(Answer specific for City of Austin projects)
A Traffic Impact Analysis (TIA) is a study which assesses the adequacy of the existing or future transportation infrastructure to accommodate additional trips generated by a proposed development, redevelopment or land rezoning.
In the City of Austin, TIA requirements apply to individual lots when an application is made to zone or rezone a lot or for site plan approval to develop the lot.
A determination as to whether a TIA is required must be made prior to submittal of a zoning, site plan, or subdivision application as appropriate. This determination is made by the City of Austin Planning and Development Review Department. A TIA is provided through a civil engineer with traffic expertise at the cost of the project applicant.
In general, a TIA is required if the expected number of NET NEW trips generated by the project exceeds 2,000 vehicle trips per day.
In a TIA analysis, credit is given for any existing development which already generates trips. The TIA trip generation calculations are done in accordance with the guidelines of the Institute of Traffic Engineers (ITE).
Keep in mind that a Neighborhood Traffic Analysis (NTA) can be required if the project has access only to a residential local or collector street and the expected number of vehicle trips generated by the project exceeds 300 vehicle trips per day over the existing uses. A neighborhood traffic analysis is a simplified TIA that assesses the impact of a proposed project on residential streets. An NTA is limited to an evaluation of existing and projected operating levels of residential streets and an identification of measures needed to minimize the impact on traffic. The NTA is typically conducted by City Staff.