4A. Basic circular curve elements Flashcards
(e.g., middle ordinate, length, chord definition, radius definition, centerline stationing)
1
Q
What is the basic curve equation and where can it be found?
A
AASHTO: Chapter 3: Equation 3-6
(0.01e+f) / (1-0.01ef) =
v^2 / (g * R) =
(0.067*V^2) / R =
V^2 / (15 * R)
where:
e = rate of roadway superelevation, percent
f = side friction (demand) factor
v = vehicle speed, ft/s
g = gravitational constant, 32.2 ft/s2
V = vehicle speed, mph
R = radius of curve measured to a vehicle’s center of gravity, ft
2
Q
What is the difference between E and M?
A
E is the external distance between the middle of the curve and the tangential lines (on the outside of curve).
M is the middle ordinate - the distance from the midpoint on the curve to Chord AB (on the inside of the curve).
