DRAFT 11/12/03
Street Standard Documentation
Summary
Street Standard Documentation examines the degree of compliance of the street design standards in the Dane County Model TND Ordinance with transportation industry guidebooks, A Policy on Geometric Design of Highways and Streets: 2001, AASHTO (Green Book) and the WisDOT Facilities Design Manual, Chapter 11, (FDM). Street Standard Documentation also examines supplemental guidebooks, provided by the transportation profession, that specifically address the design of streets in traditional neighborhoods, for additional guidance. Each street standard for each street type allowed in the Model TND Ordinance is compared to Green Book and FDM guidelines for consistency. Supplemental guidebooks are also explored for consistency with the Model standards.
The street standards of the Dane County Model TND Ordinance are consistent with the Green Book Guidelines. Some of the Model standards are inconsistent with FDM guidelines. In cases where Wisconsin DOT funds or designs local TND streets, exceptions would be required, based on WisDOT Community Sensitive Design approach. The Model standards are further supported to a large degree by supplemental transportation industry street design guidebooks.
Introduction
Street Standard Documentation examines the degree of compliance of the street design standards in the Dane County Model TND ordinance with guidelines and standards in:
A Policy on Geometric Design of Highways and Streets: 2001, American Association of State Highway and Transportation Officials (AASHTO). Commonly referred to as The Green Book.
Facilities Design Manual, Chapter 11, (FDM) State of Wisconsin, Department of Transportation (WisDOT), December 30, 2002.
This document examines the applicability of the Green Book and the FDM to the County Model TND standards, and the context of traditional neighborhoods as they relate to street design guidelines. It then compares, for consistency, each standard for each allowable street type in the Model TND ordinance to Green Book and FDM guidelines. Street Standard Documentation then examines supplemental transportation professional guidebooks that specifically address the design of streets within traditional neighborhoods, or residential neighborhoods. The document explores the degree to which these supplemental guidebooks support the Model TND standards.
Applicability
The Green Book is regarded as the primary source by roadway designers for guidance on roadway design elements. The Green Book describes its intent as that of a guide rather than as a detailed design manual:
The intent of this policy is to provide guidance to the designer by referencing a recommended range of values for critical dimensions. It is not intended to be a detailed design manual that could supercede the need for the application of sound principles by the knowledgeable design professional. Sufficient flexibility is permitted to encourage independent designs tailored to particular situations. (p. xli).
The WisDOT Facilities Design Manual (FDM) “includes the established standards and guidelines for application on all highways and streets being designed by or for WisDOT.” (p. 11-1-1-1). The Manual also states: “The standards in this [Design] chapter apply to state funded-projects.” (p. 11-1-1-2).
Thus, the Green Book is a primary guide for design elements, and the FDM provides guidance and standards for state-funded projects. The FDM may also be used as additional design guidance, where appropriate, for locally funded street projects.
Placing Street Design Guidelines and Standards in Context
The street standards of the Model TND Ordinance apply to streets in a neighborhood setting that primarily serve a local function, as well as providing mobility for all modes of transportation. The Street Standards section of the Model Ordinance states the purpose of the ordinance and standards as: “The primary purpose of streets in a Traditional Neighborhood is to foster a safe and pleasant environment for residents and pedestrians. Neighborhood streets also provide access to private lots and facilitate mobility of all transportation modes.”
The Model TND Ordinance seeks to apply AASHTO design guidelines and WisDOT standards within an urban neighborhood context to achieve the purposes stated above. In addition to the Green Book quote above, the following citation quote also points out the need to adapt designs to their contexts:
A highway necessarily has wide-ranging effects in addition to providing traffic service to users. It is essential that the highway be considered as an element of the total environment. The term “environment,” as used here refers to the totality of humankind’s surroundings: social, physical, natural, and synthetic. It includes the human, animal, and plant communities and the forces that act on all three. The highway can and should be located and designed to complement its environment and serve as a catalyst to environmental improvement. (p. 106)
The Green Book also identifies the importance of making provisions for pedestrians:
Because of the demands of vehicular traffic in congested urban areas, it is often very difficult to make adequate provisions for pedestrians. Yet provisions should be made, because pedestrians are the lifeblood of our urban areas, especially in the downtown and other retail areas. In general, most successful shopping sections are those that provide the most comfort and pleasure for pedestrians. (p. 96).
