AASHTO Superelevation - Update 6/27/2023

This program calculates superelevation rates and transition lengths using 2018 AASHTO Green Book criteria. For High Speed Roadways and Low Speed Roadways, the superelevation rates are provided by either Tables or Equations. The equations for High Speed Roadways use AASHTO Method 5 and the equations for Low Speed Roadways use AASHTO Method 2. This program also uses Method 2 for Maintenance of Traffic (MOT) superelevation rates.

To avoid multiple roundings, the superelevation transition runoff lengths are calculated and are not derived from Table 3-16a. For example, the MRG values are computed from the slope rate and not interpolated from rounded MRG values as follows: MRG % = 100 / Slope Rate. For Design Speeds of 50 mph and above, the slope rate is 1:200. Below 50 mph, Slope Rate = 200 - 2.5 * (50 - Design_Speed).

Input variables:

Criteria - General input data to define the superelevation calculation.

Basis - Select High Speed Roadways, Low Speed Roadways or Method 2 MOT Only.

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

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

Select Tables or Equations for calculating 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 with lengths equal to the Design Speed per the 2018 Green Book, section 3.3.8.7.

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

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 AASHTO Superelevation program.

Close Button - Closes the AASHTO 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.

Lane Width - This is the lane width (ft) within the transition limits.

Lanes Rotated - This is the number of lanes rotated within the transition limits.

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

MRG - The Maximum Relative Gradient (%) is automatic per the 2018 Green Book, section 3.3.8.2.1. Can be overridden.

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.

Lane Width - This is the lane width (ft) within the transition limits.

Lanes Rotated - This is the number of lanes rotated within the transition limits.

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

MRG - The Maximum Relative Gradient (%) is automatic per the 2018 Green Book, section 3.3.8.2.1. Can be overridden.

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