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Highway Functional Classification Concepts, Criteria and Procedures

Section 4. Procedures

4.1 Introduction

Agencies can use travel demand models to validate or update their functional classification assignments. These models and the software they use produce estimates of the number of trips that travel between activity centers as well as the flows of travel on roadway segments. A particularly useful feature is "select link analysis" that shows the origin and destination location of travel from a roadway segment, and select zone analysis, which shows the path of trips from or to an activity center. Travel demand model "activity centers" represent collections of smaller areas such as block groups, census tracts or even counties, so their ability to track the path of travel from smaller areas is often limited.

This section of the guidance outlines suggested procedures for assigning functional classifications to highways, including a discussion of the specific technical tasks that describe the detailed technical "how to" tasks, as well as the collaborative efforts with partner agencies to ensure the functional classification of the roadway network considers State, regional and local needs. Currently, each State maintains a categorized roadway network consistent with the Federal functional classification system. While functional classifications of some roadways can and do change over time, the functional classification of the vast majority of roadways remains stable. Consequently, the focus of each State's efforts should be to identify roadways where the functionality has changed. These changes can take the form of newly constructed, re-aligned, extended, widened or otherwise reconfigured roadways. Equally important are changing land use and development patterns - growing residential areas, newly developed commercial or industrial centers and construction of isolated traffic generators can all have a profound impact on the roadway network serving these developments. State DOTs should establish, with local planning partners, a collaborative process of monitoring development and roadway usage patterns to ensure that the functional classification system is kept current.

While the nation's roadway system is mature in comparison to the 1960's-era highway system, the concepts and processes pertaining to the original Federal functional classification system are still relevant. The following section briefly presents an adaptation of the key recommendations of the 1989 guidance document, which is based on an earlier 1960's era document.

Many State DOTs have generated their own functional classification guidance documents. For the most part, these State-specific documents are based upon FHWA's 1989 document, augmented with additional details as necessary. To obtain a complete understanding of functional classification procedures in a particular State, these supporting documents should be reviewed as well.

4.2 Identifying the Functional Classification of a Roadway Network

A primary objective of the functional classification system is to connect traffic generators (population centers, schools, shopping areas, etc.) with a roadway network that channelizes trips logically and efficiently. As classification proceeds from identifying Arterials to Collectors to Locals, the perspective (and size) of traffic generators also moves from a larger to a smaller scale (or from a smaller to a larger scale, if starting from the local development).

When developing a functional classification network in a given area, the same basic procedures should be followed, whether the functional classification is applied in a rural or an urban area. However, due to the differences in population and land development intensity between rural and urban areas, the process and considerations used to classify roadways may be different. Because functional classification is part art and part science, these procedures are a blend of detailed, task-oriented steps and qualitative guidelines. These procedures do not eliminate judgment from the classification process, but when used as a guide, they help to apply judgment in a sound and orderly fashion.

  1. Identify traffic generators. In rural areas, traffic generators may be population centers (cities and towns); recreational areas such as lakes, national and State parks; military facilities; consolidated schools; and shipping points. In urban areas, traffic generators may be business districts; air, rail, bus and truck terminals; regional shopping centers; colleges and universities; hospital complexes; military bases; industrial and commercial centers; stadiums; fairgrounds; and parks. Regional traffic generators adjacent, but outside of the area of interest, should also be identified.
  2. Rank traffic generators. Traffic generators should be categorized based on their relative ability to generate trips and be first stratified into urban and rural groupings. Traffic generators thought to be significant enough to be served by a Major Collector or higher should be categorized into five to eight groups (it is better to have too many groups than to have too few, especially toward the lower end of the scale). Traffic generators with similar significance should be placed in the same group. These groups will be used to identify the functional classification of connecting roadways. Population, sales tax receipts, retail trade, visitation and employment are some examples of factors to consider when ranking traffic generations according to their significance.
  3. Map traffic generators. Traffic generators should be mapped using graduated symbols of varying sizes and/or colors according to the group to which the generator belongs. This will produce a visual representation of the ranking. For example, the group of generators ranked highest should all be symbolized with the largest symbol.
  4. Determine the appropriate functional classification to connect traffic generators. To determine the functional classification of roadways, work from the highest mobility facilities first by identifying Interstates, Other Freeways & Expressways, Other Principal Arterials, then Minor Arterials and Collectors (Major, then Minor). Then, by definition, Local Roads will be all of the roadways that were not classified as Arterials or Collectors. In other words, begin with a wide, regional perspective to identify Principal Arterials, then gradually move to smaller, more localized perspectives as Minor Arterials, Major Collectors and Minor Collectors are identified. In this process, consider the size of the traffic generators connected and the predominant travel distances and "travel shed"[4] served.

