What is Directional Factor (D-Factor)?

Directional factor (D-factor) is the traffic volume proportion moving in the higher volume direction during the peak hour to the combined volume in both directions during the peak hour.

Further notes:

• By definition the D-factor can not be smaller than 50%
• In general, the value of D-factor for non-one way roadways range from 50% to 75%.
• D factors for one way roadways is always 100%.
• D-factor is best measured at continuous monitoring sites.
• Land use pattern near a facility affects its D-factor value.
• The directional distributions of traffic change based on hour of the day, day of the week, and season.
• The same peak hour volume used to calculate K-factor should be used to calculate D-factor.
• In some urban areas, imbalanced directional distributions can be mitigated by using reversible lanes.

Further reading:

• AADT
• DDHV
• K-factor
• Traffic Data Pocket Guide, p. 44