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Chapter 4
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Design Criteria
4.1 Introduction

The design of Seattle’s street rights-of-way has a significant impact on the livability of the city as well as the health, safety and welfare of its citizens.  The width of a sidewalk, diameter of a curb radius, number of lanes in the right-of-way and the location of utilities such as overhead power lines and underground waterlines all play a role in shaping the right-of-way.  A street is also part of the public realm and all streets provide some form of open space including view corridors and green space in between private property and the curb.

This chapter contains mandatory design criteria that must be followed when designing and constructing improvements to the public rights-of-way including streets, sidewalks, trees and landscaping, and utilities. Design criteria present a consistent approach to designing each element of the right-of-way to best serve the traveling public, support land use patterns, and encourage economic growth in the City and the region. When reviewing and approving projects in Seattle’s rights-of-way, the City of Seattle makes every attempt to balance the vision for a project with adopted policy, regulation and user acceptance.

The design criteria in this chapter are to be used in conjunction with other applicable City, State and National standards for right-of-way design. More information on these standards can be found in 4.1.2 City of Seattle Standard Plans and Specifications and 4.1.3 Washington State Minimum Design Standards.

In addition to the mandatory design criteria, this chapter contains design considerations which the City recommends be considered when designing right-of-way improvements.   Compliance with design considerations is encouraged but not required.
4.1.1 Citywide Policy Guidance for Right-of-Way Improvements

The design criteria in this chapter have been developed consistent with appropriate local, state and national guidelines for right-of-way design. The criteria also support citywide policy defined in companion documents to this Manual, including the City of Seattle Comprehensive Plan (2005), the Transportation Strategic Plan (2005), and the Complete Streets ordinance (2007) and the Stormwater Code (2009).

Seattle’s Complete Streets guiding principle is to design, operate and maintain Seattle's streets to promote safe and convenient access and travel for all users -- pedestrians, bicyclists, transit riders, for people of all abilities, as well as for freight and motor vehicle drivers.
4.1.1a City of Seattle Comprehensive Plan

The City of Seattle Comprehensive (Comp) Plan , Toward a Sustainable Seattle, is a 20-year policy plan that defines the vision of how Seattle will grow in ways that sustain its citizens' values. The City first adopted the Comp Plan in 1994 in response to the state Growth Management Act of 1990. The Comp Plan makes basic policy choices and provides a flexible framework for adapting to real conditions over time. It is a collection of the goals and policies the City will use to guide future decisions about how much growth Seattle should take and where it should be located. The Comp Plan also describes in a general way how the City will address the effects of housing and employment growth on transportation, especially in designated urban centers and villages.

The Transportation Element of the Comp Plan encourages people to use cars less than they do today. One way to do that is through the urban village strategy’s goal of concentrating most new housing, jobs and services near one another in small areas, so that more trips can be made by walking, biking or transit. Another way is to support new public transit options. The Transportation Element contains policies that set the stage for street design standards that will match future street improvements to the types of uses and neighborhoods the street is serving.
4.1.1b Transportation Strategic Plan

The Transportation Strategic Plan (TSP) was updated in 2005. Linked directly to the goals and policies in the Comp Plan, the TSP outlines the specific strategies, projects and programs that implement the broader city-wide goals and policies for transportation in Seattle. The TSP also includes detailed lists of projects and programs to carry out citywide transportation policy.

4.1.1c Comprehensive Drainage Plan

The City of Seattle adopted a Comprehensive Drainage Plan in 2005 that charts a course for how to manage stormwater in our City.  The Comprehensive Drainage Plan charts a broader commitment to protecting and, where possible, improving Seattle’s surface water resources.  The Plan divides SPU’s drainage program into four areas:

  • Stormwater and Flow Control
  • Landslide Mitigation
  • Aquatic Resource Protection – Water Quality
  • Aquatic Resource Protection – Habitat
The Plan contains the policy guidance, levels of service and direction for capital and operating programs for each of these four areas.
4.1.2 City of Seattle Standard Plans and Specifications

The City of Seattle has developed design and construction standards for improvements in public rights-of-way to protect the health, safety, and welfare of the public and to minimize post-construction maintenance and repair costs. These standards shall be followed, together with the design criteria presented in this chapter and as required by the Seattle Municipal Code (SMC).

City of Seattle Standards for the design and construction of specific elements of rights-of-way improvements are contained in two publications that are referred to in this Manual by the shortened combined title, Standard Plans and Specifications.

In the event of a conflict, Standard Plans and Specifications take precedence over the Manual. In certain cases, a deviation from the design criteria presented in the Manual may be appropriate. Get more information about the deviation process.
4.1.3 Washington State Minimum Design Standards

In addition to the design criteria in this chapter and Seattle’s Standard Plans and Specifications, right-of-way design elements must also comply with the minimum design standards for major arterial and secondary arterial streets in the State of Washington. These minimum design standards are established and adopted in the Revised Code of Washington (RCW) 35.78 Streets – Classification and Design Standards, and have been published in the City and County Design Standards.

4.1.3a Exceptions from Washington State Minimum Standards

Per the City and County Design Standards, it is noted that the professional engineer in charge of the project must evaluate each design situation, and if less than the desirable value is chosen, appropriate documentation laying out the reasons and conclusions should be placed in the project’s design files.
Thus, while this document provides design standards, it is not a substitute for engineering judgment.

“In adopting these standards, the (State’s design review) committee seek to encourage standardization of road design elements where necessary for consistency and to assure that motoring, bicycling, and pedestrian public safety needs are met. Considerations include safety, convenience, context sensitive solutions, proper drainage, and economical maintenance. The committees recognize that cities and counties must have the flexibility to carry out the general duty to provide streets, roads, and highways for the diverse and changing needs of the traveling public.”

These standards cannot provide for all situations. They are intended to assist, but not to substitute for, competent work by design professionals. It is expected that land surveyors, engineers, and architects will bring to each project the best skills from their respective disciplines. These standards are also not intended to limit any innovative or creative effort, which could result in better quality, better cost savings, or both. An agency may adopt higher standards to fit local conditions. Special funding programs may also have varying standards.”

- excerpted from the City and County Design Standards

In any case, evaluation and ultimate approval of deviations to existing street design standards and criteria are the responsibility of SDOT.
continue to section 4.2 »   
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Detailed Table of Contents
Chapter 4
Design Criteria
4.1 Introduction
4.2 Street Classifications and Street Types
4.3 Design Criteria General Notes
4.4 Grading
4.5 Design Cross Section
4.6 Roadway Width
4.7

Roadway Pavement

4.8 Intersections
4.9 Driveways
4.10 Curbs
4.11 Sidewalks
4.12 Crosswalks
4.13 Bicycle Facilities
4.14 Street Trees and Landscape Architectural Standards
4.15 Introduction to Utilities Design Criteria
4.16 Street Lighting
4.17 Street Drainage, Storm Drains and Sewers
4.18 Water Mains
4.19 Fire Protection
4.20 Seattle City Light
4.21 Clearances
4.22 Structures in the Right-of-Way
4.23 Culdesacs and Turnarounds
4.24 Traffic Operations
4.25 Transit Zones
4.26 Street Furniture, Public Art and Unique Objects in the Public Right-of-Way
4.27 Access Easements
4.28 Contact Information
   
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