Much of CSS is about creating places Discuss the key points about placemaking Places have the right combination attributes that make people want to visit and keep coming back Emphasize “lasting value” to the community and places that contribute to economic development Focus on the aspect that successful placemaking is the integration of context and infrastructure
The purpose of the design framework is to provide a way of defining and classifying both urban context and major thoroughfares. This framework is intended to assist the practitioner in developing a thoroughfare design that is compatible with its surroundings. While you can usually “feel” the characteristics of an urban area it is difficult to describe the specific features that collectively form different types of urban context. Therefore, the framework introduces the concept of “context zones” to categorize urban development density and intensity into four discrete zones. Once a context has been identified, the design framework uses the conventional functional classification system and a new thoroughfare type classification system to develop the design parameters and physical configuration of the thoroughfare.
Context zones are based on the transect developed by the architect and planner Andres Duany. The transect is a continuum of the natural and built environment ranging from rural to highly urban, divided into seven discreet context zones. For urban areas we use only four of the context zones: suburban, general urban, urban center, and urban core. [Use pointer] The reason for using context zones is to help the practitioner understand how changes in the context, and the level of activity the context generates, change the design of the thoroughfare. This slide gives examples of how metropolitan areas transition in development intensity from suburban to urban core.
For the transportation professional unfamiliar with land use planning or architecture, identifying context beyond simply rural or urban can be difficult. Some guidance is necessary, such as this table in the report that provides very general descriptions. However, the CSS approach encourages using multidisciplinary teams in thoroughfare design, in part to help identify context and the types of activities the design of the thoroughfare needs to support.
Understanding context and identifying context zones require understanding of some of the features that create context. These are a few of those features, each of which may also influence how thoroughfares are designed. For example, building design and its orientation to the thoroughfare can strongly influence whether an area is auto-oriented or pedestrian-oriented, which in turn affects how the adjacent street should be designed. Low scale buildings that are set far back from the street and surrounded by parking create a suburban auto-oriented environment. The thoroughfare design then might emphasize auto travel and higher speeds. Taller buildings with no setback and ground floor uses oriented to pedestrians creates an urban pedestrian-oriented environment. This building design may lead to greater pedestrian activity and the thoroughfare design might emphasize on-street parking, the width and function of the roadside, and streetscape.
Adjacent land use may be overlooked in the conventional design approach. Land use should be considered a design control because it has significant ramifications on thoroughfare design. One of its greatest influences is whether land use is residential or commercial and mixed use, where residential areas might emphasize livability, commercial areas might emphasize economic development, and mixed-use areas balance both livability and economic development. These different emphases will influence the design of the thoroughfare.
The design of the site can create either an auto- or pedestrian-oriented environment simply by how the buildings are oriented to the thoroughfare, how the parking is configured, and how well connected the pedestrian facilities are planned. Discuss the features of site design that differentiate auto and pedestrian orientation.
Building design and its orientation to the thoroughfare can strongly influence whether an area is auto-oriented or pedestrian-oriented, which in turn affects how the adjacent street should be designed. Low scale buildings that are set far back from the street and surrounded by parking create a suburban auto-oriented environment. The thoroughfare design then might emphasize auto travel and higher speeds. Taller buildings with no setback and ground floor uses oriented to pedestrians creates an urban pedestrian-oriented environment. This building design may leads to greater pedestrian activity and the thoroughfare design might emphasize on-street parking, the width and function of the roadside, and streetscape.
In urban areas the sense of a street enclosure is important in creating a pedestrian-oriented environment. From the perspective of someone walking on the street, the height of the buildings in relation to the width of the street provides a desirable sense of enclosure. While the height of buildings is outside the purview of the thoroughfare designer, this knowledge is yet another consideration that might be considered in determining right-of-way (RW) needs or in design.
Two important things to remember in the CSS approach to thoroughfare design: First , the thoroughfare is part of the context and its design contributes to both the character and value of a place. Secondly , the design of the thoroughfare should change as the context changes, both in response to the change in activity and to provide compatibility.
Again using simulation to show how the combination of thoroughfare design, and site and building design evolve an auto-oriented context to a multimodally oriented context. This simulation demonstrates how the combination can change the context zone. Current context includes low-intensity and underutilized land and a basic divided arterial street.
The conversion to a divided boulevard with a moderate intensification of land use to a general urban context (not high enough intensity to require on-street parking). Emphasize compatibility between thoroughfare design and context.
Ultimately, place becomes an urban center. Emphasize balance between transportation function of thoroughfare and pedestrian environment and economic development.
