Design Domain Elements Of Curves Radius & Superelevation Submitted To: Prof. R.R Kalaga Submitted By: Leeza Malik

Design Domain Concept

Curve Radius Radius is one of the most significant factor in design of curves Model shows that A = (0.96 L + 0.0245/R – 0.012S) 0.978(3.3 x W - 30) where A = crashes/million vehicles entering from both directions L = curve length (km) R = curve radius (km) S = 1, if transition curves have been provided = 0, otherwise W = roadway width (lanes plus shoulders) (m). Crash frequency increases as the curve radius decreases.

Design Domain Element of Curve Radius The upper bound is the tangent in the sense that it has a radius of infinite length. The lower bound is minimum radius for the selected design speed. Function of the centripetal force necessary to sustain travel along a circular path. The force is developed part by friction and part by superelevation. e + f = V2/127 R Select the maximum rate of superelevation, e maximum, in order to determine the minimum allowable radius of horizontal curvature for that speed.

Contd…… Higher values of emax : Rural areas Lower values of emax : urban environment. Because of congestion and the application of traffic control devices and consequently lesser speeds make it difficult for the driver to negotiate higher superelevation.

Distribution of e &f Method 1: Both superelevation and side friction are directly proportional to the inverse of the radius. Method 2: Side friction is first applied to sustain lateral acceleration down to radii requiring fmax followed by increasing e with reducing radius until e reaches emax. In short, first f and then e are increased in inverse proportion to the radius of curvature Method 3: The reverse of Method 2 with first e and then f increased in inverse proportion to the radius of curvature. Method 4: As for Method 3, except that design speed is replaced by average running speed. Method 5: Superelevation and side friction are in curvilinear relations with the inverse of the radius of curvature, with values between those of Methods 1 and 3. Method 2 has merit in the urban environment. Method 5 is recommended for adoption in the case of rural and high-speed urban roads.

References Geometric Design Guidelines, NRA ,South Africa.

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