3.3.7 Forecasting Without Travel Demand Model Outputs

Forecasting volumes without a TDM is a fourstep process:
  1. Obtain existing volumes
  2. Determine the growth rate
  3. Apply growth rate to the existing volumes
  4. Other considerations

3.3.7.1 Obtain Existing Volumes

Existing volume considerations are discussed previously in this chapter, under
Section 3.2
. These considerations include traffic data factors, seasonal factors, historical factors, peak hour/period selection, disruptive events, traffic balancing, post processing, and validation.
Existing data can be obtained from various sources, including the TxDOT STARS database, MPO counts, the statewide planning map, or big data. For more information on data collection, see
Chapter 2.

3.3.7.2 Determine Growth Rate

The growth rate is a critical component needed to forecast traffic volumes. It can be determined using various methods. All methods listed in this section can be used to determine growth rate. The growth rate may vary from method to method, so it is recommended that multiple methods be checked for validation purposes. If needed, work with the District, TPP, and DES to develop interim growth rates. Three methods of determining growth rate are as follows:
  • Historical traffic growth data
    • Analyze traffic volumes over time at a particular location. Obtaining historical traffic volumes is discussed in
      Chapter 2
      .
    • Use of the linear regression spreadsheet provided in
      Appendix D, Section 4 – Regression Calculations
       is suggested to calculate historical traffic growth rates.
  • Population growth data
    • Analyze population growth from multiple years to determine the traffic volume growth rate over time. Population data can be found in the US Census data or in the state demographer forecasts.

3.3.7.3 Apply Growth Rate to Existing Volumes

Apply the calculated growth rate to the existing volumes to develop traffic projections. The three components of the calculation are the existing volumes, the growth rate, and the number of years.

3.3.7.4 Other Considerations

  • Planned developments
    • If there are developments planned near the project location, account for growth impacts of the developments.
  • Adjacent projects
    • Adjacent roadway projects may impact traffic growth. Account for them during the traffic forecasting process.
  • Complete the traffic projections methodology outline in
    Appendix D, Section 2 – Traffic Projections Methodology Memorandum Outline
For additional guidance on traffic volume and forecasting, refer to the TxDOT TPP Traffic Forecasting Analysis SOPs and Guide. Coordinate with the TxDOT project manager to gain access to the latest documents.