The RP’s design framework introduces a new classification system for thoroughfares, called “thoroughfare types”. It is based on the classic system of boulevards, avenues, and streets used for more than one hundred years. Thoroughfare types are used in conjunction with the conventional functional classification but provide a finer grain of detail for the selection of design criteria. In the design framework thoroughfare types are used to determine the physical configuration of the thoroughfare and the selection of design criteria. Functional classification, on the other hand, is used to define the thoroughfares’ primary function in the transportation network, and to select certain critical design controls. You would use functional class to determine the type and length of trips being served, the level of land access, and the type of freight movement and transit that needs to be accommodated.
As I stated earlier thoroughfare type and functional class are used in conjunction to design a thoroughfare, but for different purposes. Functional class identifies the thoroughfare’s function in the larger network and provides input into some of the design parameters. Thoroughfare type is used for selection of most of the design criteria and design controls, and defines the physical configuration and dimensions of the cross-section and intersections.
The RP provides design parameters and dimensions for thoroughfares under different contexts. The parameters into guidance for three aspects of the thoroughfare: -adjacent land uses (the context); -the roadside area; and -the traveled way. This information is used to develop initial cross-sections. Note: in addition to context zones, the design parameters are divided into predominantly commercial and residential categories, because these distinctions play an important role in the design emphasis.
The first thoroughfare type is the boulevard. This illustration shows the basic configuration of a boulevard.
This slide lists the major design characteristics of boulevards: -They are divided streets usually with 4 or more lanes; -They are frequently major transit routes, truck routes, and primary emergency response routes; -They use access management to improve safety and increase capacity; and -They use medians and the streetside as substantial landscaping and streetscape opportunities.
This is an example of a boulevard in an urban residential setting.
Note the mature trees in this example….boulevards are valued for their landscaping.
Boulevards may accommodate longer trips and somewhat higher speeds but they still need to be highly walkable because they also serve as primary transit routes, or rail or trolley corridors such as the Embarcadero in San Francisco.
Example boulevard in an urban core context, downtown Chicago.
A special variation of the boulevard is the multiway boulevard. It is intended to combine a high-capacity thoroughfare with pedestrian-oriented local street frontages. It is not a new concept but has special design challenges, particularly at intersections. This type of boulevard is primarily characterized by a central multilane roadway with separated one-way access lanes on both sides that provide parking and land access and sometime bike facilities. The RP provides guidance on different intersection configurations.
Octavia Boulevard in San Francisco. One of the newest generations of multiway boulevard. Note that bicycle travel uses the access lanes in a shared lane (note the sharrows).
K Street in Washington, DC is a classic multiway boulevard, but has gone through many operational evolutions over the years. Note the many restrictions placed at intersections to reduce conflicts. The RP has a section that addresses this kind of thoroughfare and different ways to control its intersections.
The second type of thoroughfare is the avenue.
Avenues are the “workhorses” of urban areas and have the broadest application of all of the thoroughfare types. They serve many types of areas and have the design flexibility to serve many different functions. Some of the general characteristics of avenues are that: -They do not exceed four lanes -Usually they are undivided so they can be narrower and provide access to adjacent land uses, but they sometimes have a median. -They are usually more local serving than boulevards and therefore emphasize land access, economic activity in the streetside, and quality pedestrian space.
The design of avenues should allocate more space to pedestrians and economic activity in the streetside as shown in this example. Note that this avenue has angled parking, which can be implemented on low volume, low speed collector avenues.
This is an example of an avenue with bike lanes.
This is an example of a classic four-lane undivided avenue. Under the right circumstances, this type of avenue may be considered for a four-lane to three-lane road diet conversion, if the community desires the limited right of way be used for other purposes such as bike lanes. This thoroughfare, Congress Avenue in Austin, is unique in that is provides angled parking on one side.
The street is the third class of thoroughfare type.
Streets primarily serve land access and provide local connectivity for all modes of travel. These are very low speed, pedestrian-oriented thoroughfares, often serving as commercial main streets or in residential neighborhoods. Travel lanes are limited to one in each direction so that streets can emphasize on street parking and wide streetsides.
This is an example of a commercial main street.
The RP provides special guidance on designing traditional main streets including those that are also state highways.
Like the conventional design approach, the CSS approach relies on critical criteria that control the design of a thoroughfare such as speed, design vehicle, sight distance, and location. In CSS these design controls remain critical, but other design controls are emphasized as well, including thoroughfare type and land use and accommodation of pedestrians and bicyclists. Note that level of service is not listed as a design control. In CSS it is a very important factor, and must be considered in the design process, but does not govern the design in the same way that it does in the conventional approach.
