08 - Chapter-8 - Geometric Design Manual-2002 Chapter 8...

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Chapter 8 Horizontal Alignment Geometric Design Manual-2002 Page 8-2 Ethiopian Roads Authority Table 8-2: Minimum Radii for Horizontal Curves: 4% Superelevation (Urban Streets) Design Speed V D (km/h) 20 30 40 50 60 70 85 100 120 Min. Horiz. Radius R .(m) 15 35 60 100 150 215 320 490 810 Side Friction Factor (f) 0.40 0.32 0.25 0.22 0.19 0.17 0.14 0.12 0.10 Limiting values have been established for both e and f in the formula. Side friction coefficients are dependent on vehicle speed, type, condition and texture of roadway surface, weather conditions, and type and condition of tires. Tables 8-1 and 8-2 were developed based on the results of several studies. Figure 6-1 illustrates the graphical results of those studies for rural highways. As the driver in an urban environment tolerates a higher degree of discomfort, the values of side friction in Table 8-2 differ from those in Table 8-1, particularly at lower speeds. Figure 8-1: Side Friction Factors for Rural Highways Example: V = 100 km/hr, e max =8% f =0.12(fromTable8-1): meters, round to 395 meters Other equations used in the calculation of horizontal curve elements are given below and illustrated in Figure 8-2.
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08 - Chapter-8 - Geometric Design Manual-2002 Chapter 8...

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