In the design of curve and spiral-curve-spiral centerlines, it's very important to determine the curve radii and superelevation rates, which can significantly affect the design speed of roads. The Horizontal Speed Table function provides a few of speed tables, which utilize AASHTO's speed table data and offer the recommendations for design speeds and curve parameters. Please refer to AASHTO A Policy on Geometric Design of Highways and Streets 2004 (pp 167-174) for details.
The Horizontal Speed Table function is integrated into the Input-Edit Centerline File command. To access the speed tables, in the curve or spiral centerline design dialogs, click on the Horizontal Speed Table button to open the speed table dialog shown as below. The Table Name list contains the names of all speed tables that has been defined. There are five default speed tables: AASHTO 4% MAX MSE, AASHTO 6% MAX MSE, AASHTO 8% MAX MSE, AASHTO 10% MAX MSE and AASHTO 12% MAX MSE. You can add, edit and delete any speed tables. On the left of the dialog, the Design Speed box lists all design speeds. On the right there is a table that lists all the curve and superelevation data of the highlighted speed. The curve and superelevation data table will change when you highlight different speeds. All speed table files are in the ...\USER folder and are available for all projects.
|
|
| Horizontal Speed Table |
There are three buttons under the Design Speed list. Add button adds a new design speed to the current speed table. The New Speed dialog opens for you to enter the Design Speed, and MSE and Minimum Radius for the speed. Edit button allows you to edit the highlighted design speed . Delete button will delete the highlighted speed and all the curve and superelevation data associate to the speed.
|
| New Design Speed |
|
| Edit Design Speed |
Under the table of the curve and superelevation data, there are Add, Edit and Delete buttons which allow you to add, edit and delete the data entry for the highlighted design speed.
|
| New Curve and Superelevation
Data |
If you have a special design speed or superelevation rate that is different than any data entry in the speed table, or if you don't want to look up the tables for a curve data, the Superelevation Calculator button is here to help you to get the curve data. Click on the button to open the Superelevation Calculator dialog. Enter the values in the Superelevation and Design Speed boxes, the Minimum Radius and Curvature will be calculated and displayed.
|
| Superelevation Calculator |
New Table button creates a new speed table, Edit Table button is used to modify the name of current table or the file that stores the speed data, Duplicate Table button makes a new speed table that contains the same data as current table, and Delete Table button removes current table completely.
|
| New Horizontal Speed
Table |