GREEN STREETS AMENDMENT
FOR THE
MONTGOMERY COUNTY ROAD CODE BILL
Montgomery County Stormwater Partners*
________________________________
CONTENTS:
Purpose…………………..….Page 1
Technical Proposal………….Page 2
Toolbox of Techniques….…..Page 6
Endnotes…………………… Page 18
*
Anacostia Riverkeeper at Earth Conservation Corps, Anacostia Watershed Citizens Advisory Committee,
Anacostia Watershed Society, Audubon Naturalist Society, Chesapeake Bay Foundation, Clean Water
Action, Eyes of Paint Branch, Friends of Cabin John Creek Watershed, Friends of Hillmead Park, Friends
of Rock Creek’s Environment, Friends of Sligo Creek, Friends of the Earth, Greater Goshen Civic
Association, Montgomery County Civic Federation, Natural Resources Defense Council, Neighbors of
Northwest Branch, Northwood-Four Corners Civic Association, Potomac Conservancy, RiverSides, Sierra
Club, and the West Montgomery County Citizens Association.
PURPOSE
Of a Green Streets Amendment
______________________
The Road Code bill should be amended to mandate that a minimum
quantity of stormwater be retained and treated on-site, within the road
right-of-way, preferably using vegetation-based stormwater
management techniques.
This should be achieved using the following principles of roadway design:

Incorporate bioretention features to the maximum extent practicable,
particularly by utilizing landscaping units for this purpose†.

Utilize evolving design standards to ensure that Montgomery County’s
roadway stormwater management techniques keep pace with the national
and international state of the art.

Minimize impervious surfaces to the maximum extent practicable, once all
transportation modes, particularly pedestrian and bicycling needs, are
considered.1

Utilize “open section” roads instead of “curb and gutter” roads wherever
practicable.

Preserve existing rural and rustic roads/
†
Bioretention definition: Bioretention combines engineered soils and vegetation in a
dug-out, trenched, or depressed area to collect, treat, store, filter, and/or infiltrate
stormwater runoff. Bioretention may be incorporated into normally-landscaped roadway
features such as medians, cul de sacs, traffic circles, curb extensions, planters, street tree
containers, and swales.
1
TECHNICAL PROPOSAL
BASIC DESCRIPTION: Each category of road is required to retain a certain
volume of stormwater on-site, within the road right-of-way. Roadway designers
would use a prioritized “toolbox” of stormwater retention techniques to meet or
exceed the stormwater retention requirements. Vegetative infiltration techniques
are preferred, due to their superior performance. Although road designers are
free to choose from all the tools included in the law’s stormwater toolbox,
specific combinations are suggested for different categories of roadways, based
on the particular needs and challenges of that road category.
The Preferred Tools listed for each roadway category are further explained in the
Toolbox section, and are documented with technical, web-based references. ‡
TECHNICAL PROPOSAL:
RULE: All roadways must be designed to meet or exceed the following standards for on-site
stormwater retention, using one or more of the on-site techniques specified by this law:
Stormwater Performance Standards, by Roadway Category:

ULTRA-URBAN§
o Road Code street categories included:
Business District Streets
Priniciple Secondary Residential Streets
(w/ curbs, & 1- or 2-sided parking)
Secondary Residential Streets
(w/curbs, 1-,2-, or no-sided parking)
Tertiary Residential Street
o Minimum stormwater retention: ½ ”
‡
Detailed design drawings and specifications for roughly ten green street techniques or technique components,
including bioswales; tree boxes; planters; curb extensions, and concrete inlets are presented on Portland’s Green
Streets web page at: www.portlandonline.com/bes/index.cfm?c=44213&
§
Ultra-Urban: refers to “downtown” and Central Business District neighborhoods with high densities of
buildings, typically mixtures of retail, residential, and other adjacent uses, buildings fronting on the street/
sidewalk; and high overall imperviousness.
2
Basis: The Silver Spring Central Business District Sector Plan (2001) calls for
stormwater quality treatment on-site for redevelopment projects, but allows for
waiver payments into a stream restoration fund in lieu of stormwater quantity
volume treatment. The State of Maryland stormwater design manual requires
redevelopment projects of 5000 sq. ft. or larger to treat a portion of their
stormwater on-site.2
Preferred tools:

Stormwater planters
Street Trees with Structural Cells (or other Proven
Stormwater Retention ability)
Bioretention Medians
Permeable/ pervious pavements
(Note: Underdrains and impermeable liners will be required, as well as
overflow drainage/ conveyance; the latter for all categories.)


