Urban Scale
Choices & Guidelines
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Most of the photos of great streets seen on these pages feature street trees. Trees are among the most important – and overlooked – features of urban streets. Visual preference surveys routinely reveal that citizens greatly prefer streets that feature mature canopy trees and other vegetation to streets that do not.
Benefits of Street Trees Include:
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Reduced heat absorption. Paved streets and urban parking lots can increase localized ambient urban temperatures by 3 - 7 degrees, significantly impacting energy consumption and energy costs for homeowners, business owners and consumers.
Credit: LGCHouseholds in well-shaded neighborhoods with urban street trees can experience energy savings of 15 - 35%.
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Traffic calming. Properly-placed street trees frame and define the street as perceived by drivers. The vertical edge to the view plane that the trees provide reduces the apparent width of the street, increasing “friction” and lowering average speeds.
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Placemaking. Trees create identity, increase attractiveness and provide framing for plazas, seating areas, and sidewalks. The spatial definition added by trees helps create memorable spaces within what would otherwise be featureless sidewalks.
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Property values. The attractiveness, heightened identity and placemaking effects of mature, well-placed street trees combine to add value to abutting properties.
Credit: Charlier AssociatesIn some cases, the added property tax proceeds from increased valuations may recoup much of the cost of installing and maintaining the trees.
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Pavement preservation. The shading of pavements by street trees increases pavement life, reducing long term costs of street maintenance.
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Reduced storm water run off. Street trees can significantly reduce the percentage of rain water that reaches the ground below them. The actual percentage is greater for light rains and is highest during the early stages of extended rain events.
Credit: Walkable CommunitiesWhile this may not reduce the size of required street drainage systems, it does reduce the total amount of storm water delivered into street drainage systems over the course of a typical growing season.
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Improved air quality. Trees absorb carbon monoxide and other air borne pollutants.
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Intangible public benefits. Although difficult to measure, the public reaps significant benefits from the improved attractiveness and shading of public streets that street trees provide.
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Credit: Charlier Associates A canopy is an architectural projection from the street wall over a portion of the sidewalk, providing weather protection, identity or decoration. Canopies are primarily supported by the buildings to which they are attached but may also feature vertical support members such as poles or small columns.
Fabric canopies are commonly called awnings. Awnings can meet many of the design functions of canopies. Modern awning fabrics are durable and strong. However, larger awnings may require careful winter maintenance during snow season in the St. Louis region. Canopies (including awnings) should be at least 8 feet above the sidewalk and are normally aligned horizontally at a level above the tops of windows and doors and below the line between the first and second stories of their buildings.
Many cities allow sidewalk seating for restaurants, coffee shops and taverns in the area covered by canopies, as shown below, at right. This is most common where the building is set back from the public right of way and the canopy covers the private portion of the sidewalk. However, in some cities, sidewalk seating may also occur on a portion of the public sidewalk where sidewalk widths are adequate and in those cases such seating may occupy the zone under the canopy.
Credit: Charlier Associates
An arcade is a passage or walkway that is structurally part of its building. Some buildings with arcades have interior space within walls of the building directly above the arcade and walkway. Others are more ornamental and are attached to building fronts in a manner similar to canopies and awnings.
In such cases the distinction between an arcade and a canopy may be somewhat blurred and may have to do with significant the vertical poles or columns are and what role they play structurally in supporting the overhead portion of the structure.
Arcades are common in Southwestern cities, where they provide shade and protection from the rain and snow and reflect Mexican and Mediterranean architectural traditions.
In many of these cases, the sidewalk area under the arcade is not in the public right of way, but rather is on the abutting private property (in the setback zone, as shown below, at left). Santa Fe, Taos and Albuquerque all have many examples of arcades.
Another version of the arcade is found in the mountainous West in the form of covered boardwalks, as shown below, at right. Such boardwalks are a vestige of the days before streets and sidewalks were paved and exist today as an expression of local architectural history and often occur in tourist towns as an alternative to canopies.
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"Streets and their sidewalks, the main public places of a city, are its most vital organs."
The quote above from Jane Jacobs describes the critical role streets and sidewalks play in our communities. Our streets and sidewalks are the centerpieces around which great places can be developed.
In addition to being the primary infrastructure of our transportation network, streets and sidewalks are the major identifier of a community and have a direct impact on the overall character and feel of a place. Consider the street shown in the image at right.
While a variety of characteristics help shape this great street, the type, texture, and color of the pavement play a significant role. The character of the thoroughfare would change dramatically with standard, generic pavement type and sidewalk. In the next image, the pavement striping, color, width, and streetscape amenities found in the corridor largely contribute to the area's appeal. The bike lane's contrasting color increases driver awareness and adds to the thoroughfare's aesthetic character.
