Montana Department of Transportation

Malcolm “Mack” Long, Director


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Section Title

Traffic Data - Traffic Adjustment Factors

Unlike continuous count station (CCS) sites which collect traffic year-round, short-term counts can be taken only when weather permits, usually April through September. As a result, these counts reflect a ‘snapshot’ of the traffic conditions during that particular 48-hour period. Because of this, short-term counts must be seasonally adjusted in order to provide a better representation of traffic conditions on an average day (i.e. Average Annual Daily Traffic - AADT).

MDT factors short-term counts with a Monthly Day of Week (MDOW) adjustment factor.

Traffic Factor Groupings

All roadways are categorized into Traffic Factor Groupings based on their operational characteristics. Traffic data from CCS sites in each grouping are used to develop adjustment factors to be applied to the short-term counts in that same grouping.

RI Rural Interstate
UI Urban Interstate
RPA Rural Principal Arterial
UPA Urban Principal Arterial
RMA Rural Minor Arterial
UMA Urban Minor Arterial
RMC Rural Major Collector
UC Urban Collector
REC Recreational

The type of adjustment factor applied is based on the type of count being performed.

For Volume Counts, which is a single hose setup, a combination Axle and Seasonal factor needs to be applied.

For Vehicle Classification Counts, only a Seasonal Adjustment Factor is required because the two-hose setup accounts for the number of axles per vehicle.

Questions regarding adjustment factors? Contact 406-444-7216 or .