The term “roadway” refers to the area of the street right-of-way used for vehicular travel, including cars, trucks, bicycles and transit. The roadway may also include a number of additional uses such as on-street parking, curbed structures such as medians and crossing islands, and utility access points.

Standard Plan 411: Curb Joints and Dowels

Roadway width on streets with curbs: Where there is a curb, the roadway width is the curb to curb width of the street. Roadway widths for various land use zones are shown in Chapter 3.1 Overview of Requirements from the Land Use Code. These widths are design widths, the full roadway width deemed necessary to serve the travel and parking needs of the street for a particular land use zone when the street is fully improved with curbs and sidewalks on both sides.

Minimum pavement width —non-arterial streets: Minimum pavement width requirements are specified in the Land Use Code and shown in Chapter 3.1 Overview of Requirements from the Land Use Code. The actual extent of new paving required may be less than the roadway design widths shown in Chapter 3.1: Overview of Requirements from the Land Use Code. When street improvements are required, project applicants shall construct the half street on their side of the-right-of way, plus ensure that a minimum of one paved travel lane and 5 feet of graded shoulder exist on the other side of the centerline. When new pavement is required for this travel lane, it shall be 12 feet wide including a 2-feet wide thickened edge for drainage.

Minimum pavement width — arterial streets: Minimum pavement width requirements for arterial streets must meet the minimum design standards given in the Washington State “City and County Design Standards.” Refer to Chapter 3 Right-of-Way Improvement Requirements for existing and required roadway widths for arterials.

Lane width for arterials: Right-of-way width, roadway width, and lane channelization shall be determined by SDOT. An applicant may choose to apply for a deviation from the standard listed below. Right-of-way and roadway widths for existing arterials are listed in Chapter 3. The following standard arterial lane widths are used in the design of arterials and are compliant with the City and County Design Standards:

Road taper and transitions: For permanent roadway tapers, the standard taper length for the narrowing from two lanes to one lane or offsetting of a lane is:

• L= WS²/60, where L is the length of taper in feet, W is the lane offset in feet, and S is the design speed in miles per hour.
• On non-arterial streets, temporary asphalt tapers are allowed for narrowing a single lane when additional street improvements are anticipated in the future.
• On non-arterial streets, t he standard taper for temporary tapers is 25:1.

Dowel Bars: Dowel bars are required in the longitudinal direction on arterial streets. When two arterial streets intersect, dowel bars are required in both directions within the intersection.

Joints: Type B joints are required in intersections. Joints must be placed so that they do not interfere with the wheel tracks of vehicles, or in the area of the intersection used by bicycles.

Location of roadway within the right-of-way: The roadway is normally centered in the right-of-way, but may be offset due to topography or limited right-of-way width.

Considerations for developing minimum roadway dimensions should be made within the context of how the entire right-of-way will be developed over time. This includes public safety; available right-of-way; land use and zoning, current and projected roadway capacity; pedestrian facilities, landscaping (including natural drainage where allowable), bicycle facilities, freight and transit needs, and other intended uses of the public realm.

Considerations for establishing lane widths should be influenced by street type designations and street classifications and the need to have a reasonable balance among competing uses in the right-of-way. They are as follows:

• Wide lanes support large vehicle movements such as trucks and transit. Wider lanes can also support higher speeds for all vehicles and longer crossing distances for pedestrians. Wider lanes should be considered on Regional Connector and Industrial Access street types.
• Wide center turn lanes should be considered on streets that have high volumes of truck turning movements including intersections with one or more legs that are designated as Major Truck Streets or Industrial Access streets.
• Wide curb lanes should be considered on streets that have high volumes of transit service.
• On Commercial Connector streets, lane width should support travel demand—in areas where high pedestrian activity is occurring, consider options that keep lanes as narrow as possible. On streets with high levels of transit service or that accommodate high volumes of trucks and transit vehicles, consider options that have wider lane widths.
• Narrow lanes support slower vehicle speeds, and minimize overall roadway width which supports pedestrian activity. Narrower lanes can be challenging for larger vehicles to navigate, especially on roadways that carry high volumes of trucks and transit vehicles. Narrower lanes should be considered along Local Connectors, Mixed Use, Main Street and Green Street street types. For Green Streets and Neighborhood Green Streets, keep lane widths narrow and limit the number of lanes to minimize the crossing distance for pedestrians as much as possible.

Lane widths on designated bicycle routes shall be evaluated based on the lane width requirements given in the City and County Design Standards and WSDOT Design Manual Chapter 1020.