4.2.1 Arterial Considerations

Arterials serve a wide range of functions across the access-mobility spectrum. Some considerations and rules of thumb for designating roads as Arterials include:

Note: Under MAP-21, the National Highway System (NHS) was expanded on October 1, 2012, to include the Principal Arterials at that time. This one-time event did not create a link between the NHS and Principal Arterials. A change to the Principal Arterials does not automatically change the NHS.

4.2.2 Collector Considerations

Collectors, which may have an important land access function, serve primarily to funnel traffic between Local to Arterial roadways. In order to bridge this gap, Collectors must and do provide access to residential neighborhoods.

When deciding between Major and Minor Collectors, the following guidelines should be considered:

4.2.3 General Rules of Thumb for All Categories and the System as a Whole

While working down through the functional classification system of roadway classifications, the following additional considerations should be kept in mind:

In most cases, the most direct, most improved and most heavily traveled route should be chosen for connecting medium and small size traffic generators.

4.3 Good Practices

FHWA encourages States to develop their own more detailed and more quantifiable guidelines. The state of Wisconsin has developed robust algorithms taking into account factors of the population of the areas connected by a roadway, land use, spacing and current AADT volumes.

The following section discusses and recommends a series of good practices that State DOTs may follow to keep the functional classification of its roadways as accurate as possible.

4.3.1 Ongoing Maintenance of the Functional Classification System

State DOTs are charged with ensuring that the functional classification of their roadways is kept up-to-date. In addition, FHWA recommends that States update their functional classification system continually as the roadway system and land use developments change. States should also consider reviewing their systems every 10 years to coincide with the decennial census and the adjusted urban area boundary update cycle.

This maintenance process involves ongoing coordination with local planning partners to identify roadways that require changes to their functional classification, due to changes in transportation network and/or land use patterns.

These changes can involve:

Actively maintaining the functional classification attributes of roadways will reduce the level of effort needed for the periodic updates. As State DOTs work with their local transportation planning partners on various initiatives such as long-range planning activities and project programming and development, issues related to the functional classification should be kept in mind. Useful questions to ask are the following:

A key success factor for State DOTs is to have a well-documented process for changing the functional classification of an existing roadway. This process, along with a description of what the functional classification is and why it is important, should be readily accessible on the internet.

Many State DOTs have developed a functional classification change request form (see Figure 4-1). These forms ensure that consistent information and evidence supporting such a change are provided. Typically, information - such as the roadway location, the justification for the change and letters or signatures expressing local support - is required.

Figure 4-1: Minnesota DOT Functional Classification Change Request Form

This figure is a reproduction of a form that local planners use to request a change in the functional classification of a roadway. The form asks for information such as the route name and number, the current and proposed classification, a description of the road segment, and the justification for the proposed change. An MPO board member must sign the form.