Other Options:
Underground SW treatment devices
URBAN
o Road Code street categories included:
Arterials
Industrial Streets
Primary Residential Streets
Secondary Residential Streets
Tertiary Residential Streets
o Minimum stormwater retention: 1”
Example of a similar standard: the Anacostia Waterfront Corporation proposed
stormwater standard is on-site retention with beneficial reuse of 1” of rain over 24
hours with a 48-hour antecedent dry period.3 This standard applies to all projects
including streets and sidewalks as well as buildings and parking lots.
o Preferred tools:
Stormwater planters
Street Trees with Structural Cells
Bioretention Medians
Bioretention Swales (Bioswales)
3
(Underdrains will be necessary, but there may be a few cases where greater
infiltration can be achieved e.g. where impermeable liners will not be
necessary, as appropriate given soil type, etc.)

SUBURBAN
o Road Code street categories included:
Minor Arterials
Primary Residential Streets (with curbs)
Principle Secondary Residential Streets
Secondary Residential Streets
Tertiary Residential Streets
o Minimum stormwater retention: 2”
Example of a similar standard: The Seattle Public Utilities Natural Drainage
System Program (that has now completed five major projects) uses a multi-faceted
set of goals that includes maximizing on-site retention so as to protect streams from
the one to two-year storm event.4 The one-year, 24-hour storm size for
Montgomery County is 2.6”.
o Preferred tools:
Bioretention Cul-de-Sacs
Bioretention Medians
Bioretention Swales (Bioswales)
Bioretention curb extensions
Open Section Roads
Permeable Pavements (for sidewalks)
(Underdrains will be necessary, but there may be cases where greater
infiltration can be achieved e.g. where impermeable liners will not be
necessary.)

RURAL
o Road Code street categories included:
Country Roads
Primary Residential Streets (no curbs)
Principle Secondary Residential Streets
Secondary Residential Streets (no curbs, no parking)
4
o Minimum stormwater retention: 3”
Example: open section roads are applied by the Montgomery Planning Board for
rural developments,5 and these inherently involve the use of swales. The Pembroke
development in Frederick County, MD utilized open section roads with bioretention
swales and incorporated a design standard of 3” (the two-year storm).6
o Preferred tools:
Bioretention Swales
Bioretention Medians
Open Section Roads
Sheet flow to forested areas

HIGHWAYS/ PARKWAYS
o Road Code street categories included:
Freeways
Controlled Major Highways
Major Highways
Parkways
o Minimum stormwater retention: 3”
Examples: The Prince George’s County highway LID project yielded an average
of 35% runoff volume reduction over pre-existing levels for this highway –
bioretention retrofit project.7
o Preferred tools:
Bioretention Swales
Bioretention Medians
5
Toolbox of Techniques for On-site Stormwater Retention:
 Stormwater Planters
Stormwater Planters in the Portland OR Green Streets Program. from:
www.portlandonline.com/shared/cfm/image.cfm?id=96962
 Description: These planters, when subjected to a flow test, absorbed 70% of
the 25-year storm. This “SW 12th Avenue Green Street Project” project won
high honors from the American Society of Landscape Architects. (2006
ASLA General Design Award of Honor for Portland designer Kevin Robert
Perry.) www.asla.org/awards/2006/06winners/341.html#
 Stormwater Planter Cross Section: go to:
www.portlandonline.com/shared/cfm/image.cfm?id=149610
6
 Street Trees As Stormwater Managers
Example: Street Trees with Structural Cells
www.deeproot.com; this is the design of Jim Urban, ASLA, and it conforms to
AASHTO H-20 standards. (Provided as an example, not an endorsement.) See also:
http://www.bslaweb.org/EBulletinsArchive/ebulletin111606.htm
o Description: This is a new technology with thirty projects on the drawing
boards and scheduled for implementation in 2007 – 2008. The Street Tree
Structural Cell is a modular hard plastic unit designed to hold engineered soil
mixes for street trees; provide root controls and sidewalk support, and to
collect and retain stormwater either from sidewalk runoff or from roadway
runoff entering through specially-designed inlets. Depending upon ultimate
tree size and root requirements, each installation requires between 10 and 100
cells.8
o Technical Specifications / Design Standards:
technical specifications is available at:
The patent with detailed
http://www.freepatentsonline.com/20070022655.html
7
 Bioretention Medians
Highway bioretention features (right-hand picture) through a highway LID project of Prince
George’s County, Maryland, as reported in December 2006. 9
www.co.pg.md.us/Government/AgencyIndex/DER/ESD/pdf/Final%20Technical%20Report_P
hase%20III.pdf .
Diagram of highway bioretention facility including cross section. From: The US EPA/ US DOT “Green
Highways” program web site at www.greenhighways.org/dev/Template.cfm?FrontID=5103
8
 Bioretention Curb Extensions.
Portland Oregon’s Green Streets Program, plan-view diagram of bioretention curb
extensions. From: www.portlandonline.com/shared/cfm/image.cfm?id=96962