Street Width:
In a great street, space allocation for pavement must consider vehicular capacity needs, bicycle lane or shoulder provisions, and the design speed for the facility. Capacity considerations will generally govern how many lanes are required for vehicular traffic, while the facility's target speed and design vehicle influence how wide each lane should be. The presence and type of median treatments and the need to provide bicycle lanes will also influence overall thoroughfare width, as will the existing right-of-way. Thoroughfare width will also reflect the target level of service. If the target performance for a given thoroughfare is set at LOS B, for example, the number of lanes needed to accommodate through-traffic and turning movements will be much higher than if the target is set at LOS E. In many cases, setting higher level-of-service targets will result in a much wider thoroughfare. Setting lower targets (i.e. tolerating more congestion on a given facility) can help limit thoroughfare width and/or free up space for non-vehicular, multi-modal treatments.
Vehicular mobility is one of many considerations in thoroughfare design. It is often appropriate to design narrower thoroughfares with lower vehicular capacity to accommodate the needs of pedestrians, bicycles and transit. Thoroughfare planners should work with local agencies, businesses, and residents when determining specific requirements for each place. See the capacity section of this manual for more information.
Vehicular Travel Lane Width:
Based on the perception that wider lanes are safer, the St. Louis region has historically used 12-foot travel lanes for many thoroughfares. Recent studies show that at speeds of 35 mph or less, there is very little difference in substantive safety performance for lane widths of ten, eleven, and twelve feet. Narrower travel lanes can also have a traffic calming effect on a thoroughfare by causing vehicles to drive slower. Conversely, wider lanes often encourage motorists to travel above the facility's target speed. If narrower lanes are chosen, it is important to carefully design the pavement (whether flexible or rigid) to maximize pavement life cycle. Pavement selection for narrower lanes should focus on durability to offset the effects of a confined wheel track space, which can produce early fatigue.
Design narrow lanes. Because slower speeds are desirable, lane widths under twelve feet are recommended, with 10' as the minimum. Tables 6.2 and 6.3 of the ITE publication Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities provides excellent design parameters for arterial and collector streets. These tables recommend a lane width of 10-11' for the majority of place types, including those discussed in this guide. Chapter 9 of the ITE publication also provides useful guidance on lane width.
Bicycle Lane Considerations:
A bicycle lane should be provided along thoroughfares which are designated bicycle routes, whenever feasible. When bicycle lanes are not possible due to existing right-of-way constraints, a wider outside travel lane should be considered. A shared bicycle-parking lane may be provided along thoroughfares needing bicycle lanes and on-street parking. General width recommendations are as follows:
- Dedicated bicycle lane: minimum width is four (4) feet with an open shoulder or five (5) feet when bordered by a curb, guardrail, or other roadside barrier
- Wider outside travel lane: minimum width is 12' (at widths under 12' cyclists should take the full lane for their safety), and maximum width is 14' (lanes wider than 14' feel and may be treated like two lanes to motorists)
- Shared bicycle-parking lane: 12' (7' for parking, 5' for bicycle travel)
Sidewalk Width:
A number of (often conflicting) forces influence the appropriate width for sidewalks along a given corridor, including the current or anticipated pedestrian presence, abutting land uses, and utility requirements. See Chapter 3.2.3 of AASHTO's Guide for the Planning, Design, and Operation of Pedestrian Facilities for more guidelines on establishing a suitable sidewalk width in various types of corridors.
Although the minimum clear width required for sidewalks is four (4) feet, most of the place types discussed in this guide, especially those with a significant pedestrian presence should elect to include significantly wider sidewalks.
Even in areas of low pedestrian presence, a minimum of five (5) feet is desirable where separated from the curb by a tree lawn, or six (6) feet where adjacent to a curb. See the pedestrians section of this manual for place-type-specific recommendations on sidewalk width.
The table at right, from Oregon Metro's "Creating Livable Streets," also provides excellent guidelines for minimum width requirements as they relate to other elements of the streetscape.
Aesthetic Treatments:
Choosing the appropriate width for streets and sidewalks, although important, is just one of many considerations in creating attractive, livable streets and places. Various design treatments, such as colored or textured pavement, brick pavers, cobblestones, and granite curbs can be used to visually enhance the streetscape, as shown in the images below.
Although these treatments typically cost more to construct, in downtown areas they can help create identity and create a much safer and attractive place, which has clear economic benefits.
