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What is Directional Factor (D-Factor)?

June 1, 2024

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:
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