Overarching standards for greenway development

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While the design guidelines are an outline for the development for GRG greenway facilities, design and implementation are governed by a series of standards which need to be consulted for each greenway project.

The following standards need to be consulted and are adopted by reference. Local laws, ordinances, and codes should always be consulted for guidance.

AASHTO
The American Association of State Highway and Transportation Officials (AASHTO) is a standards setting body which publishes specifications, test protocols, and guidelines which are used in highway design and construction throughout the United States. Despite its name, the association represents not only highways, but air, rail, water and public transportation as well.

ADA
The Americans with Disabilities Act (ADA) of 1990 is a civil rights law that prohibits discrimination based on disability. The ADA also require covered employers to provide reasonable accommodations to employees with disabilities, and imposes accessibility requirements on public accommodations.

MUTCD
The Manual on Uniform Traffic Control Devices (MUTCD) is a document issued by the Federal Highway Administration (FHWA) of the United States Department of Transportation to specify the standards by which traffic signs, road surface markings, and signals are designed, installed and used. These specifications include the shapes, colors, and fonts used in road markings and signs. All traffic control devices in the United States must legally conform to these standards.

NACTO
The National Association of City Transportation Officials (NACTO) is a coalition of the Departments of Transportation in North American cities. NACTO’s mission is a commitment to “raising the state of the practice for street design and transportation by building a common vision, sharing data, peer-to-peer exchange in workshops and conferences, and regular communication among member cities.”

NACTO Urban Bikeway Design Guide
The purpose of this guide is to provide cities and municipalities with state-of-the-practice solutions that can help create complete streets safe and enjoyable for bicyclists.

PROWAG
Accessibility Guidelines for Pedestrian Facilities in the Public Right-of-Way (PROWAG) addresses design and construction of facilities in the public right-of-way and build off of the most recent accessibility guidelines, the 2004 ADA Accessibility Guidelines (ADAAG) which does not fully address public rights-of-way. These guidelines are not yet published, as the Access Board works to incorporate public comments; they anticipate PROWAG to be finalized in 2017. However, some states have begun incorporating the guidelines into their own accessibility laws.

MSD
The Metropolitan St. Louis Sewer District (MSD) provides sewer collection, pumping, and treatment services within three major watersheds located within the MSD’s service area: the Mississippi River watershed, the Missouri River watershed and the Meramec River watershed. Any GRG project that falls outside of MSD’s geographical jurisdiction should meet the same standards as those within.


A thorough review of national and local regulations served as the basis of the trail design standards below.

These standards should be followed for all trail and secondary path development. More in depth standards for trail shoulder treatment are outlined in the Trail Shoulder Standards.

AASHTO ADA PROWAG GRG Standard
Minimum width: Shared use Path 10’-0” Recommended. 4’-0” Min. (one way) 4’-0” Min. clear 12’ wide typical trail section

11’-0” to 14’-0” optimum 5’-0” Min. (two way) 5’-0” passing Min. 8’ wide where context dictates and supported through low use counts.

Maximum Longitudinal Slope 5% (1:20) 5% (1:20) 5% (1:20) 4.8% preferred for construction tolerances 5% (1:20) Max.
Deviations allowed by ADA. Allowed to exceed based on adjoining roadway slope based on approved deviation.

Maximum Cross Slope 1% (1:100) Recommended 1% (1:100) Recommended 2% (1:50) Max. 1.8% preferred for construction tolerances
2% (1:50) Max.
1% (1:100) Min.

2% (1:50) Max. 2% (1:50) Max. 1.8% preferred for construction tolerances
2% (1:50) Max.
Design and set construction forms to 1.5%

Clear Zone (See Trail Shoulder Standards for more information) 2’-0” Min. 2.5’x4’ Min. 3’-0” Optimum width (includes 1’-0” header)

3’-0” Optimum 1’-6” Min.

Minimum Vertical Clearance  8’-0” Min.  8’-0” Min.  8’-0” Min.

 10’-0” Optimum  10’-0” Optimum

Design Speed 20 mph 12 mph preferred. Design speeds have been determined to best suit users of all types and abilities.

Minimum Centerline Curve Radii 90’-0” (20 mph design speed) 42’-0” for single-unit trucks (12 mph design speed)
Unless maintenance needs absolutely warrant larger radius for access.

Railing Height 42”/48” 30” or greater 42” 42” Min. unless greater is required by local laws or owner/operator rights.
48” where conditions warrant additional protection.

Separation from Curb or Edge of Pavement 5’-0” See TRAIL SHOULDER STANDARDS

Vehicle Loading
(for maintenance or emergency access)
H5 (10,000lbs) min.
H10 (20,000lbs) where trail serves as the only access route