Detail of curb
cut enabling excess stormwater to overflow into the street and the sewer system.
Portland green street program – NE Siskiyou St. Project.
http://www.portlandonline.com/shared/cfm/image.cfm?id=78299
9
 Bioretention Cul de Sacs
A 20-foot diameter
landscaped island in a
cul-de-sac can reduce
impervious surface by
25%. Cul-de-sac
islands can also be
designed to treat and
infiltrate runoff
through bioretention.
Image: Valley Branch
(MN) Watershed
District
Source: Boston MAPC: Metropolitan Area Planning Council, at:
www.mapc.org/regional_planning/LID/roadways_parking_lots.html
o Description: The circular design of existing cul de sac centers is an easy
location for a bowl-shaped rain garden. Road grading will need to create at
least a 2% slope toward the center in order to effectively collect and treat
runoff.
o Technical Specifications / Design Standards: See the Center for Watershed
Protection’s fact sheet on alternative turnarounds at:
www.stormwatercenter.net/Assorted%20Fact%20Sheets/Tool4_Site_Design/
AlternativeTurnarounds.htm See also the Virginia Beach Green Ribbon
Committee recommendations at:
www.vbgov.com/file_source/dept/mcg/Web%20Page/Hot%20Topics/Green%
20Ribbon%20Committee/Documents/cul_de_sac_recommendations.pdf,
which recommend reducing from a 40-foot radius to a 30-foot radius.
10
 Bioswales/ Vegetated Swales
The award-winning Seattle “SEA Street” prototype (Street Edge Alternatives.)
http://www2.cityofseattle.net/util/tours/seastreet/slide2.htm
Source: Boston MAPC: Metropolitan Area Planning Council, at:
www.mapc.org/regional_planning/LID/roadways_parking_lots.html
Bioswales: Construction cost information from Seattle SEA Street Program10
11
Bioswales (continued).
Both Portland, Oregon and Seattle, Washington now have extensive design and construction
experience with right-of-way bioswales for road redevelopment projects.
o Technical Specifications / Design Standards:
Example from the Seattle SEA Street program:
http://depts.washington.edu/urbhort/html/education/BioretentionSwales101.pdf .
12
 Open Section Roads
o Description: This green street technique overlaps with the bioswale technique.
One definition of an open section road is that it is a road without curbs and
gutters. Thus, the road is designed to sheet-flow stormwater into absorptive
zones within the right of way that typically are vegetated (grassy) swales or
fully-engineered linear bioretention units.
Center For Watershed Protection,
http://www.stormwaterauthority.org/assets/Eliminating%20Curbs%20and%20Gutters.pdf
13
Example of a successful subdivision in Montgomery County that utilized open section roads:
Winchester Homes’ Auburn Village at Sandy Spring in Olney, Maryland, which
incorporated open section roads as part of its stormwater management strategy
(this subdivision is no longer included on Winchester’s web site.)
14
 Underground Stormwater Treatment devices:
 Description: Underground stormwater treatment devices range from
plastic storage/ infiltration pipes, to stainless steel underground storage and solids
settling tanks. There is a wide range of vendors selling these technologies, which
can work for road cross-sections and other urban, highly-impervious settings
where vegetated landscaping-based stormwater management simply won’t work.
As a few prominent examples, Vortechnics, StormFilter, and StormCeptor are
