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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
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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.
Table 1. Examples of Stormwater Pollutants Typical of Roads.3'4
Pollutant
Trash
Sediment/solids
Metals
• Copper
• Zinc
• Lead
• Arsenic
Organics associated
with petroleum (e.g.,
PAHs)
Nutrients
Source
—
Construction, unpaved areas
• Vehicle brake pads
• Vehicle tires, motor oil
• Vehicle emissions and engines
• Vehicle emissions, brake linings,
automotive fluids
Vehicle emissions, automotive fluids,
gas stations
Vehicle emissions, atmospheric
deposition
Effects
Physical damage to aquatic animals and
fish, release of poisonous substances
Increased turbidity, increased transport of
soil bound pollutants, negative effects on
aquatic organisms reproduction and
function
Toxic to aquatic organisms and can
accumulate in sediments and fish tissues
Toxic to aquatic organisms
Promotes eutrophication and depleted
dissolved oxygen concentrations
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 by-
products, and automotive fluids from vehicles can present a toxic mix that combines with the ubiquitous
nutrients, trash, and suspended solids.
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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.
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-of-
ways 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.
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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
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.
, 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.
". «fiW33mMWB?*w *»*; *
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
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).
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
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Table 2. Examples of Alternative Street Widths
Jurisdiction
Phoenix, AZ
Santa Rosa, CA
Orlando, FL
Birmingham, MI
Howard County, MD
Kirkland, WA
Madison, WI
Street Width
28'
30'
26' -28'
20'
20'
28'
22'
26'
20'
24'
12'
20'
24'
28'
27'
28'
Parking Condition
parking both sides
parking both sides, <1000ADT
parking one side
no parking
neck downs @ intersection
parking both sides, res. Lots<55' wide
parking both sides, res. Lots>55' wide
parking both sides
parking one side
parking unregulated
alley
parking one side
parking both sides - low density only
parking both sides
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.
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).
Table 3. Municipalities with Swale Specifications and Standard Details
Municipality
City of Austin9
City of Seattle10
Document
Standard Specifications and
Standard Details
2008 Standard Specifications for
Municipal Construction
Section Title
Grass-Lined Swale and Grass-
Lined Swale with Stone Center
Natural Drainage Systems
Section #
627S
7-21
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Table 4. Municipalities with Bioretention Pilot Projects in the Right-of-Way
Municipality
Maplewood, MN
Portland, OR
Bioretention Type
Rain gardens
• Curb extensions
• Planters
• Rain gardens
Document
Implementing Rainwater in Urban Stormwater Management 1 1
2006 Stormwater Management Facility Monitoring Report 12
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.
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 IMF'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.
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.
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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 large-
scale, 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.
Figure 3. Pervious pavers used in the roadway of a
neighborhood development in Wilsonville, OR
(Source: Abby Hall, US EPA).
The greatest concern among DOT staff
seems to be a perceived lack of long-
term 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.
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.
Table 5. Municipalities with Permeable Pavement Specifications and Standard Details
Municipality
Portland
Olympia
Document
2007 Standard Construction
Specifications
WSDOT Specification
Section Title
Unit Pavers (includes permeable
pavers)
Pervious Concrete Sidewalks
Section #
00760
8-30
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.
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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
Construction Cost
$5,003,000*
Maintenance Cost
$156,000
Total = $5,159,000
$101.16 per square yard
Permeable Concrete Sidewalk
Construction Cost
$2,615,000*
Maintenance Cost
$147,000
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.
Figure 4. Trees planted at the same time but with different
soil volumes, Washington DC
(Source: Casey Trees)
Table 7. Healthy Tree Volume and Permeable Pavement Specifications and Standard Details
Jurisdictions
Prince William County, VA
Alexandria, VA
Minimum Soil Volume
Large tree 970 cf
Medium tree 750 cf
Small tree 500 cf
300 cf
Section Title
Design Construction
Manual (Sec 800)
Landscape Guidelines
Section #
Table 8-8
II.B. (2)
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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.
Figure 5. Root Paths direct tree roots under paving and
into better soil areas for tree root growth
(Source: Arlington County, VA).
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
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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),
One of the Bureau of Environmental
Services' (BBS) 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 BBS, 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/
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.
. 24
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Figure 8: NE Siskiyou Vegetated Curb Extensions
Source: City of Portland - Bureau of Environmental Services
Table 8. Portland, OR - Green Street Pilot Projects
Location
NE Siskiyou b/w NE 35tt PI. and
NE 36th Ave
3 blocks of the Westmoreland
Neighborhood
SE Ankeny b/w SE 56tt and SE
57* Ave.
NE Fremont b/w NE 13 1st and
132nd Av
SW 12"1 Ave b/w SW
Montgomery and Mill
East Holladay Park
4 blocks of North Gay Avenue b/w
N Wygant and
N Sumner
SW Texas
Division St. - New Seasons
Market
SE Tibbetts and SE 21st Ave.
Design
Stormwater curb extension
Permeable Pavers in parking
lanes and curb to curb
Stormwater curb extensions
Stormwater curb extension
Stormwater planters
Pervious paver parking lot
Porous concrete in curb lanes
and curb to curb; porous asphalt
in curb lanes and curb to curb
Stormwater wetlands and
swales
Stormwater planters and swales
Stormwater curb extension and
planters
Year
Completed
2003
2004
2004
2005
2005
2005
2005
2007
--
--
Cost
$20,000
$412,000
$11,946
$20,400
$34,850
$165,000
$2.3
million
--
--
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 BBS. 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 BBS'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.
10
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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.
corridors to meet multiple objectives, including:
25
The city also saw the potential for transportation
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
City-initiated street
improvement projects
City-initiated stormwater
retrofits
Neighborhood-initiated
LIDs
Developer-initiated
subdivisions with public
streets
Developer-initiated
subdivisions with
private streets
Developer-related
initiated frontage
improvements on
existing public streets
Implementation
City designs, manages, maintains
City designs, manages, maintains
Developer designs and builds via
City permit and review process,
then turns over new right of way to
the City after warranty period
Developer designs and builds via
City permit and review process, and
turns over to home-owner
association
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
11
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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
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 BBS pipe replacement
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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.
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t«a»
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 well-
draining, 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:
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,
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, repaying 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
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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.
:^:-^jf^'''^: •*
*ffe-J<^:
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"
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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.
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.
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?, July 2005.
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See note 1.
4 Pollutants Commonly Found in Stormwater Runoff, http://www.stormwaterauthoritv.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?Tvpe=B BASIC&SEC=%7BF2C03470-D6B5-4572-98FO-
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/AgencvIndex/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.olvmpia.wa.us/citvutilities/stormwater/scienceandinnovations/porouspavement.htm.
16 The Case for Trees, Casey Trees, Washington, D.C.:
http://www.casevtrees.org/resources/casefortrees.htmlffEconGrowth
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.citvofchicago.org/webportal/COCWebPortal/COC_EDITORIAL/GreenAllevHandbook.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.
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