Federal Functional Classification Rebalancing Process

A story map detailing the efforts that went into the functional classification rebalancing, the results of it and future steps.

MPD GIS

Functional Classification Rebalance

The State Department of Transportation has many duties and responsibilities that include reporting and analysis of data items. An important report that must be produced and submitted annually to the Federal Highway Administration is the Highway Performance Monitoring System (HPMS). This is a report that requires data on 70 different data items. Each of these items have standards to which they meet the acceptability criteria by FHWA. One of these items is Federal Functional Classification.  

Federal Functional Classification (FFC) is a system in place by which different entities classify roadways based on, function, destination, design, context, topology and quantitative mileage. It is a character of service for roadways in each state. It is essentially a group of factors that contribute to the overall importance of a roadway. There are 7 different classifications for roadways; interstates, freeways, principal arterials, minor arterials, major collectors, minor collectors and local roads. Every public road in the state must be classified under one of these functions for both urban and rural roadways.

Background

Background 

Each functional classification has criteria to which the type of roadway can fit into. Freeways are classified by having no stop lights and it’s primary function being mobility, where Major Collectors serve residential areas and can have medians and stop lights, this is just one example of the different types of classifications. If you'd like to dig deeper into what the functional classifications are and how they are divided, click here to view the functional classification story map. However, an important part of functional classification is the percentage of each that is recommended for FHWA. For example, FHWA accepts 1-2% of state roadways to be Interstate, meaning that if a state has more than that percentage of a classification, it is out of the target area for HPMS. The apportionment for all all classifications are as follows:

  • Interstates: 1-2%
  • Freeways: 0-2% 
  • Principal Arterials: 4-5% 
  • Minor Arterials: 7-12%
  • Major Collectors: 7-13%
  • Minor Collector: 7-13%

Overall, Arterials and Collectors should not exceed 35% of statewide route mileage. 

Federal Function Class

Between 2017 and 2019 Arizona Department of Transportation began reviewing Federal Functional Classification (FFC) designations and recommending changes to more closely align Arizona classifications with the 2013 Highway Functional Classification Concepts, Criteria and Procedures guidance. This involved evaluating how closely Arizona’s existing clafficiations fit within each FFC range and upgrading or downgrading respectfully to get closer to compliance with each range. This story map will detail the process that went into the undertaking. 

The Problem

Over the course of the 2018-2019 submittal, Arizona DOT and partners have noticed that our state Functional Classification mileage percentage is out of range for FHWA guidelines. In effort to reclassify roadways to be in the acceptable percentage range, an analysis on rebalancing functional classification on state roadways was done.

As shown on the chart below, Arizona DOT was not previously in range for the FHWA function classification. Some classifications ranged much higher than the allotted percentage, and some much lower. By looking at the map of 2018 reported functional classification, we can see disparities in the mileage between functional classification. Minor Collector is most presently absent on the map, shown low in both urban and rural areas, contrary to that, it can be seen that roadways functionally classified as local represent a far greater percentage than expected. 

This starts the process of delving into boundaries and roadways to see if there are other factors that may equate to a change in functional classification. Guidance from the Federal Highway Administration states “When determining the functional classification of a given roadway, no single factor should be considered alone.” The following steps were taken to assess and rebalance the functional classification in Arizona:

  1. Review of FHWA FFC Concepts, Criteria and Procedures guidance
  2. Manual review of AZ roadways (using aerial imagery) an identification of possible FFC upgrades/downgrades
  3. Creation and distribution of Arizona specific guidance materials to support coordination with local agency partners
  4. Coordination receiving and responding to input from local agency stakeholders
  5. Submitted FFC rebalancing effort results to FHWA for approval

These steps helped to accomplish the Functional Classification rebalancing efforts. 

The Rebalancing Process

Many aspects went into the process of updating the Functional Classification of all roadways in Arizona. The first review for this project was evaluating the Functional Classification standards set by FHWA and where Arizona fit into those categories. But before delving into where Arizona was prior to the rebalancing, it is important to understand what the characteristics are for each roadway. The graphic here shows the basic elements that go into each characteristic, if you’d like to learn more about the details of Functional Classification, visit this story map  here . 

According to FHWA, each classification has a percentage of roadways that should fall in it, they are as follows:

  • Interstates 1-2%
  • Expressways 0-2%
  • Principal Arterials 4-5%
  • Minor Arterials 7-12%
  • Major Collectors 7-13%
  • Minor Collectors 7-13%
  • Local Roads 67-76%

These pie chart show where FHWA dilients each classification, the two beneath show where Arizona sat prior to the Rebalancing project. It is very clear that there is a huge disparity in local roads versus everything else. Most likely, many of these local roads no longer fit the characteristics of “Local” categories; higher trafficked, maybe paved roads now, and may be longer than ¾’s of a mile. **Note, these are just examples, much more goes into upgrades than the listed**

After evaluating where Arizona was off in the distinction of classification, a review of roadways themselves to determine if upgrade or downgrade was done in a few ways. To start, an aerial review was performed manually to focus on the evaluation of visible characteristics. These may include; where a route ends/how long it is, whether it has a median, how many lanes, is there a middle lane or is it paved? Identifying characteristics like this on a roadway may suggest a change in a roadways classification- this roadway was previously classified as a local road, however after review was upgraded to a major collector. 

