Existing traffic condition information includes traffic data that describes the current travel demand for existing roadway facilities, such as daily traffic volumes, peak hour volumes, directional distribution during peak hours, and percent trucks. The existing traffic information is obtained by conducting short-term traffic counts. To ensure the data is representative of average (typical) traffic conditions, traffic counts should not be collected during the summer or on holidays, as travel patterns during these times cannot be assumed to be representative of typical weekdays. However, for studies near recreational facilities, summer or holidays may provide the traffic analyst with more accurate “typical” patterns of travel.

Seasonal Adjustments

Data for existing roadways are collected at established traffic monitoring sites within the project’s limits. A classification count should be taken at the established traffic monitoring site in each of the current traffic breaks included in the project’s limits. When the traffic monitoring site for a traffic break is located outside the project’s limits, the data may still be collected at the established site. As an alternative, the traffic break can be subdivided at the project boundary and a new traffic count station established within the project’s limits. Directions on conducting classification counts are provided in the 2023 Traffic Monitoring Handbook. Traffic counts cannot be accepted without seasonal adjustments. These adjustments are applied as described in Section 2.4 (Traffic Adjustment Factors). Acceptable data should be uploaded to the Traffic Characteristics Inventory (TCI) for use in making the annual AADT estimate and for later use in making the project traffic forecast. Only those classification counts made during the last 12 months should be used as base year traffic data. Surveys made by individuals other than FDOT personnel should follow FDOT’s procedures.

D Factors

FDOT requires the use of two (2) different directional distribution factors: capacity analysis (D) and pavement design (D_F). The D described in traffic monitoring site reports are the ones used for capacity analysis.

A roadway near the center of an urban area often has traffic volumes equal for both directions, and therefore a D Factor near 50 percent. A rural arterial may exhibit a significantly higher D Factor because traffic is either traveling toward an urban area (AM) or traveling away from an urban area (PM).

The D factor used for pavement design (D_F) is typically 50 percent for two-way roadways. It is assumed that an equal amount of loaded trucks operates in both directions of traffic flow. For a one-way roadway, the D_F is 100 percent since all the trucks are moving in the same direction.

The project traffic forecaster may elect to change the D_F upwards from 50 percent, if there is a good reason for doing so (e.g., unequal number of lanes for the two directions). Base year directional bias in pavement loading will be used to determine the ESAL forecast D_F. A different directional bias exists for loaded trucks, which can be found by visually monitoring the traffic using the road to identify any repeating traffic and seeking the origin or destination of the traffic. For example, a concrete delivery truck whose origin is a concrete mixing plant down the road or a railroad siding serving as a destination for pulpwood trucks; in both cases, the D_F used for ESAL forecasting and subsequent pavement damage will be between 50 and 100 percent. (See Section 8.4.2.)

Roadway Data

GIS Shapefiles of existing number of lanes (Through Lanes - Feature 212) and functional classification (Feature 121) of roadways can be downloaded from the TDA Office website in the Roadway Characteristics Inventory (RCI) section. The Roadway ID and mile points of the roadway under design can be identified from the Shapefiles.