Purpose and origin
The Transit Street Design Guide provides design guidance for the development of transit facilities on city streets, and for the design and engineering of city streets to prioritize transit, improve transit service quality, and support other goals related to transit. 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.
Structure & Guidance types
The contents of the Transit Street Design 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 Transit Streets chapter incorporates elements presented in greater depth throughout the guide, with Elements sections providing the greatest level of detail.
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 list 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 a only general discussion section and have no critical, recommended, or optional points.
Key points on renderings are highlighted in yellow. Highlights refer to either the treatment or topic being discussed or the main idea of the image shown.
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. Lanes or other elements that use minimum dimensions will typically not provide a comfortable operating space for relevant users over long distances. Nonetheless, minimum dimensions often allow dedicated transit and other facilities to be constructed where space constraints and competing uses are present, especially when seeking to provide a balanced cross-section in a retrofit of existing streets.
- Desired minimum dimensions provide basic operating spaces in normal operational conditions. Larger dimensions are generally encouraged and can have comfort, operational, or other performance benefits. In other respects, desired minimum dimensions are similar to the lower end of recommended dimensions.
- Recommended dimensions provide for comfortable operations in many common conditions. Where a range of dimensions is provided, choose a dimension based on location, context, local experience. In some cases, such as turn radii and mixed-traffic lane widths, 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, if exceeded, may result in undesirable uses, such as overly high speeds or disallowed passing maneuvers.
Underlying assumptions are discussed here and in specific sections of the guide.
Transit service operates across the full spectrum of built environments and rights-of-way, with bus and rail vehicles of a variety of sizes and configurations. “Transit” and “public transportation” refer to transportation services on fixed routes intended to move many people at once, with multiple origins and destinations, and open to any paying passenger. Both publicly and privately owned operators exist for these services.
The guide assumes a variety of conditions for transit. Importantly, pre-existing streets are assumed to accommodate but not always prioritize the presence of transit vehicles, their passengers, and people walking. These modes, as well as bicycles, taxis, private motor vehicles, trucks, and emergency vehicles are assumed to exist in varying numbers by context. Design typologies and elements included in the guide assume the presence of these modes, as well as specific conditions such as on-street parking or loading, some driveways, and a moderate to high volume of movement on foot or on bicycle. Sidewalks and pedestrian crossings are assumed to exist in some form in all cases.
This guide is aimed at filling the gap that exists in transit street design guidance for city street conditions. However, most of the elements and concepts covered in the guide are applicable to streets typically found in lower-density urbanized areas, including streets with frequent or large driveways, no on-street parking, and higher traffic speeds. Many urban areas with primarily non-urban existing street design can be addressed through the application of this guide, in combination with the NACTO Urban Street Design Guide and other guidance.
Nearly all transit vehicles can be deployed on each of the transit street types presented, in a wide variety of service patterns. With a few exceptions, vehicle type and size as well as service frequency or demand are treated as inputs in street design, and street configurations are not intended here to prescribe vehicle types. Transit street types, facility types, and service types are not inherently linked to specific vehicles. Several designs in the guide are based on existing conditions whose best North American examples are associated with a specific vehicle type, but even these examples are not meant to prescribe the use of specific vehicles for specific designs.
This guide does not address transit design on controlled-access freeway facilities or grade-separated rights-of-way, or stations on off-street lots. Readers are referred to the TCQSM and the AASHTO Guide for Geometric Design of Transit Facilities on Highways and Streets for transitway design in controlled-access conditions.
For complementary information on safely designing streets for walking and bicycling, readers are referred to the NACTO Urban Street Design Guide, NACTO Urban Bikeway Design Guide, and other guidance. NACTO design guides may be accessed online at http://nacto.org.
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 transit and street design in ways that overlap with the NACTO Transit Street Design Guide.
As a national document in the United States adopted and modified by individual states, the Manual for Uniform Traffic Control Devices (MUTCD) has a special significance in street engineering and design guidance. In instances where a particular sign, signal, or marking should be used, the guide highlights its specific reference in the MUTCD. Geometric design features, such as vertical and horizontal elements that create exclusive transit, bike, or pedestrian facilities, are not traffic control devices.
The vast majority of design elements included in the guide are consistent with MUTCD standards. Some specific signal, markings, and signage elements described in the guide have been developed or adopted in the years since the last major revision of the MUTCD. Since the status of these treatments may change in pending revisions to the MUTCD, this guide does not specify the status of each item in each place where it is used. Several included signage, markings, and signal elements have received interim approval for inclusion in the next edition of the MUTCD and do not involve experimentation. Several other important design elements in widespread use in the United States are available through experimentation as of the publication of this guide. These include red/terra cotta colored transit lanes, bus-only transit signals and displays, bike boxes and two-stage turn queue boxes. NACTO strongly encourages the use of the Federal Highway Administration’s (FHWA) MUTCD experimentation process for new or innovative traffic control devices, an important method of expanding the options available to designers and engineers.
The Transit Capacity and Quality of Service Manual, 3rd Edition (TCQSM) is assumed to be the basis of most service decisions, and is a foundational tool for understanding transit passenger service needs and outcomes.
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 to transit facilities.
The U.S. Access Board’s Public Rights-Of-Way Accessibility Guidelines (PROWAG)—proposed in 2011 and under consideration for adoption as US Federal standard as of publication —includes detailed accessibility guidance developed specifically for streets. These proposed rules differ from the ADAAG, and are cited where applicable.
Many transit operators have developed transit stop criteria and station siting or equipment criteria, often connected with a transit service manual. Many cities have developed local street design guidance that discusses transit stop design in the context of street design, including bikeway design. NACTO references materials from a selection of these guides and urges municipalities to use the Transit Street Design Guide as a basis for creating or updating local standards.