some of the major underground stormwater treatment devices on the market.
Montgomery County DEP stormwater maintenance managers have testified that
on average, underground stormwater devices cost $3000 per year to maintain.11
Stormwater magazine, published by Forester Communications, contains many
articles and ads from vendors selling these underground devices; this link is for an
article reviewing the maintenance needs of these devices. The illustration is from
this article, and depicts a vacuum truck cleaning out an underground unit.
www.forester.net/sw_0407_maintenance.html
15
 Permeable Pavement
http://www.resourceventure.org/rv/issues/building/get-started/storm-mgmt/index.php
Porous Pavement
From: City of Seattle Flow Control Technical Guidance Manual 2000
16
Permeable Pavement at Northwood H.S., Silver Spring, MD. From: www.fosc.org.
Description: A wide range of choices in permeable/ porous pavements is
available for many different applications, ranging from porous concrete and asphalt to
permeable interlocking paver blocks.
17
Endnotes
1
The City of Seattle Pinehurst Green Grid Project, completed in October 2006, reported a 22% reduction in
impervious surface as a result of this “green” street redevelopment project – the roadway imperviousness
dropped from 74% down to 55%. (see the Seattle Public Utilities’ “Environmental Checklist,” part B.g., at:
www.seattle.gov/util/stellent/groups/public/@spu/@esb/documents/webcontent/cos_004403.pdf
2
Maryland-National Capitol Park and Planning Commission, Silver Spring Central Business District Sector
Plan (2001)
www.mcparkandplanning.org/community/plan_areas/silver_spring_takoma_park/master_plans/sscbd/sscbd
_toc.shtm
3
Anacostia Waterfront Corporation, Environmental Standards Development Committee, Draft
Environmental Standards, February 2007.
www.anacostiawaterfront.net/Portals/0/documents/standards/Draft%20Environmental%20Standards%2020
070212.pdf
4
Seattle Public Utilities, Natural Drainage Systems Program. Program Goals & Overview at:
www.seattle.gov/util/About_SPU/Drainage_&_Sewer_System/Natural_Drainage_Systems/Natural_Dr
ainage_Overview/COS_003596.asp.
5
See, for instance, the table on p. 6 of the Planning Board memo of Nov. 19, 2003, regarding a proposed
development in the Upper Rock Creek master plan area. Open Section Roads are listed as a design element
for two rural zones.
www.mcparkandplanning.org/board/meetings_archive/03_meeting_archive/agenda_112003/item_17_1120
03.pdf
6
Michael Clar, Ecosite Inc. Pembroke Woods Low Impact Development (LID) Residential Subdivision,
Emmittsburg, Maryland. At: www.ecosite.biz.
Prince George’s County Department of Environmental Resources, Final Report – Pilot
Projects for Urban LID Retrofit Program in the Anacostia River Watershed Phase III.
December 2006.
www.co.pg.md.us/Government/AgencyIndex/DER/ESD/pdf/Final%20Technical%20Rep
ort_Phase%20III.pdf .
7
8
Structural Cell designer Jim Urban, personal communication 3/7/07. urbantree@toad.net;
alkey@deeproot.com; www.deeproot.com.
9
Prince George’s County op. cit
10
Source: Powerpoint presentation of Tracy Tackett, Seattle SEA Street LID manager,
at: http://depts.washington.edu/urbhort/html/education/BioretentionSwales101.pdf
11
Keith Levchenko, Montgomery County Council, October 26, 2004 memo on Montgomery County Public
Schools Stormwater Management Facility Maintenance to the Education and Transportation &
Environment Committees, page 3.
18