The DDHV is the traffic volume expected to travel in the peak direction during the design hour. However, for many transportation projects, particularly PD&E or Interchange Access Request (IAR) projects, it is often necessary to forecast traffic volumes for multiple peak hours for a typical day, such as AM Peak, PM Peak, and occasionally, Midday Peak in order to perform traffic operational analysis. Depending on the characteristics of the study area, the AM Peak and PM Peak periods may have significantly different hourly volumes. Furthermore, the AM peak hour or the PM peak hour may or may not coincide with the design hour. The development of directional volumes for the peak hours requires knowledge of hourly volume distributions. For existing facilities, the best way to obtain hourly volume distribution at the project site is to conduct short-term traffic counts for 24- to 72-hours. If traffic counts cannot be collected, traffic synopsis reports at nearby traffic monitoring sites on similar facilities from Florida Traffic Online can be downloaded and hourly volumes distribution factors can be developed. If traffic synopsis reports are not available, or the project is for a new facility where no such information exists, general hourly volume distributions published in NCHRP Report 765 can be used for facilities characterized by area type, facility type, and area size. Table 6-1 presents traffic diurnal distribution factors, or hourly volume distribution factors, for an average weekday included in the NCHRP Report. Users are encouraged to refer to the NCHRP Report for more detailed descriptions of the factors.

Directional peak hour volumes can be estimated using period volumes and peak-to-period ratios when a travel demand model with a time-of-day component is used. This is often the case for corridor studies with Express Lanes, where time-of-day information is critical.

For example, the Southeast Florida Regional Planning Model (SERPM) has a three-hour period for AM Peak, and a four-hour period for PM Peak. The one-hour AM and PM peak hour directional volumes can be estimated from the period model volumes by applying appropriate peak-to-period diurnal factors. However, if a model only produces 24-hour daily volumes, or the daily volumes are estimated from trends analysis or other non-model based methodologies, directional peak hour volumes can be obtained by using the daily volumes and appropriate peak-to-daily diurnal factors and D factors. In both cases, the resulting directional peak hour volumes must be checked for effective peak-to-daily ratios and directional distribution to ensure they are within the allowable range, as specified in Chapter 2 of the Handbook.