Source: Minnesota DOT, Functional Classification, Request to Change Classification; http://www.dot.state.mn.us/roadway/data/html/roadwaydata.html

When new Local Roads get added to the State's roadway inventory databases, as a good practice, State DOTs should evaluate how closely their roadways fit within each functional classification category based on the percentage guidelines found in Tables 3-5 and 3-6. If any significant differences are found, steps may be taken to either correct or explain them. However, this refinement process should not be conducted simply to keep adding or removing roadways until certain percentage guidelines are met. Bearing in mind that the classification process is as much art and science, it should still be as systematic, reproducible and logical as possible. Additionally, states and their planning partners (to be discussed later) should document their methodology and attempt to follow it as consistently as possible.

4.4 Geographic Information Systems

Transportation agencies rely on a variety of up-to-date spatial data to carry out their planning, maintenance and operations responsibilities. The most important element of this, for functional classification purposes, is an accurate GIS-based inventory of all roadways for a given area. This inventory contains the current functional classification of all roadways and AADT estimates to calculate daily VMT.[5] Total mileage and total DMVT can then be calculated for the entire network, independent of functional classification, thereby providing the denominator for the mileage and DVMT percentages by functional classification.

State DOTs identify new roadways and roadway improvements in their Statewide Transportation Improvement Program (STIP). DOTs should maintain basic information such as mileage, functional classification, lanes and traffic forecasts in a Linear Referencing System/GIS format. A variety of other GIS data can be useful in the functional classification evaluation process - this includes land use, major traffic generators and digital ortho-photography.

As DOTs move toward integrated, enterprise-wide GIS-based asset management systems, it is becoming increasingly important to ensure consistency between traditional tabular roadway inventory data and geospatial databases representing the physical roadway network. Some State DOTs have been maintaining tabular databases that contain information on the numerous attributes of a roadway (e.g., number of lanes, speed limit and functional classification).

Figure 4-2 illustrates the potential consequences of an inconsistency between databases. The example shows the merging of a GIS network and an underlying database containing functional class information. Because the network, as represented in the GIS system, does not correlate completely with the roadway section representation of the non-GIS database, the displayed non-GIS database information appears to be inaccurate.

Figure 4-2: Example of Shifting due to Inconsistency between Tabular Event Data and Geospatial Data

Map of a small area of roadways. Three of the roadways are colored to show how they are represented by a separate GIS System. The figure shows that different mapping systems within an agency may not present roadways in their correct locations. Different offices within an agency may maintain separate roadway databases, and they should coordinate to make sure that the databases are accurate and compatible.

Source: CDMSmith

Today's geospatial technologies allow this data to be easily "viewed" in the context of a spatially accurate map display. Therefore, it is important that the linearly referenced tabular data, when integrated into a state DOT's traditionally separated databases, be dynamically segmented on a routed roadway network and be spatially correct. This issue may become apparent when roadways are mapped and symbolized according to their functional classification. The mapped functional classification designations often stop short or slightly overshoot their proper terminal location.

As shown above, GIS systems enable roadway segment color coding for validation and public display. An example of a color coding scheme for roadways by functional classification is shown in Figure 4-3. If followed, this suggestion would improve future mapping consistency.

Figure 4-3 Sample Roadway Color Scheme

 Blue Interstate 1. Purple Other Freeways and Expressways 2. Red Other Principal Arterial 3. Brown Minor Arteria l4. Orange Major Collector 5. Green Minor Collector 6. Gray Loca l7.

Source: CDMSmith

4.4.1 Proactive Communication and Accessibility of Information

State DOTs should create a 2-way communication network with internal and external users of functional classification information. The unit within the State DOT responsible for maintaining the official functional classification network should keep a list of internal and external users of functional classification information and provide them with guidance and a mechanism for updating functional classifications. Increasingly, enterprise-wide databases and information provided over the internet (either with static PDF maps or more sophisticated interactive, dynamic online mapping applications) allow end-users quick and convenient access to roadway attribute information, including functional classification. Additionally, internal linkages and strong lines of communication with the DOT offices responsible for asset management, system inventories and operations can ensure that updates and changes to their roadway databases are transferred to a master GIS inventory which the functional classification process has access.