The next part to reviewing the functional classification of roadways in Arizona came from immense local coordination and input. Local agencies received guidance on the characteristics of each functional classification and were asked to give input on their records of roadways. This would lend to assessing roadways in local areas that may be eligible for funding that was not receiving it. It also allowed ADOT to begin the process of having a better record of roadways in each agency.

Local agencies received this map, as well as an excel workbook to scrutinize in order to determine where they felt the classification should be upgraded or downgraded in their eyes. This helped ADOT immensely in accomplishing and determining the class of roadways and improved the accuracy of records on functional class.

Once the manual review and the local agencies input review was completed, a letter and table was submitted to FHWA for approval. These changes that came from the Functional Classification rebalance project was approved and submitted in the 2019 HPMS Report. You can find this letter and more on the  ADOT Data Analytics website .

Results Breakdown

VMT Results

VMT is calculated by taking AADT and multiplying by length of and the number of sections. The outcome of this will show traffic growth on a roadway. This can be used to determine if the roadway is being more(or less) heavily travelled. This can predict a change in functional classification or even a change in urban boundaries. 

VMT is based on Functional Classification of all routes above local and local routes. This means Functional Classification and VMT really go hand in hand. If the functional classification “Minor Collection” increases in mileage, then in turn, VMT of roads classified as Minor Collectors will increase. Rather than seeing a huge jump in VMT in total from 2018 to 2019, we see the breakdown of VMT by functional classification increase or decrease. Because the Functional Classification Rebalancing resulted in many roads previously classified as local being moved up in functional classification, the VMT’s of those respective classifications have changed in turn.

An important note on VMT though is that local roads still use an estimation process for calculating VMT. When there is spatial representation for all roadways, better AADT can be gathered, however, on local roads, AADT is typically not collected, so local roads that are reported are usually estimated for VMT.

Mileage Results

The Rebalance project resulted in an increase of mileage on the different road classifications. While the total state mileage did not increase by a large amount, the breakdown of mileage did. The total mileage for 2019 only saw a roughly .18% change, however, that is different when you look at the breakdown by mileage reported for each classification. For example, there was roughly an 8% decrease in local mileage between 2018 to 2019, but over a 100% increase in miles on minor collectors between 2018 and 2019. This shows how the change in mileage between classifications has been affected by the rebalance project.

Can these results affect funding?

Federal legislation continues to use functional classification in determining eligibility for funding under the Federal Aid Program. 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 classification.Essentially, this means the higher a roadway is classified, the more funding it receives, and in turn means the more roads that are classified above local, the more funding is allocated.

Overall Conclusions

As a result of this analysis on functionally classified roadways in the state of Arizona, a total of 7,800 functionally classified road miles were adjusted to the system. This also resulted in a much more acceptable percentage per classification and has put Arizona within the FHWA target for most of the functional classifications. A greater number of roads were also functionally classified, the spatial representation of roadways on the state map. 

Updated Federal Functional Classification

While the relationship between AADT, VMT and functional classification can be a reliable source for determining a roadways classification, it is important to note that these are not completely intertwined. Two roads that carry the same traffic volume may actually serve very different purposes and therefore have different functional classifications. The same can be said for the opposite, with two roadways may have the same classification, but carry different traffic volumes. 

As this analysis was completed, changes using processes like this will continue to happen  annually. There are bound to be changes in the functional classification, but with hopes that there is not as large of changes as seen this year. As a way to continue the conversation on updating functionally classified roadways, Arizona DOT and partners in Works Consulting and Arizona State University have rolled out an application that allows local agencies to suggest changes to functional classification on a need basis. This will prove to allow for greater collaboration and more spatial representation.

Another large factor that went into this analysis was collaboration with local agencies. As the functional classification of roadways effects funding, local input was incredibly important for this task. To streamline this effort, ADOT implemented the use of a data supply chain, allowing local agencies to provide their own input on functional classification as well as their GIS data. This gives the DOT a holistic picture of what state routes will look like and opens up the conversation between stakeholders.

Future Steps: AZGeo

Another large factor that went into this analysis was collaboration with local agencies. As the functional classification of roadways effects funding, local input was incredibly important for this task. To streamline this effort, ADOT implemented the use of a data supply chain, allowing local agencies to provide their own input on functional classification as well as their GIS data. This gives the DOT a wholistic picture of what state routes will look like and opens up the conversation between stakeholders.

As this project was completed, changes using processes like this will continue to happen annually. There are bound to be changes in the functional classification, and thus changes in traffic will likely reflect that. As a way to continue the conversation on updating functionally classified roadways, ADOT has rolled out an application that allows local agencies to suggest changes to functional classification on a need basis, as well as suggesting change in ownership and seeing a breakdown of mileage by agency and functional classification. This will prove helpful in allowing for greater collaboration and more spatial representation.

ADOT Data Supply Chain Application

Still have Questions?

Still have questions about the functional classification rebalancing and it's implications? Reach out to the Arizona Department of Transportation, Multi-Modal Planning Division for further explanation.

If you would like more information about the different variables required for HPMS and other transportation reporting, feel free to visit the  Data Analytics  section website or another related story map below: