WHAT IS A TRAFFIC IMPACT ANALYSIS?

The conclusion makes more sense when you understand what went into it.

By Bea Byline | Life of a Sardine™

A Traffic Impact Analysis, often called a TIA, is an engineering study used to evaluate the traffic expected from a proposed development and how that traffic may affect the surrounding transportation network.

A TIA usually begins with existing conditions. From there, the analysis estimates traffic associated with the proposed development and evaluates future conditions using the assumptions and methods described in the study.

That makes a traffic study more than a collection of numbers. To understand its conclusions, you need to understand what went into them. Start with the date. Traffic conditions change, and development proposals can change as well. Identify when the traffic data was collected and the version of the proposed development the study evaluated.

Then look at the study area. A traffic analysis does not necessarily examine every nearby road or intersection. Identify the locations included in the analysis and note the ones that were not.

Next, look at the development assumptions. The study should describe the type and size of the proposed project used in its calculations. If the development changes later, compare those changes with the project evaluated in the traffic study.

Traffic associated with a development is generally estimated rather than counted before the development exists. The study may estimate how many trips the project will generate and how those trips are expected to travel through the surrounding road network. Those assumptions help shape the results of the analysis.

Pay attention to the conditions being compared. A study may examine existing traffic and projected future traffic. It may also account for anticipated growth that is not generated by the proposed development itself. Read the study's definitions and methodology so you know what each scenario represents.

Level of Service, often abbreviated LOS, is one way traffic operating conditions may be reported. The ratings range from A through F, but the letter alone does not tell the entire story. The underlying measurements can provide additional information about the conditions being analyzed.

The conclusion deserves attention, but do not begin and end there. A traffic study's conclusion is based on the project and conditions the study evaluated. Reading the assumptions behind that conclusion helps you understand what the document supports.

A TIA is an analysis prepared at a particular point in time. It does not tell you everything that will happen after a development is built. It tells you what the study projected under the conditions and assumptions it used.

So when you read a traffic study, do not ask only:

What did the study conclude?

Ask:

What was studied, and what assumptions were used to reach that conclusion?

Then follow the record forward.

Document. Fact. Unanswered question. Next record.

Nothing to see? Hold my pencil.

BEA BYLINE

Life of a Sardine™