The Urban Street Stormwater Guide is a resource to reintroduce valuable ecological processes into the life of urban streets. As more and more cities reclaim street space for human life and habitat, and enact far-reaching plans and strategies to address climate change, this guide presents a new playbook for utilizing existing and new infrastructure to manage rainfall and reconnect ecosystems. Developed by a new network of NACTO city water, transportation, and public works departments, the Urban Street Stormwater Guide provides practitioners, leaders, advocates, and stakeholders with the tools to reintegrate water into the street.
In this Section
Using this Guide
Purpose & Origin
The Urban Street Stormwater Guide provides planning and design guidance for green stormwater infrastructure on city streets, and for the design and engineering of stormwater management practices that support goals for improving mobility and streets as human places while reducing the impacts of stormwater runoff and human activity on natural ecological processes. The guide has been developed on the basis of other design guidance, as well as city case studies, best practices in urban environments, research and evaluation of existing designs, and professional consensus. These sources, as well as the specific designs and elements included in the guide, are based on North American street design practice. The content of the guide has been developed collaboratively by practitioners and professionals across the United States.
Guideline Updates Since Release
The Urban Street Stormwater Guide references national design standards and guidance that were current at the time of its publication (2017), but may have undergone updates since then. Readers should be sure to cross-reference the most recent editions of any guidance referenced.
Structure
The contents of the Urban Street Stormwater Guide are presented in a non-linear fashion, suitable for reference during the design process. Internal cross-references, a list of further resources by topic, and endnotes are provided to assist the reader in developing a deep understanding of the subject.
The Stormwater Streets chapter assembles elements presented in greater depth throughout the guide, with “Stormwater Elements” sections providing the greatest level of detail. Some renderings illustrate potential subsurface conditions and designs.
Some sections of the guide include a CONTEXT or APPLICATION discussion. The specific applications are provided for reference and include common existing uses, rather than an exhaustive or exclusive lists of all potential uses.
For most topics and treatments in this guide, the reader will find three levels of guidance:
CRITICAL features are elements for which there is a strong consensus of absolute necessity.
RECOMMENDED features are elements for which there is a strong consensus of added value. Most dimensions and other parameters that may vary, as well as accommodations that are desirable but not universally feasible, are included in this section to provide some degree of flexibility.
OPTIONAL features are elements that may vary across cities and may add value, depending on the situation.
Note: Certain sections contain only a general DISCUSSION section and have no CRITICAL, RECOMMENDED, or OPTIONAL points. Dimension guidance is sometimes presented in multiple levels within the guide, to be applied based on the specific needs and constraints of real streets on a case-by-case basis.
MINIMUM DIMENSIONS are presented for use in geometrically constrained conditions. Bioretention cells or other elements that use minimum dimensions will typically not provide a high-performing facility. Nonetheless, minimum dimensions often allow stormwater facilities to be constructed where space constraints and competing uses are present, especially when retrofitting existing streets.
DESIRED MINIMUM DIMENSIONS provide basic functional space in normal conditions. Larger dimensions are generally encouraged and can have performance or maintainability benefits. In other respects, desired minimum dimensions are similar to the lower end of recommended dimensions.
RECOMMENDED DIMENSIONS provide for comfortable siting and performance in many common conditions. Where a range of dimensions is provided, choose a dimension based on location, context, and local experience. In some cases, such as corner radii, larger than recommended dimensions are less safe. However, if presented with factors not considered in the guidance, smaller or larger dimensions may perform better than recommended dimensions.
MAXIMUM DIMENSIONS typically refer to motor vehicle traffic facilities. Exceeding maximum dimensions may result in safety issues and should be carefully weighed in context.
Guide Context
This guide focuses on green infrastructure design within urban streets and rights-of-way. The guide does not address green stormwater management strategies on private property, such as roofs and parking lots, nor does it address drainage and infiltration around controlled-access highways.
This guide aims to bridge the gaps between city staff working in transportation, public works, and water departments. It seeks to balance multi-modal mobility and environmental performance. Street design guidance assumes that users of all modes are present, and that city streets must provide accommodation for multi-modal users regardless of age or ability. Specific conditions such as on-street parking or loading, some driveways, and a moderate-to-high volume of movement on foot or on bicycle are assumed in most contexts. Sidewalks and pedestrian crossings are assumed to exist in some form in all cases.
For complementary information on designing safe streets for walking, bicycling, and taking transit, readers are referred to other existing NACTO publications, including:
- Urban Street Design Guide
- Urban Bikeway Design Guide
- Transit Street Design Guide
- Global Street Design Guide
The treatments and topics discussed in this guide must be tailored to individual situations and contexts. NACTO encourages good engineering judgment in all cases. Decisions should be thoroughly documented. To assist with this, this guide links to references and cites relevant materials and studies.
Relation to Other Guidance
Several major national guidance documents exist that are relevant to green infrastructure and street design in ways that overlap with the NACTO Urban Street Stormwater Guide.
Specific standards in the Americans with Disabilities Act Accessibility Guidelines (ADAAG)—developed by the US Access Board, adopted by the US Department of Justice and Department of Transportation—are cited where applicable.
The US Access Board’s Public Rights-Of-Way Accessibility Guidelines (PROWAG)—proposed in 2011, under consideration for adoption as the US standard as of publication, and recommended as a best practice guide by FHWA—include detailed accessibility guidance developed specifically for streets. PROWAG differs in some cases from the ADAAG, generally calling for wider facilities than ADAAG, and is cited where dimensions or approaches differ.
The US Environmental Protection Agency enforces the Clean Water Act, including the National Pollutant Discharge Elimination System, and authorizes states and local jurisdictions to create integrated plans for managing stormwater and reducing pollutants in watersheds. This guide discusses strategies to meet local or regional NPDES requirements to reduce combined sewer overflows and sanitary flows.
Many cities have developed local guidance for both complete streets design and green stormwater infrastructure. Local guidance documents may include sizing and modeling criteria, as well as complete streets policies and green infrastructure standard designs and manuals. NACTO references materials from a selection of these guides and urges municipalities to use the Urban Street Stormwater Guide as a basis for creating or updating local standards.
While this guide discusses permeable pavements as a street design tool for stormwater management, ASCE’s Permeable Pavements Recommended Design Guidelines provides detailed technical guidance and information for choosing, sizing, and engineering using permeable paving materials. This guide refers to that document while providing additional discussion on mobility and implementation issues in urban contexts.
The Manual on Uniform Traffic Control Devices (MUTCD) does not regulate stormwater facilities, but, along with state and local standards, may specify whether a particular sign, signal, or marking should be used in a given design context. Users can check the status of specific traffic control elements included in this guide on the FHWA website. Geometric design features that separate motor vehicle traffic from other uses of the roadway, including curbs and vertical and horizontal elements, are not traffic control devices and are not regulated by the MUTCD.