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Highway Functional Classification Concepts, Criteria and Procedures

Section 5. Applications

5.1 Performance

This section of the guidance document details a variety of ways functional classification data may be used by Federal, State, local and other entities. Transportation agencies organize many of their administrative, budgetary, operations and maintenance activities around functional classification. Functional classification is also an important organizing element in data management and highway statistics reporting.

Currently, Federal and State funding programs assign a substantial share of capital and operating resources to the Principal Arterial system, in comparison to lower functional classifications. Likewise, expectations for condition and performance tend to be higher for the higher functional classifications. There is risk associated with not investing in and maintaining the system that carries the most people and goods.

5.2 Data Needs and Reporting

Statistics derived from the Federal roadway databases are organized around functional classification. This data are used in a number of ways, including reporting on the condition of the nation's roadways to Congress and in other highway statistics reports and studies.

5.2.1 Impact of Functional Classification Changes

The changes brought about in the functional classification categories with this updated guidance document will lead to more uniform and more accurate classification of roadways across the country. This will improve the tracking, monitoring and reporting on the performance of the system and specific system elements at a national and State level.

5.3 Secondary Functional Classification Uses

Functional classification is used by transportation agencies in a number of ways, from design to maintenance. The hierarchal system correlates the purpose of a roadway with all the external factors transportation agencies handle. The functional classification of a roadway is often a factor in decision-making by transportation agencies.

5.4 Highway Design

5.4.1 The Relationship between Functional Classification and Design

Functional classification does not dictate design; however, the two influence one another. There is a great deal of latitude in the design of a roadway relative to its functional classification.

Transportation agencies may maintain their own roadway typology. But it is also important that the Federal functional classification system (e.g., FHWA reporting guidelines) be followed. Secondary roadway typologies developed by transportation agencies can be descriptive of how an agency wants vehicles to interact in different settings. Some States, for example, allow for local control over design standards in roadway-dense areas. This is essentially a form of context sensitive solutions (CSS).[6]

The following presents a summary of key resources available on how functional classification can work in concert with livable and walkable communities.

5.4.1.1 AASHTO Green Book and Flexibility in Highway Design

Although States' design standards are often based on the AASHTO Green Book, FHWA's Flexibility in Highway Design document illustrates flexibility options for States to tailor their designs to incorporate community values while safely and efficiently moving people and goods.

The AASHTO Green Book and other design manuals recognize the relationship between highway functional classification and design criteria. The AASHTO Green Book states that, "The first step in the design process is to define the function that the facility is to serve. The level of service required to fulfill this function for the anticipated volume and composition of traffic provides a rational and cost effective basis for the selection of design speed and geometric criteria within the range of values available to the designer (for the specified functional classification). The use of functional classification as a design type should appropriately integrate the highway planning and design process."

The Green Book explains that functional classification decisions are made well before an individual project is selected to move into the design phase. This decision is made on a system-wide basis by cities, counties or State DOTS or MPOs as part of their transportation planning process. Because these decisions require considerable lead time, the functional classification of a roadway often represents a decision made years before the road is built. After a functional classification has been assigned to a roadway, however, there is still a degree of flexibility in the major controlling factor of design speed. There are no "cookie-cutter" designs for roadways. Instead, there is a range of geometric design options available.

5.4.1.2 Livability

By FHWA definition, "Livability is about tying the quality and location of transportation facilities to broader opportunities such as access to good jobs, affordable housing, quality schools, and safe streets." The term captures and recognizes the pervasive influence of transportation in our daily lives and provides a justification for transportation investments that address broader social goals such as quality of life. Specific investments include expanding the use of Intelligent Transportation System (ITS) technologies, quiet pavements and Travel Demand Management approaches in system planning and operations.

FHWA's Livability in Transportation Guidebook cautions that functional classification based designs may not be responsive to context. The report notes the traditional association of functional classification with the movement of vehicles, but it also notes the historical lack of recognition regarding the influence of land use density and mix on the feasibility and desirability of walking, as well as the influence of land use density and mix on setting operating speeds that are appropriate for the level of pedestrian activity present. The report describes corridor re-design initiatives that have preserved mobility for vehicles and enhanced access for travel by foot. These initiatives have produced, when considering all modes, including bicyclists, pedestrians, transit users, a more optimal outcome on the mobility-access continuum.

