance of Green Street 

projects. 

4. Outreach: 

a. Educate citizens, businesses, and the development community/industry about Green Streets and how they 

can serve as urban greenways to enhance, improve, and connect neighborhoods to encourage their 

support, demand and funding for these projects. 

b. Establish standard maintenance techniques and monitoring protocols for green street facilities across 

bureaus, and across groups within bureaus. 

5. Project Evaluation: 

a. Conduct ongoing monitoring of green street facilities to evaluate facility effectiveness as well as

performance in meeting multiple City objectives for: 

- Gallons managed; 

- Projects distributed geographically by watershed and by neighborhood; and 
13

projects with DOT maintenance, repair, and improvement projects. The mid-term approach is more 

proactive and involves forecasting potential green street projects using existing bureau data and GIS tools. 

As for the long term, green street objectives will be incorporated into the citywide systems plan which 

guides city bureaus for the next 20 years. 

The Green Street Team methodology propelled Portland’s early green street pilot projects into a 

comprehensive, citywide multi-bureau program. The program built on previous efforts by the Sustainable

Infrastructure Committee as well as other efforts such as the 2005 Portland Watershed Management Plan,

established a City Council mandated policy, and institutionalized green street development. The outcome 

of this approach is multi-agency buy-in and responsibility for the effort. For instance, because of their 

knowledge of plant maintenance, Portland Parks and Recreation is responsible for the maintenance of 

some DOT installations. 

Chicago, IL: Green Alleys Program 

The City of Chicago, Illinois has an alley system that is perhaps the largest in the world. These 13,000 

publicly owned alleys result in 1,900 miles, or 3,500 acres, of impermeable surfaces in addition to the 

street network. Because the alley system was not originally paved, there are no sewer connections as part 

of the original design. Over time the alleys were paved and flooding in garages and basements began to

occur as a result of unmanaged stormwater runoff. Since the city already spends $50 million each year to 

clean and upgrade 4,400 miles of sewer lines and 340,000 related structures, the preferred solution to the 

flooded alleys is one that doesn’t put more stress on an already overburdened and expensive sewer 

system.26 

In 2003, the Chicago Department of Transportation (CDOT) used permeable pavers and French drain 

pilot applications to remedy localized flooding problems in alleys in the 48th Ward.27 These applications 

proved to be successful and by 2006, CDOT launched its Green Alley Program with the release of the 

Chicago Green Alley Handbook (Handbook).28 

The Chicago Green Alley Program is unique because it marries green infrastructure practices in the public 

right-of-way with green infrastructure efforts on private property. The user-friendly Handbook, which 

describes both facets of the program including the design techniques and their benefits, is an award 

winning document. The American Society of Landscape Architects awarded the creators of the Handbook 

the 2007 Communications Honor Award for the clear graphics and simple, yet effective, message.29 The 

Handbook explains to the residents why green infrastructure is important, how to be good stewards of the 

Green Alley in their neighborhood, and what sorts of “green” practices they can implement on their 

property to reduce waste, save water, and help manage stormwater wisely. 

While the initial impetus behind the Green Alley Program was stormwater management, Chicago decided 

to use this opportunity to address other environmental concerns as well as reducing the urban heat island 

effect, recycling, energy conservation, and light pollution. 

Green Infrastructure in the Right-of-Way 

Chicago’s Green Alley Program uses the following five techniques in the public right-of-way to “green”

the alley: 

1. Changing the grade of the alley to drain to the street rather than pond water in the alley or drain 

toward garages or private property. 

2. Using permeable pavement that allows water to percolate into the ground rather than pond on the 

surface. 

3. Using light colored paving material that reflects sunlight rather than adsorbing it, reducing urban 

heat island effect. 
14

4. Incorporating recycled materials 

into the pavement mix to reduce 

the need for virgin materials and 

reduce the amount of waste going 

into the landfill. 

5. Using energy efficient light 

fixtures that focus light 

downward, reducing light 

pollution. 

Four design approaches were created 

using these techniques. Based on the local 

conditions, the most appropriate approach 

is selected. In areas where soils are welldraining, permeable pavement is used. In 

areas where buildings come right up to the 

edge of pavement and infiltrated water 

could threaten foundations, impermeable 

pavement strips are used on the outside 

with a permeable pavement strip down the 

middle. In areas where soils do not 

provide much infiltration capacity, the 

alley is regraded to drain properly and impermeable pavement made with recycled materials is used. 

