If you've asked three different people this question, you've probably gotten three different answers. Terminology in traffic engineering isn't always standardized across jurisdictions, and "Traffic Impact Analysis," "Traffic Impact Study," and "traffic memo" get used inconsistently — sometimes interchangeably, sometimes to mean very different scopes of work.
That inconsistency costs developers real time. Scope the wrong deliverable and you either pay for more analysis than the jurisdiction requires, or you submit something too thin and get bounced back for a redo. Here's how we think about the distinction, and how to figure out which one your project actually needs.
Traffic Impact Analysis (TIA) — The Full Study
A TIA is the most comprehensive of the three. It typically includes:
- Existing traffic counts and conditions at the study intersections
- Trip generation, trip distribution, and trip assignment for the proposed land use
- Background growth and any known committed developments in the area
- Capacity and level-of-service (LOS) analysis for existing, no-build, and build scenarios
- Turn lane warrants, signal warrants, and site access/circulation review
- Recommended mitigation, if warranted
This is the deliverable most TxDOT districts and larger municipalities expect for developments that generate a meaningful volume of new trips — new retail centers, multi-family developments, schools, or anything with more than a couple hundred peak-hour trips, though the exact threshold varies by jurisdiction. If your project needs a formal review and possible sign-off from a state or local agency before permitting, you're very likely looking at a TIA.
Traffic Impact Study (TIS) — Usually the Same Thing, Sometimes Lighter
In most of the jurisdictions we work in, "Traffic Impact Study" and "Traffic Impact Analysis" describe the same scope of work — the term just varies by agency naming convention. Some agencies use TIS as the formal term where others use TIA, and the required content is functionally identical.
Where the terms do diverge, a TIS is occasionally used to describe a scaled-back version of a full TIA — fewer study intersections, no signal warrant analysis, or a shorter time horizon — for developments that trigger a review requirement but at a smaller scale than what a full TIA process is built for.
The practical takeaway: don't assume based on the label. Always confirm with the reviewing agency what content they expect under whichever term they use in their development ordinance or access management policy.
Traffic Memo — The Scoped-Down Answer to a Specific Question
A traffic memo is a shorter, narrower deliverable. Rather than a full multi-scenario capacity analysis, a memo typically answers one or two specific questions:
Does this driveway meet spacing/sight distance requirements?
What's the expected trip generation for this specific land use, without a full LOS analysis?
Is a turn lane warranted at this one location?
A short-form response to a city's specific traffic-related comment on a site plan
Memos are common for smaller sites — a single retail pad, a small QSR, a minor site plan revision — where the jurisdiction doesn't require a full TIA but still wants documentation addressing a specific access or safety concern. They're faster and less expensive to produce, but they don't substitute for a full TIA if the agency actually requires one.
How to Figure Out Which One You Need
Check the local ordinance or access management policy first
Most cities and TxDOT districts publish trip-generation thresholds that trigger a formal TIA/TIS requirement. If your project is under that threshold, you may only need a memo — or nothing at all.
Ask the reviewing agency directly, and ask for it in writing
Given how inconsistently these terms get used, a quick email confirming exactly what they expect (and under which name) can save weeks of back-and-forth later.
Match the deliverable to the actual question being asked
If the concern is narrowly about one driveway or one turn lane, a memo answers it more efficiently than a full study. If the concern is corridor-wide capacity and level of service, nothing short of a full TIA will hold up under review.
When in doubt, scope conservatively
It's much easier to descope a study once an agency confirms a memo will suffice than to expand a memo into a full TIA after a submittal gets rejected for insufficient analysis.
The Takeaway
The label matters less than the actual scope of analysis the reviewing agency expects. If you're not sure which one your project needs, that's exactly the kind of question worth asking before the site plan is finalized — not after.
Want to go deeper?
Start with whether a TIA is required for your project in Texas for the thresholds and triggers, then read how big a traffic study area should really be for how the scope of a full study gets set.