If you are considering a new development or redevelopment in Fairfax County, Virginia, an important part of the entitlement process is often the transportation analysis. But does that mean your project will require a full Traffic Impact Analysis (TIA)? Not necessarily.
In 2025, Fairfax County changed the way it determines the level of transportation analysis required for zoning applications. New thresholds and analysis tiers are intended to better match the scope of the study to the size and potential transportation impacts of the proposed development.
For developers and property owners, understanding these requirements early can help identify the transportation work that may be needed. It can also help you avoid surprises as an application moves forward, which is something we love to help our clients avoid.
In this first of two articles, we examine Tier 1 and Tier 2, which apply to developments generating fewer than 3,000 net new average daily (24-hour) vehicle trips. In Part 2, we’ll look at the more extensive requirements associated with Tier 3 and VDOT Chapter 870 Traffic Impact Analyses.
If you want to go straight to the details of this topic, scroll down to the section, “Fairfax County’s Four Levels of Transportation Analysis”. But first, we present a quick summary about why the Comprehensive Transportation Analysis–Zoning (CTA-Z) process has changed.
Background: Why Did Fairfax County Modify Their Traffic Impact Analysis Model?
On May 6, 2025, the Fairfax County Department of Transportation (FCDOT) published a Technical Bulletin announcing that, effective immediately, it had “update[ed] the County’s process regarding trip thresholds and analysis types for Comprehensive Transportation Analyses associated with zoning proposals (CTA-Z).”
This change followed a multiyear effort to move County transportation studies beyond their traditional emphasis on automobile traffic and provide a more consistent, multimodal process for evaluating development proposals.
Based on an analysis of the 2025 Technical Bulletin, FCDOT made these changes for several reasons (quotations are from the Bulletin):
- The previous thresholds were based on an outdated, automobile-oriented model (“Historically, studies were focused primarily on vehicular (automotive) analysis related to the proposed development.”)
- Fairfax County wanted transportation studies to address more than automobile capacity (“FCDOT reflected on how to evolve the CTA-Z process to meet the multimodal initiative of Phase 1 and right-size studies commensurate with their character and scale”)
- Previous studies seldom produced unique off-site capacity improvements (in “39 non-TIA studies over [an] eight-year period … [o]nly one study identified a capacity need”)
- Applicants, developers, the Board of Supervisors, and the public wanted greater certainty about when a transportation analysis would be required and what type of analysis would be expected
- FCDOT wanted the requirements to reflect project scale and current professional practice
Fairfax County’s Four Levels of Transportation Analysis
With FCDOT’s update to its Comprehensive Transportation Analysis-Zoning (CTA-Z) process, zoning-related transportation analyses generally fall into four categories based on the number of net new average daily trips (ADT) generated by the proposed development:
- 999 or fewer net new ADT: Tier 1 Transportation Statement
- 1,000–2,999 net new ADT: Tier 2 CTA-Z
- 3,000–4,999 net new ADT: Tier 3 CTA-Z
- 5,000 or more net new ADT: VDOT Chapter 870 Traffic Impact Analysis
These distinctions matter for developers, businesses, and property owners because the analysis – not to mention the time and coordination involved – can increase considerably as a project moves through the tiers.
But before determining which tier applies, there is another important calculation to make. As noted in the introduction to this article, that calculation is “net new average daily trips.”
Traffic Analyses Are Determined by “Net New Trips”
For a developer or property owner evaluating a redevelopment opportunity, one of the most important aspects of the new thresholds is the phrase net new trips.
Fairfax County does not simply look at the total number of trips expected from the proposed use of a development. For purposes of determining the applicable transportation analysis tier, ADT is based on the net increase in trips generated by the proposal compared with the trips generated by the property’s by-right use.
In our experience, this distinction can be particularly important for redevelopment sites in the County.
For example, consider a hypothetical property that could generate a substantial number of trips under its existing by-right development potential. A proposed redevelopment might also generate several thousand daily trips, but the difference between the two scenarios could be considerably smaller.
That net difference can help determine which level of transportation analysis is required.
As in so many transportation analyses, an early trip-generation assessment can help the development team anticipate the likely analysis tier and consider its potential implications before the entitlement application moves forward.
