Collect historical traffic counts for multiple locations on the corridor and the surrounding area. These counts can be gathered from the STARS database or other publicly available count databases from regional MPO, county, or city websites. Once all the count locations are determined and the count data is gathered, linear regression analysis is typically performed for the individual locations to determine historical growth rates. It is recommended to check historical counts for any outliers and removed if necessary. Determine historical growth rates for up to 20 years’ worth of data, if available. After determining historical growth rates for individual roadway segments, an overall historical growth rate is typically calculated for the corridor. An

example

of the historical growth rate calculation is provided in

Appendix D, Section 4 – Regression Calculations

. More detailed information regarding the overall process can be found in

Chapter 3

and the TPP Traffic Forecasting Analysis SOP. Use engineering judgement to determine if the overall historical growth rate is reasonable. To help in the decision process, evaluate proposed developments, land use data, demographics, and future growth trends (see Traffic Demand Model section below) to see if the calculated projected growth rate needs to be adjusted.