FDOT Superelevation - Updated 6/27/2023

This program calculates superelevation rates and transition lengths using Florida Department of Transportation (FDOT) criteria. For High Speed Roadways, the FDOT superelevation calculations correct an error in the AASHTO Greenbook Method 5 involving the equation for hpi. The corrected equation is: hpi = ((f_max + e_max) * Dpi / D_max) - ((fr_max + e_max) * Dpi / Dr_max). The FDOT originally created and published curves emulating the corrected equation and subsequently abandoned the equation.

When FDOT made this correction to the AASHTO equations, the maximum side friction factors were different than those used by AASHTO today for Design Speeds less than 50 MPH. The 2004 AASHTO Greenbook maximum friction factor modifications have never been reflected in the FDOT's superelevation curves. Eventually, the superelevation curves were replaced with superelevation Tables based on data manually picked off the curves as accurately as possible based on the Degree of Curve.

For High Speed Roadways, this program has an option to use the Tables (FDM Table 210.9.1) or the Equations (Method 5 corrected without friction factor updates). The FDM Table 210.9.1 allows either Degree of Curve and Radius superelevation input values. But the Radius values are rounded and don't exactly match the Degree of Curves. For example 5 degrees is 1145.91' and not 1146.00' as shown in the table. This causes minor differences when interpolating intermediate values. Thus this program will interpolate based on the Degree of Curve if input or will interpolate by Radius if input, so it is possible to get different interpolated values depending on this input. And depending on any input data given, the program will attempt to fill in missing data:

For High Speed Roadways with Equations, manually enter the Design Speed. Any Design Speed can be entered within the range of 15 mph to 70 mph. The superelevation rates for non-standard Design Speeds will be calculated.

Input variables:

Criteria - General input data to define the superelevation calculation.

Basis - Select FDOT High Speed Roadways or FDOT Low Speed Roadways.

Design Speed (mph) - Once Basis has been selected, the Design Speed options will automatically be displayed.

For Equations, manually enter the design speed. Any design speed can be selected to get rates such as 48 mph.

+/- Positive or negative slope of the curve. Generally used for transition calculations.

For High Speed Roadways, an option will appear to select Tables or Equations for Superelevation Rate Calculations

Description - Enter any description to be included in the printed output.

Geometry Data - Input data specific to the Curve and Transition.

Radius R - This is the Radius of the Curve (ft). Input this or Degree of Curve.

Degree D - This is the Degree of Curve (Decimal Degrees). Input this or Radius.

Trans Type - Select the Transition Type.

Linear - The default, no transition smoothing with parabolic curves.

Equals Design Speed - Adds parabolas per the standard index, with lengths equal to the Design Speed per AASHTO.

Reverse Parabola - (Rare) Adds continuous smoothing from the beginning to end of the transition.

Interpolation - Select the Interpolation Method for FDM Tables 210.9.1 and 210.9.2.

Radius R - Interpolates superelevation rates based on the Radius in the the table.

Degree D - Interpolates superelevation rates based on the Degree of Curve.

SE Calculations - This is where the Superelevation (SE) output information is displayed.

Action Bar

Run Button - Runs input data and calculates superelevations and transitions.

Clear All Button - Clears and resets the entire page.

Print Button - Prints the data calculated in the FDOT Superelevation program.

Close Button - Closes the FDOT Superelevation program.

PC Transition - This is the input and output data for the transition at the PC of the curve.

Station - This is the PC station on the baseline. Do not enter a station plus.

e_back - This is superelevation rate ('/') prior to the curve (normal crown or the prior curve). Sign +/- is important.

Pavt Width - This is the widest pavement width (ft) within the transition limits.

Num Lanes - This is the maximum number of lanes within the transition limits.

Tan Split% - Typically 80 (80% tangent and 20% curve). Do not add the binary "%" operator.

Slope Rate - This is automatically set based on FDM criteria. Can be overridden, for example a rate of 1:150, input 150.

PC Transition output data is shown in the textbox below the input data.

Specific Station Calculator - This calculates superelevations at stations within a superelevation transition.

Beg Sta - This is the Begin Station of the increment range. Do not enter a station plus.

Increment - This is the incremental distance between stations(feet).

Calc Button - calculates the superelevation at stations in the transition area.

Output - Station and superelevation output data is shown in the textbox below the input data.

PT Transition - This is the input and output data for the transition at the PT of the curve.

Station - This is the PT station on the baseline. Do not enter a station plus.

e_ahead - This is superelevation rate ('/') after the curve (normal crown or the next curve). Sign +/- is important.

Pavt Width - This is the widest pavement width (ft) within the transition limits.

Num Lanes - This is the maximum number of lanes within the transition limits.

Tan Split% - Typically 80 (80% tangent and 20% curve). Do not add the binary "%" operator.

Slope Rate - This is automatically set based on FDM criteria. Can be overridden, for example a rate of 1:150, input 150.

PT Transition output data is shown in the textbox below the input data.