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friction factor, f

A coefficient that is a function of the design speed.  Obtained from the AASHTO Design guide.  Usually in the range 0f 0.1 to 0.3.

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Grade

Grade is the rise or fall of the roadway profile per 100 units in length.  Usually expressed as a %

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gravitational constant, g

g = 9.81 m/s2 or 32.2 ft/s2

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Super elevation, e%

The cross slope to a road that is used to counteract the centripetal forces developed as a vehicle goes around a curve.  Maximum value is approximately 10%

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Stopping Sight Distance

The distance required for a vehicle to observe, react and brake the vehicle to a stop. Calculated in two parts: the perception reaction distance and the braking distance Stopping Sight Distance Equation
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Velocity, V

Speed of the design vehicle  
 
 

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Vertical Curve

A regular curve that has a quadratic mathematical form.  For vertical curves the general equation is

Vertical Curve Equation

A is the grade difference

L is the length of parabolic curve

X= distance from beginning of the curve to the point of interest

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