Another approach utilizes an infiltration trench down the middle of the alley. Light colored (high albedo) 

pavement, recycled materials, and energy efficient, glare reducing lights are a part of each design 

approach. 

Green Infrastructure on Private Property 

The Handbook also describes actions that property owners can take to “green” their own piece of 

Chicago. The Handbook describes the costs, benefits, and utility of the following practices: 

• Recycling; 

• Composting; 

• Planting a tree; 

• Using native landscape vegetation; 

• Constructing a rain garden; 

• Installing a rain barrel; 

• Using permeable pavement for patios; 

• Installing energy efficient lighting; and 

• Utilizing natural detention. 

By bringing this wide range of “green” practices to the attention of homeowners, the positive impacts of 

the Green Alley Program spread beyond the boundaries of the right-of-way, increasing awareness and 

providing practical resources to help community members be a part of the solution. 

Chicago Green Alley Cost Considerations 

When the program began in 2006, repaving the alleys with impermeable pavement ranged in cost from 

$120,000 to $150,000, whereas a total Green Alley reconstruction was more along the lines of $200,000 

to $250,000.30 While less expensive conventional rehabilitation options may seem more attractive, they 

don’t provide a solution to the localized flooding issues or the combined sewer system overflow 

problems. Sewer system connections could be established to solve the localized flooding problem, but it 

would add to the already overburdened sewer system and increase the cost of the reconstruction to that of 

the impermeable alley option. Consequently, the higher priced Green Alley option proved to be the best

investment as it has multiple benefits in addition to solving localized flooding and reducing flow into the 

combined sewer system. The additional benefits of the Green Alley Program include not only urban heat 

Figure 9: Permeable Asphalt Installation Using Ground Tire 

Rubber. 

Source: Chicago Department of Transportation, Sustainable 

Development Initiatives; Streetscape and Urban Design Program, 

CDOT Division of Project Development. 
15

island effect reduction, material recycling, energy conservation, and light pollution reduction, but also the 

creation of a new market. 

In 2006, when the Green Alley Program began, the city paid about $145 per cubic yard of permeable 

concrete. Just one year later, the cost of permeable concrete had dropped to only $45 per cubic yard. 

Compared with the cost of ordinary concrete, $50 per cubic yard, permeable concrete may have seemed 

like an infeasible option in the past to customers wanting to purchase concrete.31 After the city’s initial 

investment in the local permeable concrete market, the product cost has come down making permeable 

concrete a more affordable option for other consumers besides the city. This has resulted in an increased 

application of permeable concrete throughout the region. 

Figure 10: Permeable Pavers and Permeable Concrete Chicago Alleys 

(Source: Abby Hall, US EPA) 

The success of the Chicago Green Alley Program is evident. Not only are the alleys been “greened” as a

result of the program, the surrounding properties and even the surrounding neighborhoods are 

experiencing the positive impacts of the program’s implementation. 

Conclusions and Recommendations

Incorporating green streets as a feature of urban stormwater management requires matching road function 

with environmental performance. Enhancing roads with green elements can improve their primary 

function as a transportation corridor while simultaneously mitigating their negative environmental 

impacts. In theory and practice many municipalities are not far removed from dedicated green streets 

programs. Street tree and other greenscaping programs are often identified and promoted along urban 

transportation corridors. Adapting them to become fully functional green streets requires minor design

modifications and an evaluation of how to maximize the benefits of environmental systems. 

Portland’s green streets program demonstrates how common road and right-of-way elements (e.g., traffic

calming curb extensions, tree boxes) can be modified and optimized to provide stormwater management 

in addition to other benefits. The curb cuts and design variations to allow runoff to enter the vegetated 

areas are subtle changes with a significant impact and demonstrate how stormwater can be managed 

successfully at the source. One of the biggest successes of the program was reassessing common design 

features and realizing that environmental performance can be improved by integrating stormwater 

management. 

