Arterial roadways for all contexts should be designed to accommodate traffic projections for a 20-year period into the future. However, some elements may be based on shorter or longer design periods (e.g., a 20-year period for flexible pavements and a 30-year period for rigid pavements). For additional guidance on selecting the appropriate periods for forecasting design traffic volumes, see or refer to .

Projected volumes for other modes of transportation, such as pedestrians and or bicyclists, must also be estimated in the design of the facility.

While future estimates of transit and non-motorized modes may not be available, the designer may use available planning and land use documents to assist in determining future levels of nonmotorized demand.