The statement in quotes is the task of the thoroughfare designer. Since its inception as a design practice, CSS has always stressed “flexibility in design.” It’s challenging to define the act of design flexibility. It’s a combination of good judgment, openness to new ideas, the ability to balance multiple and conflicting needs, managing risk and understanding liability, and most importantly, Fully understanding the engineering basis behind each design guideline or standard so that you fully understand the consequences of changing it. One of the most important concepts in thoroughfare design is that every project is unique. Remember that the position of design engineer, for those of you who are, is a discretionary profession so your analysis, judgment, and experience are crucial in applying flexibility in design.
Lets compare the conventional design speed to the concept advocated in the RP. Design Speed is the speed that governs certain geometric features of the thoroughfare, primarily horizontal curvature, superelevation, and sight distance. It is typically higher than the posted speed limit so it often results in designs that are safety conservative, but high speed. Design speed has been encouraged to be as high as is practical…..a fine notion for highways but perhaps not for multimodal urban areas. The fact is, if you design for a certain speed, you should not be surprised that people will drive that speed or even higher. In walkable urban areas, the RP recommends use of a target speed. Target Speed – is simply the desirable operating speed within a specific context. A relatively low target speed is a principal characteristic of thoroughfares in walkable, mixed-use urban areas. It should be consistent with the level of activity generated by adjacent land uses and is intended to equal the posted speed limit. Setting speed limits is a different issue, not a part of this briefing. However, we’ll discuss speed management in a bit.
The speed-crash severity relationship illustrates the benefit of reduced target speeds in walkable urban places. The slide is self-explanatory. Use it to justify the desire to reduce speeds on walkable thoroughfares. Derived from Anderson, McLean, Farmer, Lee, and Brooks, Accident Analysis & Prevention (1997).
Speed is probably the single most influential design control in thoroughfare design. In walkable urban areas, speeds range from 20–25 mph to a maximum of 35 mph. The RP also addresses thoroughfares with speeds of 40+ mph as a special Category called “Mobility Priority Thoroughfares.” This slide lists some of the design considerations that are used to keep urban thoroughfare speeds within the target range. Factors like….
Another crucial design control is the design vehicle. Transportation engineers are always challenged with designing for large vehicles in constrained conditions. In CSS we introduce the concept of design versus control vehicle. This concept addresses the conventional approach of designing thoroughfares for the largest possible vehicle that might use it. The difference between a design vehicle and a control vehicle is the frequency of the vehicle and the tolerance for encroachment. Design vehicle – a vehicle that must be regularly accommodated without encroachment into the opposing traffic lanes. Control vehicle – a vehicle that infrequently uses a facility and must be accommodated, but encroachment into the opposing traffic lanes, multiple-point turns, or minor encroachment into the roadside is acceptable.
The CSS approach to designing thoroughfares has five general steps. I want to highlight two of the steps. The first is understanding the community’s vision. This is a frequently overlooked step in the design process. And often times you will want to work with the community’s stakeholders to understand their vision, goals, and objectives. In this step you can identify the concerns and issues that might turn out later to be stumbling blocks in completing your design. The second step I want to highlight is the initial design and testing, and not just testing the thoroughfare for capacity as is often done in the conventional approach. Capacity is one of the factors you need to consider, but you should evaluate the thoroughfare in context of the entire network because often times the problems at the level of the thoroughfare can be resolved at the scale of the network. Testing includes measuring your ideal design to available RW and other constraints and then prioritizing design elements when you can’t fit them all in. Testing also means checking to see if you have addressed the community’s concerns, issues, and vision to the best of ability in the design.
So how does the CSS approach to thoroughfare design differ from the conventional approach? This table compares a few of the important determinants or design criteria that practitioners use in street design. The conventional approach provides design guidance for essentially two contexts, rural and urban. In the conventional approach the same design criteria is used for urban areas regardless of the intensity or type of development. The CSS approach provides a finer grain of classification in which the design criteria may change. In addition to context zone, the design criteria divides land use into residential and commercial categories which further influence the selection of design criteria. Conventional thoroughfare design is based primarily on functional class, design speed, and often is governed by travel demand and level of service criteria. In CSS these are still important criteria, but are balanced with other context-related criteria including community objectives, thoroughfare type, and the type and intensity of the adjacent land uses.
For the next few slides it is useful to think of the thoroughfare in terms of the three components shown in the diagram: the context, the roadside, and the traveled way. There is a 4th component not shown, that is intersections.
One of the first steps in thoroughfare design is developing the cross-section. Before determining basic geometrics, though, you should consider a number of factors that will influence the outcome of the design. This slide lists just a few of these considerations. It is important to reiterate that vehicular level of service is one consideration, and may be an important consideration, depending on local objectives. But it needs to be balanced with a multitude of other considerations.