Where Portland used vegetation, Chicago’s Green Alley Program similarly demonstrates that hardscape 

elements can be an integral part of a greening program. By incorporating permeable pavements that 

simulate natural infiltration, Chicago enhances the necessary transportation function of alleys while 

enhancing infrastructure and environmental management. Portland also contrasts the “soft” and “hard” 
16

elements of green streets by using both permeable pavements and vegetated elements. The green options 

available demonstrate the flexibility of green infrastructure to satisfy road function and environmental 

objectives and highlight why transportation corridors are well suited for green infrastructure. 

As public spaces, roads are prime candidates for green infrastructure improvements. In addition to 

enabling legislation, and technical guidance, developing a green streets program requires an institutional 

re-evaluation of how right-of-ways are most effectively managed. This process typically includes: 

• Assessing the necessary function of the road and selecting the minimum required street width to 

reduce impervious cover; 

• Enhancing streetscaping elements to manage stormwater and exploring opportunities to integrate 

stormwater management into roadway design; and 

• Integrating transportation and environmental planning to capitalize on economic benefits. 

The use of green streets offers the capability of transforming a significant stormwater and pollutant source 

into an innovative treatment system. Green streets optimize the performance of public space easing 

maintenance concerns and allowing municipalities to coordinate the progression and implementation of 

stormwater control efforts. In addition, green streets optimize the performance of both the transportation 

and water infrastructure. Effectively incorporating green techniques into the transportation network 

provides significant opportunity to decrease infrastructure demands and pollutant transport. 

 

1

 National Cooperative Highway Research Program, Evaluation of Best Management Practices and Low Impact 

Development for Highway Runoff Control, National Academy of Sciences – National Research Council, 2006. 

2

 Lance Frazer, Paving Paradise: The Peril of Impervious Cover, Environmental Health Perspectives, Volume 

113, Number 7, July 2005. 

Elements necessary for a successful green streets program:

• Pilot projects are critical. The most successful municipal green street programs to date all began with well 

documented and monitored pilot projects. These projects have often been at least partially grant funded and 

receive the participation of locally active watershed groups working with the city infrastructure programs. The 

pilot projects are necessary to demonstrate that green streets can work in the local environment, can be relied 

upon, and fit with existing infrastructure. Pilot projects will help to dispel myths and resolve concerns.

• Leadership in sustainability from the top. The cities with the strongest green streets programs are those 

with mayors and city councils that have fully bought into sustainable infrastructure. Council passed green 

policies and mayoral sustainability mandates or mission statements are needed to institutionalize green street 

approaches and bring it beyond the token green project.

• Buy-in from all municipal infrastructure departments. By their nature, green streets cross many municipal 

programs. Green street practices impact stormwater management, street design, underground utilities, public 

lighting, green space planning, public work maintenance, and budgeting. When developing green streets, all of 

the relevant agencies must be represented. Also, coordination between the agencies on project planning is 

important for keeping green infrastructure construction costs low. Superior green street design at less cost 

occurs when sewer and water line replacement projects can be done in tandem with street redevelopment.

These types of coordination efforts must happen at the long-term planning stage.

• Documentation. Green street projects need to be documented on two levels, the design and construction 

level and on a citywide tracking level. Due to the different street types and siting conditions, green street 

designs will take on many variations. By documenting the costs, construction, and design, the costs of similar 

future projects can be minimized and construction or design problems can be avoided or addressed. Tracking 

green street practices across the city is crucial for managing maintenance and quantifying aggregate benefits. 

• Public outreach. Traditional pollution prevention outreach goes hand in hand with green street programs. 

Properly disposing of litter, yard waste, and hazardous chemicals and appropriately applying yard chemicals 

will help prolong the life of green street practices. An information campaign should also give the public an 

understanding of how green infrastructure works and the benefits and trade offs. In many cases, remedial 

maintenance of green street practices will be performed by neighboring property owners; they need to know 

how to maintain the practices to keep them performing optimally. 
17

 

3

 See note 1. 

4 Pollutants Commonly Found in Stormwater Runoff, http://www.stormwaterauthority.org/pollutants/default.aspx

(accessed July 2008). 