4.5 Partners in the Functional Classification Process

Whether processing a single functional classification change request or conducting a comprehensive statewide functional classification review in response to the establishment of the updated Adjusted Census Urban Boundaries, a variety of planning partners should be involved to ensure informed consent of the functional classification designation for a State's roadways.

4.5.1 Metropolitan Planning Organizations

MPOs are the primary local contact for the DOTs in Urbanized Areas. MPOs may initiate requests for revising the functional classification of a roadway within their planning area, either on their own initiative or on behalf of member jurisdictions. For requests originating from a member jurisdiction, the MPO may conduct an initial review to ensure compliance with functional classification criteria. Typically, MPOs will forward requests along with their recommendation for approval or disapproval to the State DOT unit responsible for maintaining the functional classification information. In some cases, local governments work directly with the State DOT, with concurrence from the MPO.

State DOTs should complete the adjusted urban area boundary process within 2 years of the boundary release date.

The functional classification update should be completed within 3 years following the approval of the adjusted urban area boundaries.

4.5.2 State DOTs

For the sake of efficiency, a single specific unit with the DOT should be responsible for maintaining the official functional classification designation of all roads within the State. This unit should also be in charge of coordinating with FHWA on matters related to functional classification and be the final State decision-maker for all functional classification issues. The unit should also ensure that all submissions for changes to the functional classification of a roadway have followed the appropriate documented procedures. If the State DOT approves a change, the unit should submit the change, along with supporting information, to the FHWA Division Office for their review and approval. Upon receipt of FHWA approval (or disapproval), the DOT should notify the affected local jurisdiction of the decision.

DOT regional or district offices may be responsible for submitting system revisions for all State highways outside an MPO's planning area and coordinating proposed system revisions for areas within the planning jurisdiction of an MPO.

Once a change has been approved by the FHWA Division Office, the State DOT may revise the official repository of functional classification information and update ancillary systems and work products to reflect the change.

4.5.3 Counties and Other Agencies

Counties may be responsible for initiating functional classification changes on roadways under their jurisdiction but outside of an MPO planning area. Counties within an MPO's planning area should coordinate proposed system revisions with the MPO and submit any proposed changes to the State DOT.

In addition to MPOs, counties and State DOTs, other local government and regional entities - such as cities, rural transportation planning organizations, regional development commissions, councils of government, etc. - may also submit changes and participate in the update process.

4.6 Suggested Procedural Tasks

This section of the guidance outlines a series of recommended technical and procedural steps to review the functional classification of a State's roadway network. These tasks should be conducted through a collaborative effort between each State DOT and its local planning partners. In an ideal setting, the State and its partners should assess whether its roadways are properly classified on a continuous basis. Because new roads and major land development projects take years of advance planning, State DOTs should anticipate and respond to functional class adjustments in tandem with development activity. Additionally, the entire network of roadways should be reviewed after the development of the adjusted urban area boundaries. For those State DOTs that actively maintain and update the functional classifications of their roadway system, this formal process should be rather straightforward.

The following suggested procedures offer the most robust and detailed steps in the update process (Figure 4-4). Even for the most challenging of circumstances, the process of official review and submittal of the updated functional classification system can take less than 36 months to complete from the time of FHWA approval of the adjusted urban area boundaries.

Figure 4-4: Good-Practice Timeframe for Functional Classification Updates in Months

Source: CDM Smith

States and their partners should re-evaluate the functional classification of the road system at least every 10 years, coinciding with the decennial census. FHWA highly recommends that this process be completed within 3 years of the formal approval of the adjusted urban area boundaries so that all States are coordinated with the same census. FHWA considers the State DOT to be the authority during this process and relies upon it to take an active leadership role.

FHWA Division Offices may correspond with State DOTs to formally launch the functional classification system review. This notice, which can accompany the approval of the adjusted urban area boundaries, reminds the State DOTs of their responsibilities and provide information regarding how and when the functional classification information should be submitted.