Some treatments, such as the cobblestone midblock pedestrian crossing shown below, can also have traffic calming effects at key locations.
Linking the design of these treatments with the architectural character of surrounding land uses creates an even more attractive and cohesive corridor.
Treatments such as raised brick pavers or cobblestones should not be used in bicycle lanes, as they can be hazardous or uncomfortable for bicyclists to navigate.
Likewise, decorative sidewalk treatments should not interfere with ADA compliance. The image at right is an example of an attractive, ADA-compliant treatment.
Inserting artistic design treatments intermittently, rather than along the entire sidewalk (as shown in the image below, at left), is a cost-effective way to enhance the streetscape.
When linked with the surrounding land uses, colored sidewalks (as shown in the image below, at right) can be a great way to revamp a corridor.
This treatment is generally less expensive than pavers or other special material applications.
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For the vast majority of our history, the development of our public rights-of-way have overlooked users challenged by various physical conditions. The deaf, blind, handicapped, and others are a class of citizens that for too long were not accounted for by planners, designers, contractors, politicians, or agency officials. The Americans with Disabilities Act (ADA) was put into law in order to recognize and protect the civil liberties of people with disabilities.
The ADA was a great first step in raising the quality of life in our communities. The concept of universal design was born out of the ADA, and seeks to further its mission. Universal Design is an approach to the development of products, in this case streets, to be as usable and accessible as possible by as many people as possible regardless of age, ability or situation. To be clear, universal design is not the mere adherence to minimum accessibility standards. It is a holistic approach from the beginning planning stages all the way through construction that focuses on creating a facility that will be seamless for all users. When planning, designing, and building great streets, we must at all times remember that all streets, and especially great streets, must serve all people. A street cannot be a great street if it does not provide great service to all users, including those with disabilities.
The principles of universal design must be considered throughout all of the great street development stages. Every aspect of a great street should reflect consideration for all users, and not simply by providing minimum standards. The minimum standards must be met, yes; but that is only the beginning. In each stage of a project, we must consider how to create places that serve all users with as much efficiency, safety, and comfort as possible. This demands that we look beyond the minimum requirements. The following sections provide some key universal design elements to consider at each stage of great street development:
Universal Design in the planning stage. The planning stage of a great street represents that phase where the project team studies a variety of potential solutions to achieve the vision for the desired great street. This stage is critical to universal design success. If universal design is not thought of here, it will be very difficult to include in later stages. One of the most important elements to include at the planning stage is that of "expert opinions". For universal design, the experts are those with disabilities. Bringing these people to the table during the planning stage provides expertise that no text book can offer. They can help planners and designers to more fully understand their needs and how the various elements of a great street would likely impact them. Solutions thought to be viable may have unforeseen impacts on people with particular disabilities. Such collaboration also fosters good will within the community. It can be conducted in a variety of formats, from periodic meetings to one-time charettes.
Functionality for any design element is an important detail to consider during the planning stage, but it is especially important with respect to universal design. Careful consideration of how proposed solutions might impact the functionality of the element for all users is essential at this stage of the project. We need to be sure that the solutions recommended during the planning stage will actually be functional for all users once constructed.
Universal Design in the "design" stage. During the design stage for a great street, the preferred solution identified in the planning stage moves into a more detailed phase of development. The ultimate result of the design stage is a set of construction drawings that will direct contractors on what to build, how to build it, how much material is required, etc. Some of the many design issues to be thinking about include the following:
- Curb ramps are important universal design elements, but they must be done well to be effective. High "lips" on ramps at the street edge create tipping risk for wheelchairs. Channelized right turns should use raised crosswalks. Level landings are essential atop of each ramp. These are just a few of the many details to be thinking about for the design of curb ramps.
- Driveways can present challenging conditions for universal design, especially when streets are widened. Driveway cross slopes that are too steep are difficult for wheelchair and ambulatory persons to cross.
- Sidewalk width is an oft-debated subject. 36" minimum width is ok for one directional traffic, but two-directional is insufficient. 48" is the new "minimum", but even this can be too narrow.
- Bus stop shelters need to be wheelchair-accessible, which means appropriate offsets between the shelter and the curb. It is not enough to simply provide the bare minimum here. Consider maximizing this dimension to make wheelchair access as safe and comfortable as possible.
- Narrow sidewalks with minimal separation between the curb and live traffic are undesirable, especially for the blind.
- When selecting tree species and vegetation, be sure to consider root developmental patterns as vegetation matures. Large roots can heave pavement and crack surfaces, making them difficult for all people, but especially people with disabilities to travel along.