5.4.1.3 Smart Transportation Guidebook

The Smart Transportation Guidebook: Planning and Designing Highways and Streets that Support Sustainable and Livable Communities, New Jersey and Pennsylvania Departments of Transportation, March 2008, recommends an approach to roadway planning and design that tailors transportation investments to the specific needs of each project. The ultimate goal of the guidebook is to integrate the planning and design of streets and highways in a manner that fosters development of sustainable and livable communities. The guidebook proposes a new roadway typology to design roadways that better reflect their role in the community and the larger transportation network. The typology (Table 5.1 in the Smart Transportation Guidebook) is shown below as Figure 5-1. This scheme focuses more narrowly on the characteristics of access, mobility and speed. And, the guidebook emphasizes that this typology should be used only as a planning and design "overlay" for individual projects and should not replace the traditional functional classification system.

Figure 5-1: "Table 5.1 Roadway Categories" from the Smart Transportation Guidebook, March 2008

Roadway Class Roadway Type Desired Operating Speed (mph) Average Trip Length (mi) Volume Intersection Spacing (ft) Comments
Arterial Regional 30-35 15-35 10,000-40,000 660-1,320 Roadways in this category would be considered "Principle Arterial" in traditional functional classification.
Arterial Community 25-55 7-25 5,000-25,000 300-1,320 Often classified as "Minor Arterial" in traditional classification but may include road segments classified as "Principal Arterial."
Collector Community 25-55 5-10 5,000-15,000 300-660 Often similar in appearance to a community arterial. Typically classified as "Major Collector."
Collector Neighborhood 25-35 <7 <6,000 300-600 Similar in appearance to local roadways. Typically classified as "Minor Collector."
Local Local 20-30 <5 <3,000 200-660  

Source: Pennsylvania Department of Transportation

The guide addresses design options for roadway attributes such as:

The guidebook describes seven prototypical development types and the design attributes appropriate for each, by roadway classification. The design options for a Community Arterial (row 2 from Figure 5-1 above) are shown in Figure 5-2.

Many States and localities have adopted policies that aim to consider the needs of all roadway users. Such policies have been referred to as 'Complete Streets' policies. The PennDOT Smart Transportation Guide has been identified as a good example of addressing Complete Streets issues in the American Planning Association Report #559, "Complete Streets: Best Policy and Implementation Practices."

Figure 5-2: Community Arterial Roadway Design Guidelines in Smart Transportation Guidebook

This figure is a table showing the roadway design characteristics of a Minor Arterial or an Other Principal Arterial in different development settings. For example Arterials Roads in rural settings would have larger turn radii, and no parking lanes, while Arterial Roads in the urban core would have smaller turn radii and on-street parking.

Source: Pennsylvania Department of Transportation

5.4.1.4CSS in Designing Major Urban Thoroughfares for Walkable Communities

ITE's Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities, 2006 is another valuable resource for practitioners. This report advances the successful use of context sensitive solutions in the planning and design of major urban thoroughfares for walkable communities. The document, which can be found at http://www.ite.org/bookstore/RP036.pdf, provides guidance on how to apply CSS concepts and principles to create roadway improvement projects consistent with their physical settings.

Specifically, this work describes the principles, benefits and importance of CSS in transportation projects; identifies how CSS principles can be applied in the planning and development of improvements to major urban thoroughfares; describes the relationship, compatibility and tradeoffs that may be appropriate when balancing the needs of users, adjoining land uses, environment and community interests; presents guidance on how to identify and select appropriate thoroughfare types and corresponding design parameters to best meet the needs of a particular context; and provides criteria for specific roadway elements along with guidance on balancing stakeholder, community and environmental needs and constraints.

5.5 Assessment of Functional Classification Systems

While the Federal functional classification categories play an important role in Federal, State, regional and local transportation planning, there is an emerging trend in transportation to develop new classification categories with which to group and describe roadways. At the heart of this trend is the recognition that roadways do more than move traffic. Roadways are the basic skeleton of a community and are travelways for other modes of transportation, including walking, bicycling and public transportation. The following section describes other functional classification systems in use and touches upon emerging concepts in the realm of roadway functional classification.

5.6 Emerging/Other Functional Classification Systems

While most States only use the FHWA functional classification scheme, several States have developed additional or alternative classification systems to suit their planning and engineering needs. Reasons for developing alternative functional systems include the need to incorporate unique roadway types or roadways that are not part of the Federal-aid system and the need to develop a system to meet the unique administrative or jurisdictional requirements of a State.

Oregon DOT is one State that has employed a separate classification system. This alternate system has only four categories (Interstate, Statewide, Regional and District). While there is not a single translation to convert the Federal functional classification categories to the four State categories, Table 5-1 represents a general "rule of thumb" that Oregon DOT uses for the translation between the two systems.[7]

Table 5-1: Oregon DOT's Classification System

State Classification System (SCS)

Description

Corresponding Functional Classifications

Interstate Highways

Provide connections to major cities, regions or other states; regional trips within metro areas.

