Alabama DOT Superelevation - Updated 2/07/2024

This program calculates superelevation rates as shown in the Standard and Special Drawings for Highway Construction, Superelevation Rate Table, Index 68016 and 68017. These ALDOT tables match Superelevation Distribution Method 5, per 2018 AASHTO Green Book Table 3-10 (emax = 8%). The difference is the 2018 AASHTO Green Book says, "interpolation is not necessary as the superelevation rate should be determined from a radius equal to, or slightly smaller than, the radius provided in the table". For ALDOT, Index 68017, SSEC-1 (Sheet 2 of 14) says, "When the curve radius falls between values specified in the table, the e values should be interpolated." Thus, this program interpolates superelevation values from the tables. The program also calculates superelevation rates for low speed urban areas (emax = 4%) per ALDOT Index 68016, SSEC1 (Sheet 1 of 14) that says, "In low speed urban areas where surrounding development makes the use of full superelevation rates impractical, the designer should consult the AASHTO Green Book for tables and figures dictating the 4% maximum Superelevation rate". This program uses the 2018 AASHTO Green Book Table 3-13 using Superelevation Distribution Method 2 with the superelevation values from the table interpolated.

Superelevation transition lengths (STL) are computed using the Gradients for STL Table and Gradient Adjustment Table as shown respectively in the ALDOT Standards and Special Drawings, Index 68016 and 68017.

Input variables:

Criteria - General input data to define the superelevation calculation.

Basis - Select one of the following:

ALDOT Divided/Constant Median (travelled ways with edge pivots) - constant width medians (Half Super in Median).

ALDOT Divided Median Width Varies (travelled ways with edge pivots) - divided (bifurcated) highways where the median width varies.

ALDOT Undivided - undivided highways with center pivots.

ALDOT Low Speed - undivided streets in urban areas where full superelevation rates are impractical.

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

e_max (%) - The maximum superelevation is automatically selected when Basis is selected.

Between RC and NC - Select either NC or RC for curves falling between the NC Radius and the RC Radius.

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 - Generally prefered for bridges, no transition smoothing.

Trans Length - Select Minimum for L_{CT(min)} or Desirable for L_{CT(des)}.

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 Texas DOT Superelevation program.

Close Button - Closes the Texas DOT Superelevation 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.

NCS % - Normal cross slope before the curve. Do not add the binary "%" operator. Sign always negative (-).

Lane Width w - This is the lane width (typically 12 ft).

Num Lanes n - This is the number of travel lanes rotated from reverse crown to full superelevation.

Num Lanes n1 - Number of travel lanes rotated from normal crown to reverse crown.

Automatic when Num lanes n is entered but can be overridden.

Tangent STL% - Tangent Split from pavement edge profile. Do not add the binary "%" operator.

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

NCS % - Normal cross slope after the curve. Do not add the binary "%" operator. Sign always negative (-).

Lane Width w - This is the lane width (typically 12 ft).

Num Lanes n - This is the number of travel lanes rotated from reverse crown to full superelevation.

Num Lanes n1 - Number of travel lanes rotated from normal crown to reverse crown.

Automatic when Num lanes n is entered but can be overridden.

Tangent STL% - Tangent Split from pavement edge profile. Do not add the binary "%" operator.

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