- Metal surfaces along the street, such as manholes and tree grates, can be very slippery when wet. The blind are less able to identify such hazards.
These are just a few of the many issues that will undoubtedly be encountered during design of great streets, but it gives a sense of the types of details that need to be considered.
Job special provisions, or JSPs, are a set of written provisions included with every set of construction drawings that are intended to guide and regulate methods of construction. For universal design, it is imperative that planners and designers spell out in detail all of the various universal considerations required for a given project. In addition, it is equally important to "encourage" the contractors to carefully read the JSPs so that they understand the full requirements during construction.
Universal Design in the construction stage. The construction stage of a great street is a subtly important phase of the project. At first glance, it would seem that as long as the design phase accounts for universal design in the construction drawings, then the contractor will surely build a great street that is accessible and usable for all. This is not necessarily true. Contractors who are well versed in universal design and who care about the importance of accessibility are equipped to build a universal street. Unfortunately, these contractors are often the minority. Despite best intentions of designers, it is not uncommon for streets that were intended to be universal to be built in a less-than-accessible way. Several elements are essential for successful construction of great universal streets:
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Contractor education. In our region, universal design and great streets are not yet mainstream. Traditional design and construction has become so comfortable for many contractors that they can often build many elements without consulting the actual construction drawings.As we work implement new methods for universal and great streets, we must take the time during pre-construction coordination to educate contractors about the universal design elements contained in the plans. These elements must be prioritized, and owning agency may even choose to financially incentivize/penalize the end results.
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Beware of Standard Drawings. Standard drawings are an efficient way to implement routine design elements. They are not, however, appropriate for complex universal design elements, especially on "retrofit" projects. We need to move away from a standard drawing-based construction approaches and toward a site-specific approach when it comes to universal design elements. The contractor must be able to think critically about on-site conditions and how they might impact standard design elements. Something as simple as leaving a lip at the bottom of a curb ramp will go unnoticed if the contractor does not think about the universal impact of that lip on wheelchair users.
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Universal Construction Management. Managing construction is not easy. Resident engineers and field inspectors are doing well just to keep up with the pace of construction. These individuals must be trained to think universally during construction. How are the elements being built by the contractor going to affect all users? This question needs to be at the front of every construction managers mind.
Universal Design and post-construction maintenance. Maintaining great streets for all users is an equally important stage of the project. Once built, the owning agency should monitor the performance of all facets of the project to be sure that there are no unforeseen problems for any users. Problems that arise should be addressed immediately.
As a facility ages, pavement and other materials will deteriorate. Cracked pavement, broken curbs, lips caused by heaving, etc. can all have a negative impact on disabled users. Owning agencies should monitor deterioration patterns so they can quickly address them without risk to any user.
Vegetation is another element of great streets to be mindful of as a facility ages. Maturing trees may have branches that grow into the pedestrian realm, posing a hazard to the visually impaired. Monitoring these conditions is easy to do, and it can prevent unnecessary injury to those users unable to identify the hazard.
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Frequency of entries refers to the linear spacing of ground-floor entries over a given distance. Entries are an important characteristic of buildings and sites, as they help create a more engaging street corridor. Streets and sidewalks along which there is a high frequency of ground floor entries per a given length will generally have more pedestrian traffic than those with a low frequency of entries.
Streets lined by frequent entries are more inviting places for pedestrian activity than those with many closed, featureless walls. The images below are examples of streets with commercial building frontages with a low frequency of entries. These streets represent two rather unappealing pedestrian corridors.
The images below provide examples of streets with commercial building frontages having a high frequency of entries. In retail areas, a high frequency of entries (approximately one every 20 to 40 feet) will both support and generate pedestrian activity, while a low frequency of entries tends to discourage pedestrian activity. Many great streets are associated with a high quality as well as high frequency of entries.
Below are examples of streets with residential building frontages with a low frequency of entries (left) and a high frequency of entries (right). Again, a high frequency of entries both supports pedestrian activity and helps to generate it, and low frequency tends to discourage it. The second image depicts a much more engaging pedestrian environment.
Credit: FTB
However, not every street must have a high frequency of entries in order to be attractive and function as an effective urban corridor. At right is a parkway segment of an arterial street that is primarily focused on mobility rather than site or building access.
The corridor's mobility orientation is in part achieved by projecting a strong and effective landscape character in the absence of buildings lining the street. Behind the screening trees and hedges of the street edge are low to medium density residential neighborhoods.
Frequency of entries, then, is one factor among many that come into play when considering the necessary balance and tradeoffs between land use character, mobility, site access, pedestrian activity, transit use, and architectural character in street design and corridor planning.