5

 Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities: 

http://www.ite.org/css/ (Ch. 6, pages. 65-87) 

6 Neighborhood Street Design Guidelines, prepared by Neighborhood Streets Project Stakeholders. November 

2000 http://www.oregon.gov/LCD/docs/publications/neighstreet.pdf (accessed June 2008) 

7 Narrow Streets Database, http://www.sonic.net/abcaia/narrow.htm (accessed July 2008).

8

 City of Seattle. Street Edge Alternatives Project 

http://www.ci.seattle.wa.us/util/About_SPU/Drainage_&_Sewer_System/Natural_Drainage_Systems/Street_Edge_

Alternatives/index.asp

9

 City of Austin, Engineering Services Division. Standard Specifications and Details Website: 

http://www.ci.austin.tx.us/sd2/

10 See note 9 

11 Implementing Rainwater in Urban Stormwater Management

http://www.ci.maplewood.mn.us/index.asp?Type=B_BASIC&SEC=%7BF2C03470-D6B5-4572-98F0-

F79819643C2A%7D (accessed July 2008). 

12 2006 Stormwater Management Facilities Monitoring Report 

http://www.portlandonline.com/bes/index.cfm?c=36055 (accessed July 2008). 

13 City of Portland. Green Streets website. https://www.sustainableportland.org/BES/index.cfm?c=44407 (last 

accessed July, 2008). 

14 Prince George’s County, MD. Bioretention Design Specifications and Criteria. 

http://www.co.pg.md.us/Government/AgencyIndex/DER/ESD/Bioretention/pdf/bioretention_design_manual.pdf

(accessed July 2008). 

15 City of Olympia. Memorandum: Traditional versus Pervious Concrete Sidewalk – Construction and 

Maintenance Costs. Feb. 2005. 

http://www.ci.olympia.wa.us/cityutilities/stormwater/scienceandinnovations/porouspavement.htm. 

16 The Case for Trees, Casey Trees, Washington, D.C.:

http://www.caseytrees.org/resources/casefortrees.html#EconGrowth

17 Deep Root, LLC. http://www.deeproot.com

18 Cornell University, Urban Horticulture Institute. http://www.hort.cornell.edu/UHI/ 

19 City of Portland Bureau of Environmental Services, CSO Program, 

http://www.portlandonline.com/BES/index.cfm?c=31030, (accessed July 2008). 

20 City of Portland Sustainable Infrastructure Committee, Sustainable Infrastructure Report. December 2001. 

http://www.portlandonline.com/shared/cfm/image.cfm?id=82893 (last accessed July, 2008). 

21 City of Portland Sustainable Infrastructure Subcommittee, Sustainable Infrastructure: Alternative Paving 

Materials. Oct. 2003. http://www.portlandonline.com/shared/cfm/image.cfm?id=82898, (accessed July 2008).

22 City of Portland Sustainable Infrastructure Subcommittee, Sustainable Infrastructure: Streetscape Task Force. 

Nov. 2003. http://www.portlandonline.com/shared/cfm/image.cfm?id=82897, (accessed July 2008). 

23 City of Portland Bureau of Environmental Services, Flow Test Report: Siskiyou Curb Extension. August 4, 2004. 

http://www.portlandonline.com/shared/cfm/image.cfm?id=63097 (accessed July 2008).

24 City of Portland Bureau of Environmental Services, Environmental Assessment: Innovative Wet Weather 

Program, April 2004. 

25 Portland Stormwater Advisory Committee, 2004. 

26Chicago Department of Transportation, Sustainable Development Initiatives; Streetscape and Urban Design 

Program, CDOT Division of Project Development: http://www.railvolution.com/rv2006_pdfs/rv2006_217c.pdf

27 48th Ward Green Initiatives: http://www.masmith48.org/greeniniatives/greeniniatives.html

28 The Chicago Green Alley Handbook, Chicago Department of Transportation: 

http://egov.cityofchicago.org/webportal/COCWebPortal/COC_EDITORIAL/GreenAlleyHandbook.pdf

29 American Society of Landscape Architects, 2007 Professional Awards: 

http://www.asla.org/awards/2007/07winners/212_hdg.html

30 DeJong, Aaron, A Pilot Project Takes Off, Sustainable Urban Redevelopment: 

http://www.surmag.com/index.php?option=com_content&task=view&id=10&Itemid=2

31 Saulny, Susan, In Miles of Alleys, Chicago Finds it’s Next Environmental Frontier, New York Times

November 26, 2007.