Montana Department of Transportation

Malcolm “Mack” Long, Director

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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, and in 2020, TDCA created regions based on MDT financial districts to address variances in seasonal traffic patterns within Montana. However, adjustment factors for urban areas still remain a statewide factor. 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.

REC_MA Recreational on Minor Arterial roads
REC_PA Recreational on Principal Arterial roads
RMA_RMC_12 Rural Minor Arterial and Rural Major Collector in Financial District 1 and 2
RMA_RMC_345 Rural Minor Arterial and Rural Major Collector in Financial District 3, 4 and 5
RPA_1 Rural Principal Arterial in Financial District 1
RPA_2 Rural Principal Arterial in Financial District 2
RPA_3 Rural Principal Arterial in Financial District 3
RPA_45 Rural Principal Arterial in Financial District 4 and 5
RURAL INNER INTERSTATE Interstate roadway that falls within the travel triangle of Great Falls, Missoula, and Billings
RURAL OUTER INTERSTATE Interstate roadway that falls outside of the travel triangle of Great Falls, Missoula, and Billings
UI Urban Interstate
UMA_UC Urban Minor Arterial and Urban Collector
UPA Urban Principal Arterial
NI_URB* Non-Interstate Urban. * This is an axle factor that gets applied to UMA_UC and UPA seasonal factor groups.

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? Send an email