The FDM also explicitly acknowledges the need for application of standards to be sensitive to local context through WisDOT’s design policy of “Design Excellence Through Community Sensitive Design.” (p. 11-3-1-1). The FDM explains:
It is WisDOT policy to use a “Community Sensitive Design” (CSD) approach to enhance excellence in transportation project development and resulting solutions. CSD is the art of creating public works projects that function safely and efficiently, and are pleasing to both the users and the neighboring communities. The goal of CSD is to leave a lasting public works legacy that will stand the test of time.
Community Sensitive Design is a collaborative interdisciplinary approach that includes early involvement of all stakeholders to ensure that transportation projects not only provide safety and mobility, but are also in harmony with communities and the natural, social, economic, and cultural environments….
In accomplishing this, a variety of design, construction and safety standards must be met, along with environmental considerations. Design exceptions to standards may be used, where appropriate and necessary. These must be documented and approved, and must contain a thorough analysis of the consequences and tradeoffs involved. (p. 11-3-1-1).
The Model TND Ordinance seeks to define regulations that govern traditional neighborhoods (that are compact, diverse, pedestrian-friendly, safe and attractive). However, neither the Green Book or the FDM specifically address street design of traditional neighborhoods. Because they do not, other relevant industry guidebooks may provide supplemental design guidance. Two publications used as supplements to the Green Book and the FDM, in developing the Model Ordinance were:
Traditional Neighborhood Development Street Design Guidelines: A Recommended Practice of the Institute of Transportation Engineers, October 1999.
Residential Streets, Third Edition, by Walter Kulash, Principal Author. Urban Land Institute, National Association of Home Builders, American Society of Civil Engineers, and the Institute of Transportation Engineers.
The report, TND Street Design Guidelines, “was approved in September 1999 as an ITE recommended practice.” (p. iv). The guidelines were prepared “to aide the profession with the design and evaluation of a recently emerging, perhaps re-emerging form of development that is not the typical ‘subdivision’ of recent years. . . ITE has recommended practices for both TND streets and post-war suburban streets. This publication is not intended to endorse one design technique over the other; however, where a TND street system is proposed, these are the practices that ITE recommends.” (p. 2).
Residential Streets “is based on the premise that the design of a residential street should be appropriate to its functions. A residential street’s functions include not only its place in the transportation system but also its role as part of a residential community’s living environment.” (p. 7).
These documents provide additional design guidance that specifically applies to the traditional neighborhood contexts of the Model TND Ordinance.
The sections that follow discuss the application of the guides and standards to specific street types in the Model Ordinance.
Street Layout
The Model Ordinance requires an interconnected street layout and block sizes to facilitate connectivity and pedestrian activity.
An interconnected network of streets. All streets shall connect with other streets at their ends or shall end as stubs to facilitate connection to adjacent future development sites. Dead-end streets are prohibited unless the Plan Commission determines otherwise.
Block sizes. Block length may not exceed 600 feet in TND-R Districts and 500 feet in TND-MS and TND-E. Block width may not exceed 300 feet. The Plan Commission may approve a block width of not more than 400 feet or a block length of not more than 1000 feet if required because of existing topography or street layout. A block longer than the maximum allowed length shall be traversed near the midpoint by a pedestrian path.
Green Book
The Green Book lays out the functional classification of arterials, collectors and locals. The primary function of arterials is mobility of motor vehicles, and mainly serves to move traffic through an area. The primary function of local streets is access to land parcels, and mainly serves to vehicles accessing parcels and not through-traffic. Collectors serve both mobility and access functions, funneling traffic from collectors to arterials.
FDM
The FDM adheres to the functional classification system as described in the Green Book.
Consistency between Model TND and Design Guides
While the functional classification system does not prohibit interconnected layout of streets and TND-appropriate block sizes, it does not specifically address the needs of TNDs for connectivity and pedestrian activity. In practice the system is often implemented in a manner that reduces opportunities for pedestrian activity, by requiring many residents to travel on a major motor arterial to get to most destinations.
