Comprehensive Transportation Plan - March 2019

MULTI-USE PATH DESIGN GUIDELINES

Multi-Use Path Structures and Easements STRUCTURES Boardwalk

Boardwalks provide an opportunity to construct a path in a sensitive natural or inundated area while limiting the potential environmental impacts. They are typically used to cross wetlands or small creeks. Boardwalks are usually constructed of timber, concrete, or recycled plastic decking. Span lengths can vary but typically, the longest boardwalk span is 20 feet. If a longer span is needed, a pedestrian bridge maybe more applicable. The maximum boardwalk span will vary some depending on the material used. AASHTO prefers a boardwalk to be wide enough to provide a 2-foot clearance on both sides of the pathway, but under constrained conditions, may allow the boardwalk clearance width to taper to the path width. The boardwalk minimum width needs to be the same as the width of the multi-use path. Railing A 6-inch curb rail is recommended on boardwalks elevated less than 30 inches. Any boardwalk elevated 30 inches or greater will require a minimum of a 42-inch railing; however, a 48-inch minimum is preferred to prevent bicyclists from falling over the railing during a crash. However, NCDOT requires a height of 54 inches. In accordance with AASHTO requirements, openings between horizontal and vertical members on a railing needs to be small enough that a 6-inch sphere cannot pass through them in the lower 27 inches and an 8-inch sphere cannot pass through the portion 27 inches or higher. PROWAG also requires that a 4-inch sphere not pass under the lowest horizontal member. When a railing is provided, continuous handrails on both sides of the boardwalk must be provided. Handrails must be provided with a minimum 1.5-inch knuckle space between the railing and the vertical and horizontal members, fencing, or other portions of the rail assembly. The rails must be located 36 inches above the deck surface. The handrail will also serve as a rubrail to protect handlebars from being caught in the vertical members. Structural Design At a minimum, boardwalks must be structurally designed to support five tons of capacity (H5 loading) and signed as “No Motor Vehicles” (R5-3). Coordination with the Town is needed prior to design to ensure additional loading requirements will not be necessary. Boardwalk footings need to include uplift as well as loading considerations for flood events. Each project will be unique and member sizing and post footing design will need to be completed by a structural engineer. If a boardwalk is being used to span a creek, engineering judgement needs to be applied to the offset of the endbent from the top of bank. Some creeks tend to migrate over time and this movement of the top of bank must be factored into the location of the endbent. The endbent need to generally be offset 10 to 20 feet from the top of bank. The boardwalk vertical elevation need to be designed to provide a minimum of 6 inches of clearance below the bottom of the cap (or bottom of the stringer if spread footing) and the existing ground to allow debris to pass under the boardwalk. If the boardwalk is within a floodplain, it is preferred to set the boardwalk grade high enough to keep the bottom stringer out of the 100-year flood elevation. If the boardwalk crosses a small creek, an engineer needs to hydraulically evaluate what elevation the boardwalk needs to be set as to not restrict flow. When a boardwalk is proposed in a wetland or over a blue line stream, local, state, and federal permits will be required. Coordination will be needed with the Town and relevant review agencies to receive the latest guidance on what elevation to set the boardwalk to avoid Bridges or underpasses can be used when grade separation is needed to cross a wider stream, roadway, or railroad. The type and size of the bridge can vary depending on the multi-use path and specific site requirements. If the grade separation is for crossing a roadway or railroad, a bridge or underpass may be used. The adjacent topography typically guides which option is more practical but bridges are typically preferred because they provide less security and drainage challenges. The preferred option must be discussed with the Town prior to completing design. AASHTO prefers a bridge be wide enough to provide 2 feet of clearance on both sides of the pathway but, under constrained conditions, may allow the bridge clearance width to taper to the path width. The minimum bridge width must equal the designated path width. Railing NCDOT Bicycle Facilities Planning and Guidelines recommends a minimum 54-inch vertical hand railing to prevent bicyclists from falling over the railing during a crash. In accordance with AASHTO requirements, openings between horizontal and vertical members on railing must be small enough that a 6-inch sphere cannot pass through them in the lower 27 inches and an 8-inch sphere cannot pass through the portion 27 inches or higher. PROWAG also requires that a 4-inch sphere not pass under the lowest horizontal member. The bridge must be provided with continuous handrails on both sides of the bridge. Handrails must be provided with a minimum 1.5-inch knuckle space between the railing and the truss verticals and diagonals, fencing, or other portions of the rail assembly. The rails must be located 36 inches above the deck surface. The handrail will also serve as a rub rail to protect handlebars from being caught in the vertical members. Structural Design If authorized vehicular traffic is anticipated on the bridge, the bridge must be designed to support a minimum of 10 tons of capacity (H-10). If all vehicular traffic will be restricted and the bridge is 6 to 10 feet wide, the bridge needs to be designed to support a minimum of five tons of capacity (H-5) with signs added noting the restriction. Coordination with the Town will be needed prior to design to ensure additional loading requirements will not be necessary. Bridge decks with widths over 10 feet must be designed for H-10 loading. permanent impacts to wetlands. Bridges and Underpasses

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