The following listing presents a good practice level functional classification review process with a 24 month completion timeframe, following approval of the adjusted urban area boundaries.

  1. Mobilize the Functional Classification Update Process
    1. Form a team to specifically guide the functional classification review and update process. Establish a functional classification review team composed of State and regional planners that have a vested interest in the final delineation of the functional classification designations. Individuals with experience in Federal transportation funding, highway design, traffic operations and the metropolitan transportation planning process should have a seat on the committee. This review team should be responsible for reviewing proposed changes to the functional classification network from local planning partners.
    2. Generate data, maps, etc. for use by local planning partners. Incorporate approved adjusted urban area boundaries in the enterprise GIS system and produce functional classification maps at a variety of scales that are relevant to local planning partners. These may include statewide, district, county and municipal scales.
    3. Contact local planning partners. Contact various local planning partners to explain the task at hand and request their participation. MPO staff should be key partners, and other regional planning agencies, counties and/or local municipalities should be consulted as necessary. For many areas in which engaging local partners can be difficult, it is appropriate for State DOTs to be responsible for reviewing the functional classification of roadways.
  2. Work with Local Planning Partners in the Functional Classification Review Process
    1. Deliver data and documents to local planning partners. Transmit the maps described in #1b (and/or GIS data used to make such maps) to local planning partners. This transmittal should include specific instructions in terms of data formats, spatial accuracy, update processes and expected completion dates. The functional classification guidance document should also be shared with everyone involved in this process. A strong emphasis should be placed on transmitting the data in a timely fashion. In-person or video conference meetings can be extremely valuable to ensure proper communication and mutual understanding.
    2. Work with Local Planning Partners. As necessary, a State DOT will work with the local planning partners to ensure that the functional classification review and update process meets their expectations. In urban areas, close collaboration with MPOs is extremely important. Regional workshops hosted by MPOs can be valuable in ensuring that there is a common understanding of the process and the schedule for delivery. While the exact details surrounding information exchange may vary from state to state, the local planning partners are generally expected to review the current functional classification network, in the context of the newly revised adjusted urban area boundaries, and submit a set of proposed changes to the functional classification of roadways in their area. Whether a large or minimal number of changes, sufficient explanation should be provided to justify each recommended functional classification change (see Table 3-1: Characteristics of Urban and Rural Arterials for examples). In many areas, proposed functional classification changes require formal MPO approval.
  3. Make Functional Classification Changes
    1. Gather, review and incorporate all proposed changes. The State DOT must review a local or regional transportation agency's proposed changes to ensure that they are reasonable. Special attention should be paid to the consistency of classifications at regional boundaries, overall route continuity, spacing and mileage and DVMT percentage guidelines. In addition, DOTs should coordinate with neighboring States to ensure consistency at State boundaries. If possible, potential system-wide changes should be made in a "test" environment to avoid affecting the official enterprise system during the analysis of proposed changes. Follow-up meetings may be necessary to resolve issues discovered by the DOT.
    2. Submit draft functional classification network information to FHWA. Once the State DOT has successfully reviewed and concurred with all recommend functional classification changes, it should submit the draft final functional classification network to its FHWA Division Office for final approval. The specific geospatial format of data delivery should be worked out between the State DOT and its FHWA Division. Separately, hard copy maps at a scale sufficiently small enough to evaluate the functional classification network should be provided. Should the Division Office have any issues with the proposed functional classification network, the State DOT and the affected local planning entities should meet to decide upon a mutually agreeable solution. Note: Any changes to the National Highway System (NHS) will need to be coordinated with FHWA HQ Office of Planning, Environment and Realty. Approval of changes to the NHS happens in FHWA HQ, and the procedures for modifications are detailed in 23 CFR 470.
    3. Incorporate Functional Classification Changes into Enterprise Systems Once FHWA approval has been received, any proposed functional classification changes should be made into the enterprise database systems that house the official records of roadway functional classification. These functional classification changes should be forwarded to FHWA HEPP for inclusion into the HEPGIS database and also be incorporated into the June 15th HPMS data transmittal.