The RP suggests five stages in developing initial and final thoroughfare cross-sections. As discussed earlier, a thorough knowledge of existing and future context, and selection of an initial compatible thoroughfare type will help you identify the general parameters of the street. These general parameters are provided in the RP in Tables 6.2-6.3. We reiterate that determining the number of lanes should not be based solely on LOS objectives, but that a number of other factors play a role in thoroughfare sizing, including a network capacity analysis.
The last stage involves working within RW or other constraints. If the ideal cross-section cannot fit within the constraints you would need to prioritize the various design elements and only apply the highest priority elements. This is discussed in the next slide. Its also important not to try and squeeze in too many design elements. This only results in a poor design. For example using minimum dimensions for travel lanes, bike lanes, and on-street parking lanes so that bikes can be accommodated only creates an unsafe condition for the bicyclists. If bikes need to be accommodated, it is better to reduce the number of travel lanes or eliminate the parking lane.
When designing in constrained RW, you may want to consider developing alternative cross-sections: Optimal to the absolute minimum, which only provides the most highest priority elements. If you cannot achieve at least the absolute minimum then consider changing the thoroughfare type, or implementing the cross-section in increments over time as RW is acquired.
Note that transitions are a very important element of thoroughfare design. Functions of transitions include: -Notify drivers they are entering a different context and multimodal environment -Notify drivers of a speed change -Serve as a gateway into a town center, place, downtown, etc. Discuss the two types of transitions: Geometric transition, use conventional AASHTO, MUTCD guidance (mostly for vehicular transition) Visual, physical, and operational transition Highlight and describe the different ways these transitions can be achieved. This is a good location for local examples.
Designing Walkable Urban Thoroughfares: A Context Sensitive Approach An ITE Recommended Practice Part 2 of 3
Defining Context Zones Context Zone Distinguishing Characteristics General Character C-1 Natural Natural landscape Natural features C-2 Rural Agricultural with scattered development Agricultural activity and natural features C-3 Suburban Primarily single family residential with walkable development pattern and pedestrian facilities, dominant landscape character. Includes scattered commercial uses that support the residential uses, and connected in walkable fashion. Detached buildings with landscaped yards, normally adjacent to C-4 zone. Commercial uses may consist of neighborhood or community shopping centers, service or office uses with side or rear parking. C-4 General Urban Mix of housing types including attached units, with a range of commercial and civic activity at the neighborhood and community scale Predominantly detached buildings, balance between landscape and buildings, presence of pedestrians C-5 Urban Center Attached housing types such as townhouses and apartments mixed with retail, workplace, and civic activities at the community or sub-regional scale. Predominantly attached buildings landscaping within the public right of way substantial pedestrian activity
Classification Roles in Design Criteria Functional Classification Thoroughfare Type Continuity Trip length Movement type Sight distance (speed) Curvature Speed Physical configuration Dimensions
Thoroughfare Type Characteristics Urban Thoroughfare Type Number of Through Lanes Desired Operating Speed (mph) Transit Service Median Driveway Access Curb Parking Pedestrian Facilities Bicycle Facilities Freight Movement FREEWAY 4 to 6+ 45-65 Express Required No No No Optional Separated Pathway or Shoulder Regional Truck Route EXPRESSWAY / PARKWAY 4 to 6 45-55 Express Required No No Optional Separated Pathway Optional Separated Pathway or Shoulder Regional Truck Route BOULEVARD 4 to 6 30-35 Express and Local Required Limited Optional Sidewalk Bike Lanes or Parallel Route Regional Truck Route MULTIWAY BOULEVARD 4 to 6 25-35 Express and Local Required on access lanes Yes from access lane Yes on access roadway Sidewalk Regional Route/Local deliveries only on access roadway AVENUE 2 to 4 25-30 Local Optional Yes Yes Sidewalk Bike Lanes or Shared Local Truck Route STREET 2 25 Local or none No Yes Yes Sidewalk Shared Local Deliveries Only RURAL ROAD 2 25-35 Local or none No Yes No No Shared or Shoulder Local Deliveries Only LOCAL STREET 2 25 Local or none No Yes Yes Sidewalk Shared Local Deliveries Only ALLEY/REAR LANE 1 5-10 None No Yes No Shared Shared Local Deliveries Only
Designing Walkable Urban Thoroughfares: A Context Sensitive Approach Octavia Boulevard, San Francisco. Photo: Kimley-Horn and Associates, Inc. Example: Multiway Boulevard in an Urban Center (C-6) residential context
4 Designing Walkable Urban Thoroughfares: A Context Sensitive Approach Castro Street, Mountain View, CA. Photo: Kimley-Horn and Associates, Inc. Example: Avenue in an Urban Center (C-5) commercial context
Photo: Kimley-Horn and Associates, Inc. Danville Boulevard, Danville, CA. Photo: James M Daisa, P.E., Arup Example: Avenue in a suburban (C-3) commercial context