As part of the application-acceptance process, the applicant submits Fairfax County’s Transportation Study Determination Request Form (also found via the County’s Transportation Analysis page). FCDOT uses the information provided about the proposed development, the property’s by-right or previously approved uses, and its existing development to determine which level of transportation analysis applies.
The County can estimate the trip generation needed to make its formal determination, and its form does not require the applicant to submit a separate trip-generation table. However, in our experience we have found that many developers and property owners want to understand the likely determination before submitting the request. This can be particularly true when a proposed use is somewhat complex, such as nonstandard or mixed-use in nature.
As in so many transportation analyses, an early trip-generation assessment can help the development team anticipate the likely analysis tier and consider its potential implications before the entitlement application moves forward.
Tier 1: When a Full CTA-Z May Not Be Necessary
Projects generating 999 or fewer net new ADT generally fall into Fairfax County’s Tier 1.
In these cases, a full CTA-Z is not required. Instead, the applicant submits Fairfax County’s Tier 1 Transportation Statement with the entitlement application.
Although Tier 1 does not require a formal transportation report, our company typically prepares a trip-generation comparison table for inclusion with the Transportation Statement. This helps document the anticipated trips associated with the existing and proposed uses and provides useful context for FCDOT’s review.
For a property owner considering a smaller development or redevelopment, that is an important distinction. Crossing the 1,000-net-new-trip threshold moves the project into the CTA-Z process and introduces additional study and coordination requirements.
Tier 2: A More Focused CTA-Z Is Required
A proposal that generates between 1,000 and 2,999 net new ADT generally requires a Tier 2 Comprehensive Transportation Analysis-Zoning (CTA-Z).
Fairfax County’s CTA-Z evaluates existing transportation conditions, future conditions without the proposed development, and future conditions with the development.
For vehicular analysis, Tier 2 studies generally focus on:
- Site access points;
- Intersections along the site’s perimeter; and
- Streets along the site’s frontage.
But remember, this is not your father’s traffic study. Under the new guidelines, vehicular operations are only part of the analysis.
The CTA-Z process also considers the transportation network for people walking, bicycling, and using public transportation. That reflects an important evolution in Fairfax County transportation planning: development impacts are increasingly being considered across multiple modes rather than primarily through automobile traffic volumes and intersection operations.
A Final Note: Tier 2 Also Introduces the Scoping Process
Tier 2 represents another important change for the development team: scoping with FCDOT and VDOT.
In this scenario, the applicant’s transportation consultant prepares pre-scoping information that identifies assumptions and the information proposed for inclusion in the study. A scoping meeting with FCDOT and VDOT then establishes what will be analyzed before the transportation study proceeds.
The scoping process can address a wide range of issues, including:
- Intersections and access points to be studied
- Development and background assumptions
- Transportation modes requiring analysis
- Planned developments that may affect future conditions
- Transportation improvements that should be incorporated into the analysis
As we have said to our trusted clients for decades, establishing parameters early on can help ensure that the transportation study addresses the issues the reviewing agencies expect to see.
Why Developers Should Look at Transportation Early
It is tempting to think of a transportation study as something prepared after the development team has determined what it wants to build. But we believe that reversing that sequence can provide tangible value.
Early transportation analysis can help determine how different development programs may affect trip generation, whether a project is likely to fall within Tier 1 or Tier 2, and what transportation issues could emerge during the entitlement process.
For redevelopment properties, evaluating the site’s by-right trip generation can be particularly important because Fairfax County’s thresholds are based on net new trips, not simply the total trips generated by the proposed development.
Those findings can help inform decisions about land use, density, access, site circulation, multimodal connections, and the overall entitlement strategy.
Next Up, in Part 2: What Happens With Larger Developments?
Once a proposed development reaches 3,000 net new daily trips, the transportation analysis becomes broader.
In Part 2, we will examine Tier 3 CTA-Z requirements, including the potential analysis of off-site intersections, and what happens when a development reaches the 5,000-net-new-trip threshold and a VDOT Chapter 870 Traffic Impact Analysis comes into play.
For larger development and redevelopment proposals, understanding those requirements early can be an important part of establishing the project’s entitlement strategy.