Table 4-1 Example Massaschusetts Roadway Functional Classification Table

Ref# City/Town

Roadway

From

To

Existing
Classification

Proposed
Classification

Distance
(Miles)

Map

1 Blandford

Huntington Rd

Chester Rd / North St

Huntington Town Line

Rural Major Collector

Local Road

3.80

1

  Huntington

Blandford Hill Rd

Route 20

Blandford Town Line

Rural Major Collector

Local Road

0.83

2 Blandford

Cobble Mountain Rd

Russell Town Line

Birch Hill Rd

Rural Major Collector

Local Road

2.80

  Blandford

Birch Hill Rd

Route 23

Cobble Mountain Rd

Rural Major Collector

Local Road

0.24

  Granville

Wildcat Rd

Cobble Mountain Rd

Old Westfield Rd

Rural Major Collector

Local Road

1.94

  Granville

Phelon Rd

North Lane #2

Cobble Mountain Rd

Rural Minor Collector

Local Road

1.78

  Granville

Cobble Mountain Rd

Phelon Rd

Russell Town Line

Rural Minor Collector

Local Road

1.30

  Russell

Cobble Mountain Rd

Blandford Town Line

Granville Town Line

Rural Major Collector

Local Road

0.33

3 Chester Bromley Rd Huntington Town Line Skyline Trail Local Road Rural Minor Collector 3.14

  Huntington

Bromley Rd

Chester Town Line

Route 112

Local Road

Rural Minor Collector

1.79

4 Huntington

Country Rd

Route 112

Route 66

Local Road

Rural Major Collector

3.04

5 Holyoke

Bobala Rd

Whitney Ave

West Springfield Town Line

Local Road

Urban Minor Collector

0.83

2

  West Springfield

Interstate Dr

Holyoke Town Line

Prospect Ave

Local Road

Urban Minor Collector

0.53

6 West Springfield

Prospect Ave

Westfield Town Line

Bernie Ave

Urban Minor Collector

Local Road

2.18

  West Springfield

Morgan Rd

Prospect Ave

Amostown Rd

Urban Minor Collector

Local Road

1.24

  West Springfield

Amostown Rd

Morgan Rd

Pease Ave

Urban Minor Collector

Local Road

0.65

  Westfield

Old Holyoke Rd

East Mountain Rd

West Springfield Town Line

Urban Minor Collector

Local Road

0.60

Description of Changes

Huntington Road in the Town of Blandford and Blandford Hill Road in the Town of Huntington no longer provide access to through traffic. Additionally, portions of this roadway are unsurfaced. For this reason, it is recommended that this roadway be downgraded from a Rural Major Collector to a Local Road.

The Department of Homeland Security recently closed access to Cobble Mountain Road in the Town of Blandford in order to increase security of the Cobble Mountain Reservoir. Consequently, it is recommended that all roadways discussed in Reference #2 in Table 1 be downgraded to Local Roads due to the inaccessibility and lack of continuity of the roadway functional classification system.

Sample functional classification changes listed, with examples of supporting justification

Table 4-2 presents good practice milestones for the overall development and submittal process.

Table 4-2: Key Milestones for Development and Submittal of the Functional Classification Network

Event

Month Following FHWA Adjusted Urban Area Boundary Approval

State DOT launches the formal functional classification update process after FHWA approves the State's adjusted urban area boundaries

Month 1

State DOT works with planning partners to review and propose changes to the functional classification of its roadways

Months 2-17

State DOT gathers and processes all proposed function classification changes and submits draft final data and/or maps to FHWA Division Office for review

Months 18-20

DOT incorporates updates into planning process and related databases to ensure submittal of updated functional classification in upcoming June 15th HPMS submittal

Months 22-24

Updated: 10/07/2013
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