Additional TND Street Layout Guidance
Traditional Neighborhood Development Street Design Guidelines:
More of a TND street network is utilized than is typically the case in conventional “dendritic” street networks. In conventional networks, traffic is expected to begin at local (often cul-de-sac) streets, then flow to collector and then to arterial streets, ultimately into the more regional systems. This type of network collects and focuses traffic, often leaving few choices to drivers. Non-drivers are also conventionally excluded from large portions of the network, either by regulation or by the vehicular orientation of the designed and constructed environment itself. In a TND network with no dead-end streets there are always multiple ways to connect any two locations. With multiple routes presented to motorists and non-motorists, more options are made possible. Vehicular trips can be diffused or reduced by drivers choosing alternate routes, or by choosing to travel by means other than automobile. (p. 7).
Residential Streets, Third Edition:
Because of the lack of internal street connections [in postwar style suburban development], all traffic – even for the most local of destinations – is funneled out onto the surrounding arterial street system. Consequently, the surrounding street system becomes congested even at low levels of development, undermining the small-town or rural atmosphere sought by developers and homebuyers. . . The lack of direct routes between desitnations that is a feature of unconnected street systems is a major obstacle to pedestrian and bicycle travel. (p. 19).
Local Streets
The Model Ordinance contains three local residential street types: RS-46, RS-50, and RS-58:
RS-46: A local, yield-movement low volume street typically used to serve residents in, lower density areas of residential neighborhoods. The street typically extends short distances, and urban in character, with raised curbs, closed drainage, sidewalks, parallel parking, and trees in continuous planting areas. Character may vary somewhat, however, responding to the fronting residential uses. The RS-48/54 is intended for limited application on short segments with low traffic volumes.
RS-50: A local, yield-movement street. The street is urban in character, with raised curbs, closed drainage, sidewalks, parallel parking, and trees in continuous planting areas. Character may vary somewhat, however, responding to fronting commercial or residential uses. RS-54/60 is intended as the primary street serving local residential areas.
RS-58: A local, slow-movement street. Streets provide frontage for moderate density buildings such as townhomes, row houses and smaller apartment buildings. Some small-scale commercial uses may be mixed with the residential. RS-58 is urban in character, with raised curbs, closed drainage, sidewalks, parallel parking, and trees in individual planting areas. Character may vary somewhat, however, responding to the fronting residential uses.
Model Ordinance Standards:
H:\PLANDEV\ComDev\BUILD\Smart Codes\Model Ordinance\Street Standard Documentation.doc 15
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RESIDENTIAL STREET RS-46
right of way width 46-52 feet
pavement width 22 feet
travel lane width 15 feet
traffic flow 2 ways
movement Yield
parking lanes 1 side
design speed 15 mph
avg. daily trips <250
curb type Raised
curb radius 5-15'
planter width 7-10'
planter patterns Street trees in
continuous planting
strips
sidewalks Both sides 5'
RESIDENTIAL STREET RS-50
right of way width 50-56 feet
pavement width 26'
travel lane width 12 feet
traffic flow 2 way
movement Yield
parking lanes 2 sides
design speed 15 mph
avg. daily trips 250 – 1,500
curb type Raised
curb radius 5-15'
planter width 7-10'
planter patterns Street trees in
continuous planting
strips
sidewalks Both sides 5'
H:\PLANDEV\ComDev\BUILD\Smart Codes\Model Ordinance\Street Standard Documentation.doc 15
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RESIDENTIAL STREET RS-58
right of way width 58 feet
pavement width 32 feet
travel lane width 18 feet
traffic flow 2 ways
movement Slow
parking lanes 2 sides
design speed 20 mph
avg. daily trips approx. 1500
curb type Raised
curb radius 5-15'
planter width 8'
planter patterns Street trees in
continuous planting
strips
sidewalks Both sides 5'
Green Book Guidelines
General
Because of the relatively low traffic volumes and the extensive mileage, design criteria for local roads and streets are of a comparatively low order as a matter of practicality. However, to provide the requisite traffic mobility and safety – together with the essential economy in construction, maintenance, and operation – they must be planned, located, and designed to be suitable for predictable traffic operations and must be consistent with the development and culture abutting the right-of-way. (p. 383).