This dialog box allows you to define how the automatic super-elevation is calculated. It is accessible from the button adjacent to the super-elevation fields in the horizontal curve panel (auto must be selected).
Select table (button)
This button (at the right of the dialog box) opens the Lookup Table dialog box allowing you to view, open or save a super-elevation lookup table.
A super-elevation lookup table contains cross-fall values as a function of curve radius and design speed. An example table is shown below.
First column is radius (meters)
First row is design speed (km/hr)
Body is Super-elevation value (unitless)
40
50
70
90
55
0.060
90
0.052
0.060
190
0.037
0.046
0.060
340
0.026
0.034
0.048
0.060
700
0.000
0.021
0.033
0.045
1500
0.000
0.000
0.024
0.033
3000
0.000
0.000
0.000
0.002
6000
0.000
0.000
0.000
0.000
50000
0.000
0.000
0.000
0.000
In the example above a curve of radius 190m with a design speed of 50km/hr will have a super-elevation of 0.046 (4.6%). Note that this table clearly defines a maximum super-elevation of 0.060 (6.0%); for a design speed of 70km/hr, for example, a radius less than 190m is not allowed.
Use Table (radio button)
The automatic Super-Elevation (shown in the the horizontal curve panel) will be extracted from a lookup table based on radius and design speed.
To use this option you must define a super-elevation table (select table button - above).
Use side friction factor (radio button)
The super-elevation will be calculated using the maximum side friction factor and the maximum super-elevation defined in the horizontal curve panel.
The equation used for these calculations balances radial accelerations, so that super-elevation and side friction are the same fraction of the defined maximums:
(e/100 + f)g = V2/R
e/emax = f/fmax
where:
e = super-elevation %
f = side friction factor
g = acceleration of gravity (9.81m/s2 or 32.2ft/s2)
V = speed (m/s or ft/s)
R = radius (m or ft)
This method is recommended in the AASHTO 2001 handbook.
button adjacent to the