Trip generation is usually based on ITE’s latest publication of the

Trip Generation Manual

or other acceptable sources. ITE’s

Trip Generation Manual

includes equations for daily and study peak hour trip rates based on a specified independent variable. In many cases, this can be the square footage of the specific land use, or the number of units contained within a residential development. Example trip generation calculations can be found in

Appendix Q, Section 3 – TIA Example Problems.

Volumes are usually generated with average rates or a fitted curve equation. Consult the ITE Trip Generation Handbook Chapter 4 “Trip Generation Manual Data” to decide whether rates or equations are used.

Vehicle trip reduction may be applicable depending on the project location and type of land uses in a proposed development. If used, it is recommended this reduction follows the methodology found in the ITE

Trip Generation Manual

If reducing vehicle pass-by trips, the percentage reduced typically equates to the total vehicle trips generated minus the internal capture used for each land use. Pass-by percentage has an upper limit percentage of the existing vehicular traffic to be set while scoping with TxDOT.

Project distribution of the proposed trips is assigned using engineering judgment. If only one project driveway is proposed, all trips enter and exit through this driveway. This process is used to create a trip distribution and traffic assignment exhibit.

When analyzing the future roadway network, background growth and future project traffic is added to the existing traffic counts. Background growth data may be available from the city or MPO. Historical AADT information can be averaged for at least the last five years of data, when available, to obtain an average annual growth rate to grow the background volumes. Using this annual growth rate, existing traffic is grown to the future study years specified in the scope.

If there are other approved developments to be included in the study within close vicinity to the proposed project, traffic can be projected for each development through the process of trip generation and added to the roadway network through trip distribution and traffic assignment.

The combination of grown traffic and traffic from other approved developments are typically combined into a background traffic scenario and provided in an exhibit. This is typically completed for each future study year.

New traffic created from the proposed site is added to the background traffic scenarios, resulting in a background plus site traffic scenario for each study year. Peak hour volumes for these scenarios are usually provided in separate exhibits for each scenario.

The future traffic analysis includes all geometric characteristics of the existing analysis with the addition of proposed driveways. Background traffic and background plus site traffic scenarios are typically analyzed.

Future levels of service are obtained for all study intersections, along with any new project driveways used to access the project development. The latest HCM analysis methodology is typically used. For signalized intersections, each approach and the overall intersection are analyzed. For stop-controlled intersections, each stopcontrolled approach is analyzed by the approach. Left-turning movements of non-stop controlled approaches are typically analyzed by movement.

Traffic signal timings are typically adjusted and optimized in future scenarios in order to improve LOS. This can also be part of the proposed improvements. TxDOT area offices can request that analysis be run with existing timings in order to preserve existing signal coordination. If an intersection is operating over capacity, the mitigation requirements in Section 4 can be reviewed and used to help with capacity issues

An

example

Traffic Analysis can be found in

Appendix Q, Section 3 – TIA Example Problems.