Traffic Factors
Traffic factors are used to adjust short-term traffic counts. The traffic factors account for variability in the traffic stream and estimate "average" traffic conditions. Short-term traffic counts are typically collected for 48-hour periods using traffic counters that record hourly traffic data.
Factors are calculated from the traffic data collected from continuous traffic counters or Automatic Traffic Recorders (ATRs).
Factor Groups
The continuous counters or Automatic Traffic Recorders (ATRs) are grouped into 16 traffic factor groups:
| Factor Group |
Descriptions |
| Rural - Local Collector |
Local roads or collectors in a rural area which provide low levels of travel mobility (i.e. a subdivision road or intra-county travel corridor) |
| Rural - Minor Arterial |
Routes which provide service to corridors with trip lengths and travel densities greater than that of collectors or local roads (i.e. Appling County SR-15) |
| Rural - Major Arterial |
Routes which have a trip length and travel density indicative of substantial state wide travel (i.e. Bartow County SR-20) |
| Rural - I-75 |
I -75 Outside of an Urban Area |
| Rural - I-85 |
I-85 Outside of an Urban Area |
| Rural - Interstates |
Interstates that are accessed only using ramps and are outside of an Urban Area (i.e. I-16 in Bryan County) |
| Small Urban - Local Collector |
Local roads or collectors in a small urban area which provide low levels of travel mobility (i.e. a subdivision road or intra-county travel corridor) |
| Small Urban - Arterial |
Routes of moderate to high lengths and travel that are within a small urban area (i.e. Bulloch County SR-67 Bypass) |
| Small Urban/Urban - Freeways Interstate (Not Atlanta) |
Freeways, Expressways and Interstates which are restricted access roadways and not in Atlanta (i.e. I-95) |
| Urban - Local Collector |
Local roads or collectors in an urban area which provide low levels of travel mobility (i.e. a subdivision road or intra-county travel corridor) |
| Urban - Minor Arterial (Not Atlanta) |
Routes that serve the major centers of activity with the highest traffic volumes and the longest trip lengths not in Atlanta (i.e. Catoosa SR-146) |
| Urban - Major Arterial (Not Atlanta) |
Routes that serve the major centers of activity with the highest traffic volumes and the longest trip lengths not in Atlanta (i.e. Catoosa SR-146) |
| Urban - Minor Arterial (Atlanta) |
Routes which provide trips of moderate length linking principal arterials in Atlanta (i.e. Fulton County SR-3) |
| Urban - Major Arterial (Atlanta) |
Routes that serve the major centers of activity with the highest traffic volumes and the longest trip lengths in Atlanta (i.e. Cobb County SR-5) |
| Urban - Freeways Interstate (Atlanta) |
Freeways, Expressways and Interstates which are restricted access roadways and are in Atlanta (i.e. I-75, I-85, SR-400, I-985) |
| Urban - I-285 (Atlanta) |
I-285 Loop |
Annual Average Daily Traffic
The Annual Average Daily Traffic (AADT) for a portable count is calculated as follows:
AADT = 24-hour Short Term Volume * Daily Adjustment Factor * Monthly Adjustment Factor * Axle Adjustment Factor
Daily Adjustment Factors
Daily Adjustment Factors are applied to raw traffic counts that are collected by portable traffic counters. These factors are used to account for traffic variation from each day of the week.
Monthly Adjustment Factors
Monthly Adjustment Factors are applied to raw traffic counts that are collected by portable traffic counters. These factors are used to account for traffic variation from each month of the year.
Axle Adjustment Factors
Axle Adjustment Factors are applied to raw traffic counts that are collected by portable traffic counters. The portable traffic counters register two axle impacts as one vehicle. These factors are used to account for vehicles with more than two axles.
Federal Highway Administration Traffic Monitoring Guide
For more information about traffic factors, refer to the Federal Highway Administration (FHWA) Traffic Monitoring Guide: http://www.fhwa.dot.gov/ohim/tmguide/.
Disclaimer: The Georgia Department of Transportation makes no representation or warranties, implied or expressed, concerning the accuracy, completeness, reliability, or suitability for any particular purpose of this information and data contained on this Web Site.