General Procedure

DDHV is obtained by applying K and D factors to AADT projections, as outlined in this Handbook. AADT projections may be the result of the model generated traffic projections or they may be produced by means of other techniques, such as trend analysis or growth factor application. If the travel demand model produces Peak Season Weekday Average Daily Traffic (PSWADTs) rather than AADTs, apply the Model Output Conversion Factor (MOCF) to convert PSWADT to AADT.

The K factor converts the 24-hour AADT to an estimate of two-way traffic in the analysis hour of the year, which is required for design purposes. The result is called the Design Hour Volume or DHV. Standard K Factors are shown in Section 2.5.2 and D Factors are shown in Section 2.5.3.

The D factor converts two-way traffic volume DHV to an estimated Directional Design Hour Volume or DDHV. Appropriate D factors are developed as described in Chapter 2. By convention, the D factor always pertains to the peak direction of traffic flow during the design hour.

Project specific data is used to derive factors for obtaining DDHV from AADT. Project specific factors should be within the range of factors developed by FDOT from permanent count stations. In most instances, the range of factors provided by FDOT should be adequate for individual projects.

Using both (i.e., K and D) factors, the estimated DDHV is obtained by the following equations:

$$DDHV(Peak \space{Direction})=AADT\times{K}\times{D}$$
Equation 6-1
$$DDHV(Non-Peak \space{Direction})=AADT\times{K}\times{(1-D)}$$
Equation 6-2

Using the above procedures, DDHV project traffic forecasts are generated for roadway links and then intersection turning movements as needed to satisfy project development and design requirements.

Development of DDHVs from Model PSWADTs Example

As an example, assume that an urban arterial in Orlando is being studied for future widening. The existing roadway within the study area is to be widened from four lanes to six lanes. Following a mini-calibration within the study area, the Central Florida Regional Planning Model (CFRPM) (with a base year 2015) projects a PSWADT of 68,100 vehicles per day (vpd) for the roadway segment being studied for Year 2045, based on the adopted cost-feasible network. Using the Florida Traffic Online, the Peak Season Factor Category Report for 2022 includes five volume categories for Orange County, listed as follows:

  • Category 7500 – Orange Countywide
  • Category 7528 – Orange Beeline
  • Category 7544 – Orange I-4 Urban
  • Category 7547 – Orange Turnpike
  • Category 7549 – Orange I-4 Disney

As the facility does not fall on any of the facilities (Beeline, I-4 Urban, Florida’s Turnpike, or I-4 Disney), the adjustment factors for Category 7500 – Orange Countywide are used. From Peak Season Factor Category Report for Category 7500, the MOCF is 0.98. Therefore, AADT for the roadway segment is calculated as follows:

\(AADT=PSWADT\times{MOCF}=68,100\times{0.98}\)

\(AADT=66,738\rightarrow{67,000}\space{vpd}\)

If the Standard K Factor has been determined to be 9.0%, and D Factor 53.5%, then DHV and DDHV are derived below:

\(DHV = AADT × K = 67,000 × 0.09\)

\(DHV = 6,030\space{vph}\)

\(DDHV = DHV × D = 6,030 × 0.535\)

\(DDHV = 3,226\space{vph}\)