Project Traffic Forecasting has broad application throughout the Department and is generally applicable to later planning stages through the design phase of highway projects. Its main application is in the project development phase in which location and design concept approvals occur. It is usually during this phase where most highway capacity and Level of Service (LOS) analyses are conducted leading to final design of the roadways. For specifics on highway capacity and LOS analyses refer to the Department’s LOS Policy, Topic No. 000-525-006, and the 2023 Multimodal Quality/Level of Service Handbook. Other applications include detailed corridor studies and interchange access studies.

Table 6-1 Traffic Diurnal Distribution Factors by Functional Class for Weekday
Hour Begin Urban, small: Pop <200K Urban, medium: Pop 200K–1 million Urban, large: Pop > 1 million Rural Area
Interstate Arterial Collector Interstate Arterial CBD Arterial Others Collector Interstate Arterial CBD Arterial Others Collector Interstate Arterial Collector
12:00 AM 1.07 0.59 0.47 0.95 0.81 0.71 0.61 0.96 1.22 0.78 0.59 1.43 0.72 0.57
1:00 AM 0.79 0.39 0.29 0.65 0.47 0.46 0.36 0.61 0.75 0.48 0.38 1.12 0.49 0.36
2:00 AM 0.70 0.30 0.23 0.57 0.41 0.40 0.31 0.51 0.58 0.37 0.30 0.99 0.43 0.31
3:00 AM 0.76 0.33 0.26 0.61 0.31 0.46 0.34 0.53 0.57 0.37 0.33 1.02 0.51 0.38
4:00 AM 1.10 0.58 0.30 0.96 0.43 0.77 0.60 0.85 0.79 0.61 0.59 1.31 0.93 0.84
5:00 AM 2.20 1.44 1.16 2.10 0.98 1.80 1.32 2.13 1.74 1.70 1.16 2.12 2.28 2.19
6:00 AM 4.16 3.21 2.93 4.67 2.67 4.05 3.63 5.11 4.23 4.17 2.72 3.58 4.54 4.36
7:00 AM 5.69 6.09 6.27 7.17 5.90 6.40 6.70 7.27 6.31 6.58 5.92 4.89 6.63 6.55
8:00 AM 5.26 5.53 5.75 6.16 5.79 5.75 6.60 6.61 6.24 6.08 6.05 4.95 5.55 5.58
9:00 AM 5.04 5.12 4.95 5.13 4.96 5.18 5.60 5.27 5.43 5.04 5.82 5.23 5.24 5.25
10:00 AM 5.27 5.55 5.24 5.10 5.19 5.36 5.49 4.86 5.18 4.96 5.78 5.64 5.41 5.44
11:00 AM 5.60 6.31 6.01 5.37 6.22 5.76 5.92 5.01 5.40 5.39 6.55 5.92 5.67 5.71
12:00 PM 5.89 6.74 6.66 5.59 7.10 6.11 6.33 5.20 5.72 5.81 7.08 6.02 5.91 6.05
1:00 PM 6.12 6.72 6.72 5.78 6.95 6.25 6.40 5.39 5.77 5.93 6.95 6.26 6.13 6.24
2:00 PM 6.78 7.07 7.63 6.32 6.75 6.70 6.74 6.02 6.07 6.31 7.20 6.63 6.68 6.78
3:00 PM 7.60 8.29 8.65 7.22 7.18 7.46 7.44 7.05 6.66 7.05 7.97 7.04 7.53 7.63
4:00 PM 7.88 8.30 9.22 7.86 7.91 8.05 7.82 7.78 7.07 7.85 7.94 7.25 8.02 8.15
5:00 PM 7.54 7.91 8.45 7.97 8.27 8.14 8.18 7.98 7.45 8.33 7.60 7.07 7.98 8.16
6:00 PM 5.63 5.96 5.96 5.69 6.06 6.10 6.05 6.11 6.12 6.52 5.66 5.68 5.95 6.17
7:00 PM 4.32 4.49 4.49 4.10 4.72 4.42 4.33 4.27 4.72 4.80 4.20 4.47 4.21 4.37
8:00 PM 3.57 3.50 3.38 3.34 3.89 3.48 3.42 3.37 3.77 3.88 3.29 3.71 3.30 3.41
9:00 PM 2.99 2.63 2.46 2.88 3.18 2.82 2.71 2.97 3.30 3.17 2.66 3.13 2.62 2.59
10:00 PM 2.31 1.77 1.54 2.19 2.27 2.00 1.89 2.41 2.77 2.28 1.97 2.54 1.94 1.77
11:00 PM 1.71 1.16 0.98 1.61 1.57 1.36 1.24 1.73 2.14 1.53 1.28 1.99 1.34 1.14

Determination of Number of Lanes Required for Target LOS Example

An example of practical application of DDHV is to calculate the number of lanes needed for a given LOS. The FDOT LOS Policy stipulates that automobile mode LOS targets for the State Highway System (SHS) during peak hours are “D” in urbanized areas and “C” outside urbanized areas. Assume that a multilane highway in an urbanized area (Context Classification C4 - Urban General) is expected to be widened in the year 2045. The following traffic and roadway conditions have been established:

  • Demand volume DDHV = 3,500 vph
  • Peak Hour Factor (PHF) = 0.92
  • Heavy Vehicle Adjustment Factor fhv = 0.925
  • Observed Free Flow Speed (FFS) = 55 mph
  • Target LOS = D

Based on the Highway Capacity Manual (HCM), 7th Edition (HCM 7), the number of lanes can be calculated using the following formula:

$$N=\frac{DDHV}{MSF_{i}\times{PHF}\times{f_{hv}}}$$
Equation 6-3

Where MSFi is the Maximum Service Flow rate for a given LOS i, a value of the maximum service flow rate can be selected from Table 6-2 for an FFS of 55 mi/h and LOS D. The corresponding maximum service flow rate is 1,790 pc/h/ln.

Table 6-2 Maximum Service Flow Rates for Multilane Highway Segments Under Base Conditionss
FFS (mi/h) Maximum Service Flow Rates for Target LOS (pc/h/ln)
A B C D E
60 660 1,080 1,530 1,890 2,200
55 600 990 1,430 1,790 2,100
50 550 900 1,300 1,680 2,000
45 490 810 1,170 1,550 1,900
Source: Highway Capacity Manual, 7th Edition, Exhibit 12-38.
$$N=\frac{3,500}{1,790\times{0.92}\times{0.925}}=2.3$$

It is not possible to build 2.3 lanes. To provide a minimum of LOS D, it will be necessary to provide three lanes in each direction, or a six-lane facility.