  • Urban or Rural Interstate

Statewide Highways

Provide connection to larger urban areas, ports and recreational areas that are not directly served by interstate highways

  • Principal Arterial - Other
  • Urban Principal Arterial - Other Freeway Expressway
  • Urban or Rural Other Principal Arterial

Regional Highways

Provide links to regional centers, statewide or interstate highways or economic or activity centers of regional significance

  • Urban or Rural Minor Arterial

District Highways

Facilities of county-wide significance function largely as county and city Arterials or Collectors

  • Urban or Rural Minor Arterial
  • Urban or Rural Major Collector
  • Rural Minor Collector

With the institutionalization of new concepts such as sustainability, smart growth, new urbanism and complete streets comes a different perspective on transportation as a whole and on roadways in particular. These movements have shifted the dialogue from the movement of automobiles to the mobility of persons. Some States have developed roadway design guidelines that decouple the Federal functional classification system from the specific design needs of a roadway that are determined through a project development process.

The MassDOT Project Development and Design Guide[8] provides designers with options that reflect the needs of a considerable range of prevailing land uses and roadway user types. While the guide notes the role that the Federal functional classification system plays in ensuring mobility, access and connectivity, as well as its role in determining funding eligibility, it also points out that MassDOT's guidance on access control, cross-sections, sight distance, design speeds etc. reflect the appropriate level of flexibility that the department applies to roadway design. As an example, MassDOT provides ranges of acceptable design speeds based on roadway type (Arterial, Collector) and subtype, as well as area type (Rural, Suburban and Urban) and subtype.

The Idaho DOT also embraces this new concept. The DOT's August 2009 Technical Report 5 entitled "Highway System Classification (Functional Classification)"[9] states that the department has come to a new understanding that "streets should connect to their surrounding environment through adjustments in highway/street elements and functions." This approach bucks the traditional 'one size fits all' approach to roadway design that has been effective in supporting vehicular mobility.

The new approach of multimodal street design encompasses four distinct elements or zones (the travelway zone, the pedestrian zone, the context zone and the intersection zone). Each element works with the others to accommodate the needs of multiple modes in harmony their abutting land uses, taking into account environmental, historical preservation and economic development objectives. Idaho's new functional street classification system is consistent with other national good practices which recognize the importance of the different transportation functions that are accommodated within the roadway's right of way. Increasingly, municipal thoroughfare plans are breaking the traditional "Arterial, Collector, Local" mold and using alternate typology. These typologies expand the rural/urban construct into more granular categories that recognize aesthetic and neighborhood-level concerns and explicitly account for all modes of transportation.

Idaho's proposed functional street classification system is consistent with other national practices, which are often found at the local level. Figure 5-3 illustrates the proposed multimodal functional street classification system (which includes the categories of Freeways, Boulevards, Avenues and Streets) and relates it to the conventional street classification system. Idaho has other classes as well.

Figure 5-3: Idaho DOT's Proposed Redefinition of Functional Street Classifications

This figure shows a table of roadway functional classifications that are different than the FHWA functional classification scheme. There are four major classes of streets: freeway, boulevard, avenue and street. Each of these classifications can appear in different development settings, such as urban, suburban, industrial and transit.

Source: Idaho Department of Transportation

Idaho Department of Transportation Statewide Transportation Systems Plan

Figure 5-4: ITE Report: Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities

This figure is a picture of the cover of The Institute of Traffic Engineers' Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities.

The broadening of road typologies and design options within the context of functional classification is not limited to a few DOTs. The Institute of Traffic Engineers' Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities [10] supports and extends this way of thinking. (Figure 5-4) In addition, the ARTIST (Arterial Streets Toward Sustainability)[11] concept and the United Kingdom's Manual for Streets [12] offer new ways of categorizing roadways that support short-distance mobility and access with design options to accommodate a variety of modes and roadway treatment options.

5.7 Future Trends

Additionally, a significant change is occurring in the transportation industry related to the development of improvement projects focusing on the performance of the facility. Roadway performance can be measured in a number of ways, including mobility, speed, safety and surface condition, as well as by person throughput and the accommodation of multiple transportation modes. Increasingly, the character and context of the environment within which the roadway is located, as well as the expectation of its performance on a number of measures, are driving the design of roadway improvement projects. Gone are the days of simply verifying a roadway's functional classification and applying a "one-size-fits-all" approach to the application of design standards of a roadway improvement project.

This movement in transportation planning to categorize roadways beyond the traditional "Arterial, Collector, Local" spectrum will continue to evolve. Continuing research and dialogue among transportation practitioners will deepen the understanding of what these alternatives can offer to a functional classification system that is relevant and meaningful at the national level.

Updated: 10/07/2013
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